JP7694181B2 - Piezoelectric Device - Google Patents

Description

The present invention relates to a piezoelectric device having a piezoelectric element with a vibration region.

Conventionally, piezoelectric elements having a vibration region have been proposed (see, for example, Patent Document 1). Specifically, this piezoelectric element is configured by stacking a piezoelectric film and an electrode film connected to the piezoelectric film on a support. The piezoelectric element has a recess formed in the support, and a floating region in which a portion of the piezoelectric film and the electrode film floats above the support. In this piezoelectric element, slits are formed in the floating region, dividing the floating region into multiple regions to form the vibration region. Each vibration region is supported by the support in a cantilevered manner.

Such a piezoelectric element is manufactured as follows. That is, first, a piezoelectric film and an electrode film are formed on a support. Next, slits are formed in the piezoelectric film to form the vibration region component parts. After that, a recess is formed in the support, and the vibration region component parts are suspended to form the vibration region, thereby manufacturing the piezoelectric element.

Patent No. 5936154

However, in such piezoelectric elements, the vibration area may warp due to residual stress during the manufacture of the piezoelectric element. In addition, the piezoelectric element may warp depending on the usage environment because the linear expansion coefficients of the piezoelectric film and the electrode film are different. When the vibration area warps in this way, the slit width between adjacent vibration areas becomes wider, making it easier for pressure to escape through the slit, and detection accuracy, particularly at low frequencies, is likely to decrease.

In view of the above, the present invention aims to provide a piezoelectric device that can prevent a decrease in detection accuracy.

Claim 1 for achieving the above object provides a piezoelectric device including a piezoelectric element (1) having a vibration portion (20), the piezoelectric element including a support (10), a vibration portion arranged on the support and including a piezoelectric film (40) and an electrode film (50), the vibration portion having a support region (21a) supported by the support, and a plurality of vibration regions (22) that are connected to the support region and whose portions opposite the support region are floating from the support, and a control unit (2) that performs a predetermined process. The multiple vibration regions are separated by slits (30), and the electrode film includes a pressure electrode film (510) that is connected to the piezoelectric film and outputs a pressure detection signal corresponding to the charge of the piezoelectric film, a capacitance electrode film (520) that outputs a capacitance detection signal corresponding to the capacitance between adjacent vibration regions, and a drive electrode film (530) to which a drive voltage is applied that displaces the tip of the vibration region on the opposite side to the support region along the stacking direction of the support and the vibration region, and the control unit adjusts the drive voltage applied to the drive electrode film based on the capacitance detection signal at a predetermined timing so that the capacitance detection signal is maximized.

According to this, the control unit adjusts the drive voltage applied to the drive electrode film at a predetermined timing based on the capacitance detection signal so that the capacitance detection signal is maximized. In other words, the control unit adjusts the drive voltage applied to the drive electrode film at a predetermined timing so that the warping of the vibration area is reduced. This makes it possible to prevent pressure from being detected in a warped state of the vibration area, and to prevent a decrease in detection accuracy.

The reference symbols in parentheses attached to each component indicate an example of the correspondence between the component and the specific components described in the embodiments described below.

FIG. 2 is a schematic plan view of the piezoelectric device according to the first embodiment. FIG. 2 is a cross-sectional view taken along line IIA-IIA in FIG. FIG. 2 is a cross-sectional view taken along line IIB-IIB in FIG. 11 is a schematic diagram showing the state of the vibration region when the intermediate drive electrode film is at ground potential and no voltage is applied to the upper-layer drive electrode film and the lower-layer drive electrode film. FIG. 11 is a schematic diagram showing the state of a vibration region when the intermediate drive electrode film is at ground potential and a positive voltage is applied to the upper-layer drive electrode film and the lower-layer drive electrode film. FIG. 11 is a schematic diagram showing the state of a vibration region when the intermediate drive electrode film is at ground potential and a negative voltage is applied to the upper-layer drive electrode film and the lower-layer drive electrode film. FIG. FIG. 11 is a cross-sectional view of a piezoelectric element according to a second embodiment. FIG. 11 is a cross-sectional view of a piezoelectric element according to a third embodiment. FIG. 13 is a cross-sectional view of a piezoelectric element according to a fourth embodiment. 13 is a cross-sectional view showing a case where the vibration region is significantly warped.

The following describes embodiments of the present invention with reference to the drawings. In the following embodiments, parts that are the same or equivalent to each other are denoted by the same reference numerals.

First Embodiment
A piezoelectric device according to a first embodiment will be described with reference to Fig. 1, Fig. 2A, and Fig. 2B. The piezoelectric device according to this embodiment is suitable for use in a smartphone or an AI (artificial intelligence) speaker. Although Fig. 1 is not a cross-sectional view, a pressure electrode film 510, a capacitance electrode film 520, and a drive electrode film 530, which will be described later, are hatched to facilitate understanding.

The piezoelectric device of this embodiment includes a piezoelectric element 1 and a control unit 2. First, the configuration of the piezoelectric element 1 will be described.

