Imaging device and processing circuit

Abstract

An imaging device includes: a photoelectric conversion unit including a counter electrode, a pixel electrode, and a photoelectric conversion layer; a voltage supply circuit (150) that supplies a first voltage to the counter electrode; a detection circuit (130) that outputs a signal corresponding to a change in the potential of the pixel electrode, the change in the potential of the pixel electrode being a change in the amount of light incident on the photoelectric conversion unit; and an image processing circuit (160) that corrects the signal from the detection circuit (130). The photoelectric conversion unit has a photoelectric conversion characteristic in which, when a potential difference between the counter electrode and the pixel electrode is within a first voltage range, a photocurrent flowing between the counter electrode and the pixel electrode varies linearly with respect to the potential difference. The voltage supply circuit (160) corrects the signal so that the output linearly varies with respect to the amount of light incident to the photoelectric conversion unit on the basis of a conversion function derived from a change in the potential of the pixel electrode with respect to the amount of light incident to the photoelectric conversion unit when the potential difference is within the first voltage range.

Description

Technical Field

[0001] The present disclosure relates to a camera device and a processing circuit. Background Art

[0002] As a MOS (Metal Oxide Semiconductor) type camera device, a stacked camera device has been proposed. In a stacked camera device, a photoelectric conversion layer is stacked on the surface of a semiconductor substrate. In addition, in a stacked camera device, the charge generated by photoelectric conversion in the photoelectric conversion layer is accumulated as a signal charge in a charge accumulation region also called FD (Floating Diffusion) for each pixel. The accumulated charge is read out using a CMOS (Complementary MOS) circuit in the semiconductor substrate. In such a stacked camera device, the charge in the photoelectric conversion layer moves by an electric field. Therefore, there is a known technology that can control the sensitivity of the camera device by controlling the potential state around the photoelectric conversion layer, such as in Patent Documents 1 and 2.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Publication No. 2019-176463

[0006] Patent Document 2: Japanese Patent Application Publication No. 2019-140673 Summary of the invention

[0007] Problems to be solved by the invention

[0008] In the imaging devices that can control the sensitivity by controlling the potential state around the photoelectric conversion layer disclosed in Patent Documents 1 and 2, there may be a situation where the magnitude of the read signal no longer changes linearly with respect to the amount of incident light. In the present disclosure, an imaging device that can perform linear correction on the signal with respect to the amount of incident light by a simple method is provided.

[0009] Means used to solve problems

[0010] In order to solve the above-mentioned problems, a camera device related to a technical solution of the present disclosure comprises: a photoelectric conversion unit, including a first electrode, a second electrode, and a photoelectric conversion layer between the first electrode and the second electrode, which receives light and generates charges; a voltage supply circuit, which supplies a first voltage to the first electrode; a detection circuit, which outputs a signal corresponding to a potential change of the second electrode, and the potential change of the second electrode is a change corresponding to the amount of incident light to the photoelectric conversion unit; and an image processing circuit, which corrects the signal from the detection circuit and outputs the corrected signal, and the photoelectric conversion unit has the following photoelectric conversion characteristics: when the first electrode and the second electrode are When the potential difference between the electrodes is within the first voltage range, the photocurrent flowing between the first electrode and the second electrode changes linearly with respect to the potential difference. The voltage supply circuit supplies the first voltage to the first electrode so that the voltage range in which the potential difference can be taken corresponding to the amount of incident light to the photoelectric conversion portion includes at least a part of the first voltage range. The image processing circuit corrects the signal based on a transformation function derived from the potential change of the second electrode relative to the amount of incident light to the photoelectric conversion portion when the potential difference is within the first voltage range so that the output changes linearly with respect to the amount of incident light to the photoelectric conversion portion.

[0011] In addition, a processing circuit according to a technical solution of the present disclosure corrects an input signal based on a transformation function represented by the following (Formula 1), and outputs the corrected input signal.

[0012] [Formula 1]

[0013]

[0014] Among them, y is the input value of the above transformation function, Y is the output value of the above transformation function, ymax is the maximum value of the input value of the above transformation function, and δ is the proportional constant.

[0015] Effects of the Invention

[0016] According to the present disclosure, it is possible to provide an imaging device capable of performing linear correction on a signal in relation to the amount of incident light by a simple method. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic diagram showing the structure of an imaging device according to an embodiment.

