JP2018098725A - Imaging device and imaging apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem that, when applying a multilayer sensor as a curvature sensor, since thickness is increased in the multilayer sensor, even if curvature control of a pixel chip is tried similarly to a non-multilayer sensor, the pixel chip cannot be accurately curved or may be destroyed.SOLUTION: The present invention relates to an imaging device 13 comprising a first semiconductor substrate S1 including a photo-detection plane PD consisting of multiple photoelectric transducers 201; and a second semiconductor substrate S2 including digital circuit parts 210 and 220 each applying digital signal processing to a signal outputted from the first semiconductor substrate S1. The first semiconductor substrate S1 and the second semiconductor substrate S2 are connected while being stacked, the imaging device 13 can be curved and has structures 110a and 310a for reducing a distortion stress that is generated when curing the imaging device.SELECTED DRAWING: Figure 6

Description

  The present invention relates to an imaging element and an imaging apparatus.

  In recent years, compact digital cameras have been equipped with one or more large image sensors. As a result, it has become possible for compact digital cameras to perform ultra-high-sensitivity shooting, which has been possible with conventional single-lens reflex cameras, and shooting with a shallow depth of field and full of bokeh. . The mounting of such a large image sensor has become indispensable for a compact digital camera as a differentiating technique from a camera mounted on a smartphone or a tablet.

  However, when mounting a large image sensor compared to a conventional compact image sensor mounted on a compact digital camera, the incident angle of light incident on the lens from the subject (hereinafter referred to as the “light incident angle”). There is a problem that it becomes large. The increase in the light incident angle becomes more remarkable when the size of the camera optical system is reduced.

  As one means for solving this problem, Patent Document 1 proposes an imaging element having a structure in which a light receiving surface is curved (hereinafter referred to as a “curved sensor”). The bending sensor can receive light in a state close to vertical with respect to the light beam from the subject incident from the lens by bending the light receiving surface.

Japanese Patent Laid-Open No. 2006-134857

  By the way, the imaging element is required to have a form as a multifunctional imaging element that not only has a function of photographing a subject but also has a function that has been provided in a subsequent circuit. When the image pickup device has a large number of functions, the device itself becomes large, but an image pickup device (hereinafter referred to as a “stacked sensor”) configured by stacking a plurality of semiconductor substrates has been proposed.

  When trying to bend the laminated sensor as described above, since the thickness of the laminated sensor is increased, if the curvature control of the semiconductor substrate of the laminated sensor is performed like a non-stacked curved sensor, the curvature cannot be accurately controlled. Or, there is a problem that the semiconductor substrate is destroyed. In addition, when the laminated sensor is bent, the circuit layer is also bent and distorted, so the impedance characteristic of the circuit part changes.When the curvature of curvature is further changed, the impedance characteristic of the circuit part changes according to the curvature. There is a problem such as.

  Therefore, an object of the present invention is to provide an image sensor that can maintain flexibility when it is curved even if it is an image sensor having a thickness like a laminated sensor.

  In order to achieve the above object, an imaging device according to the present invention performs digital signal processing on a first semiconductor substrate having a light-receiving surface composed of a plurality of photoelectric conversion elements, and a signal output from the first semiconductor substrate. An image sensor comprising a second semiconductor substrate having a digital circuit portion to be applied, wherein the first semiconductor substrate and the second semiconductor substrate are stacked and connected, and the image sensor can be curved It is characterized by having a structure that reduces the strain stress generated when bending.

  ADVANTAGE OF THE INVENTION According to this invention, even if it is an image pick-up element which has a laminated structure, the image pick-up element which can maintain the softness | flexibility at the time of making it curve can be provided.

