JP2018133357A - Imaging device, imaging apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve sensitivity.SOLUTION: A lower electrode E is composed of a metal having a light reflection function. A transparent upper electrode 203 is arranged oppositely to the lower electrode E on a light incident side (upper side). A photoelectric conversion film 204 is formed between the lower electrode E and the upper electrode 203. The lower electrode E has a plurality of protrusions P on the light incident side.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a stacked imaging device having a photoelectric conversion film and an imaging device.

  In general, an imaging device such as a digital still camera or a digital video camera uses a CCD or CMOS type imaging device. This image sensor is usually configured to photoelectrically convert light incident on a photodiode (hereinafter referred to as PD) formed on a semiconductor substrate for each pixel and read a signal amount for each pixel. With the recent increase in the number of pixels in the image sensor, the light receiving area of the PD for each pixel tends to decrease, and the decrease in the light receiving area directly leads to a decrease in sensitivity of the image sensor, which is not preferable. Therefore, in order to expand the light receiving area for each pixel, a multilayer imaging device has been proposed (for example, Patent Document 1). In this imaging device, a lower electrode, an upper electrode facing the lower electrode, and a color filter are stacked above a semiconductor substrate, and an organic photoelectric conversion film is formed between the lower electrode and the upper electrode.

  By the way, in order to improve the sensitivity of the multilayer imaging device provided with the organic photoelectric conversion film, a method of increasing the light absorption rate by simply increasing the thickness of the organic photoelectric conversion film is known. However, since the electron mobility of the organic photoelectric conversion film is small, the responsiveness decreases when the layer of the organic photoelectric conversion film is thickened. When the responsiveness is lowered, a part of the signal charge generated in the organic photoelectric conversion film is not read out particularly at a position away from the lower electrode, and there is a problem that an afterimage is generated by mixing with the signal charge of the next frame. . Therefore, in order to maintain responsiveness, it is required that the organic photoelectric conversion film is not too thick, and in order to improve sensitivity, it is required to increase the light absorption rate of the organic photoelectric conversion film.

  Patent Document 2 discloses an imaging having a lower electrode that is a metal electrode having a light reflecting function, an upper electrode on a light incident side that is a transparent electrode, and a photoelectric conversion layer formed between the lower electrode and the upper electrode. An element is disclosed. In this imaging element, light that has passed through the photoelectric conversion layer is reflected by the lower electrode and reenters the photoelectric conversion layer, and light that could not be absorbed before reflection is further absorbed by the photoelectric conversion layer. As a result, the light absorption rate is increased, and the sensitivity of the image sensor is improved.

Patent No. 5087304 JP 2007-273894 A

  However, in the configuration described in Patent Document 2, light that is reflected by the lower electrode and re-entered the photoelectric conversion layer is not necessarily absorbed by the photoelectric conversion layer, but is transmitted through the upper electrode and emitted to the outside of the imaging device. There are not a few light components. Therefore, there is room for improvement in improving the sensitivity of the image sensor.

  The present invention aims to improve sensitivity.

  In order to achieve the above object, the present invention provides a first electrode made of a metal having a light reflecting function, a transparent second electrode disposed opposite to the first electrode on the light incident side, and the first electrode. An image sensor in which a plurality of pixels each having a photoelectric conversion film formed between one electrode and the second electrode are arranged, and the first electrode includes a plurality of protrusions on a light incident side. It is characterized by that.

  According to the present invention, sensitivity can be improved.

It is a schematic diagram of an image sensor. It is a schematic diagram which shows the cross section of the pixel part which follows the AA line of FIG. It is a figure which shows a mode that light reflects and diffuses with the processus | protrusion of a lower electrode. It is typical sectional drawing of the pixel part which has the processus | protrusion of the 1st modification. It is typical sectional drawing of the pixel part which has the processus | protrusion of the 2nd modification. It is a typical sectional view of a pixel part of an image sensor. It is a typical sectional view of a pixel part of an image sensor. It is a typical sectional view of a pixel part of an image sensor. It is a system block diagram of an imaging device.

  Embodiments of the present invention will be described below with reference to the drawings.

(First embodiment)
FIG. 1 is a schematic diagram of an image sensor according to the first embodiment of the present invention. In FIG. 1, the image sensor 901 is viewed from the light incident side. The image sensor 901 includes a pixel unit 101, a vertical scanning unit 102, a reading unit 103, and a horizontal scanning unit 104. In the pixel unit 101, a plurality of pixels 105 that receive an optical image formed by an optical system (not shown) are arranged in a matrix. The pixel 105 includes a photoelectric conversion film 204 (FIG. 2). In FIG. 1, only nine pixels are illustrated as the pixels 105 for the sake of explanation.

