JP7725896B2 - Bending sensor, bending detection device, and bending detection method - Google Patents

Description

The present invention relates to a bending sensor, a bending detection device, and a bending detection method.

Known bending sensor technologies include those described in Patent Documents 1 and 2. Patent Document 1 discloses a bending sensor worn on each finger of a glove-type wearing device. The bending sensor disclosed in Patent Document 1 has a configuration in which a metal resistor (strain sensor) is provided inside an elastic body. This bending sensor detects the bending state based on changes in the electrical resistance value of the metal resistor that occur in response to bending movements of the fingers wearing the wearing device. Patent Document 2 discloses a bending sensor provided in an organic EL display device. The bending sensor disclosed in Patent Document 2 has a configuration in which a first electrode layer, a piezoelectric layer, and a second electrode layer are layered in this order on a substrate. This bending sensor detects the bending state based on changes in voltage between the first electrode layer and the second electrode layer in response to bending deformation.

Japanese Patent Application Publication No. 4-233442 JP 2017-207886 A

However, the bending sensor disclosed in Patent Document 1 is attached to each finger of the attachment, and so while it can detect bending for each finger, it cannot detect which part of the finger (for example, the fingertip or the base of the finger) the bending has occurred in. Furthermore, the bending sensor disclosed in Patent Document 2 can only detect the bending state of the entire board. As such, bending sensors such as those described above provide insufficient information about the bending state, making it difficult to grasp the bending state in detail. This limits the scope of use of such bending sensors.

The present invention provides a bending sensor, bending detection device, and bending detection method that can grasp the bending state in detail.

A bending sensor according to one aspect of the present invention is a bending sensor for detecting bending, comprising: a flexible substrate; a thin-film transistor array consisting of a plurality of thin-film transistors arranged on the substrate; a plurality of pixel electrodes arranged on the thin-film transistor array; a piezoelectric layer arranged on the plurality of pixel electrodes; and a common electrode arranged on the piezoelectric layer. The piezoelectric layer has a front surface electrically connected to the common electrode and a back surface electrically connected to the plurality of pixel electrodes. The plurality of pixel electrodes are arranged spaced apart from each other in a plan view of the substrate and have first and second pixel electrodes that are electrically insulated from each other. The thin-film transistor array comprises a first thin-film transistor electrically connected to the first pixel electrode and a second thin-film transistor electrically connected to the second pixel electrode.

When bending is applied to this bending sensor, tensile or compressive stress is applied to the piezoelectric layer, causing changes in the electrical characteristics between the multiple pixel electrodes and the common electrode. The multiple pixel electrodes include first and second pixel electrodes that are spaced apart from each other in a planar view and electrically insulated from each other. Therefore, changes in the electrical characteristics between the first pixel electrode and the common electrode and changes in the electrical characteristics between the second pixel electrode and the common electrode occur independently of each other. Therefore, by separately detecting signals indicating changes in the electrical characteristics between the first pixel electrode and the common electrode and signals indicating changes in the electrical characteristics between the second pixel electrode and the common electrode using the first and second thin film transistors, it is possible to separately obtain information indicating the bending state at the position of the first pixel electrode and information indicating the bending state at the position of the second pixel electrode. This allows the local bending state at each of the first and second pixel electrodes to be grasped. Therefore, the bending sensor described above makes it possible to grasp the bending state in detail.

The multiple pixel electrodes may be arranged in a matrix. In this case, by acquiring information indicating the bending state for each pixel electrode, it is possible to grasp the bending state at a more localized level. This makes it possible to grasp the bending state of the bending sensor in more detail.

The first pixel electrode may have a shape extending in a first direction along the substrate, and the second pixel electrode may have a shape extending in a second direction along the substrate and intersecting the first direction. In this case, the first pixel electrode is strongly affected by bending in the first direction, and the second pixel electrode is strongly affected by bending in the second direction. Therefore, by detecting a signal indicating a change in the electrical characteristics between the first pixel electrode and the common electrode as information indicating the state of bending in the first direction, and detecting a signal indicating a change in the electrical characteristics between the second pixel electrode and the common electrode as information indicating the state of bending in the second direction, it is possible to distinguish between the state of bending in the first direction and the state of bending in the second direction. This makes it possible to grasp the state of bending of the bending sensor in more detail.

The first pixel electrode and the second pixel electrode may each have a Young's modulus higher than the Young's modulus of the inter-electrode region between the first pixel electrode and the second pixel electrode. In this case, it is possible to more reliably achieve a state in which the first pixel electrode is strongly affected by bending in the first direction, and the second pixel electrode is strongly affected by bending in the second direction. This makes it possible to more reliably distinguish and grasp the state of bending in the first direction and the state of bending in the second direction.

The inter-electrode region may be formed from an electrically insulating adhesive. In this case, it is possible to easily achieve a configuration in which the Young's modulus of each of the first pixel electrode and the second pixel electrode is higher than the Young's modulus of the inter-electrode region. Furthermore, by providing an electrically insulating adhesive between the first pixel electrode and the second pixel electrode, it is possible to fix the positional relationship between the first pixel electrode and the second pixel electrode while ensuring electrical insulation between them.

The neutral plane, where no tensile or compressive stress acts when the bending sensor is bent, may be located at a different height from the piezoelectric layer, and at least a portion of each of the first pixel electrode and the second pixel electrode may be located on the same side of the neutral plane as the piezoelectric layer. In this case, by utilizing the magnitude relationship between the Young's modulus of each of the first pixel electrode and the second pixel electrode and the Young's modulus of the inter-electrode region between the first pixel electrode and the second pixel electrode, it is possible to more reliably achieve a state in which the first pixel electrode is strongly affected by bending in the first direction and the second pixel electrode is strongly affected by bending in the second direction. This makes it possible to more reliably distinguish and grasp the state of bending in the first direction and the state of bending in the second direction.

The multiple pixel electrodes may include multiple first pixel electrodes and multiple second pixel electrodes, and the first pixel electrodes and second pixel electrodes may be arranged in a matrix so that they alternate with each other. In this case, by obtaining information indicating the bending state for each pixel electrode, it is possible to grasp the bending state more locally. Furthermore, by arranging the first pixel electrodes and second pixel electrodes alternately, the first pixel electrodes and second electrodes can be arranged in a dispersed manner, which prevents bias from occurring in the information indicating the bending state obtained.

The common electrode may have a first extension portion extending in a first direction to encompass the first pixel electrode in a planar view, and a second extension portion extending in a second direction to encompass the second pixel electrode in a planar view and connected to the first extension portion. In this case, by arranging the common electrode to encompass both the first pixel electrode and the second pixel electrode, the first pixel electrode is more strongly affected by bending in the first direction, and the second pixel electrode is more strongly affected by bending in the second direction. This makes it possible to more reliably distinguish and acquire information indicating the state of bending in the first direction from information indicating the state of bending in the second direction.

The multiple pixel electrodes include multiple first pixel electrodes and multiple second pixel electrodes, each of which is arranged in a matrix. The common electrode includes multiple first extension portions arranged to encompass each of the multiple first pixel electrodes in a planar view, and multiple second extension portions arranged to encompass each of the multiple second pixel electrodes in a planar view. The multiple first extension portions and multiple second extension portions may be arranged in a grid pattern in a planar view. In this case, by acquiring information indicating the bending state for each pixel electrode, it is possible to grasp the bending state of a more localized area. This makes it possible to grasp the bending state of the bending sensor in more detail.

The plurality of pixel electrodes may further include a third pixel electrode that is spaced apart from the first pixel electrode and the second pixel electrode in a planar view and electrically insulated from the first pixel electrode and the second pixel electrode. The third pixel electrode may have a shape that extends along the substrate in a third direction that intersects the first and second directions. In this case, the third pixel electrode is strongly affected by bending in the third direction. Therefore, by detecting a signal indicating a change in the electrical characteristics between the third pixel electrode and the common electrode as information indicating the bending state in the third direction, the information indicating the bending state in the third direction can be obtained separately from the information indicating the bending state in the first direction and the information indicating the bending state in the second direction. In other words, with the above-described configuration, the bending state in the third direction can be determined in addition to the bending state in the first direction and the bending state in the second direction. Therefore, with the above-described configuration, the bending state of the bending sensor can be determined in more detail.

The common electrode may have a first extension portion extending in a first direction to encompass the first pixel electrode in a planar view, a second extension portion extending in a second direction to encompass the second pixel electrode in a planar view and connected to the first extension portion, and a third extension portion extending in a third direction to encompass the third pixel electrode in a planar view and connected to the first and second extension portions. In this case, by arranging the common electrode to encompass the third pixel electrode, the third pixel electrode is more strongly affected by bending in the third direction. This makes it possible to more reliably distinguish and obtain information indicating the state of bending in the third direction.

A bending detection device according to another aspect of the present invention includes any of the bending sensors described above and a detection unit that detects bending of the bending sensor. When a bend is applied to the bending sensor, the first thin-film transistor outputs a first signal to the detection unit that indicates a change in electrical characteristics between the first pixel electrode and the common electrode in response to the bending, and the second thin-film transistor outputs a second signal to the detection unit that indicates a change in electrical characteristics between the second pixel electrode and the common electrode in response to the bending. The detection unit detects the first signal as information indicating the state of bending at the position of the first pixel electrode and the second signal as information indicating the state of bending at the position of the second pixel electrode.

The bending detection device described above includes one of the bending sensors described above. Therefore, as described above, changes in the electrical characteristics between the first pixel electrode and the common electrode and changes in the electrical characteristics between the second pixel electrode and the common electrode occur independently of each other. Therefore, by separately detecting a first signal indicating a change in the electrical characteristics between the first pixel electrode and the common electrode and a second signal indicating a change in the electrical characteristics between the second pixel electrode and the common electrode using the first thin-film transistor and the second thin-film transistor, it is possible to separately obtain information indicating the bending state at the position of the first pixel electrode and information indicating the bending state at the position of the second pixel electrode. This makes it possible to grasp the local bending state at each of the positions of the first pixel electrode and the second pixel electrode. Therefore, the bending detection device described above makes it possible to grasp the bending state in detail.

The first pixel electrode may extend in a first direction along the substrate, and the second pixel electrode may extend in a second direction along the substrate that intersects the first direction. The detection unit may detect a first signal as information indicating the bending state in the first direction at the position of the first pixel electrode, and a second signal as information indicating the bending state in the second direction at the position of the second pixel electrode. In this case, the first pixel electrode is strongly affected by bending in the first direction, and the second pixel electrode is strongly affected by bending in the second direction. Therefore, by detecting a first signal indicating a change in the electrical characteristics between the first pixel electrode and the common electrode as information indicating the bending state in the first direction, and detecting a second signal indicating a change in the electrical characteristics between the second pixel electrode and the common electrode as information indicating the bending state in the second direction, it is possible to distinguish between the bending state in the first direction and the bending state in the second direction. This makes it possible to more precisely determine the bending state of the bending sensor.

A bending detection method according to yet another aspect of the present invention is a bending detection method implemented using any of the bending sensors described above, and includes the steps of: when a bend is applied to the bending sensor, outputting from the first thin-film transistor a first signal indicating a change in electrical characteristics between the first pixel electrode and the common electrode in response to the bend; and outputting from the second thin-film transistor a second signal indicating a change in electrical characteristics between the second pixel electrode and the common electrode in response to the bend; detecting the first signal as information indicating the state of the bend at the position of the first pixel electrode; and detecting the second signal as information indicating the state of the bend at the position of the second pixel electrode.

The bending detection method described above uses one of the bending sensors described above. As described above, changes in the electrical characteristics between the first pixel electrode and the common electrode and changes in the electrical characteristics between the second pixel electrode and the common electrode occur independently of each other. Therefore, by separately detecting a first signal indicating a change in the electrical characteristics between the first pixel electrode and the common electrode and a second signal indicating a change in the electrical characteristics between the second pixel electrode and the common electrode using the first thin-film transistor and the second thin-film transistor, it is possible to separately obtain information indicating the bending state at the position of the first pixel electrode and information indicating the bending state at the position of the second pixel electrode. This makes it possible to grasp the local bending state at each of the positions of the first pixel electrode and the second pixel electrode. Therefore, the bending detection method described above makes it possible to grasp the bending state in detail.

In the step of outputting the first and second signals, the first signal may be output using a first pixel electrode having a shape extending in a first direction along the substrate, and the second signal may be output using a second pixel electrode having a shape extending in a second direction along the substrate and intersecting the first direction. In the step of detecting the first and second signals, the first signal may be detected as information indicating the bending state in the first direction at the position of the first pixel electrode, and the second signal may be detected as information indicating the bending state in the second direction at the position of the second pixel electrode. In this case, the first pixel electrode is strongly affected by the bending in the first direction, and the second pixel electrode is strongly affected by the bending in the second direction. Therefore, by detecting the first signal indicating a change in the electrical characteristics between the first pixel electrode and the common electrode as information indicating the bending state in the first direction, and detecting the second signal indicating a change in the electrical characteristics between the second pixel electrode and the common electrode as information indicating the bending state in the second direction, the bending state in the first direction and the bending state in the second direction can be distinguished and identified. This makes it possible to identify the bending state of the bending sensor in more detail.

This invention makes it possible to grasp the bending state in more detail.

FIG. 1 is a plan view illustrating an example of a bending sensor according to the first embodiment. FIG. 2 is a cross-sectional view of the bending sensor taken along line A1-A1 in FIG. Fig. 3(a) is a cross-sectional view showing the bending sensor of Fig. 2 bent into a convex shape, and Fig. 3(b) is a cross-sectional view showing the bending sensor of Fig. 2 bent into a concave shape. FIG. 4 is a cross-sectional view showing an example of the configuration of a group of thin film transistors in one pixel. FIG. 5 is a plan view showing the configuration of the thin film transistor group shown in FIG. FIG. 6 is a diagram showing an example of a circuit configuration of a thin film transistor array. FIG. 7 is a cross-sectional view showing another example of the configuration of a group of thin film transistors in one pixel. FIG. 8 is a plan view showing the configuration of the thin film transistor group shown in FIG. FIG. 9 is a diagram showing another example of the circuit configuration of a thin film transistor array. 10A is a diagram showing an example of the configuration of a current limiting circuit, and FIG. 10B is a diagram showing another example of the configuration of a current limiting circuit. 11A and 11B are diagrams illustrating another example of the configuration of a current limiting circuit. FIG. 12 is a diagram illustrating an example of the configuration of the detection unit according to the first embodiment. FIG. 13 is a diagram illustrating another example of the configuration of the detection unit. FIG. 14 is a diagram showing another example of the configuration of the detection unit. FIG. 15 is a flowchart showing an example of the operation of the bending detection device. 16(a) to 16(e) are diagrams for explaining the operation of the bending detection device shown in FIG. FIG. 17 is a plan view illustrating an example of a bending sensor according to the second embodiment. Fig. 18(a) is a cross-sectional view of the bending sensor taken along the line A2-A2 in Fig. 17. Fig. 18(b) is a cross-sectional view of the bending sensor taken along the line A3-A3 in Fig. 17. Fig. 19(a) is a cross-sectional view showing the bending sensor bent into a convex shape in the cross section shown in Fig. 18(a). Fig. 19(b) is a cross-sectional view showing the bending sensor bent into a convex shape in the cross section shown in Fig. 18(b). Fig. 20(a) is a cross-sectional view showing a state in which the bending sensor is bent concavely in the cross section shown in Fig. 18(a). Fig. 20(b) is a cross-sectional view showing a state in which the bending sensor is bent concavely in the cross section shown in Fig. 18(b). 21A to 21C are plan views showing other examples of the bending sensor according to the second embodiment. 22A and 22B are plan views showing other examples of the bending sensor according to the second embodiment. FIG. 23 is a plan view illustrating an example of a bending sensor according to the third embodiment. Fig. 24(a) is a cross-sectional view of the bending sensor taken along line A4-A4 in Fig. 23. Fig. 24(b) is a cross-sectional view of the bending sensor taken along line A5-A5 in Fig. 23. Fig. 25(a) is a cross-sectional view showing the bending sensor bent into a convex shape in the cross section shown in Fig. 24(a). Fig. 25(b) is a cross-sectional view showing the bending sensor bent into a convex shape in the cross section shown in Fig. 24(b). Fig. 26(a) is a cross-sectional view showing a state in which the bending sensor is bent concavely in the cross section shown in Fig. 24(a). Fig. 26(b) is a cross-sectional view showing a state in which the bending sensor is bent concavely in the cross section shown in Fig. 24(b). 27(a) to 27(c) are plan views showing other examples of the bending sensor according to the third embodiment. 28A and 28B are plan views showing other examples of the bending sensor according to the third embodiment. FIG. 29 is a plan view showing another example of the bending sensor according to the third embodiment. Fig. 30(a) is a cross-sectional view of the bending sensor taken along the line A6-A6 in Fig. 29. Fig. 30(b) is a cross-sectional view of the bending sensor taken along the line A7-A7 in Fig. 29. Fig. 31(a) is a cross-sectional view showing the bending sensor bent into a convex shape in the cross section shown in Fig. 30(a). Fig. 31(b) is a cross-sectional view showing the bending sensor bent into a convex shape in the cross section shown in Fig. 30(b). Fig. 32(a) is a cross-sectional view showing the bending sensor bent into a concave shape in the cross section shown in Fig. 30(a). Fig. 32(b) is a cross-sectional view showing the bending sensor bent into a concave shape in the cross section shown in Fig. 30(b). FIG. 33 is a plan view showing another example of the bending sensor according to the third embodiment. FIG. 34 is a plan view showing another example of the bending sensor according to the third embodiment. FIG. 35 is a block diagram showing an example of a care data collection and determination system to which a bending detection device is applied. 36(a) to 36(f) are perspective views showing examples of the care sensor device shown in FIG.

Below, a bending sensor, bending detection device, and bending detection method according to an embodiment of the present invention will be described in detail with reference to the drawings. In the following description, the same or equivalent elements will be designated by the same reference numerals, and duplicate explanations will be omitted where appropriate. The dimensions and dimensional ratios in the drawings do not necessarily correspond to the actual dimensions and dimensional ratios.

[First embodiment]
FIG. 1 is a plan view showing a bending sensor 10 according to a first embodiment. FIG. 2 is a cross-sectional view showing the bending sensor 10 taken along line A1-A1 in FIG. 1. The bending sensor 10 detects bending applied to the bending sensor 10. The bending sensor 10, together with a detection unit 5 described below, constitutes a bending detection device 1 (see FIG. 12). The bending sensor 10 is a sensor array in which a plurality of sensors 11 are arranged in a matrix (two-dimensionally). The plurality of sensors 11 that constitute the bending sensor 10 are arranged one for each pixel.

In this specification, the term "pixel" refers to a detection point corresponding to the intersection of scanning wiring 61 and signal wiring 62 (see Figure 6), which will be described later. In this case, in the plan view of Figure 1, multiple pixels are arranged in a matrix at a constant pitch. In this embodiment, a case where multiple pixels are arranged in N rows and M columns (M and N are integers of 2 or greater) is described. The multiple pixels can be divided into multiple pixel regions RP arranged in N rows and M columns. Figure 1 shows the boundary line BL between adjacent pixels (i.e., the boundary line between each pixel region RP). However, the boundary line BL is a virtual line that indicates the boundary between each pixel, and does not indicate the boundary of an actual component.

