JP2014033055A - Solid state imaging sensor and imaging apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve a solid state imaging sensor equipped with a microlens and a plurality of photoelectric conversion parts for a unit pixel, capable of reducing a dead band between the photoelectric conversion parts and increasing an area of the photoelectric conversion parts.SOLUTION: In the solid state imaging sensor equipped with a microlens and a plurality of photoelectric conversion parts for a unit pixel, a first unit pixel is so configured that a plurality of photoelectric conversion parts arranged in a first direction share a floating diffusion part provided in the first direction, and a second unit pixel is so configured that a plurality of photoelectric conversion parts arranged in a second direction perpendicular to the first direction share a floating diffusion part provided in the second direction, wherein the first unit pixel and the second unit pixel are alternately arranged in a matrix shape.

Description

  The present invention relates to a solid-state image sensor, and more particularly to an arrangement of elements constituting the solid-state image sensor.

  At present, various application technologies using solid-state imaging devices each including a plurality of photoelectric conversion units in a unit pixel have been proposed in imaging devices such as a digital still camera and a digital video camera.

  For example, Patent Document 1 discloses an imaging apparatus that performs so-called pupil division type focus detection using a solid-state imaging element in which a microlens is provided for each unit pixel that is two-dimensionally arranged. In the imaging apparatus of Patent Document 1, the photoelectric conversion units of the pixels constituting the imaging element are divided into a plurality of parts, and each of the divided photoelectric conversion units has different pupils divided by the photographing lens through microlenses. It is configured to receive the passed light. Then, focus detection of the imaging optical system can be performed from the amount of deviation between the left photoelectric conversion unit output and the right photoelectric conversion unit output of the pixel.

  Furthermore, Patent Document 1 also refers to 3D video shooting.

  Humans acquire two-dimensional images with the two left and right eyes that are approximately 6 to 7 cm apart in the horizontal direction, but the two left and right images have parallax according to the distance to what they are looking at. Humans recognize the stereoscopic effect and depth by processing the left and right images with parallax with the brain.

  As an apparatus for photographing a 3D image, there is an apparatus that uses two cameras or image sensors, as in the case of human eyes. However, in Patent Document 1, it is configured by one optical system and one image sensor. An image pickup apparatus is disclosed. Using the photoelectric conversion unit divided for each unit pixel, two images with parallax can be generated from the left photoelectric conversion unit output and the right photoelectric conversion unit output. By displaying these two images separately on the left and right eyes of the human by the display / playback device, the stereoscopic effect and the depth can be recognized.

  Further, in Patent Document 2, the unit pixel constituting the pixel portion of the image sensor is configured to include a plurality of divided pixels having different charge accumulation amounts, and the imaging signal of each divided pixel in the unit pixel is digitized and added. Thus, a technique for obtaining a wide dynamic range is disclosed.

  Patent Document 3 also refers to a specific configuration of the imaging apparatus according to Patent Document 1.

JP 58-024105 A JP 2010-028423 A JP 2001-250931 A

  A configuration in which a unit pixel includes a plurality of photoelectric conversion units as in Patent Document 1 increases the number of elements constituting the pixel as compared with a configuration in which one unit has one photoelectric conversion unit with the same area. The total area of the photoelectric conversion unit is reduced.

  Conventionally, in a configuration in which the unit pixel includes one photoelectric conversion unit, the floating diffusion unit (FD) is shared by a plurality of pixels, thereby reducing the number of subsequent components and suppressing the decrease in the total area of the photoelectric conversion unit. Technology exists. Patent Document 2 discloses a configuration in which an FD arranged at the center of a pixel is shared in a configuration including four photoelectric conversion units each having a 2 × 2 unit pixel.

  For example, in FIG. 7, a pixel 702 is configured under one microlens 701, and the pixel 702 includes four photoelectric conversion units 703 a, 703 b, 703 c, and 703 d that are divided into 2 × 2, and the four photoelectric conversion units The conversion unit shares the FD 704. For convenience of explanation, only nine pixels are shown, but actually, a plurality of such pixels are arranged to constitute a pixel portion.