[0018] Figure 2 It is a diagram showing an exemplary circuit configuration of an imaging device according to an embodiment.

[0019] Figure 3 It is a cross-sectional view showing a schematic cross-sectional structure of a pixel according to the embodiment.

[0020] Figure 4 It is a diagram schematically showing an example of the photoelectric conversion characteristics of the photoelectric conversion portion according to the embodiment.

[0021] Figure 5 This diagram shows the relationship between the ratio of the output value of the detection circuit to the maximum value of the output value of the detection circuit and the error amount before and after output conversion when the camera device of the embodiment is operated so that the potential difference ΔV between the electrodes of the photoelectric conversion unit enters the linear region.

[0022] Figure 6 This is a flowchart showing an example of a process flow performed by the image processing circuit according to the embodiment. DETAILED DESCRIPTION

[0023] (Understanding that is the basis of the present disclosure)

[0024] As disclosed in Patent Documents 1 and 2, if the electric field applied to the stacked photoelectric conversion layer is reduced and the signal is read out, the dynamic range can be expanded, but on the other hand, the linearity of the read signal relative to the incident light amount and the accumulation time deteriorates. That is, the signal output from the pixel no longer changes linearly relative to the incident light amount and the accumulation time. Due to the deterioration of the linearity relative to the incident light amount, for example, white balance correction cannot be performed correctly. For example, if a gain is applied to the signal of each pixel as a white balance correction, the degradation of linearity is amplified. In order to cope with this situation, a LUT (Look Up Table) used to convert data that is linear relative to the incident light amount can be prepared in advance for correction. However, since the output of the pixel changes according to the ambient temperature, for example, in order to reduce the correction error, different reference values ​​must be prepared in advance for each temperature and stored in the memory. If there are parameters such as individual differences and deviations between pixels whose pixel outputs may change, it is necessary to choose whether to prepare reference values ​​and increase the memory or to allow the correction error and deteriorate the linear accuracy according to the number of such parameters.

[0025] The present disclosure has been made in view of such a problem, and an object of the present disclosure is to provide an imaging device or the like which can perform linear correction on a signal in relation to the incident light amount by a simple method when the signal output from a pixel does not change linearly with respect to the incident light amount.

[0026] (Overview of the present disclosure)

[0027] As an overview of the present disclosure, examples of an imaging device and a processing circuit according to the present disclosure are shown below.

[0028] The camera device of the first technical solution of the present disclosure comprises: a photoelectric conversion unit, including a first electrode, a second electrode, and a photoelectric conversion layer between the first electrode and the second electrode, which generates charges by receiving light; a voltage supply circuit, which supplies a first voltage to the first electrode; a detection circuit, which outputs a signal corresponding to a potential change of the second electrode, wherein the potential change of the second electrode is a change corresponding to the amount of incident light to the photoelectric conversion unit; and an image processing circuit, which corrects the signal from the detection circuit and outputs the corrected signal, wherein the photoelectric conversion unit has the following photoelectric conversion characteristics: when the voltage between the first electrode and the second electrode is When the potential difference is within the first voltage range, the photocurrent flowing between the first electrode and the second electrode changes linearly with respect to the potential difference. The voltage supply circuit supplies the first voltage to the first electrode so that the voltage range in which the potential difference can take corresponding to the amount of incident light to the photoelectric conversion unit includes at least a portion of the first voltage range. The image processing circuit corrects the signal based on a transformation function derived from a change in the potential of the second electrode relative to the amount of incident light to the photoelectric conversion unit when the potential difference is within the first voltage range so that the output changes linearly with respect to the amount of incident light to the photoelectric conversion unit.

[0029] Thus, in an imaging device in which the signal from the detection circuit does not change linearly with respect to the amount of incident light to the photoelectric conversion unit, the image processing circuit corrects the signal using a transformation function so that the output becomes linear with respect to the amount of incident light to the photoelectric conversion unit. The transformation function at this time is derived by utilizing the linearity of the photocurrent with respect to the potential difference between the first electrode and the second electrode, so it is easy to derive, and the transformation function itself becomes simple. Therefore, the imaging device can perform linear correction of the signal in a simple manner in relation to the amount of incident light.