As shown in Figures 1 and 2, the bending sensor 10 includes a flexible substrate 15, a thin-film transistor layer 20 including multiple thin-film transistors, multiple pixel electrodes 25, a piezoelectric layer 30, and a counter electrode 35. The flexible substrate 15 is a flexible substrate made of an insulating material. Examples of materials for the flexible substrate 15 include polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyethersulfone (PES), polyimide (PI), and acrylic. As shown in Figure 2, the flexible substrate 15 has a front surface 15a and a back surface 15b facing opposite each other in the thickness direction. On the front surface 15a of the flexible substrate 15, a thin-film transistor layer 20 including multiple thin-film transistors, multiple pixel electrodes 25, a piezoelectric layer 30, and a counter electrode 35 are stacked in this order.

In the following description, one direction along the surface 15a of the flexible substrate 15 is referred to as the X direction (first direction), the direction along the surface 15a and perpendicular to that direction is referred to as the Y direction (second direction), and the direction perpendicular to the surface 15a (i.e., the thickness direction of the flexible substrate 15) is referred to as the Z direction. In this embodiment, the view from the Z direction is referred to as a "planar view," and the flexible substrate 15 side in the Z direction may be referred to as "bottom," and the opposite side (i.e., the opposing electrode 35 side) as "top." Furthermore, when describing the height of a certain configuration, the height of the back surface 15b of the flexible substrate 15 in the Z direction may be used as the reference.

In the thin film transistor (TFT) layer 20, multiple thin film transistors are arranged in a matrix along the X and Y directions, with one or one group per pixel. That is, each thin film transistor or group of thin film transistors is arranged in N rows and M columns, corresponding to each pixel. For example, the circuits shown in Figures 4 to 6 (described below) have two thin film transistors per pixel: a pixel thin film transistor 21 and a selection thin film transistor 22, and the pixel electrode 25 is connected to the gate electrode G1 of the pixel thin film transistor 21. Alternatively, the circuits shown in Figures 7 to 9 (described below) have three thin film transistors per pixel: a pixel thin film transistor 21, a selection thin film transistor 22, and a reset thin film transistor 23, and the pixel electrode 25 is connected to the gate electrode G1 of the pixel thin film transistor 21. As shown in Figures 4-5 or 7-8, these thin-film transistors are formed by arranging thin-film transistors having similar layered structures (e.g., gate electrode, gate insulating film, semiconductor layer, (source/drain electrodes), and interlayer insulating film) in a plane and connecting them with wiring. The entire layered structure is referred to as the thin-film transistor layer 20. The interlayer insulating film 51 and gate insulating film 50 account for the majority of the volume of the components of the thin-film transistor layer 20. Therefore, the Young's modulus of the thin-film transistor layer 20 may be that of the laminate of the interlayer insulating film 51 and gate insulating film 50. In particular, if the interlayer insulating film 51 and the gate insulating film 50 are made of the same material, the Young's modulus of the laminate may be used. Because the multiple thin-film transistors are arranged in an array, the multiple thin-film transistors may be referred to as the "thin-film transistor array 20" below. Each thin-film transistor may be, for example, an organic thin-film transistor (organic semiconductor) or an oxide thin-film transistor (oxide semiconductor). Organic thin-film transistors and oxide thin-film transistors, when primarily composed of an organic insulating film, have the advantage of being flexible and durable.

In Figure 2, the thin-film transistor layer 20 is depicted as a single layer, but in reality it includes multiple thin-film transistors, and as shown in Figure 4 or Figure 7, the pixel electrode 25 is connected to the gate electrode G1 of the pixel thin-film transistor 21. The multiple thin-film transistors include at least two: a first pixel thin-film transistor 21A and a second pixel thin-film transistor 21B (see Figure 6). The first pixel thin-film transistor 21A and the second pixel thin-film transistor 21B are arranged at positions spaced apart in the X direction on the surface 15a of the flexible substrate 15. The first pixel thin-film transistor 21A is electrically connected to a first pixel electrode 25A (described below), and the second pixel thin-film transistor 21B is electrically connected to a second pixel electrode 25B (described below).

The multiple pixel electrodes 25 are arranged in a matrix along the X and Y directions, with one electrode typically provided for each pixel. That is, like each thin-film transistor group, each pixel electrode 25 is arranged in N rows and M columns corresponding to each pixel. Each pixel electrode 25 is arranged at a position overlapping with or near each pixel thin-film transistor 21 in a plan view. The pixel electrodes 25 are arranged at a constant pitch along the X and Y directions, and are spaced apart from each other in both the X and Y directions.

The pixel electrodes 25 are spaced apart from one another in the X and Y directions. The pixel electrodes 25 being spaced apart from one another means that the pixel electrodes 25 are physically spaced apart from one another. A solid material may be present in the region between the pixel electrodes 25 (hereinafter referred to as the "inter-pixel electrode region 26"), or the inter-pixel electrode region 26 may not have a solid material present. If a solid material is present in the inter-pixel electrode region 26, the solid material is made of an electrically insulating material. In this case, electrical insulation between the pixel electrodes 25 is ensured.

In this embodiment, an electrically insulating adhesive is provided in the inter-pixel electrode region 26. In this case, the inter-pixel electrode region 26 can be said to be composed of an electrically insulating adhesive. The adhesive is capable of adhering to the pixel electrodes 25 and includes, for example, a pressure-sensitive adhesive. Therefore, the inter-pixel electrode region 26 between each pixel electrode 25 fixes (or maintains) the position of each pixel electrode 25 by adhering to each pixel electrode 25. If no solid material is present in the inter-pixel electrode region 26, the inter-pixel electrode region 26 is composed of air. In this case, too, the air layer present in the inter-pixel electrode region 26 ensures electrical insulation between each pixel electrode 25.

Each pixel electrode 25 has, for example, a square shape with the same length in the X direction and the same length in the Y direction. Each pixel electrode 25 is made of, for example, a metal film for molybdenum (Mo) or aluminum (Al), a metal paste such as silver (Ag) paste, or a carbon paste.

Each pixel electrode 25 has a front surface 25a facing the piezoelectric layer 30 and a back surface 25b facing the thin-film transistor layer 20. The front surface 25a of each pixel electrode 25 is electrically connected to the piezoelectric layer 30. The back surface 25b of each pixel electrode 25 is in contact with and electrically connected to each pixel thin-film transistor 21. The multiple pixel electrodes 25 have at least two first pixel electrodes 25A (first electrodes) and two second pixel electrodes 25B (second electrodes). In the example shown in FIG. 1, the first pixel electrode 25A and the second pixel electrode 25B are adjacent to each other in the X direction via an inter-pixel electrode region 26. The first pixel electrode 25A is located at a position corresponding to the first pixel thin-film transistor 21A. The back surface 25b of the first pixel electrode 25A is electrically connected to the first pixel thin-film transistor 21A (first thin-film transistor). The second pixel electrode 25B is located at a position corresponding to the second pixel thin-film transistor 21B. The back surface 25b of the second pixel electrode 25B is electrically connected to the second pixel thin film transistor 21B (second thin film transistor).

The counter electrode 35 is disposed in a position facing the multiple pixel electrodes 25 in the Z direction via the piezoelectric layer 30. The counter electrode 35 is, for example, a single common electrode disposed so as to overlap all of the pixel electrodes 25 in a planar view. The counter electrode 35 has a rectangular shape that encompasses all of the pixel electrodes 25 in a planar view. The counter electrode 35 is, for example, a thin metal film made of a metal material such as aluminum (Al), gold (Au), or molybdenum (Mo). The counter electrode 35 is, for example, electrically connected to ground (GND). In this case, a ground potential is applied to the counter electrode 35. Ground potential does not have to be applied to the counter electrode 35, and any constant voltage may be applied.

The piezoelectric layer 30 is disposed between the multiple pixel electrodes 25 and the counter electrode 35 in the Z direction. The piezoelectric layer 30 is a layer containing a piezoelectric material. Examples of piezoelectric materials include polyvinylidene difluoride (PVDF), polytrifluoroethylene (PTrFE), and poly(vinylidene difluoride-trifluoroethylene) copolymer (P(VDF-TrFE)). These materials can be imparted with strong piezoelectricity to the piezoelectric layer 30 by a poling process. The piezoelectric layer 30 has a front surface 30a facing the counter electrode 35 and a back surface 30b facing the multiple pixel electrodes 25. The front surface 30a is in contact with and electrically connected to the counter electrode 35. The back surface 30b is in contact with and electrically connected to all of the pixel electrodes 25.

When tensile or compressive stress is applied to the piezoelectric layer 30 due to bending of the bending sensor 10, a voltage corresponding to the stress is generated in the piezoelectric layer 30 due to the piezoelectric effect, which causes polarization in the piezoelectric material. This changes the electrical characteristics between the counter electrode 35 and the pixel electrode 25. Specifically, a potential difference is generated between the counter electrode 35 and the pixel electrode 25.

When a constant voltage is applied to the opposing electrode 35, the voltage of the pixel electrode 25 is the sum of the voltage of the opposing electrode 35 and the voltage of the piezoelectric layer 30. The voltage of the pixel electrode 25 is output as a voltage signal from the thin-film transistor array 20 and then detected by the detection unit 5 as information indicating the state of bending (bending information). Because the voltage indicated by this signal is proportional to the magnitude of bending, the magnitude of bending can be determined from this signal. The magnitude of bending provides information such as whether or not there is bending, the amount of bending, and the direction of bending (i.e., whether the bending is upwardly convex or downwardly concave). Therefore, bending information may include information on whether or not there is bending, the amount of bending, and the direction of bending.

In this embodiment, as described above, multiple pixel electrodes 25 are arranged in a matrix with a space between them relative to a single counter electrode 35, and the pixel electrodes 25 are electrically insulated from one another. In this case, the voltage generated at each pixel electrode 25 varies independently for each pixel electrode 25. Therefore, when stress is applied to the piezoelectric layer 30 by bending the bending sensor 10, a voltage corresponding to the stress is generated at each pixel electrode 25. In other words, of the bending applied to the entire piezoelectric layer 30, a voltage corresponding to the bending at the position of the first pixel electrode 25A is generated at the first pixel electrode 25A, and a voltage corresponding to the bending at the position of the second pixel electrode 25B is generated at the second pixel electrode 25B. Therefore, the bending sensor 10 according to this embodiment separately detects the voltage generated at each pixel electrode 25, thereby acquiring bending information for each pixel electrode 25. This allows the bending state of the bending sensor 10 to be determined for each pixel electrode 25.

As shown in FIG. 2, the piezoelectric layer 30 is positioned at a position different from the neutral plane NP so that stress is applied when the bending sensor 10 is bent. The neutral plane NP is a plane to which no tensile or compressive stress is applied when the bending sensor 10 is bent. In this embodiment, the neutral plane NP can be shown as a virtual plane along the XY plane, and is located on any of the layers that make up the bending sensor 10 (i.e., the flexible substrate 15, the thin-film transistor layer 20, the pixel electrode 25, the piezoelectric layer 30, and the counter electrode 35).

The position of the neutral plane NP in the Z direction can be expressed by the height λ from the rear surface 15b of the flexible substrate 15. The height λ of the neutral plane NP depends on the Young's modulus and thickness of each layer constituting the bending sensor 10 (i.e., the flexible substrate 15, the thin-film transistor layer 20, the pixel electrode 25, the piezoelectric layer 30, and the counter electrode 35). When the bending sensor 10 is composed of N layers (N is a natural number), the bottom layer is the first layer, and the Young's modulus of the ith layer (i is a natural number equal to or less than N) is Ei, the thickness of the ith layer is Ti, and the height of the center of the ith layer from the bottom layer is Yi. The height λ of the neutral plane NP is generally expressed by the following formula (1):
In this embodiment, if the first layer is the flexible substrate 15, the Young's modulus of the flexible substrate 15 is expressed as E1 and the thickness as T1. The Young's modulus of the thin film transistor layer 20, the second layer, is expressed as E2 and the thickness as T2. The Young's modulus of the pixel electrode 25, the third layer, is expressed as E3 and the thickness as T3. The Young's modulus of the piezoelectric layer 30, the fourth layer, is expressed as E4 and the thickness as T4. The Young's modulus of the counter electrode 35, the fifth layer, is expressed as E5 and the thickness as T5. Then, equation (1) can be rewritten as the following equation (2).

As such, the height λ of the neutral plane NP varies depending on the Young's modulus and thickness of each layer, and can be adjusted by adjusting the Young's modulus and thickness of each layer. The height λ of the neutral plane NP is, for example, located lower than the rear surface 30b of the piezoelectric layer 30. The example shown in Figure 2 shows a case where the height λ of the neutral plane NP is located at the height of the rear surface 25b of the pixel electrode 25. In this case, the entire pixel electrode 25, the entire inter-pixel electrode region 26, and the entire piezoelectric layer 30 are located higher than the height λ of the neutral plane NP. However, the height λ of the neutral plane NP is not necessarily the height of the rear surface 25b of the pixel electrode 25; it may be higher or lower than the rear surface 25b. For example, the height λ of the neutral plane NP may be the internal height of the pixel electrode 25.

Figure 3(a) is a cross-sectional view showing the bending sensor 10 bent convexly. In Figure 3(a), bending the bending sensor 10 in the X-direction causes the bending sensor 10 to bend convexly upward in the XZ cross section. When the piezoelectric layer 30 is located above the neutral plane NP, as in this embodiment, bending the bending sensor 10 convexly as shown in Figure 3(a) imparts tensile stress in the X-direction to the piezoelectric layer 30. When the curvature at the position of the first pixel electrode 25A and the curvature at the position of the second pixel electrode 25B are equal, tensile stress SS1 in the X-direction is imparted to the piezoelectric layer 30 at the positions of the first pixel electrode 25A and the second pixel electrode 25B. As a result, a voltage corresponding to the tensile stress SS1 is generated in the first pixel electrode 25A and the second pixel electrode 25B. When the curvature at the position of the first pixel electrode 25A differs from the curvature at the position of the second pixel electrode 25B, tensile stresses of different magnitudes in the X direction are applied to the piezoelectric layer 30 at the positions of the first pixel electrode 25A and the second pixel electrode 25B. In this case, voltages corresponding to the respective tensile stresses are generated in the first pixel electrode 25A and the second pixel electrode 25B.

Figure 3(b) is a cross-sectional view showing the bending sensor 10 bent concavely. In Figure 3(b), the bending sensor 10 is bent in the X-direction, causing it to bend concave upward in the XZ cross section. When the piezoelectric layer 30 is located above the neutral plane NP, as in this embodiment, bending the bending sensor 10 concavely as shown in Figure 3(b) imparts compressive stress in the X-direction to the piezoelectric layer 30. When the curvature at the position of the first pixel electrode 25A and the curvature at the position of the second pixel electrode 25B are equal, compressive stress SS2 in the X-direction is imparted to the piezoelectric layer 30 at the positions of the first pixel electrode 25A and the second pixel electrode 25B. As a result, a voltage corresponding to the compressive stress SS2 is generated in the first pixel electrode 25A and the second pixel electrode 25B. When the curvature at the position of the first pixel electrode 25A differs from the curvature at the position of the second pixel electrode 25B, compressive stresses of different magnitudes in the X direction are applied to the piezoelectric layer 30 at the positions of the first pixel electrode 25A and the second pixel electrode 25B. In this case, voltages corresponding to the respective compressive stresses are generated in the first pixel electrode 25A and the second pixel electrode 25B. The voltages generated in the first pixel electrode 25A and the second pixel electrode 25B are opposite in direction to the voltages generated in the first pixel electrode 25A and the second pixel electrode 25B in the case shown in FIG. 3(a).

Here, the voltage generated in the pixel electrode 25 (i.e., the voltage generated in the piezoelectric layer 30) will be described in more detail. If the voltage generated in the pixel electrode 25 is V, the capacitance of the capacitor formed by the counter electrode 35, the piezoelectric layer 30, and the pixel electrode 25 is C, and the charge stored in the capacitor is Q, then the relationship shown in the following equation (3) holds among the voltage V, the capacitance C, and the charge Q. Furthermore, if the electric flux density generated between the counter electrode 35 and the pixel electrode 25 is De, and the electrode area (i.e., the area of the pixel electrode 25 in a plan view) is A, then the charge Q can be expressed by the following equation (4). If the Z direction is 3, the X direction is 1, and the Y direction is 2, and the piezoelectric strain constants of the piezoelectric layer 30 are represented as d31, d32, and d33, and the tensile stress in the X direction, Y direction, and Z direction applied to the piezoelectric layer 30 is represented as σ1, σ2, and σ3, respectively, the electric flux density De is expressed by the following formula (5). When the piezoelectric layer 30 is a uniaxially stretched film, the relationship d31 >> d32 holds when the stretching direction is the X direction. On the other hand, when the piezoelectric layer 30 is a biaxially stretched or unstretched film, the relationship d31 = d32 holds.

Therefore, using equations (3) to (5), the voltage V generated in the pixel electrode 25 can be calculated. Note that the stress applied to the piezoelectric layer 30 is proportional to the strain, and the strain is proportional to the curvature of the bending of the piezoelectric layer 30, so the stress is proportional to the curvature. Furthermore, since the stress is proportional to the charge Q and the voltage V, the charge Q and the voltage V are proportional to the curvature. Therefore, the voltage V generated in the pixel electrode 25 increases as the curvature of the bending applied to the bending sensor 10 increases.

Figure 4 is a cross-sectional view showing the configuration of the thin-film transistor group of one pixel. Figure 5 is a plan view showing the configuration of the thin-film transistor group of one pixel. The voltage generated in the pixel electrode 25 is input as a voltage signal to the pixel thin-film transistor 21. As shown in Figures 4 and 5, the thin-film transistor group is composed of, for example, the pixel thin-film transistor 21 and the selection thin-film transistor 22. The pixel thin-film transistor 21 includes a gate electrode G1, a gate insulating film 50, a source electrode S1, a semiconductor layer SC1, a drain electrode D1, and an interlayer insulating film 51. The selection thin-film transistor 22 includes a gate electrode G2, a gate insulating film 50, a source electrode S2, a semiconductor layer SC2, a drain electrode D2, and an interlayer insulating film 51.

The gate electrode G1 and the gate electrode G2 are disposed on the surface 15a of the flexible substrate 15 and are spaced apart from each other in the X direction. The gate insulating film 50 is disposed on the flexible substrate 15 so as to cover the gate electrode G1 and the gate electrode G2. The gate insulating film 50 electrically insulates the gate electrode G1 and the gate electrode G2 from other electrodes. The source electrode S1, the drain electrode D1, the semiconductor layer SC1, the source electrode S2, the drain electrode D2, and the semiconductor layer SC2 are disposed on the gate insulating film 50. The source electrode S1, the drain electrode D1, and the semiconductor layer SC1 are disposed on the gate electrode G1 via the gate insulating film 50.