The piezoelectric element 1 includes a support 10 and a vibration part 20, and has a rectangular planar shape. The support 10 includes a support substrate 11 having one surface 11a and the other surface 11b, and an insulating film 12 formed on the one surface 11a of the support substrate 11. The support substrate 11 is made of, for example, a silicon substrate, and the insulating film 12 is made of, for example, an oxide film.

The vibration section 20 is disposed on the support 10. The support 10 is formed with a recess 10a for floating the inner edge side of the vibration section 20. Therefore, the vibration section 20 has a support region 21a disposed on the support 10, and a floating region 21b that is connected to the support region 21a and floats above the recess 10a. In this embodiment, the recess 10a has a planar rectangular shape at the open end on the vibration section 20 side. Therefore, the entire floating region 21b has a planar rectangular shape.

In the floating region 21b, a slit 30 is formed penetrating the floating region 21b in the thickness direction. In this embodiment, the slit 30 is formed so as to divide the floating region 21b into four. More specifically, two slits 30 are formed so as to pass through the center C of the floating region 21b and extend toward the opposite corners of the floating region 21b. In other words, the slits 30 are formed so as to extend from each corner of the floating region 21b, which is rectangular in plan view, toward the center C, and each slit 30 intersects at the center C. As a result, the floating region 21b is separated into four vibration regions 22, each of which is substantially triangular in plan view. Although not particularly limited, in this embodiment, the interval between each vibration region 22 (i.e., the width of the slit 30) is about 1 μm.

Each vibration region 22 is a cantilever with the end on the support region 21a side as a fixed end and the tip end opposite the support region 21a (hereinafter simply referred to as the tip end) as a free end. In the following description, the surface of the vibration region 22 opposite the support 10 is referred to as one surface 22a of the vibration region 22, and the surface of the vibration region 22 facing the support 10 is referred to as the other surface 22b of the vibration region 22.

The vibration section 20 is configured to have a piezoelectric film 40 and an electrode film 50 connected to the piezoelectric film 40. Specifically, the piezoelectric film 40 has a lower piezoelectric film 41 and an upper piezoelectric film 42 laminated on the lower piezoelectric film 41. The lower piezoelectric film 41 and the upper piezoelectric film 42 are configured using lead-free piezoelectric ceramics such as scandium aluminum nitride (ScAlN) and aluminum nitride (AlN).

The electrode film 50 is formed at a predetermined location in the vibration region 22 so as to be connected to the piezoelectric film 40, and is made of molybdenum, copper, platinum, titanium, or the like. In this embodiment, the electrode film 50 includes a lower electrode film 51 formed below the lower piezoelectric film 41, an intermediate electrode film 52 formed between the lower piezoelectric film 41 and the upper piezoelectric film 42, and an upper electrode film 53 formed above the upper piezoelectric film 42. The lower electrode film 51 and the intermediate electrode film 52 are arranged to face each other with the lower piezoelectric film 41 in between. The intermediate electrode film 52 and the upper electrode film 53 are arranged to face each other with the upper piezoelectric film 42 in between. The lower electrode film 51, the intermediate electrode film 52, and the upper electrode film 53 have the same shape in the normal direction to the one surface 22a of the vibration region 22. The location of the electrode film 50 in this embodiment will be described in more detail below.

First, when the vibration region 22 is cantilevered as described above, the stress generated when the vibration region 22 (i.e., the piezoelectric film 40) vibrates tends to be greater on the fixed end side where the vibration region 22 is supported than on the free end side. For this reason, the vibration region 22 is divided into a first region R1 where the stress tends to be greater, and a second region R2 where the stress tends to be smaller. In this embodiment, an electrode film 50 is formed in each of the first region R1 and the second region R2. Note that the electrode film 50 formed in the first region R1 and the electrode film 50 formed in the second region R2 are insulated from each other because they perform different functions.

The electrode film 50 formed in the first region R1 functions as a pressure electrode film 510 that detects the vibration of the vibration region 22. In the following, the lower electrode film 51 formed in the first region R1 will be described as the lower pressure electrode film 511, the intermediate electrode film 52 as the intermediate pressure electrode film 512, and the upper electrode film 53 as the upper pressure electrode film 513. The pressure electrode film 510 outputs a pressure detection signal corresponding to the change in charge, since the charge of the upper piezoelectric film 42 and the lower piezoelectric film 41 changes when the vibration region 22 vibrates. Specifically, the lower pressure electrode film 511, the intermediate pressure electrode film 512, and the upper pressure electrode film 513 are connected to electrodes for connection to the control unit 2 via wiring or the like formed in the support region 21a, although not shown in particular. In this embodiment, the lower pressure electrode film 511, the intermediate pressure electrode film 512, and the upper pressure electrode film 513 in each vibration region 22 are connected to electrodes so that the change in charge in the first region R1 of each vibration region 22 is output as a single pressure detection signal.

In the second region R2, an electrode film 50 is formed on the outer edge side and the inner edge side. However, the electrode film 50 formed on the outer edge side is insulated from the electrode film 50 formed on the inner edge side.

