JP2020120067A - Imaging element - Google Patents

Abstract

To provide an imaging element capable of improving both an imaging element performance and a focus detection performance regardless of a relationship between a high frequency direction and a pupil division direction of pixels of a subject image.SOLUTION: The imaging element is formed by stacking a first imaging element unit 11 and a second imaging element unit 12 in this order toward a light incident direction. The second imaging element unit 12 is formed by stacking a first photosensitive layer 121 and a second photosensitive layer 122 in this order in the light incident direction. Each unit pixel 121 (m,n) and 122 (m,n) of the first photosensitive layer 121 and the second photosensitive layer 122 is arranged to correspond to pixels of the first image element unit 11 in a stacking direction and to be pupil-divided in different directions from each other (e.g., one in a row direction and the other in a column direction).SELECTED DRAWING: Figure 1

Description

The present invention relates to an image pickup device having a focus detection function, that is, an image pickup device for both distance measurement and image pickup.

2. Description of the Related Art Conventionally, as an image pickup device for both distance measurement and image pickup, a device equipped with an autofocus function using a so-called phase difference detection method is known. Among them, an image pickup surface phase difference in which an image pickup device itself has a focus detection function. The type is known.
For example, in a solid-state image sensor in which a plurality of pixel units having a photoelectric conversion function are arranged in a matrix, a unit pixel is configured by grouping N adjacent pixel units into one unit, and so-called pupil division is used for both distance measurement and imaging. There is known a method for realizing the image pickup device (see Patent Document 1).

Generally, a unit pixel includes two light receiving elements (pixel portions), and the dividing direction thereof is, for example, one direction in the horizontal direction or the vertical direction.
However, depending on the subject image, the spatial frequency may be high in a direction different from the dividing direction (for example, a direction orthogonal to each other). In such a case, a sampling error is likely to occur and the utilization efficiency of the luminous flux is reduced, so that the distance measuring performance is reduced particularly for a low-luminance subject.

As a measure for improving this, there is known one including a unit pixel in which a light receiving element (pixel portion) is arranged so as to divide the pupil region in both the horizontal direction and the vertical direction (see Patent Document 2). reference). This makes it possible to detect the focus both in the horizontal direction and in the vertical direction, improve the utilization efficiency of the light flux when performing autofocus with the imaging plane phase difference method, and increase the high frequency in the subject image. The distance measuring performance can be improved regardless of the direction.

JP 2001-250931 A JP, 2013-4635, A

However, in the image sensor described in the above-mentioned Patent Document 2, in dividing the pupil region in the horizontal direction and the vertical direction, four light receiving elements (pixel portions) are arranged in a square shape to form one unit pixel. Therefore, it becomes difficult to achieve both the image pickup device performance and the focus detection performance.
That is, generally, as the number of divisions of the unit pixel increases, the number of transistors arranged in the pixel increases, and the area ratio of the transistor region in one pixel increases. For this reason, the area ratio of the charge storage portion in the pixel becomes relatively small, and the storage capacity decreases, which causes a problem such as a decrease in dynamic range. Inevitably, both the image pickup device performance and the focus detection performance are improved. Becomes difficult.

The present invention has been made in view of such circumstances, and an image pickup device capable of improving both the image pickup device performance and the focus detection performance regardless of the relationship between the high frequency direction of a subject image and the pupil division direction of pixels. It is intended to provide.

In order to achieve the above object, the image pickup device of the present invention has the following configuration.
That is, the image sensor of the present invention is
A first image pickup device section having an imaging function and a second image pickup device section having a focus detection function are laminated in this order on a substrate in the light incident direction, and the second image pickup device section is provided with A first photosensitive layer and a second photosensitive layer are laminated in this order toward the direction, and the first photosensitive layer and the second photosensitive layer are formed of the first image sensor section and each unit pixel. The unit pixels of the first photosensitive layer and the unit pixels of the second photosensitive layer are arranged so as to correspond to the stacking direction, and are arranged so as to be pupil-divided in directions different from each other. It is a feature.