The source electrode S2, drain electrode D2, and semiconductor layer SC2 are arranged on the gate electrode G2 via the gate insulating film 50. The interlayer insulating film 51 is arranged on the gate insulating film 50 to cover the source electrode S1, drain electrode D1, semiconductor layer SC1, source electrode S2, drain electrode D2, and semiconductor layer SC2. The pixel electrode 25 is stacked on the interlayer insulating film 51. The interlayer insulating film 51 electrically insulates the source electrode S1, drain electrode D1, source electrode S2, and drain electrode D2 from the pixel electrode 25.

The gate electrode G1 is electrically connected to the pixel electrode 25 via a first via wiring 53 formed in the gate insulating film 50 and a second via wiring 54 formed in the interlayer insulating film 51. The source electrode S1 is electrically connected to the drain electrode D2 via a connection wiring 55. As shown in FIG. 5, the thin-film transistor array 20 is provided with a drain wiring 60, a scanning wiring 61, and a signal wiring 62. The drain wiring 60 is connected to the drain electrode D1 and extends along the Y direction. The drain electrode D1 is electrically connected to the drain wiring 60, which is electrically connected to a power supply. The scanning wiring 61 is connected to the gate electrode G2 and extends along the Y direction. The gate electrode G2 is electrically connected to the scanning wiring 61. The signal wiring 62 extends along the Y direction and is spaced apart from the drain wiring 60 in the X direction. The source electrode S2 is electrically connected to the signal wiring 62.

Figure 6 is a diagram showing the circuit configuration of the thin-film transistor array 20. Multiple signal wirings 62 are arranged at intervals in the X direction, with one wiring per column. Multiple scanning wirings 61 are arranged at intervals in the Y direction, with one wiring per row. In this embodiment, N scanning wirings 61 and M signal wirings 62 are provided. As shown in Figure 6, the gate electrodes G2 of multiple thin-film transistor groups arranged in a row in the X direction are connected to one scanning wiring 61, and the source electrodes S2 of multiple thin-film transistor groups arranged in a row in the Y direction are connected to one signal wiring 62.

When stress is applied to the piezoelectric layer 30, a voltage is generated in the pixel electrode 25, and this voltage is input to the pixel thin-film transistor 21 connected to the pixel electrode 25. For simplicity's sake, focusing on one pair of thin-film transistors, the voltage of the pixel electrode 25 is input to the gate electrode G1 of the pixel thin-film transistor 21. Based on the voltage of the power supply connected to the drain wiring 60, the pixel thin-film transistor 21 outputs a signal corresponding to the voltage input to the gate electrode G1 from the drain electrode D1 to the source electrode S1. The signal output to the source electrode S1 is input to the drain electrode D2 of the selection thin-film transistor 22. The pixel thin-film transistor 21, including the load resistance of the signal detection circuit described below, forms a drain-grounded (source follower) circuit. Furthermore, when a given constant voltage is applied to the counter electrode 35, the sum of the voltage of the counter electrode 35 and the voltage of the piezoelectric layer 30 is applied to the gate electrode G1. Therefore, the operating point of the pixel thin-film transistor 21 can be adjusted by adjusting the voltage of the counter electrode 35.

The selection thin-film transistor 22 controls whether or not a signal input to the drain electrode D2 is output to the signal wiring 62. A gate voltage that switches the selection thin-film transistor 22 on/off is applied from the scanning wiring 61 to the gate electrode G2 of the selection thin-film transistor 22. The selection thin-film transistor 22 functions as a switch that switches on/off between the drain electrode D2 and the source electrode S2 based on the gate voltage applied to the gate electrode G2. When a gate voltage (off voltage) that turns the selection thin-film transistor 22 off is applied from the scanning wiring 61 to the gate electrode G2, the signal input to the drain electrode D2 is not output to the signal wiring 62. On the other hand, when a gate voltage (on voltage) that turns the selection thin-film transistor 22 on is applied from the scanning wiring 61 to the gate electrode G2, the signal input to the drain electrode D2 is output from the source electrode S2 to the signal wiring 62.

The signal output to the signal wiring 62 is then detected by the detection unit 5 (see FIG. 12), which will be described later. In this embodiment, the signal provides the sum of the magnitude of bending in the X direction and the magnitude of bending in the Y direction. Bending in the X direction refers to bending when stress is applied in the X direction. More specifically, bending in the X direction refers to bending in a direction in which the bending sensor 10 becomes convex or concave in the Z direction on an XZ cross section. Bending in the Y direction refers to bending when stress is applied in the Y direction. More specifically, bending in the Y direction refers to bending in a direction in which the bending sensor 10 becomes convex or concave in the Z direction on a YZ cross section. Hereinafter, bending in the X direction may be abbreviated as X bending, and bending in the Y direction may be abbreviated as Y bending.

However, if a uniaxially stretched film (e.g., uniaxially stretched PVDF) is used as the piezoelectric layer 30, it is possible to detect the magnitude of bending in the X direction and the magnitude of bending in the Y direction independently. For example, a configuration is conceivable in which two bending sensors 10 using uniaxially stretched films as the piezoelectric layer 30 are prepared and the two bending sensors 10 are stacked in the Z direction so that the stretching directions of the piezoelectric layers 30 are shifted by 90°. In this configuration, the stretching direction of the piezoelectric layer 30 of one bending sensor 10 is the X direction, and the stretching direction of the piezoelectric layer 30 of the other bending sensor 10 is the Y direction. In this case, if the voltage output from the bending sensor 10 in the stretching direction _X is voltage VX, the voltage obtained from the bending sensor 10 in the stretching direction Y is voltage _VY , the magnitude of the X bending is _BX , and the magnitude of the Y bending is _BY , then voltage _VX and voltage _VY can be formulated as shown in the following equations (6) and (7), respectively. Here, k ₁ and k ₂ are constants that satisfy k1>k2.

Therefore, if k1 and k2 are experimentally determined, the magnitude of bending in the X direction _BX and the magnitude of bending in the Y direction _BY can be derived from equations (6) and (7) as follows: (8) and (9) In this way, even when using the bending sensor 10 according to this embodiment, it is possible to independently detect the magnitude of bending in the X direction _BX and the magnitude of bending in the Y direction _BY .

In this way, bending information can be obtained based on the signal output to the signal wiring 62. However, to obtain bending information for each pixel electrode 25, it is necessary to distinguish between the signals output from each pixel thin film transistor 21. For this reason, the detection unit 5 (see FIG. 12), described below, is configured to distinguish between the signals. As shown in FIG. 12, each signal wiring 62 is connected to a load resistor 76 located in a detection circuit external to the thin film transistor array 20. In this case, current flows through each signal wiring 62, reducing impedance and reducing the likelihood of noise contamination of the signal. Furthermore, because the pixel thin film transistor 21 forms a drain-grounded (source follower) circuit, only the current is amplified, and the potential of the source electrode S1 is close to the potential of the gate electrode G1. Therefore, the signal is less susceptible to variations in the mobility of the pixel thin film transistor 21.

On the other hand, if a load resistor is located inside the thin-film transistor array 20, the current flowing through each signal wiring 62 will be smaller, and if each signal wiring 62 is long, noise will be more likely to be mixed into the signal. Furthermore, if the impedance of the detection unit 5 is lowered to prevent noise from being mixed into the signal, the current of the detection unit 5 will also flow through the load resistor in addition to the current flowing through the pixel thin-film transistor 21. In this case, the voltage drop across the load resistor due to the current of the detection unit 5 will result in an error. Furthermore, if the pixel thin-film transistor 21 forms a source-grounded circuit, both the voltage and current are amplified, increasing sensitivity, but the signal will be more susceptible to variations in the mobility and threshold of the pixel thin-film transistor 21.

Furthermore, in the circuit shown in FIG. 6 , when the voltage of the drain wiring 60 is set from zero to V _dd (power supply voltage) immediately before bending detection by the bending sensor 10, if the capacitance between the gate electrode G1 and drain electrode D1 of the pixel thin film transistor 21 (including the pixel electrode 25 connected to the gate electrode G1 and the drain wiring 60 connected to the drain electrode D1) is C _gd1 and the capacitance between the pixel electrode 25 and the counter electrode 35 is C _p , then the voltage deviation ΔV _p of the pixel electrode 25 is expressed by the following equation (10):

Here, the voltage deviation ΔVp of the pixel electrode 25 needs to be sufficiently smaller than the maximum potential change ΔV _MAX of the piezoelectric layer 30. For example, the voltage deviation ΔVp of the pixel electrode 25 should be kept within 10% of the maximum potential change ΔV _MAX . In other words, it is preferable to satisfy the following formula (11). The maximum potential change ΔV _MAX is the amount of change in potential of the piezoelectric layer 30 when the bending sensor 10 is subjected to a maximum bending (i.e., a bending at which the detection range set for the bending sensor 10 is at its maximum) from a state in which no bending is applied to the bending sensor 10. For example, if the maximum potential change ΔV _MAX is 4 V, the voltage deviation ΔVp of the pixel electrode 25 should be 0.4 V or less.

Figure 7 is a cross-sectional view showing the configuration of another example of the thin-film transistor array 20. Figure 8 is a plan view showing the thin-film transistor array 201 shown in Figure 7. As shown in Figures 7 and 8, the thin-film transistor array 201 has a reset thin-film transistor 23 in addition to the pixel thin-film transistor 21 and the selection thin-film transistor 22. The reset thin-film transistor 23 includes a gate electrode G3, a gate insulating film 50, a source electrode S3, a semiconductor layer SC3, a drain electrode D3, and an interlayer insulating film 51. The reset thin-film transistor 23 shares the gate insulating film 50 and the interlayer insulating film 51 with the pixel thin-film transistor 21 and the selection thin-film transistor 22.

The gate electrode G3, along with the gate electrodes G1 and G2, is covered by the gate insulating film 50. The source electrode S3, the semiconductor layer SC3, and the drain electrode D3 are disposed on the gate insulating film 50. The source electrode S3, the drain electrode D3, and the semiconductor layer SC3 are disposed on the gate electrode G3 with the gate insulating film 50 interposed therebetween. The source electrode S3, the drain electrode D3, and the semiconductor layer SC3 are covered by the interlayer insulating film 51.

The drain electrode D3 is connected to the first via wiring 53 and the second via wiring 54, and is electrically connected to the gate electrode G1 of the pixel thin film transistor 21 via the first via wiring 53 and the second via wiring 54. As shown in FIG. 8, the reset thin film transistor 23 is provided with a common wiring 63 and a reset wiring 64. The common wiring 63 is connected to the source electrode S3 and extends along the Y direction. The source electrode S3 is electrically connected to the common wiring 63. The common wiring 63 is set to the same potential as the counter electrode 35. The reset wiring 64 extends along the X direction so as to intersect with the common wiring 63 and the signal wiring 62. The gate electrode G3 is electrically connected to the reset wiring 64. A gate voltage that switches the reset thin film transistor 23 on and off is applied to the reset wiring 64.

Figure 9 is a diagram showing the circuit configuration of the thin-film transistor array 201 shown in Figures 7 and 8. The reset thin-film transistor 23 has the role of resetting the voltage of the piezoelectric layer 30 to zero by shorting the pixel electrode 25 to the common wiring 63 (i.e., setting the pixel electrode 25 to the same potential as the opposing electrode 35) before bending detection by the bending sensor 10. This enables the circuit shown in Figure 9 to perform more precise detection than the circuit shown in Figure 6. Note that the circuits shown in Figures 6 and 9 are merely examples of circuit configurations for thin-film transistor arrays, and other circuits may be used.

9 , before bending detection is performed by the bending sensor 10, a gate voltage (on voltage) that turns on the reset thin film transistor 23 is applied to the reset wiring 64 while no stress is being applied to the piezoelectric layer 30. At this time, the pixel electrode 25 is electrically connected to the common wiring 63 via the reset thin film transistor 23, so that the charge accumulated in the pixel electrode 25 can be reduced to zero. Thereafter, a gate voltage (off voltage) that turns off the reset thin film transistor 23 is applied to the reset wiring 64, and a voltage _Vdd is applied to the drain wiring 60.

Normally, when no stress is applied to the piezoelectric layer 30, the voltage of the piezoelectric layer 30 is zero. However, depending on past history, for example, if stress continues to be applied to the piezoelectric layer 30 until just before the bending sensor 10 is used, the voltage of the piezoelectric layer 30 may not be zero. In this case, errors may occur due to residual charge in the piezoelectric layer 30. In contrast, with the circuit shown in Figure 9, the charge in the pixel electrode 25 can be reset by turning on the reset thin-film transistor 23 before detection by the bending sensor 10, thereby suppressing errors due to residual charge in the piezoelectric layer 30.

9 , the capacitance between the gate electrode G1 and drain electrode D1 of the pixel thin film transistor 21 (including the capacitance of the pixel electrode 25 connected to the gate electrode G1 and the drain wiring 60 connected to the drain electrode D1) is defined as C _gd1 , the capacitance between the gate electrode G3 and drain electrode D3 of the reset thin film transistor 23 (including the capacitance of the reset wiring 64 connected to the gate electrode G3 and the pixel electrode 25 connected to the drain electrode D3) is defined as C _gd3 , the capacitance between the pixel electrode 25 and the counter electrode 35 is defined as C _p , and other capacitances are ignored because they are small. In this case, when the reset thin film transistor 23 is turned off by applying an off voltage to the _reset wiring 64, the voltage deviation ΔV _p1 of the pixel electrode 25 is expressed by the following equation ₍ 12):

When the voltage of the drain wiring 60 is set from zero to V _dd (power supply voltage), the voltage deviation ΔV _p2 of the pixel electrode 25 is expressed by the following equation (13).
When the thin film transistor is an n-channel TFT, ΔV _p1 is negative and ΔV _p2 is positive. When the thin film transistor is a p-channel TFT, ΔV _p1 is positive and ΔV _p2 is negative. Therefore, in either case, ΔV _p1 and ΔV _p2 cancel each other out in voltage change. If the total voltage change is expressed as |ΔV _p2 - ΔV _p1 |, the voltage change |ΔV _p2 - ΔV _p1 | must be sufficiently smaller than the maximum potential change ΔV _MAX of the piezoelectric layer 30. For example, the voltage change |ΔV _p2 - ΔV _p1 | should be kept within 10% of the maximum potential change ΔV _MAX of the piezoelectric layer 30. In other words, it is desirable to satisfy the following equation (14). For example, when the maximum potential change ΔV _MAX is 4 V, the voltage change |ΔV _p2 - ΔV _p1 | should be 0.4 V or less.

In the circuits shown in FIG. 6 or FIG. 9, the drain wiring 60 may be provided with a current limiting circuit (protection circuit). FIGS. 10(a), 10(b), 11(a), and 11(b) are diagrams showing examples of the configuration of a current limiting circuit. The current limiting circuit is provided to prevent excessive current from flowing through the drain wiring 60 and other wiring (e.g., the scanning wiring 61, the signal wiring 62, and the common wiring 63) in the event of a short circuit between these wirings within the thin-film transistor array 20. In the example shown in FIG. 10(a), a power supply 70 and multiple drain wirings 60 are connected by a connection portion 72. The connection portion 72 includes a single connection line 73 connected to the power supply 70 and multiple branch lines 74 branching from the connection line 73 and connected to the multiple drain wirings 60, respectively. One current limiting circuit 71 is provided for each connection line 73.

In the example shown in FIG. 10(a), if an abnormality occurs in one current limiting circuit 71, the voltage of all drain wirings 60 will drop, and the entire bending sensor 10 will become abnormal. Therefore, as shown in the example shown in FIG. 10(b), a configuration in which multiple current limiting circuits 71A are provided for multiple branch lines 74 is possible. In this example, each branch line 74 passes through a current limiting circuit 71A before connecting to a corresponding drain wiring 60. Typically, drain wirings 60 are provided for each column or row, so it is preferable to provide one current limiting circuit 71A for each drain wiring 60. In this case, if an abnormality occurs in one current limiting circuit 71A, the voltage of the drain wiring 60 connected to that current limiting circuit 71A will drop, potentially causing an abnormality in one column or row of pixels. However, the abnormality in one column or row of pixels can be corrected by interpolation.

As shown in FIG. 11(a), each branch line 74 may be further branched into multiple parts, resulting in a first branch portion 74a and a second branch portion 74b. In this example, the first branch portion 74a and the second branch portion 74b are arranged adjacent to each other. Alternatively, as shown in FIG. 11(b), the first branch portion 74a and the second branch portion 74b may be arranged so that they are not adjacent to each other. In this example, the first branch portions 74a of each branch line 74 are arranged adjacent to each other, and the second branch portions 74b of each branch line 74 are arranged adjacent to each other. In the example shown in FIG. 11(b), if an abnormality occurs in one current limiting circuit 71A, the abnormal drain wiring 60 can be dispersed rather than clustered, making it possible to correct the abnormality by complementation. The current limiting circuit is not limited to the above example, and other types of current circuits may also be used.

[Bending detection device]
Next, a description will be given of the bending detection device 1 including the bending sensor 10. The bending detection device 1 includes the bending sensor 10 and a detection unit 5 for detecting a signal from the bending sensor 10.

Fig. 12 is a diagram showing the configuration of the detection unit 5 according to this embodiment. As shown in Fig. 12, the detection unit 5 has a signal detection circuit 75, a control circuit 80, and a drive circuit 85. In the example shown in Fig. 12, the M signal wirings 62 are divided into _M2 blocks B (areas surrounded by dashed lines in Fig. 12) for _each M signal wiring. In other words, _M1 signal wirings 62 are provided in each of the _M2 blocks B. _M1 and _M2 are each integers equal to or greater than 2 that satisfy the relationship M = _M1 × _M2 .

The signal detection circuit 75 is electrically connected to the M signal wirings 62 and detects signals output from the M signal wirings 62. The signal detection circuit 75 is configured to sequentially read out each signal row by row in order to distinguish and detect each signal output from each signal wiring 62. The signal detection circuit 75 has, for example, M ₂ first switching circuits 81, M ₂ load resistors 76, M ₂ amplifiers 77, one second switching circuit 78, and one AD converter 79. The _{M 2} first switching circuits 81, the M ₂ load resistors 76, and the M ₂ amplifiers 77 are each divided into M ₂ blocks B. That is, each block B includes, in addition to M ₁ signal wirings 62, one first switching circuit 81, one load resistor 76, and one amplifier 77.

The first switching circuit 81 is, for example, an analog multiplexer including _M1 input terminals and one output terminal. An analog multiplexer can perform high-speed switching without losing analog signal information. However, when it is difficult to use an analog multiplexer, such as when the signal voltage range is wide, a relay may be used instead of the analog multiplexer. The _M1 input terminals of the first switching circuit 81 are electrically connected to the _M1 signal wirings 62 in the block B. The first switching circuit 81 switches the connection destination of the output terminal to one of the _M1 input terminals in response to a control signal S81 from the control circuit 80. In other words, the first switching circuit 81 selects one of the _M1 signal wirings 62 as the connection destination of the output terminal.