The electrode film 50 formed on the outer edge side of the second region R2 functions as a capacitance electrode film 520 that detects the capacitance between adjacent vibration regions 22. In this embodiment, adjacent vibration regions 22 refer to vibration regions 22 adjacent in the circumferential direction with the center C as the reference. In other words, adjacent vibration regions 22 refer to vibration regions 22 adjacent to each other without the center C in between. In the following, the lower layer electrode film 51 formed on the outer edge of the second region R2 will be described as the lower layer capacitance electrode film 521, the intermediate electrode film 52 as the intermediate capacitance electrode film 522, and the upper layer electrode film 53 as the upper layer capacitance electrode film 523.

The lower layer capacitance electrode film 521, the intermediate capacitance electrode film 522, and the upper layer capacitance electrode film 523, which are formed in adjacent vibration regions 22 and face each other, output a capacitance detection signal according to the capacitance between the adjacent vibration regions 22. Specifically, the lower layer capacitance electrode film 521, the intermediate capacitance electrode film 522, and the upper layer capacitance electrode film 523 are connected to electrodes for connection to the control unit 2 via the lead-out wiring 61 formed in the vibration region 22 and wiring (not shown) formed in the support region 21a. In this embodiment, the lower layer capacitance electrode film 521, the intermediate capacitance electrode film 522, and the upper layer capacitance electrode film 523 formed in each vibration region 22 are connected so that the capacitance between each vibration region 22 is output as a capacitance detection signal. Note that the capacitance detection signal may be the sum of the capacitance between the lower layer capacitance electrode film 521, the capacitance between the intermediate capacitance electrode film 522, and the capacitance between the upper layer capacitance electrode film 523, or each capacitance may be output separately.

The electrode film 50 formed on the inner edge side of the second region R2 functions as a drive electrode film 530 to which a drive voltage is applied to displace (i.e., drive) the vibration region 22. In the following, the lower layer electrode film 51 formed on the inner edge of the second region R2 will be described as a lower layer drive electrode film 531, the intermediate electrode film 52 as an intermediate drive electrode film 532, and the upper layer electrode film 53 as an upper layer drive electrode film 533.

The lower-layer drive electrode film 531, the intermediate drive electrode film 532, and the upper-layer drive electrode film 533 are connected to electrodes for connection to the control unit 2 via the lead-out wiring 62 formed in the vibration region 22 and wiring (not shown) formed in the support region 21a. A predetermined drive voltage is applied to each of the drive electrode films 531 to 533 based on a capacitance detection signal, as described below.

In this embodiment, the lower pressure electrode film 511, the lower capacitance electrode film 521, and the lower drive electrode film 531 are each disposed below the lower piezoelectric film 41, and are formed by patterning a common metal film. Similarly, the intermediate pressure electrode film 512, the intermediate capacitance electrode film 522, and the intermediate drive electrode film 532 are each disposed between the lower piezoelectric film 41 and the upper piezoelectric film 42, and are formed by patterning a common metal film. Furthermore, the upper pressure electrode film 513, the upper capacitance electrode film 523, and the upper drive electrode film 533 are each disposed above the upper piezoelectric film 42, and are formed by patterning a common metal film.

Furthermore, the vibration section 20 of this embodiment has an undercoat film 70 on which the lower piezoelectric film 41 and the lower electrode film 51 are disposed. That is, the piezoelectric film 40 and the electrode film 50 are disposed on the support 10 via the undercoat film 70. The undercoat film 70 is not necessarily required, but is provided to facilitate crystal growth when forming the lower piezoelectric film 41 and the like. In this embodiment, the undercoat film 70 is made of aluminum nitride or the like. The piezoelectric film 40 has a thickness of about 1 μm, and the undercoat film 70 has a thickness of about several tens of nm. That is, the undercoat film 70 is made extremely thin compared to the piezoelectric film 40.

The above is the configuration of the piezoelectric element 1 in this embodiment. The control unit 2 is composed of a microcomputer equipped with a CPU and storage units such as ROM, RAM, and non-volatile RAM, and is connected to the piezoelectric element 1. The control unit 2 realizes various control operations by the CPU reading and executing a program from the ROM or non-volatile RAM. Note that the ROM or non-volatile RAM stores in advance various data (e.g., initial values, lookup tables, maps, etc.) used when executing the program. Furthermore, the storage medium such as ROM is a non-transient physical storage medium. CPU stands for Central Processing Unit, ROM stands for Read Only Memory, and RAM stands for Random Access Memory.

Specifically, the control unit 2 grasps the state of warping of the vibration region 22 based on the capacitance detection signal from the capacitance electrode film 520. In more detail, the capacitance between adjacent vibration regions 22 is maximum when the adjacent vibration regions 22 are not warped, because the distance between each capacitance electrode film 520 is shortest. When the vibration region 22 is warped, the capacitance between adjacent vibration regions 22 becomes smaller because the distance between each capacitance electrode film 520 becomes longer. Therefore, the control unit 2 grasps the state of warping of the vibration region 22 based on the magnitude of the capacitance detection signal.