  The vertical scanning unit 102 sequentially selects a plurality of rows of the pixel unit 101 in the vertical direction, and samples the signal of the pixel 105 to the reading unit 103 for each row. The horizontal scanning unit 104 outputs the signals of the pixels 105 sampled by the reading unit 103 to a circuit such as an analog front end (AFE) 902 (FIG. 9) in the subsequent stage by sequentially selecting in the horizontal direction.

  FIG. 2 is a schematic diagram showing a cross section of the pixel portion 101 taken along line AA in FIG. Hereinafter, for convenience, the upper and lower portions of the image sensor 901 are referred to with reference to FIG. However, the posture when the image sensor 901 is used does not matter. Light enters from the upper side to the lower side in FIG. The image sensor 901 is a stacked image sensor. Since the configuration of the plurality of pixels 105 is common, the configuration of one pixel 105 will be mainly described as a representative.

  The pixel portion 101 includes a semiconductor substrate 208. On the semiconductor substrate 208, an insulating film 206, a plurality of lower electrodes E (first electrode), a photoelectric conversion film 204, an upper electrode 203 (second electrode), and a plurality of color filters. (CF) 202 and a plurality of microlenses 201 are stacked. The lower electrode E, the CF 202 and the microlens 201 are configured for each pixel 105, and a large number of the lower electrodes E, CF202 and microlenses 201 are arranged on the respective planes above the semiconductor substrate 208 on a matrix. The microlens 201 further collects the light that passes through an optical system (not shown) and is imaged on the image sensor 901 for each pixel. The CF 202 transmits only light of a specific wavelength such as red, blue, or green, for example, according to the corresponding pixel 105. The plurality of CFs 202 are arranged according to, for example, a Bayer array. The upper electrode 203 is a transparent electrode disposed to face the lower electrode E on the light incident side (upper side). The photoelectric conversion film 204 is formed between the lower electrode E and the upper electrode 203.

  Here, the upper electrode 203 is preferably highly transparent because it is necessary to make light incident on the photoelectric conversion film 204. For example, a transparent conductive oxide is suitable as the transparent electrode material, and ITO (indium tin oxide) is a candidate. The upper electrode 203 may be divided for each pixel, or may be shared by two or more pixels or all pixels. The photoelectric conversion film 204 is composed of a photoelectric conversion material that absorbs light and generates a charge corresponding to the absorbed light. Note that an inorganic material or an organic material can be used as the photoelectric conversion material, but an organic material is used in this embodiment because of excellent spectral characteristics and sensitivity. The photoelectric conversion film 204 may have a single layer structure or a multilayer structure.

  The insulating film 206 is formed between the plurality of metal wirings 207 and between the plurality of lower electrodes E, and electrically insulates each other. Impurity regions corresponding to the plurality of pixels 105 are formed in the semiconductor substrate 208, and signal charges generated by the photoelectric conversion film 204 can be held. Further, a circuit for reading out signal charges (not shown) is formed on the semiconductor substrate 208 (described later in FIG. 9).

  In the pixel 105 configured in this manner, only light of a specific wavelength that is condensed by the microlens 201 and transmitted through the CF 202 is photoelectrically converted by the photoelectric conversion film 204 to generate a signal charge. The pixel unit 101 can extract a signal charge moved to the lower electrode E to the outside by applying a bias voltage between the upper electrode 203 and the lower electrode E and applying an electric field in the photoelectric conversion film 204. It has a configuration.

  The lower electrode E is a metal electrode made of a metal having a light reflection function. Examples of the material constituting the lower electrode E include Al (aluminum) and Ti (titanium), but are not limited thereto. The lower electrode E includes a plurality of protrusions P on the light incident side. That is, the lower electrode E has a plate-like base portion B, and a large number of protrusions P project from the base portion B toward the upper electrode 203 side. The protrusion P is formed integrally with the base part B, but may be formed separately and fixed. When the protrusion P is formed separately from the base portion B, the protrusion P is formed of a metal having a light reflecting function. The tip of the projection P is formed in a convex curved surface. The pixel 105 has a property of diffusing reflected light from the lower electrode E in various directions by providing a plurality of protrusions P. In FIG. 2, optical paths 210, 211, 212, 213, and 214 indicate examples of light incident and reflection paths that enter the pixel 105.