The amplifier 77 is, for example, a voltage detection amplifier. The amplifier 77 is, for example, a voltage follower circuit. The output terminal of the first switching circuit 81 is connected to the positive input terminal of the amplifier 77. The negative input terminal of the amplifier 77 is connected to the output terminal. The amplifier 77 current-amplifies the signal input from the signal wiring 62 via the first switching circuit 81. The load resistor 76 is disposed between the first switching circuit 81 and the amplifier 77. One end of the load resistor 76 is connected to a connection line connecting the output terminal of the first switching circuit 81 and one input terminal of the amplifier 77, and the other end of the load resistor 76 is connected to ground (GND).

The second switching circuit 78 is, for example, an analog multiplexer including _M1 input terminals and one output terminal. _{The M1} input terminals are respectively connected to the output terminals of the amplifiers 77 of the _M1 blocks B. The second switching circuit 78 switches the connection destination of the output terminal to one of the _M1 input terminals in response to the drive signal S61 from the drive circuit 85. In other words, the second switching circuit 78 selects one of the _M1 blocks B as the connection destination of the output terminal. The AD converter 79 is electrically connected to the output terminal of the second switching circuit 78. Therefore, the AD converter 79 is electrically connected to one of the signal wirings 62 selected by the first switching circuit 81 and the second switching circuit 78. The AD converter 79 converts a signal output from one of the signal wirings 62 into a digital value and outputs the digital value to the control circuit 80.

The drive circuit 85 is electrically connected to the N scanning wirings 61. The drive circuit 85 receives a control signal S85 from the control circuit 80 and outputs a drive signal S61 to the scanning wirings 61, thereby applying an ON voltage to one of the N scanning wirings 61 and an OFF voltage to all the other scanning wirings 61. The control circuit 80 is electrically connected to the signal detection circuit 75 and the drive circuit 85, and controls the signal detection circuit 75 and the drive circuit 85. The control circuit 80 is composed of, for example, a computer (e.g., a microcomputer) equipped with a processor such as a CPU and a storage device such as a memory.

The control circuit 80 outputs a control signal S81 to the signal detection circuit 75, which switches the connection destination of the first switching circuit 81 to one of the signal lines 62. The control circuit 80 also outputs a control signal S78 to the second switching circuit 78, which switches the connection destination of the second switching circuit 78 to one of the blocks B. The control circuit 80 then outputs a control signal S85 to the drive circuit 85, which applies an ON voltage to one of the scanning lines 61 and an OFF voltage to all other scanning lines 61.

As a result, an on-voltage is applied only to the scanning wiring 61 of one row, and signals are output to the signal wiring 62 connected to each of the M thin film transistor groups arranged in that row. The signal output from the pixel thin film transistor 21 of one pixel is then input to the AD converter 79 via the first switching circuit 81, the second switching circuit 78, etc., and read out by the control circuit 80. This obtains bending information for one pixel. Next, with the on-voltage applied only to the scanning wiring 61 of one row, the control circuit 80 switches the connection destination of the first switching circuit 81 and the connection destination of the second switching circuit 78 so that signals are sequentially read out from each signal wiring 62 of one row. This obtains bending information for one row. The operation of switching the connection destination of the first switching circuit 81 and the connection destination of the second switching circuit 78 will be described in detail below.

Next, the control circuit 80 outputs a control signal S85 to the drive circuit 85, causing it to apply an ON voltage to the scanning lines 61 in the next row and an OFF voltage to all other scanning lines 61. In this state, the control circuit 80 sequentially reads out signals from each signal line 62 by switching the connection destination of the first switching circuit 81 and the connection destination of the second switching circuit 78, as described above. This obtains bending information for the next row. The control circuit 80 repeats the above operation, sequentially switching the scanning lines 61 to which the ON voltage is applied, and sequentially reads out signals from each row. This obtains bending information for each row. When signals from all rows have been read out, bending information for all pixels, i.e., bending information for each pixel for one screen, is obtained. Furthermore, by repeating the above operation, bending information for each pixel for multiple screens, i.e., time-dependent bending information for all pixels, is obtained.

12 uses a first switching circuit 81, so the number of required load resistors 76 and the number of required amplifiers 77 are _M2 each, which can be reduced compared to the number (M) of signal wirings 62. Furthermore, the signal detection circuit 75 uses a second switching circuit 78, so when the number of input terminals of one second switching circuit 78 is L, the number of required AD converters 79 is _M2 /L, which can be reduced compared to the number ( _M ) of amplifiers 77. Note that when the number of input terminals of the second switching circuit 78, L, is equal to _M2 , the number of required AD converters 79 is one. In this way, by using the first switching circuit 81 and the second switching circuit 78 in the signal detection circuit 75, the number of required load resistors 76 and the number of required amplifiers 77 can be reduced compared to the number of signal wirings 62, and the number of required AD converters 79 can be reduced compared to the number of required amplifiers 77. This allows the circuit scale of the signal detection circuit 75 to be reduced, and the installation area and manufacturing costs of the signal detection circuit 75 to be reduced.

Furthermore, in the signal detection circuit 75, a load resistor 76 is provided on the output side (specifically, on the connection line between the output terminal of the first switching circuit 81 and the input terminal of the amplifier 77) rather than on the input side of the first switching circuit 81. This allows current to flow more easily through the first switching circuit 81, lowering impedance and reducing the influence of noise. Furthermore, in the signal detection circuit 75, current flows only through the one signal wiring 62 selected by the first switching circuit 81 out of the _M signal wirings 62 connected to the first switching circuit 81, thereby reducing power consumption.

The amplifier 77 is not limited to a voltage follower circuit, but may be a circuit with an amplification factor other than 1, or an inverting amplifier circuit. The amplifier 77 may also include a known oscillation prevention circuit, phase compensation circuit, capacitance correction circuit, and protection circuit. A FET (Field Effect Transistor) or the like may be used instead of the amplifier 77. In FIG. 12, the load resistor 76 is provided on the connection line connecting the signal wiring 62 and GND. However, for example, if the amplifier 77 is an inverting amplifier circuit, the load resistor 76 may be provided on the connection line connecting the signal wiring 62 and the output terminal of the amplifier 77. The detector 5 is not limited to the example shown in FIG. 12 and may have other configurations.

Figure 13 is a diagram showing another example of the detection unit 5. In the detection unit 5A shown in Figure 13, the signal detection circuit 75A has multiple counters 82. The multiple counters 82 are provided for each block B. In other words, one counter 82 is provided for each block B. In each block B, the counter 82 is electrically connected to the first switching circuit 81 and the control circuit 80. The counter 82 receives a control signal S82 from the control circuit 80 and outputs a control signal S81 to the first switching circuit 81 to control switching of the connection destination of the first switching circuit 81.

In the detection unit 5 shown in FIG. 12, in order for the control circuit 80 to control the first switching circuit 81, digital wiring with a bit number n (where n is an integer satisfying 2 ^n-1 < M ₁ ≦ 2 ⁿ ) capable of switching M ₁ input terminals is required. For example, the number of digital wirings required in each block B is two when M ₁ = 4, three when M ₁ = 8, and four when M ₁ = 16. In contrast, when a counter 82 is used for each block B as in the detection unit 5A shown in FIG. 13, it is sufficient to provide one digital wiring for each block B. This configuration is particularly effective when the number of digital outputs of the control circuit 80 is small.

Figure 14 is a diagram showing another example of the detection unit 5. In the detection unit 5B shown in Figure 14, the signal detection circuit 75B does not have a first switching circuit 81. In this case, the M signal wirings 62 are not divided into blocks B, so M load resistors 76 and M amplifiers 77 are required corresponding to the M signal wirings 62. An analog switch, for example, is used as the second switching circuit 78. Even with configurations such as the detection unit 5A shown in Figure 13 and the detection unit 5B shown in Figure 14, signals can be read out sequentially row by row, just like the detection unit 5 shown in Figure 12, so bending information can be obtained for each pixel.

[Bending detection method]
Next, the operation of the bend detection device 1 and the bend detection method according to this embodiment will be described with further reference to Figures 15 and 16. Figure 15 is a flowchart showing the operation of the bend detection device 1. Figures 16(a) to 16(e) are diagrams for explaining the operation of the bend detection device 1.

12, the _M2 blocks B will be referred to as blocks _B1 to _B2 , and the signal wirings 62 divided into the blocks _B1 to _B2 will be referred to as signal wirings _W1 to _W1 . In this case, the signal wirings 62 in the 1st to _M1st columns are the signal wirings _W1 to _W1 of block _B1 , and the signal wirings 62 in the ( _M1 + 1)th to _2M1st columns are the signal wirings _W1 to _W1 of block _B2 . The signal wirings 62 in the ( _M1 ( _M2 - 1) + 1)th to Mth columns are the signal wirings _W1 to _W1 of block _B2 . Furthermore, the signals output from the pixels arranged in N rows and M columns will be referred to as signals _D11 to _DNM .

FIG. 16(a) shows the gate voltage (drive signal S61) applied to the scanning wiring of the first row. FIG. 16(b) shows the relationship between the connection (selection) of the first switching circuit 81 and the output voltage of the amplifier 77 of block _B1 when applied to the scanning wiring of the first row. FIG. 16(c) shows the relationship between the connection (selection) of the first switching circuit 81 and the output voltage of the amplifier 77 of block _B2 when applied to the scanning wiring of the first row. FIG. 16(d) shows the relationship between the connection (selection) of the first switching circuit 81 and the output voltage of the amplifier 77 of block _B2 when applied to the scanning wiring of the first row. FIG. 16(e) shows the connection (selection) of the second switching circuit 78.

First, the control circuit 80 sets the connection destination of the first switching circuit 81 of each of the blocks _B1 to _BM2 to the signal wiring _W1 in advance. Then, the control circuit 80 applies an ON voltage to the scanning wiring 61 of the first row and an OFF voltage to the scanning wiring 61 of all other rows (step S11). Next, after waiting for a certain period of time, the control circuit 80 sets the connection destination of the second switching circuit 78 to the block _B1 .

Next, the control circuit 80 sequentially reads out signals from the signal wirings 62 connected to the pixels in the first row (step S12). First, with an on-voltage applied to the scanning wiring 61 in the first row, a signal _D11 is output from the signal wiring _W1 of the block _B1 (i.e., the signal wiring 62 in the first column). The control circuit 80 detects (reads out) the signal _D11 as bending information for the pixel in the first row and first column. The signal _D11 may be the signal (first signal) output from the first pixel thin film transistor 21A. Next, the control circuit 80 switches the connection destination of the first switching circuit 81 in the block _B1 to the signal wiring _W2 (i.e., the signal wiring 62 in the second column). Here, the control circuit 80 switches the connection destination of the second switching circuit 78 to the block _B2 without reading out the signal _D12 from the signal wiring _W2 . Then, a signal D1 _(M1+1) is output from the signal wiring _W1 of the block _B2 . The control circuit 80 detects the signal D _{1 (M 1 +1)} as bending information for the first row and the (M ₁ +1)th column.

Next, the control circuit 80 switches the connection destination of the first switching circuit 81 in block _B2 to signal wiring _W2 (i.e., signal wiring 62 in the ( _M1 +2)th column). Here, the control circuit 80 switches the connection destination of the second switching circuit ₇₈ to block _B3 without reading out the signal D1 _(M1+2) from the signal wiring _W2 in block B2. The control circuit 80 performs the above operation in the same way for blocks _B3 and onwards. Then, the control circuit 80 switches the connection destination of the second switching circuit 78 to block _B2M2 , reads out the signal D1 _(M1(M2-1)+1) from the signal wiring _W1 in block _B2M2 , and switches the connection destination of the first switching circuit 81 in block _B2M2 to signal wiring _W2 (i.e., signal wiring 62 in the ( _M1 ( _M2-1 )+2)th column). In this way, the control circuit 80 performs the first process of repeating, for each of the blocks B ₁ to B _M2 , the reading of the signal from the signal wiring W ₁ and the switching of the connection destination of the first switching circuit 81 to the signal wiring W ₂ .

Next, the control circuit 80 switches the connection destination of the second switching circuit 78 back to block _B1 . As a result, signal _D12 is output from signal wiring _W2 of block _B1 . At this point, the control circuit 80 finally detects signal _D12 as bending information for the first row and second column. Signal _D12 may be the signal (second signal) output from the second pixel thin film transistor 21B. Next, the control circuit 80 switches the connection destination of the first switching circuit 81 of block _B1 to signal wiring _W3 (i.e., signal wiring 62 in the third column). Here, the control circuit 80 switches the connection destination of the second switching circuit 78 to block _B3 without reading out signal _D13 from signal wiring _W3 of block _B2 . The control circuit 80 performs the above operation in the same way for blocks _B3 and onwards. Then, the control circuit 80 switches the connection destination of the second switching circuit 78 to block B _M2 , reads out the signal _{D1 (M1(M2-1)+2)} from the signal wiring _W2 of block B _M2 , and switches the connection destination of the first switching circuit 81 of block _{B M2} to the signal wiring _W3 (i.e., the signal wiring 62 in _the ( _M1 ( _M2-1 )+3)th column). In this way, the control circuit 80 performs the second process of repeatedly reading (detecting) the signal from the signal wiring _W2 and switching the connection destination of the first switching circuit 81 to the signal wiring W3 for each of blocks B 1 to _{B M2} .

The control circuit 80 performs a third process, similar to the first and second processes, in which, for each of the blocks _B1 to _B1M2 , it repeatedly reads out the signal from the signal wiring _W3 and switches the connection of the first switching circuit 81 to the signal wiring _W4 . Similarly, the control circuit 80 performs a fourth process in which it repeatedly reads out the signal from the signal wiring _W4 and switches the connection of the first switching circuit 81 to the signal wiring _W5 . The control circuit 80 then performs a similar process, performing an _M1 process in which, for each of the blocks _B1 to _B1M2 , it repeatedly reads out the signal from the signal wiring _W1M and switches the connection of the first switching circuit ₈₁ to the signal wiring W1. In this way, the control circuit 80 sequentially reads out signals _D11 to _D1M for one row and obtains bending information for each of the pixels for one row (step S13).

Next, the control circuit 80 applies an ON voltage to the scanning wiring 61 in the second row and an OFF voltage to the scanning wiring 61 in all other rows (step S11). Next, after waiting for a certain period of time, the control circuit 80 switches the connection destination of the second switching circuit 78 to block _B1 . Next, the control circuit 80 performs the first process through the _M2nd process, similar to when the ON voltage is applied only to the scanning wiring 61 in the first row (steps S12 and S13). This allows the control circuit 80 to acquire bending information for the second row. The control circuit 80 performs the above operations up to N rows, sequentially reading out signals _D21 to _DNM for all remaining rows. In this way, the control circuit 80 detects signals _D11 to _DNM for each pixel and acquires bending information for each pixel in one screen (i.e., the overall bending distribution). Furthermore, the control circuit 80 repeats the above operations to acquire bending information for multiple screens, i.e., time-dependent bending information for all pixels.

In this way, the control circuit 80 reads a signal from the signal wiring 62 connected to the first switching circuit 81, switches the connection of the first switching circuit 81 to the next signal wiring 62, and then, before reading the signal from the next signal wiring 62, switches the connection of the second switching circuit 78 to another block B and reads the signal from the first switching circuit 81 in that other block B. The control circuit 80 repeats this operation for each block B, thereby obtaining bending information for n rows. The control circuit 80 then performs the same operation for all rows to obtain bending information for one screen.

However, the control circuit 80 may reverse the procedure for switching the connection destination of the first switching circuit 81 to the next signal wiring 62 and the procedure for switching the connection destination of the second switching circuit 78 to the next block B. In this case, the control circuit 80 applies an ON voltage to the scanning wiring 61 in the nth row, reads out a signal from the signal wiring 62 connected to the first switching circuit 81, and then switches the connection destination of the second switching circuit 78 to the next block B. The control circuit 80 then switches the connection destination of the first switching circuit 81 to the next signal wiring 62, and before reading out a signal from the next signal wiring 62, reads out a signal from the signal wiring 62 connected to the first switching circuit 81 in the next block B. The control circuit 80 may repeat this operation for each block B to acquire bending information for n rows.

In the above-described operation, it takes a certain amount of time for the read signal to stabilize after the first switching circuit 81 switches its connection to the signal wiring 62. Therefore, as described above, the control circuit 80 measures (reads) the signal _D11 a certain time after applying an on-voltage to the scanning wiring 61 of the first row (see FIG. 16(b)). This "certain time" may be, for example, at least (M ₂ - 1) times the measurement time of the AD converter. In this case, a time of at least (M ₂ - 1) times the measurement time of the AD converter can be inserted between the time the first switching circuit 81 switches its connection to the signal wiring 62 and the time the signal is measured, thereby ensuring time for the signal to stabilize. This improves the accuracy of signal detection.

As described above, in the above-described operation, before reading a signal from the signal wiring 62 immediately after switching in a certain block B, the control circuit 80 reads a signal from the switched signal wiring 62 in another block B at least once (M ₂ −1 times in this embodiment) (see FIGS. 16( b) to 16(d)). While it takes some time for the signal from the signal wiring 62 immediately after switching to stabilize, the signal from the switched signal wiring 62 (i.e., the signal wiring 62 a certain amount of time has passed since switching) is in a stable state. Therefore, after switching the signal wiring 62 in a certain block B, the control circuit 80 does not wait until the signal from the switched signal wiring 62 stabilizes, but reads a signal from the switched signal wiring 62 in another block B while the signal from the switched signal wiring 62 stabilizes. This allows for efficient reading of signals from each signal wiring 62. Furthermore, reading signals in a stable state can improve signal detection accuracy.

[Operation and effect of the first embodiment]
The effects achieved by the bending sensor 10 and bending detection device 1 according to the present embodiment described above will now be described. When bending is applied to the bending sensor 10, stress is applied to the piezoelectric layer 30, generating a voltage in the piezoelectric layer 30, which in turn generates a potential difference between the counter electrode 35 and the pixel electrodes 25 (i.e., a voltage is generated in the pixel electrodes 25). The pixel electrodes 25 are spaced apart from each other in a planar view and are electrically insulated from each other. Therefore, the voltages of the first pixel electrode 25A and the second pixel electrode 25B change independently. Therefore, by separately detecting a signal indicating the voltage of the first pixel electrode 25A and a signal indicating the voltage of the second pixel electrode 25B using the first pixel thin film transistor 21A and the second pixel thin film transistor 21B, bending information at the position of the first pixel electrode 25A and bending information at the position of the second pixel electrode 25B can be separately obtained. This allows the local bending state at the position of each pixel electrode 25 to be grasped. Therefore, the bending sensor 10 according to this embodiment makes it possible to grasp the bending state in detail.

In this embodiment, the multiple pixel electrodes 25 are arranged in a matrix. This allows bending information to be acquired for each pixel electrode 25, making it possible to grasp the bending state more locally. As a result, it becomes possible to grasp the bending state of the bending sensor 10 in more detail.