It is preferable that the mutually different directions are directions orthogonal to each other, with one being a row direction and the other being a column direction.
Further, it is preferable that the first image pickup device section includes a photoelectric conversion film that separates a predetermined color light from the light transmitted through the second image pickup device section.
Further, it is preferable that the first image pickup device section is formed by laminating a plurality of photoelectric conversion films for separating each of a plurality of predetermined color lights from the light transmitted through the second image pickup device section.
Moreover, it is preferable that the first photosensitive layer and the second photosensitive layer photoelectrically convert light in a predetermined wavelength band of infrared rays.

According to the image sensor of the present invention, the first photosensitive layer and the second photosensitive layer, which are included in the second image sensor section and are laminated in the light incident direction, are pupil-divided in mutually different directions. Therefore, regardless of the relationship between the high frequency direction of the subject image and the pupil division direction of the unit pixel, focus detection can be performed satisfactorily, so that it is possible to suppress the occurrence of sampling error and to improve the light beam utilization efficiency. Is improved, it is possible to suppress a decrease in distance measurement performance even when the subject has low brightness.

In addition, unit pixels that are pupil-divided in a predetermined direction are arranged in the first photosensitive layer, and unit pixels that are pupil-divided in a direction different from the predetermined direction are arranged in the second photosensitive layer. Is configured. As a result, the number of pupil division pixel portions (light receiving portions) per layer can be reduced, and the area ratio of the transistor region in each pixel can be made relatively small, as compared with the above-described conventional technique, and layout can be improved. Since the margin can be provided, the focus detection performance can be further improved while the imaging device performance such as the dynamic range is improved.

In the image sensor according to the embodiment of the present invention, (A) is a plan view showing a first photosensitive layer, (B) is a plan view showing a second photosensitive layer, and (C) is this image sensor. FIG. 7 is a sectional view taken along line AA′ of FIG. In this embodiment, it is a schematic diagram which shows the layer structure of each of two aspects (A) and (B) of the photoelectric conversion film of a 1st imaging element part. It is sectional drawing (hatching is abbreviate|omitted) which shows in detail the layer structure of the aspect shown to FIG. 2(B). In the present embodiment, it is a schematic diagram showing a configuration of each of two connection modes (A) and (B) between layers by a via plug. 6 is a graph showing two examples (A) and (B) of light absorptance of each photosensitive layer in the present embodiment.

Hereinafter, an image sensor according to an embodiment of the present invention will be described with reference to the drawings.

1A and 1B show an image pickup element for performing an image pickup surface phase difference autofocus (AF) according to the present embodiment, where FIG. 1A is a plan view showing a first photosensitive layer, and FIG. 2 is a plan view showing a photosensitive layer of No. 2, and FIG. 6(C) is a cross-sectional view taken along the line AA′ of this image pickup device (hatching is not added to make the drawing easy to see). The imaging plane phase difference AF can perform focus detection for distance measurement using an image capturing element.
As shown in FIG. 1C, in the image sensor 10 according to the present embodiment, the second image sensor section 12 is arranged on the first image sensor section 11, and each unit on the second image sensor section 12 is arranged. Microlenses 13 are arranged at positions corresponding to the pixels. The microlenses 13 are formed in an array as a whole.

The 1st image pick-up element part 11 is provided with photoelectric conversion films 11AC and 11BC, as mentioned below in detail. The second image pickup device section 12 is formed by stacking a first photosensitive layer 121 and a second photosensitive layer 122 in this order, and each of the photosensitive layers 121 and 122 has a photoelectric conversion film and a signal reading circuit superimposed on each other. Let me do it. The unit pixels 121(m,n) of the first photosensitive layer 121 and the unit pixels 122(m,n) of the second photosensitive layer 122 are the same as the unit pixels of the first image sensor section 11. , Unit pixels corresponding to each other are arranged so as to correspond to the stacking direction.
The first photosensitive layer 121 is arranged so that each unit pixel 121 (m, n) is pupil-divided in the row direction (horizontal direction), while the second photosensitive layer 122 is arranged in each unit pixel. 122 (m, n) are arranged so as to be pupil-divided in the column direction (vertical direction). The numerical value corresponding to m in the figure indicates the unit pixel row number from the left end, and the numerical value corresponding to n in the figure indicates the unit pixel column number from the upper end.