  In FIG. 2, 15 protrusions P are illustrated in the row direction for each pixel, but in reality, a large number of such protrusions P are two-dimensionally formed on the upper surface of the lower electrode E. In addition, the arrangement pitch (interval) of the protrusions P is desirably small so that incident light from various directions can be uniformly diffused.

  FIG. 3 is a diagram illustrating a state in which light in the optical path 210 is reflected and diffused by the protrusion P of the lower electrode E. FIG. In FIG. 3, for convenience of explanation, the light of the optical path 210 that has entered the pixel 105 is divided into five incident lights 301, 302, 303, 304, and 305, and is shown by a solid line. The lights reflected by the projections P of the incident lights 301, 302, 303, 304, and 305 correspond to the reflected lights 306, 307, 308, 309, and 310 indicated by broken lines, respectively. As can be seen from FIG. 3, the reflected lights 306 to 310 are reflected once or more on the surface of the protrusion P and diffused in various directions.

  By the way, when the lower electrode is formed of a simple flat plate as in the prior art of Patent Document 2, for example, the specular reflected light component having strong energy is dominant in the light reflected by the lower electrode. Since this specular reflection light component is a component that reflects toward the upper electrode according to Snell's law, the optical path length in the photoelectric conversion film is short, and there are many light components that go out without being absorbed by the photoelectric conversion film. There was a problem. On the other hand, according to the image sensor 901 of the present embodiment, the diffuse reflection component is dominant in the light reflected by the protrusion P of the lower electrode E. This diffuse reflected light component is a component that is dispersed and reflected in various directions. Therefore, the distance (optical path length) that the reflected light travels through the photoelectric conversion film 204 can be increased. As the light component having a longer optical path length in the photoelectric conversion film than in the prior art increases, the light is easily absorbed by the photoelectric conversion film, and the sensitivity of the image sensor 901 is increased by improving the light absorption rate (photoelectric conversion efficiency).

  According to the present embodiment, since the lower electrode E made of a metal having a light reflecting function includes the plurality of protrusions P on the light incident side, the sensitivity of the pixel 105 can be improved. Since the sensitivity is improved, it is not necessary to increase the thickness of the photoelectric conversion film 204, and a decrease in responsiveness is avoided.

  In the present embodiment, the protrusion P has a curved tip. However, the shape of the protrusion P is not limited to the illustrated example, and it is free as long as the diffuse reflection component is dominant and the above effect is exhibited. You may deform | transform into. 4 and 5, modifications of the shape of the protrusion P will be given.

  4 and 5 are schematic cross-sectional views of the pixel portion 101 having the protrusions P of the first and second modified examples, respectively. In the first and second modifications, the pixel unit 101 includes lower electrodes E2 and E3 instead of the lower electrode E, and the lower electrodes E2 and E3 are provided with protrusions P2 and P3 instead of the protrusions P, respectively. .

  In the first modification (FIG. 4), the protrusion P2 protrudes from the base portion B of the lower electrode E2 toward the upper electrode 203 side. The protrusion P2 is a column body, and more specifically, a cylinder, a square column, or the like. In addition, the cross-sectional shape of the column is not limited and may be an ellipse or a polygon. The protrusion P2 having this shape can be easily manufactured by a known semiconductor manufacturing process technique.

  In the second modification (FIG. 5), the protrusion P3 protrudes from the base portion B of the lower electrode E3 toward the upper electrode 203 side. The protrusion P3 is a cone, and more specifically, a cone or a quadrangular pyramid. The cross-sectional shape of the cone is not limited and may be an ellipse or a polygon.

  Note that in this embodiment and the modification, the shape of the protrusion provided on the lower electrode may not be common among all the pixels 105 in the pixel portion 101. Pixels 105 having different projections (projections P, P2, and P3) may be mixed. For example, the shape of the protrusions provided in the central pixel 105 of the pixel portion 101 and the peripheral region pixel 105 in the array plane direction (two-dimensional plane direction) of the pixels 105 may be different. Alternatively, the shape of the protrusion and the arrangement pitch may be changed for each color of the CF 202 of the pixel 105.

  Note that in the present embodiment and the modification, the pixel 105 has been described as including the CF 202; however, including the CF 202 is not essential. Even when the CF 202 is not provided in the pixel 105, the photoelectric conversion film 204 can be configured so that different spectral sensitivity characteristics can be obtained for each pixel by changing the material forming the photoelectric conversion film 204 for each pixel. .