Second Embodiment
Next, a bending sensor according to a second embodiment will be described. In the second embodiment, the shape of the pixel electrodes is different from that of the first embodiment. In the following second embodiment, the description of the same points as in the first embodiment will be omitted as appropriate, and the points different from the first embodiment will be mainly described.

Figure 17 is a plan view of the bending sensor 10A according to the second embodiment. Figure 18(a) is a cross-sectional view of the bending sensor 10A taken along line A2-A2 in Figure 17. Figure 18(b) is a cross-sectional view of the bending sensor 10A taken along line A3-A3 in Figure 17. In the bending sensor 10A, the multiple pixel electrodes 25 include multiple first pixel electrodes 25A (first electrodes) extending in the Y direction and multiple second pixel electrodes 25B (second electrodes) extending in the X direction. "A shape extending in the Y direction" means a shape whose longitudinal direction is the Y direction. "A shape extending in the X direction" means a shape whose longitudinal direction is the X direction.

The first pixel electrode 25A has, for example, a rectangular shape with its longitudinal direction in the Y direction and its transverse direction in the X direction (i.e., a rectangular shape that is long in the Y direction and short in the X direction). Therefore, the length of the first pixel electrode 25A in the Y direction is longer than its width in the X direction. The width of the first pixel electrode 25A in the X direction may be constant, for example, at each position of the first pixel electrode 25A along the Y direction. The second pixel electrode 25B has, for example, a rectangular shape with its longitudinal direction in the X direction and its transverse direction in the Y direction (i.e., a rectangular shape that is long in the X direction and short in the Y direction). Therefore, the length of the second pixel electrode 25B in the X direction is longer than its width in the Y direction. The width of the second pixel electrode 25B in the Y direction may be constant, for example, at each position of the second pixel electrode 25B along the X direction.

When the second pixel electrode 25B is rotated 90° in a plan view, the shape of the second pixel electrode 25B becomes the same as that of the first pixel electrode 25A. Therefore, the length of the first pixel electrode 25A in the Y direction is longer than the width of the second pixel electrode 25B in the Y direction, and the length of the second pixel electrode 25B in the X direction is longer than the width of the first pixel electrode 25A in the X direction. Also, as in the first embodiment, each pixel electrode 25 has a higher Young's modulus than each inter-pixel electrode region 26. As shown in FIG. 17 , the first pixel electrodes 25A and the second pixel electrodes 25B are arranged alternately, for example, along the X and Y directions.

In the example shown in Figures 18(a) and 18(b), the neutral plane NP is located on the back surface 25b of each pixel electrode 25. The layer including each pixel electrode 25, the piezoelectric layer 30, and the counter electrode 35 are located above the neutral plane NP. Therefore, the entire pixel electrode 25 and the entire inter-pixel electrode region 26 are located on the same side of the neutral plane NP as the piezoelectric layer 30. Note that at least a portion of the pixel electrode 25 and at least a portion of the inter-pixel electrode region 26 may also be located on the same side of the neutral plane NP as the piezoelectric layer 30.

For ease of understanding, consider only the portion above the neutral plane NP, where stress is applied in the same direction as the piezoelectric layer 30, when the neutral plane NP coincides with the rear surface 25b of the pixel electrode 25. Here, let P be the pitch between adjacent pixels, U be the length of the long side of the pixel electrode 25, V be the length of the short side of the pixel electrode 25, T1 be the thickness of the pixel electrode 25 and the thickness of the inter-pixel electrode region 26, E11 be the Young's modulus of the pixel electrode 25, E12 be the Young's modulus of the inter-pixel electrode region 26, T2 be the thickness of the piezoelectric layer 30, E2 be the Young's modulus of the piezoelectric layer 30, T3 be the thickness of the counter electrode 35, and E3 be the Young's modulus of the counter electrode 35. In this case, as shown in Figures 18(a) and 18(b), the width in the X direction of the first pixel electrode 25A is represented by V. The length in the X direction of the second pixel electrode 25B is represented by U, which is longer than V (V<<U). The length U may be set to be equal to or shorter than the pixel pitch P.

When the parameters are set as described above, if the composite Young's modulus of the pixel electrode 25, the piezoelectric layer 30, and the counter electrode 35 is EC1, and the composite Young's modulus of the inter-pixel electrode region 26, the piezoelectric layer 30, and the counter electrode 35 is EC2, the composite Young's modulus EC1 and the composite Young's modulus EC2 are expressed by the following equations (15) and (16), respectively.
When stress S (tensile stress or compressive stress) is applied in the X direction above the neutral plane NP in the cross section shown in FIG. 18(a), the displacement in the X direction of the bending sensor 10A is denoted as ΔL1. The displacement ΔL1 can be expressed by the following equation (17):
If E12<<E11, the composite Young's modulus EC1 of the pixel electrode 25, piezoelectric layer 30, and counter electrode 35 is greater than the composite Young's modulus EC2 of the inter-pixel electrode region 26, piezoelectric layer 30, and counter electrode 35, and therefore the portion where the inter-pixel electrode region 26 is located is more likely to displace in the X direction than the portion where the pixel electrode 25 is located. Then, when the displacement ΔL1 is the same for any (U+V)/2P, the smaller (U+V)/2P is, the smaller the stress S is, and the larger (U+V)/2P is, the larger the stress S is. Furthermore, as the stress S increases, more charge is generated in the piezoelectric layer 30, and the voltage generated in the piezoelectric layer 30 increases.

On the other hand, when stress S is applied in the X direction above the neutral plane NP in the cross section shown in FIG. 18(b), if the displacement in the X direction that occurs in the bending sensor 10A is ΔL2, the displacement ΔL2 can be expressed as follows:
In equation (18), (U + V) in equation (17) is replaced with V. Because V is smaller than (U + V), when the displacement ΔL2 is equal to the displacement ΔL1, the stress S in equation (18) is smaller than the stress S in equation (17). Therefore, in the cross section shown in FIG. 18( b ), fewer charges are generated in the piezoelectric layer 30 than in the cross section shown in FIG. 18( a ), and the voltage generated in the piezoelectric layer 30 is smaller.

In Figure 17, the region RA where the pixel electrodes 25 exist in the cross section shown in Figure 18(a) is indicated by diagonal hatching, and the region RB where the pixel electrodes 25 exist in the cross section shown in Figure 18(b) is indicated by dotted hatching. In region RA, (U + V)/2P (i.e., the proportion of the total X-direction length of the pixel electrodes 25 to the pitch P of two pixels) is large, so a large voltage is generated when the bending sensor 10A is bent in the X direction. On the other hand, in region RB, V/2P is smaller than (U + V)/2P, so a smaller voltage is generated when the bending sensor 10A is bent in the X direction than in region RA. Thus, when the bending sensor 10A is bent in the X direction, the second pixel electrode 25B, which is entirely occupied by region RA, generates a large amount of charge, while the first pixel electrode 25A, which is mostly occupied by region RB, generates a small amount of charge. Therefore, the voltage generated in the first pixel electrode 25A is smaller than the voltage generated in the second pixel electrode 25B. In other words, the second pixel electrode 25B has a higher sensitivity to X-bending than the first pixel electrode 25A. The same effect can be achieved even if the neutral plane NP does not coincide with the rear surface 25b of the pixel electrode 25.

Similarly, when bending sensor 10A in the Y direction, a large amount of charge is generated in first pixel electrode 25A and a small amount of charge is generated in second pixel electrode 25B, so that first pixel electrode 25A generates a larger voltage than second pixel electrode 25B. In other words, it can be said that first pixel electrode 25A is more sensitive to Y bending than second pixel electrode 25B. If the voltage of second pixel electrode 25B is _VX and the voltage of first pixel electrode 25A is _VY , these can be formulated in the same way as equations (6) and (7), and the magnitude of X bending _BX and the magnitude of Y bending _BY can be found in the same way as equations (8) and (9).

In this embodiment, it is also possible to assume that two first pixel electrodes 25A and two second pixel electrodes 25B are arranged within one pixel, i.e., four sub-pixels are arranged within one pixel. In this case, the voltage _VX may be the average value of the voltages obtained from the two second pixel electrodes 25B, and the voltage _VY may be the average value of the voltages obtained from the two first pixel electrodes 25A. The number of pixels (sub-pixels) arranged within one pixel does not have to be four, and may be any number such as two, three, six, or eight.

Note that equations (17) and (18) assume that the Young's modulus E11 of the pixel electrode 25 is greater than the Young's modulus E12 of the inter-pixel electrode region 26. Therefore, the voltage relationship between the above-mentioned region RA and region RB is derived using the difference between the Young's modulus E11 of the pixel electrode 25 and the Young's modulus E12 of the inter-pixel electrode region 26. To take advantage of this difference in Young's modulus, it is preferable that most of the pixel electrode 25 and most of the inter-pixel electrode region 26 are located on the same side of the neutral plane NP as the piezoelectric layer 30. Furthermore, when considering the composite Young's modulus EC1 and composite Young's modulus EC2 when the bending sensor 10A is bent, the equations become more complex, but the pixel electrode 25 displaces more than the inter-pixel electrode region 26, and the larger (U + V) the greater the voltage.

Figure 19(a) is a cross-sectional view showing the bending sensor 10A bent convexly in the cross section shown in Figure 18(a). Figure 19(b) is a cross-sectional view showing the bending sensor 10A bent convexly in the cross section shown in Figure 18(b). In Figures 19(a) and 19(b), bending the bending sensor 10A in the X direction causes the bending sensor 10A to bend so that it is convex upward in the XZ cross section. When the piezoelectric layer 30 is located above the neutral plane NP, as in this embodiment, bending the bending sensor 10A convexly as shown in Figures 19(a) and 19(b) applies tensile stress in the X direction to the piezoelectric layer 30.

As shown in FIG. 19(a), in the region RA of the first pixel electrode 25A, a tensile stress SS1A in the X direction is applied to the piezoelectric layer 30, and in the region RA of the second pixel electrode 25B, a tensile stress SS1A in the X direction is applied to the piezoelectric layer 30. In the region RB of the first pixel electrode 25A, a tensile stress SS1B in the X direction is applied to the piezoelectric layer 30. However, |SS1A| >> |SS1B| holds. In this case, as can be seen from FIG. 17, a voltage corresponding mainly to the tensile stress SS1B is generated in the first pixel electrode 25A, and a voltage corresponding to the tensile stress SS1A is generated in the second pixel electrode 25B. In this embodiment, the tensile stress SS1B is smaller than the tensile stress SS1A, so the absolute value of the voltage generated in the first pixel electrode 25A is smaller than the absolute value of the voltage generated in the second pixel electrode 25B.

Figure 20(a) is a cross-sectional view showing the bending sensor 10A bent concavely in the cross section shown in Figure 18(a). Figure 20(b) is a cross-sectional view showing the bending sensor 10A bent concavely in the cross section shown in Figure 18(b). In Figures 20(a) and 20(b), bending the bending sensor 10A in the X direction causes the bending sensor 10A to bend concavely upward in the XZ cross section. When the piezoelectric layer 30 is located above the neutral plane NP, as in this embodiment, bending the bending sensor 10A concavely as shown in Figures 20(a) and 20(b) applies compressive stress in the X direction to the piezoelectric layer 30.

As shown in Figure 20(a), at the position of region RA of the first pixel electrode 25A, compressive stress SS2A in the X direction is applied to the piezoelectric layer 30, and at the position of region RA of the second pixel electrode 25B, compressive stress SS2A in the X direction is applied to the piezoelectric layer 30. At the position of region RB of the first pixel electrode 25A, compressive stress SS2B in the X direction is applied to the piezoelectric layer 30, where |SS2A|>>|SS2B|. In this case, a voltage corresponding mainly to compressive stress SS2B is generated in the first pixel electrode 25A, and a voltage corresponding to compressive stress SS2A is generated in the second pixel electrode 25B. In this embodiment, compressive stress SS2B is smaller than compressive stress SS2A, so the absolute value of the voltage generated in the first pixel electrode 25A is smaller than the absolute value of the voltage generated in the second pixel electrode 25B. Note that the voltage generated in the first pixel electrode 25A and the second pixel electrode 25B in the cases shown in Figures 20(a) and 20(b) is opposite in direction to the voltage generated in the first pixel electrode 25A and the second pixel electrode 25B in the cases shown in Figures 19(a) and 19(b).

With this element configuration, it is possible to independently detect the magnitude of bending in the X direction and the magnitude of bending in the Y direction, even when a non-stretched film or a biaxially stretched film (e.g., non-stretched PVDF) is used as the piezoelectric layer 30. To further improve accuracy, let _VX be the voltage output from the thin-film transistor connected to the second pixel electrode 25B long in the X direction, VY be the voltage output from the thin-film transistor connected to the first pixel electrode 25A long in the _Y direction, _BX be the magnitude of X bending, and _BY be the magnitude of Y bending. The voltages _VX and _VY can be formulated as shown in the above-mentioned equations (6) and (7), respectively. Here, _k1 and _k2 are constants that satisfy k1>>k2.

Therefore, if k1 and k2 are experimentally determined, the magnitude of bending in the X direction _BX and the magnitude of bending in the Y direction _BY can be derived from equations (6) and (7) as equations (8) and (9). In this way, even when using the bending sensor 10A according to this embodiment, it is possible to independently detect the magnitude of bending in the X direction _BX and the magnitude of bending in the Y direction _BY .

[Operation and effect of the second embodiment]
The effects achieved by the bending sensor 10A according to the present embodiment described above will now be described. In this embodiment, the first pixel electrode 25A has a shape extending in the Y direction, and the second pixel electrode 25B has a shape extending in the X direction. Therefore, the first pixel electrode 25A is strongly affected by Y bending, and the second pixel electrode 25B is strongly affected by X bending. Therefore, by detecting a signal indicating the voltage of the first pixel electrode 25A as bending information in the Y direction and a signal indicating the voltage of the second pixel electrode 25B as bending information in the X direction, it is possible to distinguish between Y bending and X bending. This makes it possible to grasp the bending state of the bending sensor 10A in more detail.

In this embodiment, the pixel electrodes 25 have a higher Young's modulus than the inter-pixel electrode region 26. Therefore, the inter-pixel electrode region 26 is more easily stretched than the pixel electrodes 25. Therefore, the stress applied to the piezoelectric layer 30 at the pixel electrodes 25 is greater than the stress applied to the piezoelectric layer 30 at the inter-pixel electrode region 26. In this case, the stress at the positions of the first pixel electrodes 25A, which are more prevalent in the Y direction, is greater during Y bending, while the stress at the positions of the second pixel electrodes 25B, which are more prevalent in the X direction, is greater during X bending. In other words, the voltage of the first pixel electrode 25A exhibits a greater value during Y bending, and the voltage of the second pixel electrode 25B exhibits a greater value during X bending. Therefore, the above-described configuration more reliably achieves a configuration in which the first pixel electrode 25A is strongly influenced by Y bending and the second pixel electrode 25B is strongly influenced by X bending. This makes it possible to more reliably distinguish and grasp the Y bending state and the X bending state.

In this embodiment, the inter-pixel electrode region 26 is made of an electrically insulating adhesive. In this case, a configuration in which the Young's modulus of the pixel electrodes 25 is higher than that of the inter-pixel electrode region 26 can be easily achieved. Furthermore, by providing an electrically insulating adhesive between each pixel electrode 25, the positional relationship between each pixel electrode 25 can be fixed while ensuring electrical insulation between each pixel electrode 25.

In this embodiment, all of the pixel electrodes 25 and all of the inter-pixel electrode regions 26 are arranged on the same side of the neutral plane NP as the piezoelectric layer 30. In this case, by utilizing the magnitude relationship between the Young's modulus of the pixel electrodes 25 and the Young's modulus of the inter-pixel electrode regions 26, it is possible to more reliably achieve a state in which the first pixel electrode 25A is strongly influenced by Y bending and the second pixel electrode 25B is strongly influenced by X bending. This makes it possible to more reliably distinguish and grasp the Y bending state and the X bending state.

In this embodiment, each first pixel electrode 25A and each of the plurality of second pixel electrodes 25B are arranged in a matrix, alternating with one another. In this case, by acquiring bending information for each pixel electrode 25, it is possible to grasp the bending state more locally. Furthermore, by arranging each first pixel electrode 25A and each second pixel electrode 25B alternately, it is possible to disperse each first pixel electrode 25A for obtaining bending information in the Y direction and each second pixel electrode 25B for obtaining bending information in the X direction, thereby preventing bias in the bending state information obtained.

In the bending sensor 10 according to the first embodiment, in order to independently detect bending information in the X and Y directions, two bending sensors 10 each having a uniaxially stretched piezoelectric layer 30 had to be prepared and stacked so that the stretching directions of the piezoelectric layers 30 were perpendicular to each other. However, in the second embodiment, a single bending sensor 10A having a biaxially stretched or non-stretched piezoelectric layer 30 can be used to independently detect bending information in the X and Y directions. Furthermore, in the second embodiment, a thin-film transistor array 201 may be used instead of the thin-film transistor array 20, or a thin-film transistor array having another circuit configuration may be used.

[Modification of the second embodiment]
The shapes of the first pixel electrode 25A and the second pixel electrode 25B are not limited to the example of the second embodiment described above. FIGS. 21(a) to 21(c), 22(a), and 22(b) are plan views showing other examples of the bending sensor 10A according to the second embodiment. As in the bending sensor 101A shown in FIG. 21(a), the first pixel electrode 251A and the second pixel electrode 251B may each have a cross shape. In this case, the first pixel electrode 251A has a portion 251a extending in the Y direction and a portion 251b extending in the X direction. The portion 251b is disposed, for example, so as to intersect with the center of the portion 251a. The length of the portion 251b in the X direction is set shorter than the length of the portion 251a in the Y direction. The second pixel electrode 251B similarly has a portion 251c extending in the X direction and a portion 251d extending in the Y direction. The portion 251d is disposed, for example, so as to intersect with the center of the portion 251c. The length of the portion 251d in the Y direction is set to be shorter than the length of the portion 251c in the X direction.

As in the bending sensor 102A shown in FIG. 21(b), the first pixel electrode 252A may have an elliptical (oval) shape extending in the Y direction. Similarly, the second pixel electrode 252B may have an elliptical (oval) shape extending in the X direction. Alternatively, as in the bending sensor 103A shown in FIG. 21(c), the first pixel electrode 253A may have an isosceles triangular shape extending in the Y direction. In this case, the first pixel electrode 253A may be arranged so that the apex of the isosceles triangle faces one side in the Y direction, or so that the apex of the isosceles triangle faces the other side in the Y direction. Similarly, the second pixel electrode 253B may have an isosceles triangular shape extending in the X direction. In this case, the second pixel electrode 253B may be arranged so that the apex of the isosceles triangle faces one side in the X direction, or so that the apex of the isosceles triangle faces the other side in the X direction.