Then, the control unit 2 applies a driving voltage to the driving electrode film 530 based on the capacitance detection signal to displace the piezoelectric film 40, thereby performing a reduction process to reduce the warp of the vibration region 22. Hereinafter, a method for reducing the warp of the vibration region 22 will be described with reference to Figures 3A to 3C. Note that Figures 3A to 3C show schematic diagrams in which the pressure electrode film 510 and the capacitance electrode film 520 are omitted. In addition, in Figures 3A to 3C, the direction along the stacking direction of the lower piezoelectric film 41 and the upper piezoelectric film 42 is the Y-axis direction, and the direction along the surface direction of the lower piezoelectric film 41 and the upper piezoelectric film 42 is the X-axis direction. In addition, in the following, in the Y-axis direction, the side from the lower piezoelectric film 41 toward the upper piezoelectric film 42 is the positive side, and the side from the upper piezoelectric film 42 toward the lower piezoelectric film 41 is the negative side.

First, as shown in FIG. 3A, a case will be described in which the intermediate drive electrode film 532 is at ground potential and no drive voltage is applied to the lower-layer drive electrode film 531 and the upper-layer drive electrode film 533. In this case, the dipole D in the lower-layer piezoelectric film 41 and the dipole D in the upper-layer piezoelectric film 42 are in a neutral state.

3B, when a positive drive voltage is applied to the lower-layer drive electrode film 531 and the upper-layer drive electrode film 533, in the upper-layer piezoelectric film 42, the positive side of the dipole D repels the upper-layer drive electrode film 533 and the negative side is attracted to the upper-layer drive electrode film 533. Therefore, in the upper-layer piezoelectric film 42, the dipole D rotates to the negative side in the Y-axis direction as shown by the arrow in the figure, and tries to extend in the X-axis direction. In contrast, in the lower-layer piezoelectric film 41, the positive side of the dipole D repels the lower-layer drive electrode film 531 and the negative side is attracted to the lower-layer drive electrode film 531. Therefore, in the lower-layer piezoelectric film 41, the dipole D rotates to the positive side in the Y-axis direction as shown by the arrow in the figure, and tries to shrink in the X-axis direction. Therefore, the tip of the vibration region 22 is displaced to the negative side in the Y-axis direction. In other words, when a positive drive voltage is applied to the lower-layer drive electrode film 531 and the upper-layer drive electrode film 533, the tip of the vibration region 22 is displaced toward the other surface 22b of the vibration region 22.

Also, as shown in FIG. 3C, when a negative drive voltage is applied to the lower-layer drive electrode film 531 and the upper-layer drive electrode film 533, in the upper-layer piezoelectric film 42, the positive side of the dipole D is attracted to the upper-layer drive electrode film 533, and the negative side repels the upper-layer drive electrode film 533. Therefore, in the upper-layer piezoelectric film 42, the dipole D rotates to the positive side in the Y-axis direction as shown by the arrow in the figure, and tries to shrink in the X-axis direction. In contrast, in the lower-layer piezoelectric film 41, the positive side of the dipole D is attracted to the lower-layer drive electrode film 531, and the negative side repels the lower-layer drive electrode film 531. Therefore, in the lower-layer piezoelectric film 41, the dipole D rotates to the negative side in the Y-axis direction as shown by the arrow in the figure, and tries to extend in the X-axis direction. Therefore, the tip of the vibration region 22 is displaced to the positive side in the Y-axis direction. In other words, when a negative drive voltage is applied to the lower-layer drive electrode film 531 and the upper-layer drive electrode film 533, the tip of the vibration region 22 is displaced toward one surface 22a of the vibration region 22.

Therefore, when the control unit 2 determines that the vibration region 22 is warped based on the capacitance detection signal from the capacitance electrode film 520, the control unit 2 adjusts the voltage applied to the drive electrode film 530 to perform a reduction process to reduce the warping of the vibration region 22. In this embodiment, four vibration regions 22 are configured. Therefore, the control unit 2 performs a reduction process on each vibration region 22 so that the warping of each vibration region 22 is reduced. For example, the control unit 2 first performs a reduction process to reduce the warping by increasing or decreasing the drive voltage applied to two predetermined adjacent vibration regions 22. Next, the control unit 2 performs a reduction process to reduce the warping by increasing or decreasing the drive voltage applied to one vibration region 22 that has been subjected to the warping reduction process and the vibration region 22 adjacent to the vibration region 22 that has not been subjected to the warping reduction process. Thereafter, the control unit 2 performs the same process sequentially on the remaining vibration regions 22, and performs a reduction process to reduce the warping by increasing or decreasing the drive voltage applied to all vibration regions 22.

Furthermore, when the control unit 2 performs the reduction process, a reference drive voltage may be stored in a memory unit or the like and applied first, after which the drive voltage to be applied may be fine-tuned. The reference drive voltage may be, for example, a drive voltage that minimizes warping due to residual stress when the piezoelectric element 1 is manufactured. In other words, the reference drive voltage may be, for example, a drive voltage that maximizes the capacitance detection signal immediately after the piezoelectric element 1 is manufactured. This can shorten the time required for the reduction process and simplify the program on the control unit 2 side.

The reference drive voltage may be set as follows. First, a positive voltage is applied to one of the capacitance electrode films 520 in the adjacent vibration regions 22, and a negative voltage is applied to the other capacitance electrode film 520. As a result, an electrostatic attraction is generated between the adjacent vibration regions 22, and if the vibration region 22 is warped, the vibration region 22 is displaced and the warping is reduced. If the vibration region 22 is displaced, an adjustment signal based on the displacement is output from the drive electrode film 530. If the vibration region 22 is not warped, the adjustment signal does not change even if the voltage applied to the capacitance electrode film 520 of the adjacent vibration region 22 is increased. For this reason, the magnitude of the voltage applied to the adjacent capacitance electrode film 520 may be adjusted, and the reference drive voltage may be set based on the voltage when the adjustment signal no longer changes.