  FIG. 8 shows an arrangement of photoelectric conversion units sharing the FD 704 in FIG. For convenience of explanation, only two pixels are shown. Fig.8 (a) is II-II sectional drawing of FIG.8 (b). FIG. 8A shows a state where the photoelectric conversion unit receives light emitted from the exit pupil 803 of the photographing lens via the microlens 701. The divided photoelectric conversion units receive light emitted from different regions of the exit pupil 803, respectively.

  However, in the configuration of FIGS. 7 and 8, a region 801 (dead zone) that does not contribute to photoelectric conversion is formed between the photoelectric conversion units 703a and 703b as shown in FIG. 8A. This dead zone region 801 is a region including the FD 704. Furthermore, the structure body 802 including the light shielding member and the wiring, which is configured along with the FD 704, blocks a light beam incident on the photoelectric conversion unit, thereby causing a decrease in sensitivity.

  On the other hand, in Patent Document 3, in a configuration in which four photoelectric conversion units each having a 2 × 2 unit pixel are provided, FDs are arranged on both the upper and lower sides or both the left and right sides of the pixel, and each is shared by the two photoelectric conversion units. A configuration is disclosed.

  For example, in FIG. 9, a pixel 902 is formed under one microlens 901, and the pixel 902 includes four photoelectric conversion units 903a, 903b, 903c, and 903d divided into 2 × 2. The photoelectric conversion units 903a and 903c share the FD 904a, and the photoelectric conversion units 903b and 903d share the FD 904b. For convenience of explanation, only nine pixels are shown, but actually, a plurality of such pixels are arranged to constitute a pixel portion.

  FIG. 10 illustrates an arrangement of photoelectric conversion units that share the FDs 904a and 904b in FIG. For convenience of explanation, only two pixels are shown. Fig.10 (a) is III-III sectional drawing of FIG.10 (b). FIG. 10A shows a state where the photoelectric conversion unit receives light emitted from the exit pupil 1004 of the photographing lens through the microlens 901. The divided photoelectric conversion units respectively receive light emitted from different areas of the exit pupil 1004. Reference numerals 1001a and 1001b denote structures including light shielding members, wirings, and the like.

  However, in the configuration shown in FIGS. 9 and 10, the FD 904b and the FD 905 protruding from the adjacent pixels in the horizontal direction are arranged in a region 1002 between the pixels. Since the FD 904b and the FD 905 need to be separated by a semiconductor region, the pixel boundary region 1002 needs a wide horizontal width. As a result, in this configuration, the horizontal width of the region 1003 of the photoelectric conversion unit becomes narrow, and the area of the photoelectric conversion unit becomes small.

  In order to obtain the same performance when shooting an image pickup apparatus using this configuration in the vertical position and in the horizontal position, the vertical width and the horizontal width of the photoelectric conversion unit are equal (such as Should be laid out) With this configuration, when it is attempted to configure the photoelectric conversion region isotropically, it becomes more difficult to perform efficient layout.

  The present invention has been made in view of the above problems, and an object of the present invention is to reduce a dead zone between photoelectric conversion units in a fixed imaging device having a unit lens including a microlens and a plurality of photoelectric conversion units, and a photoelectric conversion unit. It is to realize a solid-state imaging device capable of widening the area.

  In order to solve the above-described problems and achieve the object, a solid-state imaging device according to the present invention is a solid-state imaging device including a microlens and a plurality of photoelectric conversion units in a unit pixel. The plurality of photoelectric conversion units arranged in the first direction share a floating diffusion unit provided in the first direction, and the second unit pixel has a second direction orthogonal to the first direction. A plurality of photoelectric conversion units arranged in the same configuration are configured to share a floating diffusion unit provided in the second direction, and the first unit pixels and the second unit pixels are alternately arranged in a matrix did.

  ADVANTAGE OF THE INVENTION According to this invention, in the solid-state image sensor provided with the micro lens and the some photoelectric conversion part in the unit pixel, the dead zone between photoelectric conversion parts can be reduced and the area of a photoelectric conversion part can be enlarged.