(Second Embodiment)
FIG. 6 is a schematic cross-sectional view of the pixel unit 101 of the image sensor 901 according to the second embodiment of the present invention. In contrast to the first embodiment, the pixel unit 101 in the present embodiment includes a lower electrode E4 instead of the lower electrode E. Detailed description of the same components as those of the image sensor 901 of the first embodiment will be omitted.

  The light incident side of the lower electrode E4 is formed on an uneven surface E4a having irregular unevenness. As the lower electrode E4, a metal electrode having a function of reflecting light is used as in the first embodiment. Since the lower electrode E4 has the uneven surface E4a, it has a property of diffusing reflected light into light in various directions and reflecting it. The uneven surface E4a is desirably formed finely so that incident light from various directions can be uniformly diffused. With such a configuration, the distance (optical path length) that the reflected light diffused in various directions travels through the photoelectric conversion film 204 is increased.

  According to the present embodiment, the same effect as that of the first embodiment can be achieved with respect to improving the sensitivity of the pixel 105 while avoiding a decrease in responsiveness.

(Third embodiment)
FIG. 7 is a schematic cross-sectional view of the pixel unit 101 of the image sensor 901 according to the third embodiment of the present invention. In contrast to the first embodiment, the pixel unit 101 in the present embodiment includes a lower electrode E5 instead of the lower electrode E. Detailed description of the same components as those of the image sensor 901 of the first embodiment will be omitted.

  The lower electrode E5 has a plurality of protrusions P as in the first embodiment. From the outer edge portion Ba of the base portion B of the lower electrode E5, a light shielding wall portion 701 is provided so as to project toward the upper electrode 203 side (upward). The wall portion 701 is formed integrally with the base portion B, but may be formed separately and fixed. The wall portion 701 is provided so as to surround the plurality of protrusions P from the periphery. The tip height of the wall 701 is higher than the protrusion P (the tip position is close to the upper electrode 203).

  Since the light reflected by the protrusions P diffuses, the diffused light may enter the photoelectric conversion film 204 of the adjacent pixel 105. That is, the diffusely reflected light contains many components that are reflected obliquely with respect to the arrangement surface direction of the pixels 105, and thus the light reflected by the lower electrode E5 of a certain pixel 105 enters the adjacent pixel 105 and color mixing occurs. There is concern. Therefore, in this embodiment, a wall portion 701 is provided as a light shielding portion at the outer peripheral end portion (outer edge portion Ba) of the lower electrode, and leakage of reflected light between the pixels 105 is suppressed.

  According to the present embodiment, the same effect as that of the first embodiment can be achieved with respect to improving the sensitivity of the pixel 105 while avoiding a decrease in responsiveness. In addition, since the wall portion 701 higher than the protrusions P is provided so as to surround the plurality of protrusions P from the periphery, the occurrence of color mixing can be suppressed.

(Fourth embodiment)
FIG. 8 is a schematic cross-sectional view of the pixel portion 101 of the image sensor 901 according to the fourth embodiment of the present invention. In contrast to the first embodiment, the pixel unit 101 in the present embodiment includes a lower electrode E6 instead of the lower electrode E. Detailed description of the same components as those of the image sensor 901 of the first embodiment will be omitted.

  The lower electrode E6 includes a plurality of protrusions P4 on the light incident side. That is, a large number of protrusions P4 protrude from the base portion B toward the upper electrode 203 side. The tip shape of the protrusion P4 is the same as that of the protrusion P in the first embodiment. In the first embodiment, the height of the tip of each protrusion P is common. On the other hand, in the present embodiment, the protrusion height of each protrusion P4 from the base portion B is not common, and therefore the tip position of each protrusion P4 in the vertical direction is not common. Specifically, the height of the tip of each protrusion P4 is the lowest at the protrusion P4 located at the center of the pixel 105 in the arrangement plane direction of the pixels 105, and is higher as the protrusion P4 near the outer edge part Ba of the base part B. Yes. The height of the tip of the protrusion P4 gradually increases from the center of the lower electrode E6 toward the outside (outer edge Ba side), and a virtual concave curved surface that is recessed downward contacts the tip of each protrusion P4. .

  With such a configuration, similarly to the first embodiment, the light reflected by the protrusion P4 has a dominant diffuse reflection component, and the reflected light is dispersed in various directions. Furthermore, the light reflected by the protrusion P4 close to the outer edge portion Ba has a larger component toward the center side of the lower electrode E6 (inside the outer edge portion Ba). Thereby, since most of the light can be reflected toward the center side of the pixel 105, the reflected light component entering the adjacent pixel 105 can be reduced. Therefore, the occurrence of color mixing can be suppressed.