Furthermore, when the reduction process is performed periodically as described below, the reference drive voltage may be updated each time the reduction process is performed on the vibration region 22, and the drive voltage set in the previous reduction process may be used as the reference drive voltage. In this way, the effect of setting the reference drive voltage can be obtained even for warping over time in the vibration region 22.

The above is the configuration of the piezoelectric device in this embodiment. Next, we will explain the operation of the piezoelectric device.

First, the control unit 2 performs the reduction process of the vibration region 22 as described above at a predetermined timing before detecting pressure such as sound pressure. Note that this process is performed, for example, when the piezoelectric device is manufactured in a factory, etc. Also, this process is performed periodically, for example, immediately after the equipment in which the piezoelectric device is mounted is switched from an off state to an on state, or at predetermined intervals.

The piezoelectric device detects the pressure (e.g., sound pressure) applied to the vibration region 22 with the warping of the vibration region 22 reduced. Specifically, when pressure is applied to the vibration region 22, the vibration region 22 vibrates. Then, charges are generated in the lower piezoelectric film 41 and the upper piezoelectric film 42 based on stress corresponding to the displacement of the vibration region 22. Therefore, the piezoelectric device detects the pressure applied to the vibration region 22 based on the pressure detection signal from the pressure electrode film 510. At this time, because the warping of the vibration region 22 is reduced, a decrease in detection accuracy can be suppressed.

According to the present embodiment described above, the control unit 2 performs a reduction process to reduce the warping of the vibration region 22 based on the capacitance detection signal. This makes it possible to prevent pressure from being detected in a warped state of the vibration region 22, and to prevent a decrease in detection accuracy. Furthermore, in order to reduce the warping of the vibration region 22 in this manner, the control unit 2 periodically performs a reduction process, thereby making it possible to suppress warping of the vibration region 22 over time.

(1) In this embodiment, the pressure electrode film 510, the capacitance electrode film 520, and the drive electrode film 530 are each arranged in the same manner with respect to the piezoelectric film 40. That is, the lower pressure electrode film 511, the lower capacitance electrode film 521, and the lower drive electrode film 531 are each arranged below the lower piezoelectric film 41. The intermediate pressure electrode film 512, the intermediate capacitance electrode film 522, and the intermediate drive electrode film 532 are each arranged between the lower piezoelectric film 41 and the upper piezoelectric film 42. The upper pressure electrode film 513, the upper capacitance electrode film 523, and the upper drive electrode film 533 are each arranged above the upper piezoelectric film 42. Therefore, when arranging the lower pressure electrode film 511, the lower capacitance electrode film 521, and the lower drive electrode film 531, the lower pressure electrode film 511, the lower capacitance electrode film 521, and the lower drive electrode film 531 can be arranged simultaneously by arranging a metal film and then patterning the metal film. Similarly, when arranging the intermediate pressure electrode film 512, the intermediate capacitance electrode film 522, and the intermediate driving electrode film 532, the intermediate pressure electrode film 512, the intermediate capacitance electrode film 522, and the intermediate driving electrode film 532 can be arranged simultaneously by arranging a metal film and then patterning the metal film. When arranging the upper pressure electrode film 513, the upper capacitance electrode film 523, and the upper driving electrode film 533, the upper pressure electrode film 513, the upper capacitance electrode film 523, and the upper driving electrode film 533 can be arranged simultaneously by arranging a metal film and then patterning the metal film. Therefore, the process for manufacturing the piezoelectric element 1 can be simplified.

(2) In this embodiment, when the control unit 2 performs a process to reduce the warping of the vibration region 22, the control unit 2 uses a reference drive voltage, thereby shortening the time required for the process and simplifying the program on the control unit 2 side.

(3) In this embodiment, the control unit 2 performs a process for reducing the warping of the vibration region 22 based on the capacitance detection signal. Therefore, compared to, for example, a case in which the thickness of the piezoelectric film 40, the electrode film 50, etc. is adjusted when forming the vibration region 22 to reduce the warping of the vibration region 22, the manufacturing process can be simplified and a decrease in yield can be suppressed.

Second Embodiment
A second embodiment will be described. This embodiment is different from the first embodiment in that the configuration of the capacitor electrode film 520 is changed. As the rest is similar to the first embodiment, the description will be omitted here.

As shown in FIG. 4, in the piezoelectric element 1 of this embodiment, if the surface exposed from the slit 30 in the vibration region 22 is defined as the side surface 22c, a side capacitance electrode film 524 is formed as a capacitance electrode film 520 on each side surface 22c in the second region R2 of the vibration region 22. Note that in this embodiment, the capacitance electrode film 520 is not formed below the lower piezoelectric film 41, between the lower piezoelectric film 41 and the upper piezoelectric film 42, or above the upper piezoelectric film 42. Also, FIG. 4 corresponds to a cross-sectional view taken along line IIB-IIB in FIG. 1.