1 is a block diagram showing a configuration of an imaging apparatus according to an embodiment of the present invention. The figure which shows the structure of the solid-state image sensor of this embodiment. FIG. 3 is a diagram illustrating a configuration of a pixel portion of the present embodiment. FIG. 3 is a diagram illustrating in detail a configuration of a pixel portion of the present embodiment. FIG. 3 is an equivalent circuit diagram of a pixel portion of the present embodiment. The figure which shows the structure of the floating diffusion part and transfer switch of this embodiment. The figure which shows the structure of the pixel part of a prior art. The figure which shows the structure of the pixel part of a prior art in detail. The figure which shows the structure of the pixel part of another prior art. The figure which shows the structure of the pixel part of another prior art in detail.

  Hereinafter, embodiments for carrying out the present invention will be described in detail. The embodiment described below is an example for realizing the present invention, and should be appropriately modified or changed according to the configuration and various conditions of the apparatus to which the present invention is applied. It is not limited to the embodiment. Moreover, you may comprise combining suitably one part of each embodiment mentioned later.

  <Apparatus Configuration> With reference to FIG. 1, the configuration of an imaging apparatus according to an embodiment of the present invention will be described.

  In FIG. 1, a CMOS solid-state imaging device 101 receives an optical image formed by an optical system (not shown). An analog front end (AFE) 102 performs reference level adjustment (clamp processing) and analog-digital conversion processing. A digital front end (DFE) 103 receives digital output of each pixel and performs digital processing such as image signal correction and pixel rearrangement. The image processing unit 104 performs development processing on the digital output from the DFE 103. The memory circuit 105 is a working memory for the image processing unit 104, and is also used as a buffer memory in continuous shooting or the like. The control circuit 106 comprehensively controls the entire imaging apparatus, and incorporates a known CPU. The operation circuit 107 electrically accepts an operation input from an operation member of the imaging apparatus. The display unit 108 is an LCD or the like that displays an image or the like. The recording circuit 109 is specifically a recording medium such as a memory card or a hard disk. A timing generation circuit (TG) 110 generates various timings for driving the solid-state imaging device 101.

  FIG. 2 is a schematic diagram showing the configuration of the solid-state imaging device 101 of the present embodiment.

  As illustrated in FIG. 2, the solid-state imaging device 101 includes a pixel unit 201, a vertical scanning unit 202, a reading unit 203, and a horizontal scanning unit 204. The pixel unit 201 has a plurality of unit pixels arranged in a matrix and receives an optical image formed by an optical system (not shown). The vertical scanning unit 202 sequentially selects a plurality of rows of the pixel unit 201, and the horizontal scanning unit 204 sequentially selects a plurality of columns of the pixel unit 201, thereby sequentially selecting a plurality of pixels of the pixel unit 201. . The reading unit 203 reads the signal of the pixel selected by the vertical scanning unit 202 and the horizontal scanning unit 204 and outputs the read signal to the AFE 102.

  FIG. 3 shows the configuration of the pixel unit 201 in the solid-state image sensor 101. For convenience of explanation, only nine pixels are shown, but actually, a plurality of such pixels are arranged to constitute the pixel unit 201.

  As shown in FIG. 3, the pixel unit 201 is provided with one unit pixel 302 for one microlens 301. Further, the pixel 302 includes four photoelectric conversion units 303a, 303b, 303c, and 303d divided into 2 × 2. Each of the photoelectric conversion units 303a, 303b, 303c, and 303d photoelectrically converts light received through the optical system and accumulates signal charges.

  The pixels 301 and 306 include microlenses 302 and 305, and include four photoelectric conversion units 303a to 303d and 307a to 307d divided into 2 × 2. In addition, the four photoelectric conversion units 303a to 303d and 307a to 307d of each pixel 301 and 306 have the same vertical and horizontal widths, that is, isotropic layout. The signal charges accumulated in the photoelectric conversion units 303a and 303b, 303c and 303d, 307a and 307c, and 307b and 307d are read to the reading unit via the floating diffusion units (FD) 304a, 304b, 308a, and 308b, respectively. In the present embodiment, the plurality of photoelectric conversion units 303a and 303b adjacent in the horizontal direction of the unit pixel 302 share the FD 304a, and the other plurality of photoelectric conversion units 303c and 303d adjacent in the horizontal direction of the unit pixel 302 have the FD 304b. Sharing. In addition, the plurality of photoelectric conversion units 307a and 307c adjacent to the unit pixel 302 in the vertical direction of the unit pixel 306 share the FD 308a and the other plurality of photoelectric conversion units adjacent to the unit pixel 306 in the vertical direction. 307b and 307d share the FD 308b.