It is a figure which shows the outline | summary of the imaging device 1 in the Example of this invention. It is the schematic which shows the structure of the image pick-up element 13 in the Example of this invention. FIG. 3 is a diagram illustrating a configuration of a pixel 200 of an image sensor 13 and a configuration of an AD conversion circuit unit 210 corresponding thereto in an embodiment of the present invention. It is a conceptual diagram which shows the structure of the image pick-up element 13 in the Example of this invention. (A) It is a side view of the image pick-up element 13 in the Example of this invention. (B) It is the perspective view seen from the pixel chip 100 side. (C) It is the perspective view seen from the processing chip 110 side. (D) It is a side view of the image pick-up element 33 in the modification of this invention. It is sectional drawing which shows the curvature control apparatus 15 of the image pick-up element 13 in the Example of this invention. (A), (C) It is a figure which shows the stress when the image pick-up element 13 in the Example of this invention curves. (B), (D) It is a figure which shows the stress in the past. (A) It is a figure which shows the curvature control table in the Example of this invention. (B) It is a figure which shows the form of the curved part C in each curvature X in the Example of this invention. It is a flowchart which shows the curvature control procedure in the Example of this invention.

(Example)
Examples of the present invention will be described below. 1 includes a lens 11, a lens control device 12, an image sensor 13, an image sensor control device 14, a curvature control device 15, a DSP 16, a memory unit 17, a display unit 18, a recording device 19, and an operation unit 20. It is configured.

  The lens 11 is a zoom lens, and the focal length of the lens 11 is controlled by a control signal of the lens control device 12 that has received an instruction from the DSP 16. In addition to the focal length, the lens control device 12 can perform aperture control, focus control, and the like.

  The light of the subject image that has passed through the lens 11 is formed on the image sensor 13. The image sensor 13 photoelectrically converts the formed subject image under the control of the image sensor control device 14 that has received an instruction from the DSP 16. The shape of the image sensor 13 is controlled by the control of the bending control device 15 in response to the instruction of the DSP 16 so that the image sensor 13 has an optimal curvature of the curved shape in accordance with the state of the lens 11.

  An image signal photoelectrically converted by the image pickup device 13 and subjected to correction such as AD conversion processing and defect correction is transmitted to the DSP 16. In the DSP 16, various image signal processes are performed on the image signal, and the processed image signal is stored in the memory unit 17. On the display unit 18, an image based on the processed image signal from the memory unit 17 and a recorded image from the recording device 19 are displayed. The recording device 19 is a recording means typified by a memory card, and can record captured images and images. The operation unit 20 includes an operation member that allows a user to operate a camera such as a release.

  FIG. 2 schematically shows the configuration of the image sensor 13 in the embodiment of the present invention. The imaging device 13 includes a pixel chip 100 in which a plurality of pixels 200 are arranged in an array in the horizontal direction and the vertical direction, and a processing chip 110 having an AD conversion circuit unit 210 and a digital image processing circuit unit 220. The pixel chip 100 and the processing chip 110 are electrically connected via the micro bumps 120, and are bonded and laminated in a configuration as shown in FIG.

  First, the pixel chip 100 will be described. The pixel chip 100 is formed with a light receiving surface including a pixel group in which a plurality of pixels 200 are arranged in an array in the horizontal direction (row direction) and the vertical direction (column direction). In FIG. 2, for simplification, the configuration is 6 pixels in the horizontal direction and 3 pixels in the vertical direction, but in general, millions of pixels 200 are arranged. In this configuration, since one AD conversion circuit unit 210 is shared by the same column in the vertical direction, one vertical signal line (column signal line) 101 is arranged in each column.

  Each pixel 200 is provided with a selection signal line for turning on the selection transistor (see FIG. 3). The signals of the pixels 200 in each column are sequentially selected by the selection signal line and output from the shared vertical signal line 101. The vertical signal line 101 is connected to the micropad 102 and transmits an image signal to the processing chip 110 via the microbump 120.

  Next, the processing chip 110 will be described. In the processing chip 110, AD conversion circuit units 210 corresponding to the respective columns of the respective pixel groups of the pixel chip 100 are arranged. Further, the processing chip 110 is provided with a micropad 112, and an imaging signal of the pixel chip 100 is input to the micropad 112 via the microbump 120. That is, the micropad 112 is an input terminal for imaging signals. Further, the imaging signal digitized by the AD conversion circuit unit 210 is input to the digital image processing circuit unit 220 via the horizontal signal line (row signal line) 111. The digital image processing circuit unit 220 performs image processing such as defect correction.