The control unit 2 of this embodiment then performs a reduction process to reduce the warping of the vibration region 22 based on a capacitance detection signal corresponding to the capacitance between the side capacitance electrode films 524 in adjacent vibration regions 22.

According to the present embodiment described above, the warping of the vibration region 22 is reduced based on the capacitance detection signal, so that the same effect as the first embodiment can be obtained.

(1) In this embodiment, the capacitance electrode film 520 is formed on each side surface 22c in the second region R2 of the vibration region 22. This makes it easier to increase the area of the opposing capacitance electrode films 520 in adjacent vibration regions 22, and the capacitance between the opposing capacitance electrode films 520 can be increased. This makes it possible to increase the signal-to-noise ratio, which is the ratio of signal to noise, and reduce the effect of noise.

Third Embodiment
A third embodiment will be described. This embodiment is different from the second embodiment in that the configuration of the capacitor electrode film 520 is changed. As the rest is similar to the second embodiment, the description will be omitted here.

In the piezoelectric element 1 of this embodiment, as shown in FIG. 5, the side capacitance electrode film 524 is divided into a one-side capacitance electrode film 524a located on the one surface 22a side of the vibration region 22, and an other-side capacitance electrode film 524b located on the other surface 22b side of the vibration region 22. The piezoelectric element 1 outputs a first capacitance detection signal corresponding to the capacitance between the one-side capacitance electrode films 524a formed on adjacent vibration regions 22, and outputs a second capacitance detection signal corresponding to the capacitance between the other-side capacitance electrode films 524b formed on adjacent vibration regions 22.

Note that FIG. 5 corresponds to a cross-sectional view taken along line IIB-IIB in FIG. 1. Also, although not particularly limited, in this embodiment, the one-side capacitance electrode film 524a and the other-side capacitance electrode film 524b are divided at the boundary between the lower piezoelectric film 41 and the upper piezoelectric film 42.

The control unit 2 determines the direction of warping of the vibration region 22 based on the first capacitance detection signal and the second capacitance detection signal, and adjusts the drive voltage applied to the drive electrode film 530. Specifically, when the vibration region 22 warps toward the one surface 22a, the distance between the opposing one-surface side capacitance electrode films 524a in adjacent vibration regions 22 becomes longer than the distance between the opposing other-surface side capacitance electrode films 524b. Therefore, the first capacitance detection signal becomes smaller than the second capacitance detection signal. On the other hand, when the vibration region 22 warps toward the other surface 22b, the distance between the opposing one-surface side capacitance electrode films 524a in adjacent vibration regions 22 becomes shorter than the distance between the opposing other-surface side capacitance electrode films 524b. Therefore, the first capacitance detection signal becomes larger than the second capacitance detection signal.

Therefore, the control unit 2 determines the warped direction of the vibration region 22 based on the first capacitance detection signal and the second capacitance detection signal, and adjusts the drive voltage applied to the drive electrode film 530 based on the determination result. Specifically, when the first capacitance detection signal is smaller than the second capacitance detection signal, the control unit 2 determines that the tip of the vibration region 22 is warped toward the one surface 22a. Then, as described with reference to FIG. 3B above, the control unit 2 displaces the tip of the vibration region 22 toward the other surface 22b by applying a positive drive voltage to the upper layer drive electrode film 533 and the lower layer drive electrode film 531. Also, when the first capacitance detection signal is larger than the second capacitance detection signal, the control unit 2 determines that the tip of the vibration region 22 is warped toward the other surface 22b. Then, as described with reference to FIG. 3C above, the control unit 2 displaces the tip of the vibration region 22 toward the one surface 22a by applying a negative drive voltage to the upper layer drive electrode film 533 and the lower layer drive electrode film 531.

According to the present embodiment described above, the warping of the vibration region 22 is reduced based on the capacitance detection signal, so that the same effect as the first embodiment can be obtained.

(1) In this embodiment, the control unit 2 determines the direction in which the vibration region 22 is warped, and adjusts the drive voltages applied to the lower-layer drive electrode film 531 and the upper-layer drive electrode film 533 based on the determination result. This makes it possible to shorten the time required for the warping reduction process.

Fourth Embodiment
A fourth embodiment will be described. This embodiment is a combination of the second embodiment with the lower layer capacitor electrode film 521 and the upper layer capacitor electrode film 523 of the first embodiment. As the rest is the same as the first embodiment, the description will be omitted here.

The piezoelectric element 1 of this embodiment is a combination of the lower layer capacitance electrode film 521 and the upper layer capacitance electrode film 523 of the first embodiment with the second embodiment. Specifically, the capacitance electrode film 520 is configured to have a lower layer capacitance electrode film 521, an upper layer capacitance electrode film 523, and a side capacitance electrode film 524, as shown in FIG. 6. The piezoelectric element 1 outputs a side capacitance detection signal related to the capacitance between the side capacitance electrode films 524 formed in adjacent vibration regions 22. The piezoelectric element 1 outputs an upper layer capacitance detection signal related to the capacitance between the upper layer capacitance electrode films 523 formed in adjacent vibration regions 22. The piezoelectric element 1 outputs a lower layer capacitance detection signal related to the capacitance between the lower layer capacitance electrode films 521 formed in adjacent vibration regions 22. Note that FIG. 6 corresponds to a cross-sectional view taken along the line IIB-IIB in FIG. 1. Also, in this embodiment, the intermediate capacitance electrode film 522 is not formed.