  In FIG. 3, 304a, 304b, 308a, and 308b are FDs. In the pixel 301, the two photoelectric conversion units 303a and 303b arranged side by side share the FD 304a, and the photoelectric conversion units 303c and 303d share the FD 304b. On the other hand, the pixel 306 adjacent to the pixel 302 shares the FD 308a between the two vertically arranged photoelectric conversion units 307a and 307c, and shares the FD 308b between the photoelectric conversion units 307b and 307d. However, in practice, a signal charge transfer switch for controlling the transfer of signal charges from the photoelectric conversion unit to the FD is arranged between each photoelectric conversion unit and the FD. Omitted for convenience, a detailed configuration will be described later.

  As illustrated in FIG. 3, the pixel unit 201 includes an FD that is shared by two horizontally aligned photoelectric conversion units such as the pixel 302 and two vertically aligned photoelectric conversion units such as the pixel 306. The shared pixels are alternately arranged in a matrix. And FD is arrange | positioned between each pixel. By configuring the pixel portion in this manner, the FD region is equally distributed between pixels adjacent in the horizontal direction and pixels adjacent in the vertical direction. Therefore, it is possible to efficiently increase the area of the photoelectric conversion unit while realizing an isotropic layout of the photoelectric conversion unit.

  FIG. 4 shows how the photoelectric conversion unit receives light emitted from the exit pupil 404 of the photographing lens via the microlens 302. The divided photoelectric conversion units respectively receive light emitted from different areas of the exit pupil 404. 4A is a cross-sectional view taken along the line II of FIG. 4B, and FIG. 4B is a diagram illustrating the configuration of the pixel unit 201. However, in practice, a signal charge transfer switch for controlling the transfer of signal charges from the photoelectric conversion unit to the FD is arranged between each photoelectric conversion unit and the FD. Omitted for convenience, a detailed configuration will be described later.

  As illustrated in FIG. 4, the FD 308 a is disposed between the pixel 302 and the pixel 306. With this configuration, the area of the dead zone between the photoelectric conversion units of each pixel can be reduced. In addition, since the structure 403 is formed in the region 402 between the pixels along with the FD 308a, the amount of light beams that are blocked from entering the photoelectric conversion unit by the structure is reduced. The area for separating the photoelectric conversion portions of each pixel becomes a dead zone, but its width is narrower than the width of the area 402. Further, the horizontal width of the region 402 can be narrowed. That is, it is possible to ensure a wide horizontal width of the region 401 of the photoelectric conversion unit.

  The relationship between the present invention and the embodiment will be described. The first unit pixel corresponds to the pixel 302, the first direction corresponds to the horizontal direction, and the first floating diffusion portion corresponds to the FDs 304a and 304b. The second unit pixel corresponds to the pixel 305, the second direction orthogonal to the first direction corresponds to the vertical direction, and the second floating diffusion portion corresponds to the FDs 308a and 308b.

  The first and second photoelectric conversion units correspond to the photoelectric conversion units 303a and 303b, respectively. The third and fourth photoelectric conversion units correspond to the photoelectric conversion units 303c and 303d, respectively. The fifth and sixth photoelectric conversion units correspond to the photoelectric conversion units 307a and 307c, respectively. The seventh and eighth photoelectric conversion units correspond to the photoelectric conversion units 307b and 307d, respectively.

  Furthermore, the third floating diffusion portion corresponds to the FD 303b, and the fourth floating diffusion portion corresponds to the FD 308b.