Further, the microlens 13 is provided to collect incident light carrying object information from the main lens of the camera for each unit pixel, and as shown in FIG. In the unit pixel 122(1,1) of the photosensitive layer 122, the light flux represented by the solid line in the pair of light fluxes condensed by one microlens 13 is the light flux that has passed through the right side of the imaging optical system, The light beam received by the left (upper) light receiving unit 122(1,1)U and represented by the dotted line is the light beam that has passed through the left side of the imaging optical system, and the right (lower) light receiving unit 122(1,1). The light is received by D. The image signal captured by the U light receiving unit group on the left side is the A image, the image signal captured by the D light receiving unit group on the right side is the B image, and the defocus amount and its direction are detected by detecting the relative position of these two images. Can be detected.
As shown in FIG. 1B, the pixels of the second photosensitive layer 122 are divided in the column direction (upper (U) lower (D) direction) and pupil division is performed in the column direction. On the other hand, as shown in FIG. 1A, the pixels of the first photosensitive layer 121 are divided in the row direction (left (L) right (R) direction), and pupil division is performed in the row direction. ..

The photoelectric conversion film of each of the photosensitive layers 121 and 122 described above is a material having absorption wavelength selectivity, such as an organic material, which absorbs and photoelectrically converts only light in a specific wavelength range and transmits other light. And a photoelectric conversion film of. The absorption wavelength range of each of the photosensitive layers 121 and 122 constituting the second image pickup device section 12 can be not only visible but also ultraviolet or infrared (particularly near infrared).

The first image pickup device section 11 serving as a base of each of the photosensitive layers 121 and 122 has photoelectric conversion films 11AC and 11BC (FIG. 2(A) that absorb the light in the wavelength band that is transmitted without being absorbed by the photosensitive layers 121 and 122. ), (B)), for example, when each of the photosensitive layers 121 and 122 is a material that absorbs green light (G light) and performs photoelectric conversion, the first image sensor If the photoelectric conversion film portions 11AB and 11BB of the portions 11A and 11B are configured to photoelectrically convert blue light (B light), and the photoelectric conversion film portions 11AR and 11BR to photoelectrically convert red light (R light), Since the RGB three primary color lights can be converted, a color image of the subject can be obtained.
As described above, in the present embodiment, the first photosensitive layer 121 and the second photosensitive layer 122, which are included in the second image sensor unit 12 and are stacked in the light incident direction, are arranged in the pupil direction in the directions orthogonal to each other. It is divided. That is, as shown in FIGS. 1A and 1B, the pixels of the first photosensitive layer 121 and the second photosensitive layer 122 are pupil-divided in one in the row direction and in the other in the column direction. The focus detection can be performed with high accuracy even when imaging a subject having a high spatial frequency in only one of the column directions. As a result, it is possible to suppress the occurrence of sampling errors and improve the utilization efficiency of the light flux. Therefore, it is possible to suppress the deterioration of the ranging performance even when the subject has low brightness. it can.

Further, in the first photosensitive layer 121, the unit pixels 121 (1, 1) which are pupil-divided in the row direction are arranged, while in the second photosensitive layer 122, the pupils are arranged in the column direction orthogonal to the predetermined direction. The divided unit pixel 122(1,1) is arranged. As a result, the number of divided pixel portions (light receiving portions) of the unit pixel per layer can be reduced, the area ratio of the transistor region in the unit pixel can be made relatively small, and the layout can have a margin. Therefore, it is possible to further improve the focus detection performance while improving the imaging device performance such as the dynamic range.

FIG. 2 shows image pickup devices 10A and 10B according to two aspects of the image pickup device of the present embodiment.
That is, in the image pickup device 10A and the image pickup device 10B, as shown in FIGS. 2A and 2B, the arrangement state of the photoelectric conversion films 11AC and 11BC provided in the first image pickup device portions 11A and 11B. Are different, and it is possible to select either one.