The control unit 2 determines the direction of the warp of the vibration region 22 based on the side capacitance detection signal, the upper layer capacitance detection signal, and the lower layer capacitance detection signal, and adjusts the drive voltage applied to the drive electrode film 530.

Specifically, as shown in FIG. 7, when the vibration region 22 is significantly warped, the opposing area of the side capacitance electrode film 524 becomes smaller, and the capacitance between the side capacitance electrode films 524 becomes smaller. In this case, in the example of FIG. 7, since the vibration region 22 is significantly warped toward the one surface 22a, the opposing area of the lower layer capacitance electrode film 521 becomes larger, and the lower layer capacitance detection signal becomes larger. In contrast, although not specifically shown, when the vibration region 22 is significantly warped toward the other surface 22b, the opposing area of the upper layer capacitance electrode film 523 becomes larger, and the upper layer capacitance detection signal becomes larger.

Therefore, the control unit 2 determines the warping direction of the vibration region 22 based on the side capacitance detection signal, the upper layer capacitance detection signal, and the lower layer capacitance detection signal, and adjusts the drive voltage applied to the drive electrode film 530 based on the determination result. Specifically, as in the third embodiment, when the control unit 2 determines that the tip of the vibration region 22 is warped toward the one surface 22a, the control unit 2 applies a positive drive voltage to the upper layer drive electrode film 533 and the lower layer drive electrode film 531 to displace the tip of the vibration region 22 toward the other surface 22b. When the control unit 2 determines that the tip of the vibration region 22 is warped toward the other surface 22b, the control unit 2 applies a negative drive voltage to the upper layer drive electrode film 533 and the lower layer drive electrode film 531 to displace the tip of the vibration region 22 toward the one surface 22a.

According to the present embodiment described above, the warping of the vibration region 22 is reduced based on the capacitance detection signal, so that the same effect as the first embodiment can be obtained.

(1) In this embodiment, the control unit 2 determines the direction in which the vibration region 22 is warped, and adjusts the drive voltages applied to the lower-layer drive electrode film 531 and the upper-layer drive electrode film 533 based on the determination result. Therefore, as in the third embodiment, the time required for the warp reduction process can be shortened.

(2) In this embodiment, in addition to the side capacitance electrode film 524, the lower layer capacitance electrode film 521 and the upper layer capacitance electrode film 523 are also formed. Therefore, even if the vibration region 22 is significantly warped and the side capacitance detection signal becomes small, the warping of the vibration region 22 can be suitably reduced.

Other Embodiments
Although the present disclosure has been described based on the embodiment, it is understood that the present disclosure is not limited to the embodiment or structure. The present disclosure also encompasses various modifications and modifications within the equivalent range. In addition, various combinations and forms, as well as other combinations and forms including only one element, more than one element, or less than one element, are also within the scope and concept of the present disclosure.

For example, in each of the above embodiments, the floating region 21b may have a polygonal planar shape, such as a pentagon, hexagon, or octagon, rather than a rectangular shape. The number of vibration regions 22 formed in the floating region 21b may be changed as appropriate. Furthermore, the piezoelectric element 1 may have a polygonal planar shape, such as a pentagon or hexagon, rather than a rectangular shape.

Furthermore, in each of the above embodiments, the positions at which the pressure electrode film 510, the capacitance electrode film 520, and the drive electrode film 530 are formed can be changed as appropriate. For example, the pressure electrode film 510 may be formed in the second region R2, and the capacitance electrode film 520 and the drive electrode film 530 may be formed in the first region R1. The capacitance electrode film 520 may also be formed on the free end side of each vibration region 22. In this case, the control unit 2 may perform a reduction process to reduce the warping of the vibration region 22 based on a capacitance detection signal between adjacent vibration regions 22 across the center C in the floating region 21b.

The above embodiments may be combined as appropriate. For example, the third embodiment may be combined with the fourth embodiment, and the side capacitance electrode film 524 may be configured to have a one-side capacitance electrode film 524a and an other-side capacitance electrode film 524b.

The control unit and the method described in the present disclosure may be realized by a dedicated computer provided by configuring a processor and a memory programmed to execute one or more functions embodied in a computer program. Alternatively, the control unit and the method described in the present disclosure may be realized by a dedicated computer provided by configuring a processor with one or more dedicated hardware logic circuits. Alternatively, the control unit and the method described in the present disclosure may be realized by one or more dedicated computers configured by combining a processor and a memory programmed to execute one or more functions with a processor configured with one or more hardware logic circuits. In addition, the computer program may be stored in a computer-readable non-transient tangible recording medium as instructions executed by the computer.