  FIG. 5 is an equivalent circuit diagram of the pixel unit 201. For convenience of explanation, only two pixels 302 and 306 are shown, but the plurality of pixels are two-dimensionally arranged to constitute the pixel unit 201. Further, although only one column readout unit is shown, a plurality of readout units are arranged for each column to constitute the readout unit 203.

  As shown in FIG. 5, the photoelectric conversion units 303a to 303d in the pixel 302 and the photoelectric conversion units 307a to 307d in the pixel 306 are respectively shown as photodiodes (PD) in FIG. Each photoelectric conversion unit has a function of receiving light in each region of the exit pupil, and generating and accumulating signal charges corresponding to the amount of received light.

  The signal charge transfer switches 501 and 502 are driven by transfer pulse signals φTX1 and φTX2, respectively, and transfer the signal charges generated by the photoelectric conversion units 303a and 303b to the FD 304a, respectively. Similarly, the signal charge transfer switches 503 and 504 are driven by transfer pulse signals φTX3 and φTX4, respectively, and transfer the signal charges generated by the photoelectric conversion units 307a and 307c to the FD 308a, respectively.

  The photoelectric conversion units 303c and 303d and the photoelectric conversion units 307b and 307d share the FD with adjacent pixels (not shown).

  The reset switches 505 and 508 are driven by reset pulse signals φRES1 and φRES2, respectively, so that the reference potential VDD can be supplied to the FD 304a and the FD 304b, respectively.

  The FD 304a functions as a charge-voltage conversion unit that holds the transferred charges from the photoelectric conversion units 303a and 303b, and the FD 308a converts the held charges into a voltage signal from the photoelectric conversion units 307a and 307c, respectively.

  The amplifying units 506 and 509 amplify voltage signals based on the charges held in the FDs 304a and 308a, respectively, and output them as pixel signals. Here, as an example, a source follower circuit using a MOS transistor and a constant current source 512 is shown.

  The selection switches 507 and 510 are driven by vertical selection pulse signals φSEL 1 and φSEL 2, respectively, and the signals amplified by the amplification units 506 and 509 are output to the vertical signal line 511. The signal output to the vertical signal line 511 is read by the reading unit 203 and then output to the AFE 102.

  FIG. 6 shows a detailed configuration of the FD and the signal charge transfer switch. For convenience of explanation, only the FD 304a and the signal charge transfer switches 501 and 502 are shown, but each FD and signal charge transfer switch as shown in the figure are configured in the entire pixel portion.

  In FIG. 6, high impurity concentration regions 601, 602, and 604 are formed on a semiconductor substrate. A wiring 603 connects the region 601 and the region 602.

  As illustrated in FIG. 6A, the FD 304 a includes two regions 601 and 602 that are electrically connected by a wiring 603. The transfer switch 501 is disposed between the photoelectric conversion unit 303a and the region 601 and transfers the signal charge generated by the photoelectric conversion unit 303a to the region 601. The transfer switch 502 is disposed between the photoelectric conversion unit 303b and the region 602, and transfers the signal charge generated by the photoelectric conversion unit 303b to the region 602.

  As shown in FIG. 6B, the FD 304a may be configured by one region 604. In this case, the transfer switch 501 is disposed between the photoelectric conversion unit 303a and the region 604, and transfers the signal charge generated by the photoelectric conversion unit 303a to the region 604. The transfer switch 502 is disposed between the photoelectric conversion unit 303b and the region 602, and transfers the signal charge generated by the photoelectric conversion unit 303b to the region 604.

  In the present embodiment, the FD is shared by the two photoelectric conversion units arranged side by side in the pixel 302, but is shared by the two photoelectric conversion units arranged vertically in the adjacent pixel 306. According to this configuration, as described above, the area of the dead zone between the photoelectric conversion units can be reduced, and the amount of light that is blocked from entering the photoelectric conversion unit by the structure in the pixel is also reduced. And while realizing the isotropic layout of a photoelectric conversion part, the area of a photoelectric conversion part can be ensured widely and the sensitivity of an image pick-up element can be improved.

  Here, the arrangement of the reset switches 505 and 508, the amplification units 506 and 509, the selection switches 507 and 510, and the like in the pixel unit 201 may be arranged at appropriate positions between the pixels. You may arrange in.