  With reference to FIG. 3, the configuration of the pixel 200 and the corresponding AD conversion circuit unit 210 in the embodiment of the present invention will be described. The pixel 200 according to the embodiment of the present invention includes four transistors including a transfer transistor 202, a reset transistor 203, an amplification transistor 204, and a selection transistor 205 in addition to the photodiode 201. These transistors 202 to 205 constitute an analog circuit portion that performs a signal reading process of the photodiode 201. In the embodiment of the present invention, for example, N-channel MOS transistors are used as the transistors 202 to 205.

  The photodiode 201 is a so-called photoelectric conversion element that photoelectrically converts received light into photoelectric charges (here, electrons) having a charge amount corresponding to the amount of light. The cathode of the photodiode 201 is electrically connected to the gate of the amplification transistor 204 through the transfer transistor 202. A node electrically connected to the gate of the amplification transistor 204 is referred to as an FD (floating diffusion) unit 206.

  The transfer transistor 202 is connected between the cathode of the photodiode 201 and the FD unit 206, and is turned on when a transfer pulse φTRS is applied to the gate via a transfer pulse signal line (not shown). Then, the photoelectric charge photoelectrically converted by the photodiode 201 is transferred to the FD unit 206.

  The reset transistor 203 is turned on when a drain is connected to the pixel power source Vdd, a source is connected to the FD unit 206, and a gate is supplied with a reset pulse φRST via a reset pulse signal line (not shown). The reset transistor 203 resets the FD unit 206 by discarding the charge of the FD unit 206 to the pixel power supply Vdd prior to the transfer of the signal charge from the photodiode 201 to the FD unit 206.

  The amplification transistor 204 has a gate connected to the FD unit 206 and a drain connected to the pixel power supply Vdd, and outputs the potential of the FD unit 206 after being reset by the reset transistor 203 as a reset level. Furthermore, the amplification transistor 204 outputs the potential of the FD unit 206 after transferring the signal charge by the transfer transistor 202 as a signal level.

  In the selection transistor 205, for example, the drain is connected to the source of the amplification transistor 204, the source is connected to the output signal line 207, and the selection pulse φSEL is applied to the gate via the selection pulse signal line (not shown). Become. The selection transistor 205 relays the signal output from the amplification transistor 204 to the output signal line 207 with the pixel 200 in a selected state.

  The selection transistor 205 may have a circuit configuration connected between the pixel power supply Vdd and the drain of the amplification transistor 204. Further, the configuration of the pixel 200 is not limited to the above-described four transistor configuration, and may be a three-transistor configuration in which the amplification transistor 204 and the selection transistor 205 are combined.

  An imaging signal output from the pixel 200 via the output signal line 207 is transmitted to the AD conversion circuit unit 210 via the vertical signal line 101, micropad 102, microbump 120, micropad 112, and input signal line 215. The The AD conversion circuit unit 210 includes a comparator 211, an up / down counter 212, a memory 213, and a DAC (DA converter) 214. The input signal line 215 is connected to one of a pair of input terminals included in the comparator 211, and the DAC 214 is connected to the other. The DAC 214 outputs a ramp signal whose signal level changes over time based on the value input from the image sensor control device 14.

  The comparator 211 compares the level of the ramp signal input from the DAC 214 with the level of the imaging signal from the output signal line 207 and outputs a comparison signal. For example, when the level of the imaging signal is less than the level of the ramp signal, a high level comparison signal is output, and when the level of the imaging signal is equal to or higher than the level of the ramp signal, a low level comparison signal is output. .

  The up / down counter 212 receives the comparison signal from the comparator 211 and counts a period during which the comparison signal is at a high level or a period at which the comparison signal is at a low level. By the counting process by the up / down counter 212, the imaging signal of the pixel 200 is converted into a complete digital value. An AND circuit may be provided between the comparator 211 and the up / down counter 212, a pulse signal may be input to the AND circuit, and the number of pulse signals may be counted by the up / down counter 212.