As in the bending sensor 104A shown in FIG. 22(a), the X-direction width of the first pixel electrode 254A may vary at each position on the first pixel electrode 254A along the Y direction. Specifically, the X-direction width of the first pixel electrode 254A may be smallest at the center of the first pixel electrode 254A in the Y direction, and gradually increase as the distance from the center increases in the Y direction. The Y-direction width of the second pixel electrode 254B may vary at each position on the second pixel electrode 254B along the X direction. Specifically, the Y-direction width of the second pixel electrode 254B may be smallest at the center of the second pixel electrode 254B in the X direction, and gradually increase as the distance from the center increases in the X direction.

As in the bending sensor 105A shown in FIG. 22(b), the first pixel electrode 255A and the second pixel electrode 255B do not have to be arranged to fit within one pixel, but may extend outside the pixel. In this case, the first pixel electrode 255A extends in the Y direction beyond the boundary line BL to a position where it does not contact the second pixel electrode 255B adjacent in the Y direction. Similarly, the second pixel electrode 255B extends in the X direction beyond the boundary line BL to a position where it does not contact the first pixel electrode 255A adjacent in the X direction. Furthermore, the multiple pixel electrodes 25 may include a third pixel electrode other than the first pixel electrode 25A and the second pixel electrode 25B. In this case, the third pixel electrode may extend in a direction inclined with respect to both the X direction and the Y direction. The bending sensor described above also achieves the same effects as the bending sensor 10A according to the second embodiment.

[Third embodiment]
Next, a bending sensor according to a third embodiment will be described. In the third embodiment, the shape of the pixel electrode and the shape of the counter electrode are different from those of the first embodiment. In the following third embodiment, the description of the same points as in the first embodiment will be omitted as appropriate, and the differences from the first embodiment will be mainly described.

Figure 23 is a plan view of a bending sensor 10B according to the third embodiment. Figure 24(a) is a cross-sectional view of the bending sensor 10B taken along line A4-A4 in Figure 23. Figure 24(b) is a cross-sectional view of the bending sensor 10B taken along line A5-A5 in Figure 23. In the bending sensor 10B, the multiple pixel electrodes 25 include multiple first pixel electrodes 25A (first electrodes) extending in the Y direction and multiple second pixel electrodes 25B (second electrodes) extending in the X direction. "A shape extending in the Y direction" refers to a shape whose longitudinal direction is the Y direction. "A shape extending in the X direction" refers to a shape whose longitudinal direction is the X direction. As shown in Figure 23, the first pixel electrodes 25A and the second pixel electrodes 25B are alternately arranged along the X and Y directions.

The first pixel electrode 25A has, for example, a rectangular shape with its longitudinal direction in the Y direction and its transverse direction in the X direction (i.e., a rectangular shape that is long in the Y direction and short in the X direction). Therefore, the length of the first pixel electrode 25A in the Y direction is longer than its width in the X direction. The width of the first pixel electrode 25A in the X direction may be constant, for example, at each position of the first pixel electrode 25A along the Y direction. The second pixel electrode 25B has, for example, a rectangular shape with its longitudinal direction in the X direction and its transverse direction in the Y direction (i.e., a rectangular shape that is long in the X direction and short in the Y direction). Therefore, the length of the second pixel electrode 25B in the X direction is longer than its width in the Y direction. The width of the second pixel electrode 25B in the Y direction may be constant, for example, at each position of the second pixel electrode 25B along the X direction.

When the second pixel electrode 25B is rotated 90° in a plan view, the shape of the second pixel electrode 25B becomes the same as that of the first pixel electrode 25A. Therefore, the length in the Y direction of the first pixel electrode 25A is longer than the width in the Y direction of the second pixel electrode 25B, and the length in the X direction of the second pixel electrode 25B is longer than the width in the X direction of the first pixel electrode 25A. Also, as in the first embodiment, each pixel electrode 25 may have a higher Young's modulus than each inter-pixel electrode region 26.

Furthermore, in the third embodiment, the counter electrode 35 has a lattice shape in plan view. The counter electrode 35 has a plurality of first extension portions 35A extending in the Y direction and a plurality of second extension portions 35B extending in the X direction. In plan view, each first extension portion 35A extends linearly along the Y direction so as to encompass each first pixel electrode 25A, and is spaced apart at regular intervals along the X direction. The state in which the first extension portion 35A encompasses the first pixel electrode 25A refers to the state in which the first pixel electrode 25A is contained within the first extension portion 35A in plan view.

Therefore, the X-direction width of the first extension portion 35A is the same as or greater than the X-direction width of the first pixel electrode 25A. The Y-direction length of the first extension portion 35A is greater than the Y-direction length of the first pixel electrode 25A. The first extension portion 35A extends continuously in the Y direction from one end to the other end of the flexible substrate 15. Note that the first extension portion 35A does not necessarily have to encompass the first pixel electrode 25A; the first extension portion 35A may overlap the first pixel electrode 25A in a planar view. Therefore, the first pixel electrode 25A may be positioned to extend beyond the first extension portion 35A in a planar view, or the X-direction width of the first extension portion 35A may be smaller than the X-direction width of the first pixel electrode 25A.

In a plan view, each second extension portion 35B extends linearly along the X direction to encompass each second pixel electrode 25B, and is spaced apart at regular intervals along the Y direction. Each second extension portion 35B is connected perpendicularly to each first extension portion 35A. Therefore, each first extension portion 35A and each second extension portion 35B are arranged in a grid pattern in the X and Y directions. A state in which the second extension portion 35B encompasses a second pixel electrode 25B refers to a state in which the second pixel electrode 25B is contained within the second extension portion 35B in a plan view.

Therefore, the Y-direction width of the second extension portion 35B is the same as or greater than the Y-direction width of the second pixel electrode 25B. The X-direction length of the second extension portion 35B is greater than the X-direction length of the second pixel electrode 25B. The second extension portion 35B extends continuously in the X-direction from one end to the other end of the flexible substrate 15. Note that the second extension portion 35B does not necessarily have to encompass the second pixel electrode 25B; the second extension portion 35B may overlap the second pixel electrode 25B in a planar view. Therefore, the second pixel electrode 25B may be positioned to extend beyond the second extension portion 35B in a planar view, or the Y-direction width of the second extension portion 35B may be smaller than the Y-direction width of the second pixel electrode 25B.

As shown in Figures 24(a) and 24(b), the neutral plane NP is located on the back surface 25b of each pixel electrode 25, and the layer including each pixel electrode 25, the piezoelectric layer 30, and the counter electrode 35 are located above the neutral plane NP. Therefore, the entire pixel electrode 25 and the entire inter-pixel electrode region 26 are located on the same side of the neutral plane NP as the piezoelectric layer 30. Note that at least a portion of the pixel electrode 25 and at least a portion of the inter-pixel electrode region 26 may be located on the same side of the neutral plane NP as the piezoelectric layer 30.

For ease of understanding, consider only the portion above the neutral plane NP where stress is applied in the same direction as the piezoelectric layer 30 when the neutral plane NP coincides with the rear surface 25b of the pixel electrode 25. Here, let P be the pitch between adjacent pixels, U be the length of the long side of the pixel electrode 25, V be the length of the short side of the pixel electrode 25, T1 be the thickness of the pixel electrode 25 and the thickness of the inter-pixel electrode region 26, E11 be the Young's modulus of the pixel electrode 25, E12 be the Young's modulus of the inter-pixel electrode region 26, T2 be the thickness of the piezoelectric layer 30, E2 be the Young's modulus of the piezoelectric layer 30, T3 be the thickness of the counter electrode 35, and E3 be the Young's modulus of the counter electrode 35. In this case, as shown in Figures 24(a) and 24(b), the X-direction length of the first pixel electrode 25A is represented by V, and the X-direction length of the second pixel electrode 25B is represented by U, which is longer than V (V<<U). The length U may be set to be equal to or shorter than the pixel pitch P.

When the parameters are set as described above, if the composite Young's modulus of the pixel electrode 25, the piezoelectric layer 30, and the counter electrode 35 is EC1, the composite Young's modulus of the inter-pixel electrode region 26, the piezoelectric layer 30, and the counter electrode 35 is EC2, and the composite Young's modulus of the inter-pixel electrode region 26 and the piezoelectric layer 30 is EC3, the composite Young's modulus EC1 and the composite Young's modulus EC2 are respectively expressed by the above-mentioned formulas (15) and (16). Moreover, the composite Young's modulus EC3 is expressed by the following formula (19).

24(a), if stress S (tensile stress or compressive stress) is applied in the X direction above the neutral plane NP, and the displacement in the X direction of the bending sensor 10B is ΔL1, the displacement ΔL1 can be expressed by the above-mentioned formula (17). On the other hand, if stress S is applied in the X direction above the neutral plane NP in the cross section shown in FIG. 24(b), if the displacement in the X direction of the bending sensor 10B is ΔL2, the displacement ΔL2 can be expressed by the following formula (20).
Here, the composite Young's moduli EC1 and EC2 of the portions of the bending sensor 10B where the counter electrode 35 is located are greater than the composite Young's modulus EC3 of the portions where the counter electrode 35 is not located. Therefore, the portions where the counter electrode 35 is not located are more likely to displace (stretch) in the X direction than the portions where the counter electrode 35 is located. Then, when the displacements ΔL1 and ΔL2 are equal, the charge generated in the piezoelectric layer 30 is smaller in the cross section shown in Figure 24(b) than in the cross section shown in Figure 24(a), and the voltage generated in the piezoelectric layer 30 is smaller.

In Figure 23, the region RA where the counter electrode 35 exists in the cross section shown in Figure 24(a) is indicated by diagonal hatching, and the region RB where the counter electrode 35 exists in the cross section shown in Figure 24(b) is indicated by dotted hatching. In region RA, the counter electrode 35 is located over the entire region. Therefore, in region RA, a large voltage is generated when bending sensor 10B in the X direction.

On the other hand, in region RB, the opposing electrode 35 is present in only a small portion. Therefore, in region RB, the voltage generated when bending sensor 10B in the X direction is smaller than in region RA. Thus, when bending sensor 10B in the X direction, a large amount of charge is generated in second pixel electrode 25B, which is entirely in region RA, while a small amount of charge is generated in first pixel electrode 25A, which is mostly in region RB. Therefore, the voltage generated in first pixel electrode 25A is smaller than the voltage generated in second pixel electrode 25B. In other words, it can be said that second pixel electrode 25B, which extends in the X direction, is more sensitive to X bending than first pixel electrode 25A, which extends in the Y direction. The same effect is achieved even when neutral plane NP does not coincide with the rear surface 25b of pixel electrode 25.

Similarly, when bending sensor 10B is bent in the Y direction, the first pixel electrode 25A extending in the Y direction generates a large amount of charge, while the second pixel electrode 25B extending in the X direction generates a small amount of charge, resulting in a larger voltage being generated in the first pixel electrode 25A than in the second pixel electrode 25B. In other words, it can be said that the first pixel electrode 25A is more sensitive to Y bending than the second pixel electrode 25B. If the voltage of second pixel electrode 25B is _VX and the voltage of first pixel electrode 25A is _VY , these can be formulated in the same way as equations (6) and (7), and the magnitude of X bending _BX and the magnitude of Y bending _BY can be found in the same way as equations (8) and (9).

In this embodiment, it is also possible to assume that two first pixel electrodes 25A and two second pixel electrodes 25B are arranged within one pixel, i.e., four sub-pixels are arranged within one pixel. In this case, the voltage _VX may be the average value of the voltages obtained from the two second pixel electrodes 25B, and the voltage _VY may be the average value of the voltages obtained from the two first pixel electrodes 25A. The number of pixels (sub-pixels) arranged within one pixel does not have to be four, and may be any number such as two, three, six, or eight.

Figure 25(a) is a cross-sectional view showing the bending sensor 10B bent convexly in the cross section shown in Figure 24(a). Figure 25(b) is a cross-sectional view showing the bending sensor 10B bent convexly in the cross section shown in Figure 24(b). In Figures 25(a) and 25(b), bending the bending sensor 10B in the X direction causes the bending sensor 10B to bend so that it is convex upward in the XZ cross section. When the piezoelectric layer 30 is located above the neutral plane NP, as in this embodiment, bending the bending sensor 10B convexly as shown in Figures 25(a) and 25(b) applies tensile stress in the X direction to the piezoelectric layer 30.

As shown in FIG. 25A, in the region RA of the first pixel electrode 25A, a tensile stress SS1A in the X direction is applied to the piezoelectric layer 30, and in the region RA of the second pixel electrode 25B, a tensile stress SS1A in the X direction is applied to the piezoelectric layer 30. In the region RB of the first pixel electrode 25A, a tensile stress SS1B in the X direction is applied to the piezoelectric layer 30, where |SS1A|>>|SS1B|. In this case, a voltage corresponding mainly to the tensile stress SS1B is generated in the first pixel electrode 25A, and a voltage corresponding to the tensile stress SS1A is generated in the second pixel electrode 25B. In this embodiment, the tensile stress SS1B is smaller than the tensile stress SS1A, so the absolute value of the voltage generated in the first pixel electrode 25A is smaller than the absolute value of the voltage generated in the second pixel electrode 25B.

Figure 26(a) is a cross-sectional view showing the bending sensor 10B bent concavely in the cross section shown in Figure 24(a). Figure 26(b) is a cross-sectional view showing the bending sensor 10B bent concavely in the cross section shown in Figure 24(b). In Figures 26(a) and 26(b), bending the bending sensor 10B in the X direction causes the bending sensor 10B to bend concavely upward in the XZ cross section. When the piezoelectric layer 30 is located above the neutral plane NP, as in this embodiment, bending the bending sensor 10B concavely as shown in Figures 26(a) and 26(b) applies compressive stress in the X direction to the piezoelectric layer 30.

As shown in Figure 26(a), at the position of region RA of the first pixel electrode 25A, compressive stress SS2A in the X direction is applied to the piezoelectric layer 30, and at the position of region RA of the second pixel electrode 25B, compressive stress SS2A in the X direction is applied to the piezoelectric layer 30. At the position of region RB of the first pixel electrode 25A, compressive stress SS2B in the X direction is applied to the piezoelectric layer 30, where |SS2A|>>|SS2B|. In this case, a voltage corresponding mainly to compressive stress SS2B is generated in the first pixel electrode 25A, and a voltage corresponding to compressive stress SS2A is generated in the second pixel electrode 25B. In this embodiment, compressive stress SS2B is smaller than compressive stress SS2A. Therefore, the absolute value of the voltage generated in the first pixel electrode 25A is smaller than the absolute value of the voltage generated in the second pixel electrode 25B. Note that the voltage generated in the first pixel electrode 25A and the second pixel electrode 25B in the cases shown in Figures 26(a) and 26(b) is opposite in direction to the voltage generated in the first pixel electrode 25A and the second pixel electrode 25B in the cases shown in Figures 25(a) and 25(b).

With this element configuration, it is possible to independently detect the magnitude of bending in the X direction and the magnitude of bending in the Y direction, even when a non-stretched film or a biaxially stretched film (e.g., non-stretched PVDF) is used as the piezoelectric layer 30. To further improve accuracy, if the voltage output from the thin-film transistor connected to the second pixel electrode 25B long in the X direction is _VX , the voltage output from the thin-film transistor connected to the first pixel electrode 25A long in the Y direction is _VY , the magnitude of X bending is _BX , and the magnitude of Y bending is _BY , the voltages _VX and _VY can be formulated as in the above-mentioned equations (6) and (7), respectively. Therefore, if k1 and k2 are experimentally determined, the magnitude of X bending _BX and the magnitude of Y bending _BY can be derived from equations (6) and (7) as the above-mentioned equations (8) and (9). In this way, even when the bending sensor 10B according to this embodiment is used, it is possible to independently detect the magnitude of bending in the X direction _BX and the magnitude of bending in the Y direction _BY .

[Operation and effect of the third embodiment]
The effects achieved by the bending sensor 10B according to the present embodiment described above will now be described. In this embodiment, the first pixel electrode 25A has a shape extending in the Y direction, and the second pixel electrode 25B has a shape extending in the X direction. Therefore, as described above, the first pixel electrode 25A is strongly affected by the Y bending, and the second pixel electrode 25B is strongly affected by the X bending. Furthermore, in this embodiment, the counter electrode 35 has a first extension portion 35A extending in the Y direction to encompass the first pixel electrode 25A, and a second extension portion 35B extending in the X direction to encompass the second pixel electrode 25B. The portion where the counter electrode 35 is not located is more likely to stretch than the portion where the counter electrode 35 is located. Therefore, the stress in the portion where the counter electrode 35 is located is greater than the stress in the portion where the counter electrode 35 is not located.

In this case, the stress at the position of the first pixel electrode 25A where the first extension portion 35A of the opposing electrode 35 is located increases during Y bending, and the stress at the position of the second pixel electrode 25B where the second extension portion 35B of the opposing electrode 35 is located increases during X bending. In other words, the voltage of the first pixel electrode 25A exhibits a large value during Y bending because the opposing electrode 35 is located on the first pixel electrode 25A. The voltage of the second pixel electrode 25B exhibits a large value during X bending because the opposing electrode 35 is located on the second pixel electrode 25B. Therefore, in this embodiment, the first pixel electrode 25A is more strongly affected by Y bending, and the second pixel electrode 25B is more strongly affected by X bending.

As a result, the first pixel electrode 25A is more strongly affected by Y bending, and the second pixel electrode 25B is more strongly affected by X bending. Therefore, by detecting the signal indicating the voltage of the first pixel electrode 25A as bending information in the Y direction and the signal indicating the voltage of the second pixel electrode 25B as bending information in the X direction, it is possible to distinguish between the Y bending state and the X bending state. This makes it possible to grasp the bending state of the bending sensor 10B in more detail.

In this embodiment, each first pixel electrode 25A and each of the plurality of second pixel electrodes 25B are arranged in a matrix so that they alternate along the Y and X directions. In this case, by acquiring bending information for each pixel electrode 25, it is possible to grasp the local bending state more precisely. Furthermore, by arranging each first pixel electrode 25A and each second pixel electrode 25B alternately, it is possible to disperse each first pixel electrode 25A for obtaining bending information in the Y direction and each second pixel electrode 25B for obtaining bending information in the X direction, thereby preventing bias in the bending state information obtained.

In the bending sensor 10 according to the first embodiment, in order to independently detect bending information in the X and Y directions, two bending sensors 10 each having a uniaxially stretched piezoelectric layer 30 had to be prepared and stacked so that the stretch directions of the piezoelectric layers 30 were perpendicular to each other. However, in the third embodiment, a single bending sensor 10B having a biaxially stretched or non-stretched piezoelectric layer 30 can be used to independently detect bending information in the X and Y directions. Also, in the third embodiment, a thin-film transistor array 201 may be used instead of the thin-film transistor array 20, or a thin-film transistor array having another circuit configuration may be used.