  In the present embodiment, the amplification unit 506 and the amplification unit 509 share the vertical signal line 511 for outputting a signal. However, the amplification unit 506 and the amplification unit 509 may each be provided with a vertical signal line. Good.

  Further, in the imaging apparatus according to the present embodiment, when driving for focus detection or 3D video shooting, the addition signal of the outputs of the left two photoelectric conversion units and the addition signal of the outputs of the two right photoelectric conversion units are performed. Each signal is used. Alternatively, it is possible to use the addition signals of the outputs of the upper and lower photoelectric conversion units. By using both of these signals in combination, more accurate focus detection can be performed.

  In the present embodiment, such addition at the time of focus detection driving can be realized by each shared FD and can be performed at an arbitrary position of the pixel portion on the surface of the solid-state imaging device. Is possible.

  On the other hand, at the time of imaging driving, it is necessary to obtain a signal obtained by adding the outputs of four photoelectric conversion units for each pixel. Alternatively, when driving for 3D video shooting, it is necessary to obtain, for each pixel, an addition signal output from the left two photoelectric conversion units and an addition signal output from the two right photoelectric conversion units. This embodiment may be anything as long as the function is realized. For example, it may be performed at an arbitrary position in the output path, may be performed by the reading unit 203, and may be performed by the subsequent AFE 102, DFE 103, the image processing unit 104, or the like. Of course, the addition of the outputs of the two photoelectric conversion units among the four photoelectric conversion units of one pixel can be performed by a shared FD.

  Further, in the present embodiment, the configuration of the color filter (CF) that performs color separation of light incident on the photoelectric conversion unit may be freely configured according to the use of the solid-state imaging device. For example, in a certain pixel, all of the plurality of photoelectric conversion units may include a CF having the same color spectral transmittance, or may have a spectral transmittance of different colors. In addition, pixels in which the CF colors corresponding to the plurality of photoelectric conversion units in the pixel are all the same color and pixels including different colors may be mixed in the pixel unit.

  As described above, according to the present embodiment, in a solid-state imaging device including a micro lens and a plurality of photoelectric conversion units in a unit pixel, the area of the dead zone between the photoelectric conversion units is reduced, and The light flux that is blocked from entering the photoelectric conversion unit by the structure is also reduced. In addition, while realizing an isotropic layout of the photoelectric conversion unit, it is possible to realize a solid-state imaging device that secures a large area of the photoelectric conversion unit and improves the sensitivity of the imaging device.

Claims (7)

In a solid-state imaging device including a microlens and a plurality of photoelectric conversion units in a unit pixel,
The first unit pixel is configured such that a plurality of photoelectric conversion units arranged in the first direction share a floating diffusion unit provided in the first direction,
The second unit pixel is configured such that a plurality of photoelectric conversion units arranged in a second direction orthogonal to the first direction share a floating diffusion unit provided in the second direction,
A solid-state imaging device, wherein the first unit pixels and the second unit pixels are alternately arranged in a matrix. The first unit pixel includes a first floating diffusion portion shared by the first and second photoelectric conversion units arranged in the first direction, and a third and a third unit arranged in the first direction. A second floating diffusion part shared by the fourth photoelectric conversion part,
The second unit pixel includes a third floating diffusion unit shared by the fifth and sixth photoelectric conversion units disposed in the second direction, and a seventh floating unit disposed in the second direction. The solid-state imaging device according to claim 1, further comprising a fourth floating diffusion unit shared by the eighth photoelectric conversion unit.   3. The solid-state imaging device according to claim 1, wherein a length in the first direction and a length in the second direction of the plurality of photoelectric conversion units are equal.   4. The solid-state imaging device according to claim 1, wherein the plurality of photoelectric conversion units of one unit pixel include color filters having the same spectral transmittance. 5.   4. The solid-state imaging device according to claim 1, wherein the plurality of photoelectric conversion units of one unit pixel include color filters having different spectral transmittances. 5.   The solid-state imaging device according to claim 1, wherein the floating diffusion part is connected to an amplifying part.   An imaging apparatus comprising the solid-state imaging device according to claim 1.

Images