  The memory 213 is connected to the up / down counter 212 and stores the count value counted by the up / down counter 212. The up / down counter 212 counts the count value corresponding to the reset level based on the imaging signal when the pixel 200 is reset, and counts the count value based on the imaging signal after a predetermined imaging time. The difference value may be stored in the memory 213. The count value (signal) stored in the memory 213 is transmitted to the downstream digital image processing circuit unit 220 and subjected to image processing such as defect correction as a digital image signal together with signals from other pixels 200, and the image sensor 13. To the DSP 16. The AD conversion circuit unit 210 and the digital image processing circuit unit 220 constitute a digital circuit unit that performs digital signal processing.

  FIG. 4 is a conceptual diagram showing a bonding structure of the pixel chip 100 and the processing chip 110 of the image sensor 13 in the embodiment of the present invention. A light receiving portion PD is formed on one surface of the pixel chip 100 on which the plurality of pixels 200 are arranged, and a micropad 102 (not shown) is formed on the other surface, and a processing chip 110 is attached. . That is, the pixel chip 100 and the processing chip 110 are stacked on each other.

  FIG. 5A is a side view of the image sensor 13 in the embodiment of the present invention. FIG. 5B is a perspective view of the image sensor 13 viewed from the pixel chip 100 side. FIG. 5C is a perspective view of the image sensor 13 viewed from the processing chip 110 side. The image sensor 13 has a micro bump 120 between the pixel chip 100 and the processing chip 110.

  The pixel chip 100 has a rectangular shape, and a light receiving portion (light receiving surface) PD in which a plurality of pixels 200 are arranged in an array is formed on the surface thereof. On the back surface, a micropad 102 is provided. Further, the processing chip 110 has a micropad 112 at a position corresponding to the micropad 102 of the pixel chip 100. An image signal from the pixel chip 100 is output to the micropad 102 and transmitted to the processing chip 110 via the microbump 120. The imaging element 13 including the pixel chip 100 and the processing chip 110 has a structure that can be bent as shown in FIG. 6 and absorbs and reduces distortion stress generated when the imaging element 13 is bent. It has the structure of.

  The processing chip 110 according to the embodiment of the present invention includes a deforming portion 110a for absorbing and reducing distortion stress generated when the imaging element 13 is curved on the surface opposite to the surface to which the pixel chip 100 is attached. The deformed portion 110a has a groove shape, and can be formed by etching or mechanical scribing, for example. The deformation unit 110a can bend the pixel chip 100 including the pixels 200 with high accuracy, and can avoid risks such as destruction of the image sensor 13. And the effect that the flexibility of the image sensor 13 is maintained is brought about.

  A plurality of the deforming portions 110a may be provided. 5C, the processing chip 110 has at least two groove-shaped deformable portions 110a in the major axis direction and at least one groove-shaped deformable portion 110a in the minor axis direction. It should be noted that other shapes may be used as long as the same effect can be obtained by partially changing the thickness of the surface of the processing chip 110 into a groove shape. For example, the groove shape may be a V shape, a U shape, or the like.

  FIG. 5D shows a side view of an image sensor 33 which is a modification of the embodiment of the present invention. In the modified example, the processing chip 110 in the embodiment is divided into a plurality of parts such as the processing chip 310b and the processing chip 310c, and each divided part is connected to the pixel chip 100. A dividing unit 310a is provided between the processing chip 310b and the processing chip 310c, and the dividing unit 310a absorbs and reduces the strain stress generated when it is bent, like the deforming unit 110a of the embodiment. . Further, as in the embodiment, a configuration in which a plurality of division units 310a are provided is also possible.

  Next, the outline of the curvature control mechanism of the light receiving surface of the image sensor 13 in the embodiment of the present invention will be described with reference to FIG. FIG. 6 is a cross-sectional view showing the image sensor 13 and the bending control device 15 and shows a state in which the image sensor 13 is curved. The imaging element 13 is configured by superimposing a first semiconductor substrate S1 constituting the pixel chip 100 and a second semiconductor substrate S2 constituting the processing chip 110, and firmly fixing each of them. The micro pad 102 disposed on the back surface of the first semiconductor substrate S1 and the micro pad 112 disposed on the front surface of the second semiconductor substrate S2 are electrically connected by a micro bump 120 (not shown). The imaging signal is transmitted.