REFERENCE SIGNS LIST 1 Piezoelectric element 2 Control unit 10 Support 21a Support region 22 Vibration region 30 Slit 40 Piezoelectric film 50 Electrode film 510 Pressure electrode film 520 Capacitive electrode film 530 Drive electrode film

Claims (7)

A piezoelectric device including a piezoelectric element (1) having a vibration portion (20),
a support (10); and a vibration section disposed on the support and including a piezoelectric film (40) and an electrode film (50), the vibration section having a support region (21a) supported by the support and a plurality of vibration regions (22) connected to the support region and having portions on the opposite side to the support region suspended from the support;
A control unit (2) that performs a predetermined process,
The plurality of vibration regions are separated from each other by slits (30),
The electrode film includes a pressure electrode film (510) connected to the piezoelectric film and outputting a pressure detection signal corresponding to the charge of the piezoelectric film, a capacitance electrode film (520) outputting a capacitance detection signal corresponding to the capacitance between the adjacent vibration regions, and a drive electrode film (530) to which a drive voltage is applied to displace a tip end of the vibration region on the opposite side to the support region along a stacking direction of the support body and the vibration region,
The control unit adjusts the drive voltage applied to the drive electrode film at a predetermined timing based on the capacitance detection signal so that the capacitance detection signal is maximized. The vibration region has a first region (R1) on the support region side and a second region (R2) on the opposite side to the support region,
the pressure electrode film is formed in the first region,
The piezoelectric device according to claim 1 , wherein the capacitance electrode film and the drive electrode film are formed in the second region. The piezoelectric film has a lower piezoelectric film (41) and an upper piezoelectric film (42) disposed on the lower piezoelectric film,
The pressure electrode film includes an intermediate pressure electrode film (512) disposed between the lower layer piezoelectric film and the upper layer piezoelectric film, a lower layer pressure electrode film (511) disposed on the opposite side of the intermediate pressure electrode film across the lower layer piezoelectric film, and an upper layer pressure electrode film (513) disposed on the opposite side of the intermediate pressure electrode film across the upper layer piezoelectric film,
the capacitance electrode film includes an intermediate capacitance electrode film (522) disposed between the lower layer piezoelectric film and the upper layer piezoelectric film, a lower layer capacitance electrode film (521) disposed on the opposite side of the intermediate capacitance electrode film with the lower layer piezoelectric film in between, and an upper layer capacitance electrode film (523) disposed on the opposite side of the intermediate capacitance electrode film with the upper layer piezoelectric film in between;
The piezoelectric device according to claim 1 or 2, wherein the control unit adjusts the driving voltage based on a capacitance detection signal of the intermediate capacitance electrode film, a capacitance detection signal of the lower layer capacitance electrode film, and a capacitance detection signal of the upper layer capacitance electrode film, which are respectively formed in the vibration regions adjacent to each other across the slit. The piezoelectric film has a lower piezoelectric film (41) and an upper piezoelectric film (42) disposed on the lower piezoelectric film,
The capacitance electrode film has side capacitance electrode films (524) formed on the mutually opposing side surfaces (22c) of the adjacent vibration regions with the slit therebetween,
The piezoelectric device according to claim 1 , wherein the control unit adjusts the drive voltage based on a capacitance detection signal of the side capacitance electrode film formed on each of the side surfaces of the adjacent vibration regions.

When a surface of the capacitance electrode film on the opposite side to the support in the vibration region is defined as one surface (22a) and a surface of the capacitance electrode film on the support side in the vibration region is defined as another surface (22b), the capacitance electrode film is divided into a one-surface-side capacitance electrode film (524a) on the one surface side and an other-surface-side capacitance electrode film (524b),
The piezoelectric device according to claim 4 , wherein the control unit determines a direction of warping of the vibration region based on a capacitance detection signal of the one-side capacitance electrode film and a capacitance detection signal of the other-side capacitance electrode film, and adjusts the driving voltage based on the determination result. The piezoelectric film has a lower piezoelectric film (41) and an upper piezoelectric film (42) disposed on the lower piezoelectric film,
The pressure electrode film includes an intermediate pressure electrode film (512) disposed between the lower layer piezoelectric film and the upper layer piezoelectric film, a lower layer pressure electrode film (511) disposed on the opposite side of the intermediate pressure electrode film across the lower layer piezoelectric film, and an upper layer pressure electrode film (513) disposed on the opposite side of the intermediate pressure electrode film across the upper layer piezoelectric film,
The capacitance electrode film includes a lower capacitance electrode film (521) arranged on the opposite side of the upper piezoelectric film with the lower piezoelectric film in between, an upper capacitance electrode film (523) arranged on the opposite side of the lower piezoelectric film with the upper piezoelectric film in between, and side capacitance electrode films (524) formed on the mutually opposing side surfaces of the adjacent vibration regions with the slit in between,
The control unit determines a direction of warping of the vibration region based on a lower layer capacitance detection signal of the lower layer capacitance electrode film, a capacitance detection signal of the upper layer capacitance electrode film, and a side capacitance detection signal of the side capacitance electrode film, and adjusts the driving voltage based on the determination result. The piezoelectric device according to any one of claims 1 to 6, wherein the control unit stores a predetermined reference drive voltage that brings the capacitance detection signal closer to a maximum, and when adjusting the drive voltage, the control unit applies the reference drive voltage to the drive electrode film and then adjusts the drive voltage based on the capacitance detection signal.

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