JP7705299B2 - STACKED IMAGING DEVICE AND ITS MANUFACTURING METHOD - Google Patents

Description

The present invention relates to a stacked imaging element and a manufacturing method thereof, and more specifically to a stacked imaging element having a pixel configuration in which multiple imaging element units each having a photoelectric conversion element formed on a substrate are stacked together, and the pixel electrodes of the photoelectric conversion elements are connected to a readout circuit on the substrate for operation, and a manufacturing method thereof.

As CMOS image sensor technology advances, image sensors have become more precise and pixels have become finer, leading to the commercialization of small, high-performance cameras suitable for capturing high-quality video. On the other hand, as image sensors are made increasingly more pixelated, the selection time for each pixel becomes shorter, making it difficult to read the image sufficiently, resulting in degradation of image quality. As a device configuration that can alleviate these image sensor problems, an image sensor has been proposed in which photodiodes and readout circuits are formed on a silicon substrate, and multiple of these are stacked together to illuminate the image from the side (see Patent Documents 1 to 3 below).

These devices allow the light receiving section and readout circuit to be formed within the substrate surface, making it possible to perform single line driving and single pixel driving in addition to digital driving, thus significantly improving the increased processing time that accompanies matrix driving as seen in conventional CMOS image sensors.

Japanese Unexamined Patent Publication No. 152176/1986 Japanese Patent Application Publication No. 3-50973 JP 2002-77524 A

The devices described in the above Patent Documents 1 to 3 are based on semiconductors such as Si and GaAs, and have wavelength dependence in the depth direction. Therefore, when light is incident on the side surface of the photoelectric conversion element stack, the amount of incident light in only a portion of the depth direction may be used as the detection value, resulting in poor utilization efficiency of the incident light and making it difficult to obtain good wavelength characteristics according to the material.
Furthermore, in recent years, there has been a strong demand for such devices to satisfy the demand for an increased number of pixels and a larger display area.

In other words, the present invention has been made to solve these problems, and aims to provide a stacked imaging element and a manufacturing method thereof that has a photoelectric conversion element that has good efficiency in using incident light and can obtain good wavelength characteristics according to the material, and that can also meet the demands for a larger number of pixels and a larger area.

In order to achieve the above object, the stacked image pickup device and the manufacturing method thereof according to the present invention are configured as follows.
That is, the stacked type imaging element according to the present invention has
A substrate;
an organic photoelectric conversion element in which a pixel electrode, an organic film, and a counter electrode are laminated in a region on the light incident side of the substrate in a direction perpendicular to the direction in which the light is incident, so as to form a light receiving portion into which the light is incident from the side of the substrate;
a readout circuit for reading out a signal from the organic photoelectric conversion element, the readout circuit being formed in a predetermined region on the substrate and electrically connected to the pixel electrode;
A flat-plate-shaped image pickup element unit comprising :
The imaging element is characterized in that it is made up of a plurality of stacked flat image pickup element units of a predetermined length, each of which is a combination of image pickup element components whose light receiving surfaces have different lengths in directions perpendicular to the direction in which the light is incident and the direction in which the image pickup element units are stacked.

The flat image pickup element unit may be configured so that R, G and B image pickup element units are stacked in order for capturing a color image.
It is also preferable that an adhesive layer be provided between the stacked flat plate-like image pickup element units.

The substrate is preferably made of a plastic material .

Furthermore, a method for manufacturing a stacked-type imaging element according to the present invention includes the steps of:
a first step of forming a light receiving section for receiving light incident from a side of a substrate by stacking a pixel electrode, an organic film and a counter electrode constituting an organic photoelectric conversion element in a region on the light incident side of the substrate in a direction perpendicular to the direction in which the light is incident;
a second step of forming a readout circuit for reading out a signal from the organic photoelectric conversion element, the readout circuit being electrically connected to the pixel electrode in a predetermined region on the substrate;
a third step of stacking a plurality of image pickup element units prepared by carrying out the first step and the second step in a direction perpendicular to the direction in which the light is incident ;
In a method for manufacturing a stacked type imaging element,
The third step is characterized by including a step of stacking the flat plate-shaped imaging element units of a predetermined length, which are combined with imaging element components having light receiving surfaces of different lengths in directions perpendicular to the direction in which the light is incident and the direction in which the imaging element units are stacked .