  On the surface of the first semiconductor substrate S1, a light receiving portion (light receiving surface) PD in which pixels 200 including photoelectric conversion elements are two-dimensionally arranged is formed. The second semiconductor substrate S2 includes an AD conversion circuit unit 210 and a digital image processing circuit unit 220. The flat portion at the peripheral edge of the first semiconductor substrate S1 is fixed to the flat surface 132 of the pedestal 131 via an adhesive layer, and the surface of the pedestal 131 opposite to the flat surface 132 is fixed to the bottom plate 134. By fixing the pedestal 131 to the bottom plate 134, an airtightly closed space 133 is formed in the pedestal 131. The bending control device 15 having the suction part 140 is attached to the bottom plate 134.

  The suction unit 140 sucks the gas in the sealed space 133 and controls the atmospheric pressure (negative pressure) in the sealed space 133 to form a three-dimensional curved portion C such as an arc shape on the sealed space 133 side of the image sensor 13. Is done. The bending control device 15 can variably control the curvature of the bending portion C as shown by the arrow in FIG. 6 by controlling the suction portion 140. The imaging element 13 constituted by the first semiconductor substrate S1 and the second semiconductor substrate S2 is supported on the pedestal 131 by fixing the flat portion of the periphery of the curved portion C to the flat surface 132 of the pedestal 131. Is done.

  The dotted line shown in FIG. 6 shows a state in which the pressure in the sealed space 133 is controlled by the bending control device 15 and the bending portions C of the first semiconductor substrate S1 and the second semiconductor substrate S2 are controlled with high accuracy. Show. With such a bending control mechanism, it is possible to control the curvature of the light receiving surface. The feature of the image sensor 13 of the embodiment of the present invention is that the second semiconductor substrate S2 has a structure for reducing strain stress.

  FIG. 7A shows a second semiconductor substrate S2 of the image sensor 13 according to the embodiment of the present invention. FIG. 7C shows a state of strain stress when the second semiconductor substrate S2 of FIG. 7A is curved. FIG. 7B shows a conventional semiconductor substrate S. FIG. 7D shows a state of strain stress when the conventional semiconductor substrate S of FIG. 7B is curved. Arrows indicate the magnitude and direction of strain stress (compressive stress, tensile stress) that acts by bending.

  In FIG. 7D, strain stress is generated in the conventional semiconductor substrate S due to the bending. A compressive stress is generated on the upper side of the conventional semiconductor substrate S, and a tensile stress is generated on the lower side of the semiconductor substrate S, thereby distorting the semiconductor substrate S. On the other hand, in FIG. 7C, strain stress is similarly generated in the second semiconductor substrate S2, but the deformed portion 110a is deformed and absorbs a part of the strain stress, so that the second semiconductor substrate S2 is deformed. The lower tensile stress is reduced. By adopting the configuration of the embodiment of the present invention, it is possible to maintain flexibility when the image pickup device 13 is bent. Therefore, it is possible to function as a bending sensor while maintaining the merit of the laminated sensor. .

  Next, the bending control device 15 according to the embodiment of the present invention will be described with reference to FIGS. FIG. 8A is a curvature control table that shows the relationship between the zoom position of the lens 11 and the curvature X of the bending portion C that is controlled accordingly via the bending control device 15. It is stored in the memory unit 17. In the curvature control table, zoom points such as Wide and M1 are adopted as the zoom position, but a similar curvature control table can be created even if the focal length at each zoom position is adopted.

  FIG. 8B shows a form of the bending portion C controlled by the bending control device 15. The curvature X of the curved portion C is defined as curvatures X0 to X5. The curvature X5 has the largest curvature, the curvature X0 has the smallest curvature, and includes the case where the curvature is zero.

  The lens 11 according to the embodiment of the present invention has a configuration in which the incident angle to the image sensor 13 becomes stricter as the zoom position is closer to Wide during the imaging operation. However, in the embodiment of the present invention, the imaging characteristics can be kept optimal by controlling the curvature X of the curved portion C of the imaging element 13 with respect to the light incident angle of the lens 11 that changes according to the zoom position. .