  According to the present embodiment, the same effect as that of the first embodiment can be achieved with respect to improving the sensitivity of the pixel 105 while avoiding a decrease in responsiveness. Moreover, since the height of the tip of each projection P4 is higher as the projection P4 is closer to the outer edge portion Ba, the occurrence of color mixing can be suppressed.

  Finally, a schematic configuration of an imaging apparatus including the imaging element 901 will be described. FIG. 9 is a system block diagram of the imaging apparatus. The imaging apparatus is configured as a digital still camera, for example.

  The AFE 902 is connected to the image sensor 901, and performs reference level adjustment (clamp processing) and analog-digital conversion processing by an A / D conversion circuit. A digital front end (DFE) 903 is connected to the AFE 902 and receives the digital output of each pixel and digitally processes image signal correction, pixel rearrangement, and the like. The digital signal processing unit 904 is connected to the DFE 903, and performs development processing and defective pixel interpolation processing on the digital output from the DFE 903. A memory unit 905 is a working memory for the digital signal processing unit 904, and is also used as a buffer memory in continuous shooting or the like. The control unit 906 includes a CPU (not shown) and the like, and controls the entire imaging apparatus in an integrated manner. The operation unit 907 electrically receives a user operation on an operation member (not shown) provided in the imaging apparatus. The display unit 908 displays an image or the like. The recording unit 909 is a recording medium such as a memory card or a hard disk. A timing generation circuit (TG) 910 generates various timings for driving the image sensor 901.

  By the imaging apparatus having such a configuration, the driving of the imaging element 901 and the reading driving of the imaging element 901 are realized. However, the configuration of the imaging apparatus according to the present invention is not limited to the exemplified one. For example, the image sensor 901 may include an A / D conversion circuit for each column. In that case, the image sensor 901 outputs the read digital signal for each pixel to the DFE 903. In addition, the image sensor 901 may include an A / D conversion circuit and a DFE block.

  In the third embodiment (FIG. 7), the light shielding wall 701 is provided in the first embodiment (FIG. 2), the first and second modifications (FIGS. 4 and 5). ) And the second and fourth embodiments (FIGS. 6 and 8). When applied to the fourth embodiment, the wall portion 701 may be provided so as to protrude toward the light incident side so that the tip is higher than the highest position of the uneven surface E4a. Further, in the fourth embodiment (FIG. 8), the configuration in which the height of the protrusion P4 closer to the outer edge Ba is made higher in the height of the tip of each protrusion P4 is the first and second modifications (FIGS. 4 and 5 ) Is also applicable. Further, by applying the fourth embodiment (FIG. 8) to the second embodiment (FIG. 6), the rough shape of the uneven surface E4a of the lower electrode E4 may be a concave curved surface recessed downward, Alternatively, a configuration may be employed in which irregular and fine irregularities are formed on the concave curved surface.

  Although the present invention has been described in detail based on preferred embodiments thereof, the present invention is not limited to these specific embodiments, and various forms within the scope of the present invention are also included in the present invention. included. A part of the above-described embodiments may be appropriately combined.

E, E2, E3, E4 Lower electrode P, P2, P3, P4 Projection 105 Pixel 203 Upper electrode 204 Photoelectric conversion film 901 Imaging element

Claims (8)

A first electrode made of a metal having a light reflection function;
A transparent second electrode disposed opposite the light incident side with respect to the first electrode;
An image sensor in which a plurality of pixels each including a photoelectric conversion film formed between the first electrode and the second electrode are arranged,
The image pickup device, wherein the first electrode includes a plurality of protrusions on a light incident side.   The image sensor according to claim 1, wherein the protrusion is a column.   The image sensor according to claim 1, wherein the protrusion is a cone.   4. The image pickup device according to claim 1, wherein a height of a tip of each of the plurality of protrusions is higher as a protrusion is closer to an outer edge portion of the first electrode. 5. A first electrode made of a metal having a light reflection function;
A transparent second electrode disposed opposite the light incident side with respect to the first electrode;
An image sensor in which a plurality of pixels each including a photoelectric conversion film formed between the first electrode and the second electrode are arranged,
The image sensor according to claim 1, wherein the light incident side of the first electrode is formed on an irregular uneven surface.   The imaging device according to claim 1, wherein a light-shielding wall portion having a tip height higher than that of the protrusion is provided on an outer edge portion of the first electrode.   The image pickup device according to claim 5, wherein a light-shielding wall portion projects from the outer edge portion of the first electrode on the light incident side. An imaging apparatus comprising the imaging device according to claim 1.