[Modification of the third embodiment]
The shapes of the first pixel electrode 25A and the second pixel electrode 25B are not limited to those of the third embodiment. FIGS. 27(a) to 27(c), 28(a), and 28(b) are plan views showing other examples of the bending sensor 10B according to the third embodiment. As in the bending sensor 101B shown in FIG. 27(a), the first pixel electrode 251A and the second pixel electrode 251B may each have a cross shape. In this case, the first pixel electrode 251A has a portion 251a extending in the Y direction and a portion 251b extending in the X direction. The portion 251b is disposed, for example, so as to intersect with the center of the portion 251a. The length of the portion 251b in the X direction is set shorter than the length of the portion 251a in the Y direction. Similarly, the second pixel electrode 251B has a portion 251c extending in the X direction and a portion 251d extending in the Y direction. The portion 251d is disposed, for example, so as to intersect with the center of the portion 251c. The length of the portion 251d in the Y direction is set to be shorter than the length of the portion 251c in the X direction.

As in the bending sensor 102B shown in FIG. 27(b), the first pixel electrode 252A may have an elliptical (oval) shape extending in the Y direction. Similarly, the second pixel electrode 252B may have an elliptical (oval) shape extending in the X direction. Alternatively, as in the bending sensor 103B shown in FIG. 27(c), the first pixel electrode 253A may have an isosceles triangular shape extending in the Y direction. In this case, the first pixel electrode 253A may be arranged so that the apex of the isosceles triangle faces one side in the Y direction, or so that the apex of the isosceles triangle faces the other side in the Y direction. Similarly, the second pixel electrode 253B may have an isosceles triangular shape extending in the X direction. In this case, the second pixel electrode 253B may be arranged so that the apex of the isosceles triangle faces one side in the X direction, or so that the apex of the isosceles triangle faces the other side in the X direction.

As in the bending sensor 104B shown in FIG. 28(a), the X-direction width of the first pixel electrode 254A may vary at each position on the first pixel electrode 254A along the Y direction. Specifically, the X-direction width of the first pixel electrode 254A may be smallest at the center of the first pixel electrode 254A in the Y direction, and gradually increase as the distance from the center increases in the Y direction. The Y-direction width of the second pixel electrode 254B may vary at each position on the second pixel electrode 254B along the X direction. Specifically, the Y-direction width of the second pixel electrode 254B may be smallest at the center of the second pixel electrode 254B in the X direction, and gradually increase as the distance from the center increases in the X direction.

As in the bending sensor 105B shown in FIG. 28(b), the first pixel electrode 255A and the second pixel electrode 255B do not have to be arranged to fit within one pixel, but may extend outside the pixel. In this case, the first pixel electrode 255A extends in the Y direction beyond the boundary line BL to a position where it does not contact the second pixel electrode 255B adjacent in the Y direction. Similarly, the second pixel electrode 255B extends in the X direction beyond the boundary line BL to a position where it does not contact the first pixel electrode 255A adjacent in the X direction. Even with the bending sensor described above, the same effects as those of the bending sensor 10B according to the third embodiment can be obtained.

The first pixel electrode 25A and second pixel electrode 25B according to this embodiment can be modified in various ways. Figure 29 is a plan view showing another example of a bending sensor 106B according to the third embodiment. Figure 30(a) is a cross-sectional view of the bending sensor 106B taken along line A6-A6 in Figure 29. Figure 30(b) is a cross-sectional view of the bending sensor 106B taken along line A7-A7 in Figure 29. In the bending sensor 106B shown in Figure 29, each first pixel electrode 25A and each second pixel electrode 25B extends in a direction inclined relative to the pixel arrangement direction.

In the bending sensor 106B, if the extension directions of each first pixel electrode 25A and each second pixel electrode 25B are defined as the Y direction and the X direction, respectively, the first pixel electrodes 25A are arranged adjacent to each other at a distance in the Y direction, and the second pixel electrodes 25B are arranged adjacent to each other at a distance in the X direction. Each first extension portion 35A of the opposing electrode 35 extends along the Y direction to encompass each first pixel electrode 25A, and each second extension portion 35B extends along the X direction to encompass each second pixel electrode 25B. Meanwhile, the matrix is aligned vertically and horizontally in Figure 29. That is, as shown in Figure 29, the matrix alignment direction and the X and Y directions do not have to coincide. Note that in adjacent pixels in the vertical and horizontal directions in Figure 29, the first pixel electrodes 25A and second pixel electrodes 25B are aligned alternately.

Figure 31(a) is a cross-sectional view showing the bending sensor 106B bent convexly in the cross section shown in Figure 30(a). Figure 31(b) is a cross-sectional view showing the bending sensor 106B bent convexly in the cross section shown in Figure 30(b). Because the piezoelectric layer 30 is located above the neutral plane NP, when the bending sensor 106B is bent convexly as shown in Figures 31(a) and 31(b), a tensile stress in the X direction is applied to the piezoelectric layer 30. At the position of the second pixel electrode 25B, a tensile stress SS1B in the X direction is applied to the piezoelectric layer 30. In this case, a voltage corresponding to the tensile stress SS1B is generated in the second pixel electrode 25B. Meanwhile, at the position of the first pixel electrode 25A, a tensile stress SS1A in the X direction is applied to the piezoelectric layer 30. In this case, a voltage corresponding to the tensile stress SS1A is generated in the first pixel electrode 25A. Because the opposing electrode 35 is present over the entire area and because the second pixel electrode 25B is long, the tensile stress SS1B is greater than the tensile stress SS1A, and the voltage generated in the second pixel electrode 25B is greater than the voltage generated in the first pixel electrode 25A.

Figure 32(a) is a cross-sectional view showing the bending sensor 106B bent concavely in the cross section shown in Figure 30(a). Figure 32(b) is a cross-sectional view showing the bending sensor 106B bent concavely in the cross section shown in Figure 30(b). Because the piezoelectric layer 30 is located above the neutral plane NP, a compressive stress in the X direction is applied to the piezoelectric layer 30. When the bending sensor 106B is bent concavely as shown in Figures 32(a) and 32(b), a compressive stress in the X direction is applied to the piezoelectric layer 30. At the position of the second pixel electrode 25B, a compressive stress SS2B in the X direction is applied to the piezoelectric layer 30. In this case, a voltage corresponding to the compressive stress SS2B is generated in the second pixel electrode 25B.

On the other hand, at the position of the first pixel electrode 25A, a compressive stress SS2A in the X direction is applied to the piezoelectric layer 30. In this case, a voltage corresponding to the compressive stress SS2A is generated in the first pixel electrode 25A. Because the opposing electrode 35 covers the entire area and the second pixel electrode 25B is long, the compressive stress SS2B is greater than the compressive stress SS2A, and the voltage generated in the second pixel electrode 25B is greater than the voltage generated in the first pixel electrode 25A. Note that the voltage generated in the first pixel electrode 25A and the second pixel electrode 25B in the cases shown in Figures 32(a) and 32(b) is opposite in direction to the voltage generated in the first pixel electrode 25A and the second pixel electrode 25B in the cases shown in Figures 31(a) and 31(b). This bending sensor 106B also achieves the same effect as bending sensor 10B.

Figure 33 is a plan view showing another example of a bending sensor 10B according to the third embodiment. The bending sensor 107B shown in Figure 33 includes a plurality of first pixel electrodes 25A and a plurality of second pixel electrodes 25B, as well as a plurality of third pixel electrodes 25C (third electrodes) and a plurality of fourth pixel electrodes 25D. Each third pixel electrode 25C has a shape extending along a direction DD1 (third direction) that is inclined with respect to the X and Y directions. The direction DD1 is, for example, the (X, Y) = (1, -1) direction. In other words, the direction DD1 is inclined 45 degrees to one side (negative side) of the Y direction with respect to the X direction. Each fourth pixel electrode 25D has a shape extending along a direction DD2 that is inclined with respect to the X and Y directions and is perpendicular to the direction DD1. The direction DD2 is, for example, the (X, Y) = (1, 1) direction. In other words, direction DD2 is inclined 45 degrees to the other side (positive side) of the Y direction with respect to the X direction. Therefore, directions DD1 and DD2 are inclined with respect to the X direction and Y direction and are perpendicular to each other.

The third pixel electrode 25C and the fourth pixel electrode 25D are arranged on both sides of the first pixel electrode 25A in the Y direction. Therefore, the third pixel electrode 25C, the first pixel electrode 25A, and the fourth pixel electrode 25D are arranged alternately in this order in the Y direction. The third pixel electrode 25C and the fourth pixel electrode 25D are arranged on both sides of the second pixel electrode 25B in the X direction. Therefore, the third pixel electrode 25C, the second pixel electrode 25B, and the fourth pixel electrode 25D are arranged alternately in this order in the X direction.

In addition to multiple first extension portions 35A and multiple second extension portions 35B, the opposing electrode 351 also has multiple third extension portions 35C and multiple fourth extension portions 35D. Each third extension portion 35C extends in direction DD1 so as to encompass each third pixel electrode 25C in a plan view. One end of each third extension portion 35C in direction DD1 is connected to the second extension portion 35B adjacent to it in the X direction and the first extension portion 35A adjacent to it in the Y direction. Similarly, the other end of each third extension portion 35C in direction DD1 is connected to the second extension portion 35B adjacent to it in the X direction and the first extension portion 35A adjacent to it in the Y direction.

Each fourth extension portion 35D extends in direction DD2 so as to encompass each fourth pixel electrode 25D in plan view. One end of the fourth extension portion 35D in direction DD2 is connected to the second extension portion 35B adjacent to it in the X direction and the first extension portion 35A adjacent to it in the Y direction. The other end of the fourth extension portion 35D in direction DD2 is similarly connected to the second extension portion 35B adjacent to it in the X direction and the first extension portion 35A adjacent to it in the Y direction. The opposing electrode 351 forms a lattice pattern in plan view due to the connections between each first extension portion 35A, each second extension portion 35B, each third extension portion 35C, and each fourth extension portion 35D.

In the bending sensor 107B shown in FIG. 33, similar to the bending sensor 10B, the first pixel electrode 25A is strongly affected by Y bending, and the second pixel electrode 25B is strongly affected by X bending. Furthermore, the third pixel electrode 25C is strongly affected by bending in direction DD1, and the fourth pixel electrode 25D is strongly affected by bending in direction DD2. Therefore, by detecting the signal indicating the voltage of the third pixel electrode 25C as bending information in direction DD1 and the signal indicating the voltage of the fourth pixel electrode 25D as bending information in direction DD2, it is possible to distinguish and grasp the bending state in direction DD1 and the bending state in direction DD2, in addition to the bending state in the Y direction and the bending state in the X direction. Therefore, the bending sensor 107B shown in FIG. 33 makes it possible to grasp the bending state in more detail.

Furthermore, by arranging each third extension portion 35C to encompass each third pixel electrode 25C, and each fourth extension portion 35D to encompass each fourth pixel electrode 25D, the third pixel electrode 25C is more strongly affected by bending in direction DD1, and the fourth pixel electrode 25D is more strongly affected by bending in direction DD2. This makes it possible to more reliably distinguish and acquire bending information in direction DD1 and bending information in direction DD2.

Note that in the bending sensor 107B shown in Figure 33, there are pixels where the pixel electrode 25 and counter electrode 351 are not present. In this case, the thin-film transistor located in that pixel may be used as a reference circuit. In other words, the voltage indicated by the signal from a pixel where the pixel electrode 25 and counter electrode 351 are not present may be subtracted from the voltage indicated by the signal from each pixel where the first pixel electrode 25A, second pixel electrode 25B, third pixel electrode 25C, and fourth pixel electrode 25D are located. This makes it possible to suppress characteristic variations due to the in-plane distribution of the thin-film transistor array 20.

Figure 34 is a plan view showing another example of a bending sensor 10B according to the third embodiment. The bending sensor 108B shown in Figure 34 includes multiple first pixel electrodes 25A, multiple second pixel electrodes 25B, and multiple fifth pixel electrodes 25E. Each fifth pixel electrode 25E has a cross shape extending in both the X and Y directions. The fifth pixel electrode 25E has a first portion 251E extending in the Y direction and a second portion 252E extending in the X direction. The first portion 251E has a rectangular shape with its longitudinal direction in the Y direction, and the second portion 252E has a rectangular shape with its longitudinal direction in the X direction. The length of the first portion 251E in the Y direction and the length of the second portion 252E in the X direction are set to be the same, for example. The first portion 251E and the second portion 252E are arranged, for example, so as to be perpendicular to each other at their centers.

In a plan view, each fifth pixel electrode 25E is arranged at a position that overlaps with each intersection (connection point) of each first extension portion 35A and each second extension portion 35B of the opposing electrode 352. In a plan view, the first portion 251E of each fifth pixel electrode 25E is arranged so as to be encompassed by each first extension portion 35A of the opposing electrode 352, and the second portion 252E of each fifth pixel electrode 25E is arranged so as to be encompassed by each second extension portion 35B of the opposing electrode 352.

Between two adjacent fifth pixel electrodes 25E in the X direction, one first pixel electrode 25A is arranged so as to be encompassed by the first extension portion 35A in plan view. Therefore, each first pixel electrode 25A and each fifth pixel electrode 25E are arranged alternately along the X direction. Between two adjacent fifth pixel electrodes 25E in the Y direction, one second pixel electrode 25B is arranged so as to be encompassed by the second extension portion 35B in plan view. Therefore, each second pixel electrode 25B and each fifth pixel electrode 25E are arranged alternately along the Y direction.

In the bending sensor 108B shown in FIG. 34, similar to bending sensor 10B, the first pixel electrode 25A is strongly affected by Y bending, and the second pixel electrode 25B is strongly affected by X bending. On the other hand, the fifth pixel electrode 25E extends equally in the X and Y directions, and is therefore equally affected by X bending and Y bending. Even with this bending sensor 108B, by detecting the signal indicating the voltage of the first pixel electrode 25A as bending information in the Y direction and the signal indicating the voltage of the second pixel electrode 25B as bending information in the X direction, it is possible to distinguish between Y bending and X bending, thereby achieving the same effect as bending sensor 10B.

Note that the bending sensor 108B shown in Figure 34 has pixels where the pixel electrode 25 and counter electrode 352 are not present (for example, the pixel in the center of Figure 34). In this case, the thin-film transistor located in that pixel may be used as a reference circuit. That is, the voltage indicated by the signal from a pixel where the pixel electrode 25 and counter electrode 352 are not present may be subtracted from the voltage indicated by the signal from each pixel where the first pixel electrode 25A, second pixel electrode 25B, and third pixel electrode 25C are located. This makes it possible to suppress characteristic variations due to the in-plane distribution of the thin-film transistor array 20.

[Care data collection and assessment system]
Next, a care data collection and determination system (health condition estimation system) will be described as an example to which a bending detection device according to an embodiment of the present invention is applied. FIG. 35 is a block diagram showing an example of a care data collection and determination system to which a bending detection device is applied. The care data collection and determination system 300 shown in FIG. 35 is used to estimate the health condition of a care recipient. The care data collection and determination system 300 includes a plurality of care sensor devices 200 and a data collection and determination device 210. Each care sensor device 200 includes a bending sensor 110, a signal detection circuit 175, a drive circuit 185, a control circuit 180 (e.g., a microcomputer), and a communication circuit 202.

The bending sensor 110 has the same configuration as, for example, the bending sensors according to any of the first to third embodiments described above. The signal detection circuit 175 has the same configuration as, for example, any of the signal detection circuits 75, 75A, and 75B described above. The drive circuit 185 has the same configuration as the drive circuit 85 described above. The control circuit 180 has the same configuration as the control circuit 80 described above. The bending sensor 110, signal detection circuit 175, drive circuit 185, and control circuit 180 constitute a bending detection device.

The communication circuit 202 performs wired or wireless communication between the control circuit 180 and external circuits. Examples of wireless communication include Wi-Fi (registered trademark) and Bluetooth (registered trademark). The communication circuit 202 may be connected to the Internet. The communication circuit 202 transmits bending data indicating bending information for each pixel from the control circuit 180 to the data collection and determination device 210.

The data collection and determination device 210 has a control circuit 211 (e.g., a computer), a communication circuit 212, and a database 213. The communication circuit 212 performs wired or wireless communication between the control circuit 211 and the communication circuit 202 of the care sensor device 200. The communication circuit 202 receives bending data from the communication circuit 202 of each care sensor device 200 and sends the received bending data to the control circuit 211. The control circuit 211 processes the bending data. The control circuit 211 sends the bending data to the database 213 either directly or after processing. The database 213 stores the bending data sent from the control circuit 211. The database 213 may store data indicating the medical condition of the care recipient. The control circuit 211 may use artificial intelligence to analyze the big data in the database 213 through machine learning, etc. This makes it possible to clarify the relationship between the posture of the care recipient and their medical condition. The control circuit 211 may also determine the condition of the care recipient by comparing the bending data sent from the care sensor device 200 with the data in the database 213.

In this way, the care data collection and determination system 300 can perform the following operations: store the bending data sent from the care sensor device 200 in the database 213 either directly or after processing; use artificial intelligence to analyze the big data in the database 213 through machine learning, etc.; and compare the bending data from the care sensor device 200 with the data in the database 213 to determine the medical condition of the care recipient.

In the above-described care data collection and determination system 300, one data collection and determination device 210 may be communicatively connected to multiple care sensor devices 200, or one data collection and determination device 210 may be communicatively connected to only one care sensor device 200. When one data collection and determination device 210 is communicatively connected to only one care sensor device 200, the exchange of bending data between the data collection and determination device 210 and the care sensor device 200 becomes easier, but the care sensor device 200 is required to have a fast response speed.

On the other hand, the response speed of the data collection and judgment device 210 does not need to be very fast. When one data collection and judgment device 210 is communicatively connected to multiple care sensor devices 200, the exchange of data between the data collection and judgment device 210 and each care sensor device 200 becomes complicated, but the response speed of each care sensor device 200 may be slow. On the other hand, a fast response speed is required for the data collection and judgment device 210. In addition, the control circuit 211 and database 213 may be communicatively connected via a communication circuit (not shown).

Figures 36(a) to 36(f) are perspective views showing examples of care sensor devices. As shown in Figures 36(a) to 36(f), a large, sheet-like care sensor device is placed on a rectangular parallelepiped bed. In Figures 36(a) to 36(f), the care sensor device on the bed is shown in a visible state, but in reality, a sheet is placed over the care sensor device and the care recipient is placed on the sheet. In Figures 36(a) to 36(f), the circuit including the control circuit 180 and communication circuit 202 is described as the control/communication circuit 203.

In the care sensor device 200 shown in Figure 36 (a), a large sheet-like bending sensor 110 is placed in the center of the bed, a signal detection circuit 175 is placed at the end of the long side of the bed, and a drive circuit 185 is placed at the end of the short side of the bed. Each scanning wiring 61 of the bending sensor 110 extends in the longitudinal direction of the bed and is connected to the drive circuit 185, and each signal wiring 62 of the bending sensor 110 extends in the lateral direction of the bed and is connected to the signal detection circuit 175. The control and communication circuit 203 is placed at the corner between the long and short sides of the bed and is connected to the signal detection circuit 175 and drive circuit 185.