In the stacked imaging element and its manufacturing method according to the present invention, an organic photoelectric conversion element, which is a light receiving section that receives light incident from the side of a substrate, is formed by stacking a pixel electrode, an organic film, and a counter electrode in a region on the light incident side of the substrate in a direction perpendicular to the direction in which the light is incident. This allows the pixel electrode to have a large length in the depth direction relative to the light receiving surface, and since a semiconductor such as Si or GaAs that has wavelength dependency in the depth direction is not used as the photoelectric conversion film, but an organic film that does not have wavelength dependency in the depth direction is used, the incident light can be absorbed without waste, and good wavelength characteristics according to the material can be obtained.
Furthermore, in the stacked imaging element and the manufacturing method thereof according to the present invention, since flat imaging element units are used, it is possible to easily meet the demand for an increased number of pixels and a larger area.

1A and 1B are schematic perspective views showing a conceptual structure of a stacked imaging element according to an embodiment of the present invention ((a) shows an imaging element unit which is a basic unit of a stacked imaging element, and (b) shows a stacked imaging element in which a plurality of imaging element units are stacked). 2 is a schematic perspective view showing a light receiving surface of the stacked-type imaging element shown in FIG. 1A to 1F are schematic perspective views illustrating steps in a method for manufacturing a stack-type imaging element according to an embodiment of the present invention. A diagram showing a modified example of the stacked imaging element shown in Figure 1 (b) ((a) is a schematic diagram showing the components of each imaging element unit, and (b) is a diagram showing a stacked imaging element formed by stacking imaging element units consisting of the components shown in (a)).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A stacked image sensor and a manufacturing method thereof according to an embodiment of the present invention will now be described with reference to the drawings.
(Structure of stacked imaging element)
FIG. 1A is a schematic diagram of an imaging element unit, which is a basic unit of a stack-type imaging element according to this embodiment.
An organic photoelectric conversion element 22 consisting of a pixel electrode 23, an organic film 24, and a counter electrode 25 is formed on one side (light incident side) of a single thin film substrate 21, and a readout circuit 26 is formed in a region on the thin film substrate 21 following the formation region of the organic photoelectric conversion element 22. Furthermore, an input/output electrode 27 is formed on the other side (opposite the light incident side) of the thin film substrate 21.

The pixel electrode 23, readout circuit 26, and input/output electrode 27 of the organic photoelectric conversion element 22 are electrically connected in this order, and an external voltage is applied between the pixel electrode 23 and the counter electrode 25 of the organic photoelectric conversion element 22 via the input/output electrode 27 and readout circuit 26, while the detection signal (image signal) of the organic photoelectric conversion element 22 read out by the readout circuit 26 is output to the outside from the input/output electrode 27.

As described above, the pixel electrodes 23 are formed along the edge portion on one side of the thin film substrate 21, and are arranged in an area such that light incident on this one side from the side can be easily received.
In addition, one imaging element unit 10 may be formed on one thin film substrate 21, or multiple imaging element units 10 may be formed as shown in Figure 1(b) (three in the example of Figure 1(b): basically corresponding to the number of pixels arranged in the depth direction of Figure 1(b)).

Figure 1(b) shows a stacked type imaging element 10A formed by stacking a plurality of imaging element units 10 as the basic units. The light receiving surface 31 of this stacked type imaging element 10A is the surface on which the stacked organic photoelectric conversion elements 22 of the imaging element units 10 in the stacked type imaging element 10A are shown, and this light receiving surface 31 is formed to be flat.

The stack-type imaging element 10A according to this embodiment will be described in further detail below.
As described above, the stacked imaging element 10A is of a side illumination type in which incident light is illuminated onto the light receiving surface 31 provided on the side surface.
The counter electrode 25 may be formed as a common electrode for all the organic photoelectric conversion elements 22 on the same plane.

Since the stacked imaging element 10A is of the side-illuminated type, the pixel electrodes 23 and the counter electrodes 25 do not have to be transparent. By making these electrodes 23 and 25 opaque, color mixing between adjacent imaging element units 10 can be prevented and color mixing between pixels can be significantly reduced, so it is preferable that these electrodes are opaque.
Therefore, it becomes possible to apply various electrode materials, and it is possible to increase the freedom to select materials that cause less damage to the organic film.

As the material for the organic photoelectric conversion film, a material sensitive to a predetermined wavelength can be applied to each thin film substrate 21, and thin film substrates 21 using different materials can be stacked adjacent to each other. For example, a color image pickup element can be formed by stacking the imaging element units 10 corresponding to R, G, and B (or R, G, B, G, etc.) in order.