As shown in FIG. 2A, in the image pickup device 10A, the second image pickup device portion 12A is laminated on the first image pickup device portion 11A, and the second image pickup device portion 12A includes the first photosensitive layer 121 and the second photosensitive layer 121A. The photosensitive layer 122 is laminated in this order. On the other hand, the first imaging element unit 11A includes a photoelectric conversion film 11AC in which a blue light photoelectric conversion film unit 11AB and a red light photoelectric conversion film unit 11AR are alternately arranged on one plane. (In FIG. 2A, the photoelectric conversion film portions 11AB for blue light and the photoelectric conversion film portions 11AR for red light are alternately arranged in one direction, but when viewed from above. In addition, it is preferable that the photoelectric conversion film portions 11AB for blue light and the photoelectric conversion film portions 11AR for red light are arranged alternately in a grid pattern). In addition, insulation for electrically separating these adjacent layers from each other is provided between the photoelectric conversion film 11AC and the first photosensitive layer 121 and between the first photosensitive layer 121 and the second photosensitive layer 122. The membrane 123 is provided (the same applies to FIG. 2B).

As shown in FIG. 2B, in the image sensor 10B, the second image sensor section 12B is laminated on the first image sensor section 11B, and the second image sensor section 12B includes the first photosensitive layer 121 and the second photosensitive layer 121. The photosensitive layer 122 is laminated in this order, which is the same as the configuration of the image pickup device 10A, but in the first image pickup device section 11B, the blue light photoelectric conversion film section 11BB is a red light photoelectric conversion film section. It is different from the configuration of the image pickup device 10A in that it is stacked on the 11BR.
Thus, as shown in FIG. 2(B), the first image pickup device section is referred to as a so-called vertical color separation type first image pickup device section 11B (reference: Shinichi Teranishi, "vertical color separation type sensor", image input). Camera, Institute of Electronics, Information and Communication Engineers (eds.), pp.116-117, Ohmsha, Tokyo, 2012.), and the color light transmitted through the photosensitive layers 122 and 121 is deepened by using an organic photoelectric conversion film or the like. Color separation in the vertical direction is more desirable because an image without deterioration of resolution can be obtained in all layers of the photoelectric conversion film 11BC.

If the absorption wavelength range of each of the photosensitive layers 121 and 122 is not the visible light range but the invisible light range such as infrared rays, the first image pickup device section 11 separates the RGB three color lights. It will be photoelectrically converted. In this case, the imaging processing of the three color lights becomes similar to each other, which is also preferable from the viewpoint of signal processing.

FIG. 3 shows the photoelectric conversion film 11BC of the image pickup device 10B of FIG. 2B in detail. As described above, in the photoelectric conversion film 11BC, the R light photoelectric conversion film portion 11BR and the B light photoelectric conversion film portion 11BB are sequentially stacked on the substrate.
Each of the photoelectric conversion film portions 11BB and 11BR is sandwiched between the pixel electrodes 32B and 32R connected to the readout circuit portions 34B and 34R and the counter electrodes 31B and 31R, and a voltage between both electrodes is applied to the photoelectric conversion film portions 11BB and 11BR. Light and R light) are absorbed to generate electric charges according to the intensity of each color light. Insulating films 35B and 35R are provided below the read circuit portions 34B and 34R in the figure. In addition, interlayer insulating films 33 and 36 are provided between the photoelectric conversion film portions 11BB and 11BR and below the R light photoelectric conversion film portion 11BR.

As described above, an organic material can be used for each of the photoelectric conversion film parts 11BB and 11BR. Specifically, as an organic material that absorbs blue light and performs photoelectric conversion, for example, a porphyrin derivative, as an organic material that absorbs green light and performs photoelectric conversion, for example, perylene derivative, absorbs red light and performs photoelectric conversion. Examples of the organic material include phthalocyanine derivatives. The material forming each of the photoelectric conversion film portions 11BB and 11BR is not limited to the organic material, and the photoelectric conversion film may be formed of an organic-inorganic mixed material or an inorganic material. For the pixel electrodes 32B and 32R and the counter electrodes 31B and 31R, it is desirable to use a transparent conductive material having high light transmittance, such as ITO.