In the care sensor device 200A shown in FIG. 36(b), the signal detection circuit 175 and the drive circuit 185 are swapped compared to the care sensor device 200. That is, in the care sensor device 200A, the drive circuit 185 is located at the end of the long side of the bed, and the signal detection circuit 175 is located at the end of the short side of the bed. The care sensor device 200B shown in FIG. 36(c) and the care sensor device 200D shown in FIG. 36(e) have multiple strip-shaped bending sensors 110A instead of the large sheet-shaped bending sensor 110. The bending sensors 110A are arranged spaced apart in the longitudinal direction of the bed and extend in the lateral direction of the bed. In the care sensor device 200B shown in FIG. 36(c), a connecting part 205 is provided between adjacent bending sensors 110A in the longitudinal direction. The connecting part 205 connects the scanning wiring 61 of each bending sensor 110A in the longitudinal direction.

The care sensor device 200D shown in Figure 36 (e) has multiple drive circuits 185A and multiple control and communication circuits 203A instead of the drive circuit 185 and control and communication circuit 203. The multiple drive circuits 185A are arranged to correspond to the multiple bending sensors 110A. That is, each drive circuit 185A is arranged between adjacent bending sensors 110A in the longitudinal direction. Each drive circuit 185A is connected to the scanning wiring 61 of each bending sensor 110A. Each control and communication circuit 203A is arranged in a position opposite each drive circuit 185A in the lateral direction.

36(d) and the care sensor device 200E shown in FIG. 36(f) have multiple small sheet-shaped bending sensors 110B instead of the large sheet-shaped bending sensor 110. The bending sensors 110B are arranged in a matrix so as to be spaced apart from each other in the longitudinal and lateral directions. In the care sensor device 200C shown in FIG. 36(d), a connecting part 206 is provided between adjacent bending sensors 110B in the longitudinal direction. The connecting part 206 connects the scanning wiring 61 of each bending sensor 110A in the longitudinal direction. A connecting part 207 is provided between adjacent bending sensors 110B in the lateral direction. The connecting part 207 connects the signal wiring 62 of the bending sensors 110A in the lateral direction. In the care sensor devices 200B and 200C, the positions of the drive circuit 185 and the signal detection circuit 175 may be reversed, as in the care sensor device 200A.

The care sensor device 200E shown in Figure 36 (f) has multiple drive circuits 185A and multiple control and communication circuits 203A instead of the drive circuit 185 and control and communication circuit 203. Each drive circuit 185A is arranged to extend in the short direction between adjacent bending sensors 110A in the long direction. In addition, in the care sensor device 200E, a connecting part 207 is provided between adjacent bending sensors 110B in the short direction. The connecting part 207 connects the signal wiring 62 of each bending sensor 110A in the short direction.

When determining the posture of a care recipient using any of the care sensor devices described above, it is not necessary to accurately detect the bending (stimulus value) of all pixels. Even if a defect occurs in one pixel, resulting in abnormal bending data, it is possible to interpolate using bending data obtained from pixels surrounding the defect. Even if defects occur in multiple pixels, resulting in abnormal bending data, it is possible to complement using bending data from pixels surrounding those multiple pixels. In this case, if the defective pixels are dispersed, it is easier to interpolate bending data than when the defective pixels are densely packed. However, even when the defective pixels are densely packed, it is possible to interpolate bending data. Therefore, even if a defect occurs in one or multiple pixels, it is possible to determine the posture of a care recipient by complementing using bending data from surrounding pixels.

Below, we will explain Examples 1 to 4 of the bending sensor 10 according to the present invention. However, the present invention is not limited to Examples 1 to 4.

Example 1
The bending sensor 10 shown in Figure 1 was fabricated. A thin-film transistor array 20 was fabricated using a PEN film on a glass substrate as the flexible substrate 15. The circuit of the thin-film transistor array 20 is the circuit shown in Figure 6. Next, Ag paste was printed as pixel electrodes 25, and a separately prepared PVDF film with Al was placed on top of it, baked, and peeled off from the glass substrate, thereby fabricating the bending sensor 10. The region 26 between the pixel electrodes was air.

The flexible substrate 15 is 100 um thick, the thin-film transistor layer 20 is 4 um thick, the pixel electrode 25 is 10 um thick, the piezoelectric layer 30 is 20 um thick, and the counter electrode 35 is 0.1 um thick. The Young's modulus of the flexible substrate 15 is 5 GPa, the Young's modulus of the pixel electrode 25 is 6 GPa, the Young's modulus of the piezoelectric layer 30 is 3 GPa, and the Young's modulus of the counter electrode 35 is 70 GPa. In this case, the neutral plane NP is located inside the flexible substrate 15, and the pixel electrode 25 and piezoelectric layer 30 are located above the neutral plane NP. The pixel pitch is 5 mm, and the pixel electrode 25 is a square with sides of 3.6 mm.

The detection unit 5B shown in Figure 14 was used to detect the signal output from the bending sensor 10. By detecting this signal, bending information including the presence or absence of bending, the bending direction, and the bending amount was obtained for each pixel.

Example 2
The bending sensor 10A shown in Figure 17 was fabricated. A thin-film transistor array 201 was fabricated using a PI film on a glass substrate as the flexible substrate 15. The circuit of the thin-film transistor array 201 is the circuit shown in Figure 9. Next, Ag paste was printed as pixel electrodes 25, and a separately prepared PVDF film with Al was placed on top of it, baked, and peeled off from the glass substrate to fabricate the bending sensor 10A. There was air between the pixel electrodes 25.

The flexible substrate 15 is 25 um thick, the thin-film transistor layer 201 is 4 um thick, the pixel electrode 25 is 10 um thick, the piezoelectric layer 30 is 20 um thick, and the counter electrode 35 is 0.1 um thick. The Young's modulus of the flexible substrate 15 is 5 GPa, the Young's modulus of the pixel electrode 25 is 6 GPa, the Young's modulus of the piezoelectric layer 30 is 3 GPa, and the Young's modulus of the counter electrode 35 is 70 GPa. Since the region 26 between the pixel electrodes is air, the Young's modulus of the region 26 between the pixel electrodes can be considered to be 0. In this case, the neutral plane NP is located inside the thin-film transistor layer 201, and the pixel electrode 25 and piezoelectric layer 30 are located above the neutral plane NP. The pixel pitch is 5 mm, and the pixel electrode 25 is rectangular with long sides of 4 mm and short sides of 0.6 mm.

The signals (voltages _VX and _VY ) output from bending sensor 10A were detected using detection unit 5B shown in Fig. 14. By experimentally determining _k1 and _k2 in equations (8) and (9), the magnitude of X bending _BX and the magnitude of Y bending _BY could be determined independently using the detected voltages _VX and _VY .

Example 3
The bending sensor 10B shown in Figure 23 was fabricated. A thin-film transistor array 201 was fabricated using a PI film on a glass substrate as the flexible substrate 15. The circuit of the thin-film transistor array 201 is the circuit shown in Figure 9. Next, Ag paste was printed and baked as pixel electrodes 25, and an adhesive was placed on the backside of a separately prepared PVDF film with an Al pattern. The films were then bonded together using a laminator, and the adhesive was inserted between the pixel electrodes 25. Therefore, the inter-pixel electrode region 26 was adhesive. By appropriately selecting the pressure and temperature, electrical connection between the pixel electrodes 25 and the piezoelectric layer 30 was ensured. The bending sensor 10B was then fabricated by peeling it off from the glass substrate.

The flexible substrate 15 is 25 um thick, the thin-film transistor layer 201 is 4 um thick, the pixel electrode 25 is 10 um thick, the piezoelectric layer 30 is 20 um thick, and the counter electrode 35 is 0.1 um thick. The Young's modulus of the flexible substrate 15 is 5 GPa, the Young's modulus of the pixel electrode 25 is 6 GPa, the Young's modulus of the inter-pixel electrode region 26 is 1 MPa, the Young's modulus of the piezoelectric layer 30 is 3 GPa, and the Young's modulus of the counter electrode 35 is 70 GPa. The neutral plane NP is located inside the thin-film transistor layer 201, and the pixel electrode 25 and piezoelectric layer 30 are located above the neutral plane NP. The pixel electrode 25 is rectangular with long sides of 4 mm and short sides of 0.6 mm. The pixel pitch is 5 mm, and the width of the counter electrode 35 is 0.7 mm.

The signals (voltages _VX and _VY ) output from bending sensor 10B were detected using detection unit 5B shown in Fig. 14. By experimentally determining _k1 and _k2 in equations (8) and (9), the magnitude of X bending _BX and the magnitude of Y bending _BY could be independently determined using the detected voltages _VX and _VY .

Example 4
The bending sensor 10B shown in Figure 23 was fabricated. A thin-film transistor array 201 was fabricated using a PI film on a glass substrate as the flexible substrate 15. The circuit of the thin-film transistor array 201 is the circuit shown in Figure 9. Next, Al was sputter-deposited as pixel electrodes 25 and processed by photolithography. An adhesive was then layered on the backside of the PVDF film, and the films were bonded together using a laminator, with the adhesive filling the gaps between the pixel electrodes 25. Therefore, the inter-pixel electrode region 26 was adhesive. By appropriately selecting the pressure and temperature, electrical connection between the pixel electrodes 25 and the piezoelectric layer 30 was ensured. Furthermore, Ag paste was printed and baked as the counter electrode 35, and the film was peeled off from the glass substrate to fabricate the bending sensor 10B.

The flexible substrate 15 is 10 μm thick, the thin-film transistor layer 201 is 4 μm thick, the pixel electrode 25 is 0.1 μm thick, the piezoelectric layer 30 is 20 μm thick, and the counter electrode 35 is 10 μm thick. The Young's modulus of the flexible substrate 15 is 5 GPa, the Young's modulus of the pixel electrode 25 is 70 GPa, the Young's modulus of the inter-pixel electrode region 26 is 1 MPa, the Young's modulus of the piezoelectric layer 30 is 3 GPa, and the Young's modulus of the counter electrode 35 is 6 GPa. The neutral plane NP is located near the back surface 30b of the piezoelectric layer 30. The pixel electrode 25 is below the neutral plane NP, but most of the piezoelectric layer 30 is above the neutral plane NP. The pixel pitch is 5 mm, and the pixel electrode 25 is rectangular with long sides of 4 mm and short sides of 0.6 mm. The width of the counter electrode 35 is 0.7 mm.

The signals (voltages _VX and _VY ) output from bending sensor 10B were detected using detection unit 5B shown in Fig. 14. By experimentally determining _k1 and _k2 in equations (8) and (9), the magnitude of X bending _BX and the magnitude of Y bending _BY could be independently determined using the detected voltages _VX and _VY .

The bending sensor, bending detection device, and bending detection method according to the present invention are not limited to the above-described embodiments and can be modified as appropriate. The bending sensor according to any of the first to third embodiments may include components other than the flexible substrate, thin-film transistor array, pixel electrode, piezoelectric layer, counter electrode, and area between the pixel electrodes. For example, the bending sensor may include an insulating cover layer on the counter electrode. In this case, the cover layer may be thin and have a small Young's modulus. The cover layer has little effect on the composite Young's modulus of the laminate. For example, a rubber material with a small Young's modulus may be selected as the material for the cover layer. Furthermore, even if the bending sensor includes other components between the layers, the effect on the composite Young's modulus is small if the film thickness of the component is thin or the Young's modulus of the component is small.

In each of the above-described embodiments, the potential difference between the counter electrode and pixel electrode is detected as a "change in electrical characteristics." However, a change in current between the counter electrode and pixel electrode may also be detected as a "change in electrical characteristics." In this case, the signal output from the bending sensor may indicate a current. Alternatively, a change in resistance between the counter electrode and pixel electrode may be detected as a "change in electrical characteristics." Also, in each of the above-described embodiments, a constant voltage may be applied to the counter electrode.

1... bending detection device, 5, 5A, 5B... detection unit, 10, 10A, 10B, 101A, 101B, 102A, 102B, 103A, 103B, 104A, 104B, 105A, 105B, 106B, 107B, 108B, 110, 110A, 110B... bending sensor, 15... flexible substrate (substrate), 30a... front surface, 30b... rear surface, 20, 201... thin film transistor layer (thin film transistor array), 21A... first pixel thin film transistor (first thin film transistor 25B...second pixel electrode; 25C...third pixel electrode; 26...region between pixel electrodes (inter-electrode region); 30...piezoelectric layer; 35, 351, 352...opposing electrode (common electrode); 35A...first extension portion; 35B...second extension portion; 35C...third extension portion; D ₁₁ to D _NM ...signal; NP...neutral plane.

Claims (16)

A bending sensor for detecting bending, comprising:
a flexible substrate;
a thin film transistor array consisting of a plurality of thin film transistors arranged on the substrate;
a plurality of pixel electrodes disposed on the thin film transistor array;
a piezoelectric layer disposed on the plurality of pixel electrodes;
a common electrode disposed on the piezoelectric layer,
the piezoelectric layer has a front surface electrically connected to the common electrode and a back surface electrically connected to the plurality of pixel electrodes,
the plurality of pixel electrodes include a first pixel electrode and a second pixel electrode that are arranged spaced apart from each other in a plan view of the substrate and are electrically insulated from each other;
the thin film transistor array includes a first thin film transistor electrically connected to the first pixel electrode and a second thin film transistor electrically connected to the second pixel electrode;
When a bending force is applied in a first direction along the substrate, a voltage generated in the first pixel electrode is greater than a voltage generated in the second pixel electrode;
A bending sensor , wherein when bending is applied in a second direction along the substrate and intersecting the first direction, a voltage generated in the second pixel electrode is greater than a voltage generated in the first pixel electrode . The bending sensor of claim 1, wherein the plurality of pixel electrodes are arranged in a matrix. the first pixel electrode has a shape extending in a first direction along the substrate,
The bending sensor according to claim 1 , wherein the second pixel electrode has a shape extending along the substrate and in a second direction intersecting the first direction. The bending sensor of claim 3, wherein each of the first pixel electrode and the second pixel electrode has a Young's modulus higher than the Young's modulus of an inter-electrode region between the first pixel electrode and the second pixel electrode. The bending sensor of claim 4, wherein the inter-electrode region is formed from an electrically insulating adhesive. a neutral plane on which no tensile stress or compressive stress acts when bending occurs in the bending sensor is located at a height different from that of the piezoelectric layer;
The bending sensor according to any one of claims 3 to 5, wherein at least a portion of each of the first pixel electrode and the second pixel electrode is arranged on the same side as the piezoelectric layer with respect to the neutral plane. the plurality of pixel electrodes include a plurality of the first pixel electrodes and a plurality of the second pixel electrodes;
7. The bending sensor according to claim 3, wherein the first pixel electrodes and the second pixel electrodes are arranged in a matrix so as to alternate with each other. The common electrode is
a first extension portion extending in the first direction so as to encompass the first pixel electrode in the plan view;
The bending sensor according to any one of claims 3 to 7, further comprising: a second extension portion connected to the first extension portion and extending in the second direction so as to encompass the second pixel electrode in the planar view. the plurality of pixel electrodes include a plurality of the first pixel electrodes and a plurality of the second pixel electrodes;
the plurality of first pixel electrodes and the plurality of second pixel electrodes are arranged in a matrix,
The common electrode is
a plurality of first extension portions arranged so as to respectively include the plurality of first pixel electrodes in the plan view;
a plurality of second extension portions arranged so as to respectively include the plurality of second pixel electrodes in the plan view;
The bending sensor according to claim 8 , wherein the plurality of first extending portions and the plurality of second extending portions are arranged in a lattice pattern in a plan view. the plurality of pixel electrodes further include a third pixel electrode that is disposed apart from the first pixel electrode and the second pixel electrode in the plan view and is electrically insulated from the first pixel electrode and the second pixel electrode;
The bending sensor according to any one of claims 3 to 9, wherein the third pixel electrode has a shape extending along the substrate and in a third direction intersecting the first direction and the second direction. The common electrode is
a first extension portion extending in the first direction so as to encompass the first pixel electrode in the plan view;
a second extension portion that extends in the second direction so as to encompass the second pixel electrode in the plan view and is connected to the first extension portion;
The bending sensor according to claim 10 , further comprising: a third extension portion that extends in the third direction so as to encompass the third pixel electrode in the plan view and is connected to the first extension portion and the second extension portion. A bending sensor according to any one of claims 1 to 11;
a detection unit that detects bending of the bending sensor,
when a bend is applied to the bending sensor, the first thin film transistor outputs a first signal to the detection unit, the first signal indicating a change in an electrical characteristic between the first pixel electrode and the common electrode in response to the bend, and the second thin film transistor outputs a second signal to the detection unit, the second signal indicating a change in an electrical characteristic between the second pixel electrode and the common electrode in response to the bend;
a bending detection device, wherein the detection unit detects the first signal as information indicating the bending state at the position of the first pixel electrode, and detects the second signal as information indicating the bending state at the position of the second pixel electrode. the first pixel electrode has a shape extending in a first direction along the substrate,
the second pixel electrode has a shape extending along the substrate and in a second direction intersecting the first direction;
13. The bending detection device according to claim 12, wherein the detection unit detects the first signal as information indicating the bending state in the first direction at the position of the first pixel electrode, and detects the second signal as information indicating the bending state in the second direction at the position of the second pixel electrode. A bending detection method carried out using the bending sensor according to any one of claims 1 to 11, comprising:
When a bend is applied to the bending sensor, outputting from the first thin film transistor a first signal indicating a change in an electrical characteristic between the first pixel electrode and the common electrode in response to the bend, and outputting from the second thin film transistor a second signal indicating a change in an electrical characteristic between the second pixel electrode and the common electrode in response to the bend;
detecting the first signal as information indicating the state of the bending at the position of the first pixel electrode, and detecting the second signal as information indicating the state of the bending at the position of the second pixel electrode. In the step of outputting the first signal and the second signal,
outputting the first signal using the first pixel electrode having a shape extending in a first direction along the substrate, and outputting the second signal using the second pixel electrode having a shape extending in a second direction along the substrate and intersecting the first direction;
In the step of detecting the first signal and the second signal,
15. The bending detection method according to claim 14, wherein the first signal is detected as information indicating the state of bending in the first direction at the position of the first pixel electrode, and the second signal is detected as information indicating the state of bending in the second direction at the position of the second pixel electrode. A bending sensor for detecting bending, comprising:
a flexible substrate;
a thin film transistor array consisting of a plurality of thin film transistors arranged on the substrate;
a plurality of pixel electrodes disposed on the thin film transistor array;
a piezoelectric layer disposed on the plurality of pixel electrodes;
a common electrode disposed on the piezoelectric layer,
the piezoelectric layer has a front surface electrically connected to the common electrode and a back surface electrically connected to the plurality of pixel electrodes,
the plurality of pixel electrodes include a first pixel electrode and a second pixel electrode that are arranged spaced apart from each other in a plan view of the substrate and are electrically insulated from each other;
the thin film transistor array includes a first thin film transistor electrically connected to the first pixel electrode and a second thin film transistor electrically connected to the second pixel electrode;
the first pixel electrode has a shape extending in a first direction along the substrate,
The second pixel electrode has a shape extending along the substrate and in a second direction intersecting the first direction.