Furthermore, in the case where the organic film 24 can be created using a coating method, different color image capturing materials can be applied to different areas of the same imaging element unit 10 (such as a coating process using RGB imaging materials, etc.), thereby making it possible to obtain different color images (different RGB color images) for each line of the same imaging element unit 10.
It is also possible to obtain a color image by combining a color filter with the organic photoelectric conversion element 22 having sensitivity over the entire visible range. In this case, the color filters can be color-coded for each line or for each pixel.

The readout circuit 26 is a circuit necessary for reading out a signal from the organic photoelectric conversion element 22, and can employ various circuit technologies used in conventional CMOS image sensors, such as a drive TFT, a selection TFT, a reset TFT, a load capacitance, etc. used in conventional CMOS pixel circuits, as well as an amplifier circuit, various arithmetic circuits, a circuit for noise reduction, etc.
Moreover, oxide semiconductor TFTs can also be combined to configure a signal readout circuit 26. As a method for reading out a signal from the organic photoelectric conversion element 22, a readout method corresponding to various digital driving methods may be used, or a normal method for amplifying and reading out the signal for each pixel may be applied.

In addition, in this stacked image sensor 10A, since a readout circuit and an arithmetic circuit are built into each pixel, the readout method can be freely set for each image sensor unit 10, such as line sensor readout, single pixel readout, multiple pixel readout, etc.

As the thin film substrate 21, a thin plastic substrate or a substrate in which an insulating film is formed on a thin metal such as aluminum foil can be used.
The thickness of the thin film substrate 21 can be freely selected depending on the material, for example, within a range of several hundred nm to several hundred μm depending on the simplicity of the manufacturing process during lamination, the efficiency of light utilization, and the application of the element.

When a resin material that can be applied to form a film is used for the thin film substrate 21, the thickness can be controlled to 1 μm or less by applying a very thin film and curing it, but it is also possible to form a film thickness of 100 μm or more. Furthermore, when a plastic substrate or the like is used as the thin film substrate 21, not only is it easy to control the film thickness, it is also advantageous for mass production and has a great advantage in terms of manufacturing costs.

In this stacked imaging element 10A, the light receiving area (volume) of the organic photoelectric conversion element 22 depends on the size of the pixel electrode 23 and the thickness of the organic film 24. Here, the thickness of the organic film 24 is generally about several hundreds of nm. When attempting to maximize the light receiving area (volume) of the organic photoelectric conversion element 22, it is effective to reduce the thickness of the thin film substrate 21 and read out several layers of the organic film 24 as the same pixel.

In addition, the pixel electrode 23 can be made large in the depth direction (horizontal direction in FIG. 1B) relative to the light receiving surface, and the organic film 24 has no wavelength dependency in the depth direction. Therefore, the incident light can be absorbed and utilized entirely without waste, and further, good wavelength characteristics can be obtained according to the material.
2 shows the stacked imaging element 10A in a state where the light incident surface (light receiving surface 31) on which the incident light 30 is incident faces upward. In the stacked imaging element 10A in FIG. 2, the imaging element units 10 for R, G and B are repeatedly arranged in sequence.

(Method of manufacturing stacked image pickup element)
Next, a method for manufacturing the stacked type imaging element according to this embodiment will be described with reference to FIG.
First, a thin film substrate 21 of a predetermined size is prepared (a), and pixel electrodes 23, readout circuits 26, input/output electrodes 27, and further, arithmetic circuits and the like, if necessary, are formed on the surface of this thin film substrate 21 (b).

Next, an organic film 24 is formed on the pixel electrode 23 formed on the light incident side of the thin film substrate 21 (c). The organic film 24 can be formed by any of a dry method such as a vapor deposition method, a spin coating method, and a wet method such as an inkjet method.

Next, a counter electrode 25 is formed on the organic film 24 (which can be common to all the organic films 24 arranged on the same plane) (d). Any method such as vapor deposition, sputtering, or coating can be used as the formation method. At this time, if the input/output electrodes 27 cannot be formed up to the ends of the thin film substrate 21, a cutting process is performed on the thin film substrate 21, and auxiliary processing is performed so that the input/output electrodes 27 are arranged on the ends of the thin film substrate 21.

Finally, adhesive is applied to a predetermined position on the surface of each thin film substrate 21 to form an adhesive layer 28, and then the thin film substrates 21 to be stacked are aligned and bonded together using the adhesive layer 28 (e). This bonding process is repeated to form a laminate 29 and complete the stacked image sensor 10A (f).