In addition, in FIG. 3, as a semiconductor material used for the transistors of the read circuit portions 34B and 34R, silicon-based materials such as single crystal Si, polycrystalline Si and amorphous Si, oxide semiconductors such as IGZO and ZnO, and pentacene. Organic semiconductor materials such as Further, from the viewpoint of improving the light transmittance of the circuit, it is desirable to use thin silicon or oxide semiconductor having a thickness of several tens nm or an organic semiconductor material having high transmittance.

Although the interlayer insulating film 33 is interposed between the photoelectric conversion film portions 11BB and 11BR for each color light as described above, the interlayer insulating film 33 allows the lower photoelectric conversion film portion (see FIG. 3). In the case of the aspect, the photoelectric conversion film portion 11BR for blue light can be protected. This also improves the flatness of the layer surface and the insulation between the integrated circuits of each layer.

Although not shown in FIGS. 2 and 3, the counter electrode of the uppermost photoelectric conversion film portion (B photoelectric conversion film portion 11BB in the case of FIG. 3) (the counter electrode in the case of FIG. 3) It is possible to further form an insulating layer functioning as a passivation film (surface protection film) on 31B).

Although not shown in FIG. 3, when the characteristic variation according to the light incident on the read circuit units 34B and 34R has a problematic influence on the operation of the image pickup device 10B, the read circuit unit is used. Light may be prevented from entering the transistor by forming light-shielding layers on the upper, lower, and side surfaces of 34B and 34R.

In the image pickup devices 10A and 10B of the above-described embodiment, the first image pickup device portions 11A and 12A and the second image pickup device portions 11B and 12B are connected by electrical wiring, respectively.
As this connection method, the modes shown in FIGS. 4A and 4B will be described.
In each pixel of the second image pickup device section 42, 52, a transistor and its wiring for reading out an optical signal generated by photoelectric conversion to the outside and amplifying the signal are provided in each photosensitive layer 421, 422, 521, 522. It is provided for each. In the mode shown in FIG. 4B, the read circuit units 521B and 522B are represented by blocks independent of the photosensitive layers 521 and 522.

First, in the method shown in FIG. 4A, the first image pickup device section 41 and the first photosensitive layer 421 are formed by the via plug 421A for each pixel, and the first image pickup device section 41 and the second photosensitive layer 422 are formed. Are connected for each pixel by a via plug 422A. In this case, the first image sensor section 41 and the second image sensor section 42 are electrically connected for each pixel.

Further, in the method shown in FIG. 4B, in each of the photosensitive layers 521 and 522, read circuits 521B and 522B, which are blocks for all pixels, are independently provided, and signals for all pixels read by this block are provided. Is transmitted to the peripheral circuit 53 of the first image sensor unit 51, and the peripheral circuit 53 of the first image sensor unit 51 and the first photosensitive layer readout circuit 521B for all pixels are connected via the via plug 521A. The peripheral circuit 53 of the first image sensor section 51 and the second photosensitive layer readout circuit 522B for all pixels are connected by a via plug 522A.

Although it is possible to use either of the modes shown in FIGS. 4A and 4B, for example, in the case of an image sensor including fine pixels having a size of about 1 μm square, a via plug is provided for each pixel. The embodiment shown in FIG. 4(B) is preferable because it can increase the aperture ratio without necessity.
In the embodiment shown in FIG. 4B, the readout circuits 521B and 522B are made of a material such as TFT or SOI which is an oxide semiconductor that is substantially transparent to visible light.

In the image sensor 10 having the layer structure as shown in FIG. 1, when the first photosensitive layer 121 and the second photosensitive layer 122 both have the same wavelength region as an absorption band, the graph of FIG. As shown, the upper layer (second photosensitive layer 122) on the light incident side should be set to a light absorption rate of about 50%, and the lower layer (first photosensitive layer 121) should be set to a light absorption rate close to 100%. Therefore, the absorptances of both the photosensitive layers 121 and 122 can be made approximately the same, which is preferable.
Further, when the first photosensitive layer 121 and the second photosensitive layer 122 have absorption bands in different wavelength bands from each other, for example, both may be within the wavelength band of green light. In that case, as shown in the graph of FIG. 5(B), it is preferable that the light absorptances of both the photosensitive layers 121 and 122 are set to be as large as nearly 100% and substantially equal to each other.