  Next, details of the control of the bending control device 15 in the embodiment of the present invention will be described with reference to the flowchart of FIG. First, in step S <b> 10, the user performs an operation of starting the imaging operation of the camera by the operation unit 20 of the imaging device 1. In the next step S20, an initial setting for starting imaging is performed. In the subsequent step S30, the zoom position set by the user is acquired by the DSP 16. In subsequent step S40, the curvature X that the DSP 16 gives to the bending control device 15 is selected based on the zoom position acquired in step S30 and the curvature control table of FIG.

  Next, in step S50, the bending control device 15 bends the imaging element 13 to change the curvature of the bending portion C of the imaging element 13 so as to form the curved shape having the curvature X selected in step S40. Next, in step S60, an imaging operation end command from the DSP 16 is confirmed. If the DSP 16 has not issued an imaging operation end command and the imaging operation continues, the operation returns to step S30 and the operation of acquiring the zoom position is performed again. On the other hand, when an instruction to end the imaging operation is instructed from the DSP 16, the process proceeds to the next step S70 and the imaging operation is terminated.

  As described above, in the image sensor 13 configured as a stacked sensor, the first semiconductor substrate including the pixel 200 is ensured by ensuring the flexibility of the second semiconductor substrate S2 that does not include the pixel 200 as in the embodiment of the present invention. It becomes possible to control the curved shape of S1 with high accuracy. In addition, it is possible to avoid risks such as destruction of the second semiconductor substrate S2 and changes in the impedance of the circuit portion due to distortion of the second semiconductor substrate S2. As a result, it is possible to form a curved shape while being in the form of a laminated sensor. Furthermore, even in a photographing optical system in which the light incident angle from the lens 11 is high, the curved shape can be changed according to the photographing optical system, so that a high-quality image can be obtained and The imaging device 1 having various functions unique to the sensor can be provided. In the embodiment of the present invention, as a method of changing the curvature, a method of controlling the curvature of the curved portion C by sucking the central portion of the image sensor 13 is shown. However, in another case where the curvature is controlled by another method. Even if it exists, it is realizable similarly.

  The present invention has been described in detail based on the preferred embodiments thereof, but 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 embodiments may be appropriately combined.

13 Image sensor 15 Bending control device (bending control mechanism)
100 Image chip 110 Processing chip 110a Deformed portion (structure for reducing strain stress)
120 Micro bump 201 Photodiode (photoelectric conversion element)
202 to 205 transistor (analog circuit part)
210 AD conversion circuit (digital circuit)
220 Digital image processing circuit (digital circuit)
310a Dividing part (structure for reducing strain stress)
S1 First semiconductor substrate S2 Second semiconductor substrate PD Light receiving portion (light receiving surface)

Claims (9)

A first semiconductor substrate having a light receiving surface composed of a plurality of photoelectric conversion elements;
A second semiconductor substrate having a digital circuit section for performing digital signal processing on a signal output from the first semiconductor substrate;
An imaging device comprising:
The first semiconductor substrate and the second semiconductor substrate are stacked and connected, and the imaging element can be bent, and has a structure that reduces strain stress generated when the imaging element is bent. An imaging device as a feature.   The image sensor according to claim 1, wherein the second semiconductor substrate has a structure that reduces the strain stress.   The imaging device according to claim 1, wherein the structure that reduces the strain stress is a deformed portion that deforms a groove shape.   The imaging device according to claim 3, wherein the deformable portion is formed by etching or mechanical scribing.   The image pickup device according to claim 1, wherein the structure for reducing the strain stress is a divided portion formed by dividing the digital circuit portion into a plurality of portions.   The structure for reducing the strain stress is provided with at least two in the major axis direction and at least one in the minor axis direction of the second semiconductor substrate. The imaging device according to item.   The imaging device according to claim 1, wherein the first semiconductor substrate and the second semiconductor substrate are connected by a micro bump.   8. A bending control mechanism that controls a curvature of a curved shape when the imaging element is bent, wherein the bending control mechanism changes the curved shape according to a photographing optical system. An imaging apparatus comprising the imaging device according to any one of the above.   The imaging apparatus including the imaging device according to claim 8, wherein the bending control mechanism changes the bending shape by suction.

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