The lamination process can appropriately bond portions of the thin film substrate 21. For example, as shown in Fig. 4, it is also possible to create a stacked-type imaging element 10B by appropriately combining and bonding device members ((1), (2), (3)) having light receiving surfaces with different sizes (lengths).
In this manner, by appropriately combining device components (1), (2), and (3) of different sizes (lengths) to form a single imaging element unit 10', it is possible to efficiently align the dimensions of the imaging element unit 10', which is preferable.

The stacked-type imaging element and the manufacturing method thereof according to the present invention are not limited to the above-described embodiment, and various other modifications are possible. For example, it is also possible to use an imaging element unit to which a photoelectric conversion layer having sensitivity to ultraviolet light or infrared light is applied.
In addition, in order to align the stacking positions of the image pickup element units, a method of stacking the image pickup element units in sequence using a jig or the like can be appropriately used.
Furthermore, in the above embodiment, the readout circuit is formed in an area where the organic photoelectric conversion elements are not formed, but in the stacked imaging element of the present invention, the readout circuit may be formed in an area where the organic photoelectric conversion elements are formed, and this readout circuit may be configured to be covered by an organic film or a counter electrode.
Furthermore, the manufacturing method for the stacked imaging element of the present invention is not limited to the order of the steps in the above-described embodiment, and in particular, either the manufacturing step (first step) of the light receiving section (organic photoelectric conversion element) or the manufacturing step (second step) of the readout circuit may be performed first, or any of the stages of the first step and any of the stages of the second step may be performed first (or simultaneously).

The readout circuit, input/output electrodes, etc. can be formed using general methods used in semiconductor processes, and there are no particular limitations on the materials or manufacturing methods used. For example, general conductive materials such as metals and organic conductive films can be used as electrodes, and these films can be formed using methods such as sputtering, deposition, CVD, and various printing methods, as appropriate for the material.

Moreover, the patterning of the electrodes can be performed simultaneously with the film formation by a printing method or the like other than the photolithography method.
In addition, when various wirings are crossed, an insulating film can be formed as necessary, and the materials and film formation methods thereof can be the same as those generally used in semiconductor processes.

REFERENCE SIGNS LIST 10, 10' Imaging element unit 10A, 10B Stacked imaging element 21 Thin film substrate 22 Organic photoelectric conversion element 23 Pixel electrode 24 Organic film 25 Counter electrode 26 Readout circuit 27 Input/output electrode 28 Adhesive layer 29 Stacked body 30 Incident light 31, 31a Light receiving surface

Claims (5)

A substrate;
an organic photoelectric conversion element in which a pixel electrode, an organic film, and a counter electrode are laminated in a region on the light incident side of the substrate in a direction perpendicular to the direction in which the light is incident, so as to form a light receiving portion into which the light is incident from the side of the substrate;
a readout circuit for reading out a signal from the organic photoelectric conversion element, the readout circuit being formed in a predetermined region on the substrate and electrically connected to the pixel electrode;
A flat-plate-shaped image pickup element unit comprising :
A stacked imaging element, characterized in that it is formed by stacking a plurality of flat imaging element units of a predetermined length, each of which combines imaging element components whose light receiving surfaces have different lengths in directions perpendicular to the direction in which the light is incident and the direction in which the imaging element units are stacked. The stacked imaging element according to claim 1, characterized in that the flat imaging element unit is configured for capturing a color image by stacking R, G, and B imaging element units in order. The stacked imaging element according to claim 1 or 2, characterized in that an adhesive layer is provided between the stacked flat imaging element units. The stacked imaging element according to any one of claims 1 to 3, characterized in that the substrate is made of a plastic material. a first step of forming a light receiving section for receiving light incident from a side of a substrate by stacking a pixel electrode, an organic film and a counter electrode constituting an organic photoelectric conversion element in a region on the light incident side of the substrate in a direction perpendicular to the direction in which the light is incident;
a second step of forming a readout circuit for reading out a signal from the organic photoelectric conversion element, the readout circuit being electrically connected to the pixel electrode in a predetermined region on the substrate;
a third step of stacking a plurality of image pickup element units prepared by carrying out the first step and the second step in a direction perpendicular to the direction in which the light is incident ;
In a method for manufacturing a stacked type imaging element,
a third step of stacking the imaging element units in a plate shape of a predetermined length, the third step being a combination of imaging element components having light receiving surfaces of different lengths in directions perpendicular to the direction in which the light is incident and the direction in which the imaging element units are stacked .

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