The image pickup device of the present invention is not limited to the above-mentioned embodiment, and various other modes can be modified.
For example, the layers constituting the photoelectric conversion film are not limited to those in the above embodiment, and other layers may be sandwiched between the above layers. In the second embodiment, the second image pickup device section 12 photoelectrically converts infrared rays or green light for use in distance measurement. When light other than visible light such as infrared rays is photoelectrically converted by the second image sensor unit 12, only distance measurement is performed by the second image sensor unit 12, and each of the three primary color lights is measured by the first image sensor unit 11. It is only necessary to pick up the image. On the other hand, when green light is photoelectrically converted by the second image sensor unit 12, distance measurement and image capturing of green light are performed by the second image sensor unit 12, and blue light and red light are captured by the first image sensor unit 11. The imaging of each is performed as described in the above embodiment.
Note that, for example, in the image pickup of green light in the second image pickup device section 12, the image pickup of green light is performed by adding together the signal values received and photoelectrically converted by the light receiving sections of the unit pixels. The calculation related to these image pickups is performed in a calculation unit arranged in the subsequent stage of the image pickup device, and the respective color signal values related to these image pickups are output to the outside from an output unit (not shown).

It should be noted that instead of the green light, blue light or red light is used to perform distance measurement and image pickup of the color light by the second image pickup device section 12, and the first image pickup device section 11 picks up the image of the other two color lights. It may be performed.
Further, in the above embodiment, the three primary color lights are R, G and B, but it is also possible to use three primary color lights of M (magenta), C (cyan) and Y (yellow).

Further, in the above-described embodiment, the pupil division direction of the pixels of the first photosensitive layer 121 and the second photosensitive layer 122 is set to the row direction in the former and the column direction in the latter so that the division directions are orthogonal to each other. However, the former may be in the column direction and the latter may be in the row direction.
Further, the intersecting angles of the dividing directions are not limited to the case of being orthogonal to each other, and may be set to an angle smaller than that, for example, 45 degrees.

10, 10A, 10B Image sensor 11, 11A, 11B, 41, 51 First image sensor section 11AR, 11BR Red light photoelectric conversion film section 11AB, 11BB Blue light photoelectric conversion film section 11AC, 11BC Photoelectric conversion film 12, 12A , 12B, 42, 52 Second imaging element section 13 Microlens 14, 14A Incident light 31R, 31B Counter electrode 32R, 32B Pixel electrode 33, 36 Interlayer insulating film 34R, 34B Readout circuit section 35R, 35B, 123, 423 Insulating film 53 Peripheral circuits 121, 421, 521 First photosensitive layer 121(m,n), 122(m,n) Unit pixel 121(m,n)L, 121(m,n)R, 122(m,n) U, 122(m,n)D Pixel unit (light receiving unit)
122, 422, 522 second photosensitive layer 421A, 422A, 521A, 522A via plug 521B first photosensitive layer readout circuit 522B second photosensitive layer readout circuit

Claims (5)

A first image pickup device section having an imaging function and a second image pickup device section having a focus detection function are laminated in this order on a substrate in the light incident direction, and the second image pickup device section is provided with A first photosensitive layer and a second photosensitive layer are laminated in this order toward the direction, and the first photosensitive layer and the second photosensitive layer are formed of the first image sensor section and each unit pixel. The unit pixels of the first photosensitive layer and the unit pixels of the second photosensitive layer are arranged so as to correspond to the stacking direction, and are arranged so as to be pupil-divided in directions different from each other. Characteristic image sensor. The image pickup device according to claim 1, wherein the different directions are directions orthogonal to each other, one of which is a row direction and the other of which is a column direction. The image pickup device according to claim 1 or 2, wherein the first image pickup device portion is provided with a photoelectric conversion film that separates a predetermined color light from the light transmitted through the second image pickup device portion. The said 1st image pick-up element part laminated|stacked the some photoelectric conversion film which isolate|separates each of a predetermined several colored light from the light which permeate|transmitted the said 2nd image pick-up element part, It is characterized by the above-mentioned. The image sensor described. The image pickup device according to claim 1, wherein the first photosensitive layer and the second photosensitive layer photoelectrically convert light in a predetermined wavelength band of infrared rays. ..

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