[0030] Furthermore, for example, in the imaging device according to the second technical aspect of the present disclosure, in the imaging device according to the first technical aspect, the image processing circuit corrects the signal based on the conversion function represented by the following (Formula 1).

[0031] [Formula 2]

[0032]

[0033] Among them, y is the input value of the above transformation function, Y is the output value of the above transformation function, ymax is the maximum value of the input value of the above transformation function, and δ is the proportional constant.

[0034] Thus, the influence of parameters such as temperature change, individual differences of the imaging device, and inter-pixel deviation within the pixel area is included in the input value y of the conversion function, and the proportional constant δ can be set to a unique value. Therefore, the image processing circuit can simply perform linear correction without being affected by the parameters.

[0035] Furthermore, for example, in the imaging device according to the third technical solution of the present disclosure, in the imaging device according to the second technical solution, the image processing circuit calculates the δ according to the following (Formula 2) using the y that is 10% or less of the ymax.

[0036] [Formula 3]

[0037]

[0038] Thus, the proportional constant δ can be calculated using the input value y, so the proportional constant δ of the conversion function can be calculated in a simple way. By calculating the proportional constant δ in advance using (Formula 2), the value of the output value Y corresponding to the input value y can also be calculated in advance based on (Formula 1).

[0039] In addition, for example, in the camera device of the fourth technical solution of the present disclosure, in the camera device of any one of the first to third technical solutions, the image processing circuit includes a memory for storing a table, and the signal is corrected based on the table, and the table includes a transformation result based on the transformation function.

[0040] This can reduce the processing load on the image processing circuit.

[0041] Furthermore, for example, an imaging device according to a fifth aspect of the present disclosure is the imaging device according to any one of the first to fourth aspects, further comprising a semiconductor substrate on which the photoelectric conversion layer is stacked.

[0042] Thereby, a photoelectric conversion portion having the above-mentioned photoelectric conversion characteristics can be easily formed.

[0043] Furthermore, for example, the imaging device according to the sixth technical solution of the present disclosure is the imaging device according to the fifth technical solution, and includes a substrate on which the image processing circuit is formed; and the semiconductor substrate and the substrate are stacked.

[0044] This makes it possible to reduce the area of ​​the imaging device.

[0045] Furthermore, for example, the imaging device according to the seventh technical solution of the present disclosure is, in the imaging device according to the fifth technical solution, provided with a substrate on which the image processing circuit is formed; and the semiconductor substrate is electrically connected to the substrate.

[0046] Thereby, the area of ​​the semiconductor substrate can be reduced.

[0047] In addition, for example, in the camera device related to the 8th technical solution of the present disclosure, in the camera device related to any one of the 1st to 7th technical solutions, the above-mentioned image processing circuit performs at least one of gain correction and gamma correction after correcting the above-mentioned signal based on the above-mentioned transformation function.

[0048] Thus, when performing gain correction and gamma correction, since the signal from the detection circuit is corrected based on the conversion function so as to change linearly with respect to the incident light amount, gain correction and gamma correction can be accurately performed.

[0049] In addition, the processing circuit according to the ninth technical solution of the present disclosure corrects the input signal based on the conversion function represented by the following (Formula 1) and outputs the corrected input signal.

[0050] [Formula 4]

[0051]

[0052] Among them, y is the input value of the above transformation function, Y is the output value of the above transformation function, ymax is the maximum value of the input value of the above transformation function, and δ is the proportional constant.

[0053] This makes it possible to perform linear correction on the output of the detection circuit of the photodetector of the above-mentioned imaging device or the like by a simple method.

[0054] Furthermore, for example, the processing circuit according to the 11th technical solution of the present disclosure, in the imaging device according to the 9th technical solution, includes a memory for storing a table including transformation results based on the transformation function.

[0055] This can reduce the processing load on the processing circuit.

[0056] In addition, for example, the processing circuit according to the 11th technical solution of the present disclosure calculates the above-mentioned δ according to the following (Formula 2) using the above-mentioned y which is 10% or less of the above-mentioned ymax in the processing circuit according to the 9th technical solution or the 10th technical solution.

[0057] [Formula 5]

[0058]

[0059] Thus, since the proportionality constant δ can be calculated using the input value y, the proportionality constant δ of the conversion function can be calculated by a simple method.

[0060] Hereinafter, the embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. In addition, the embodiments described below all represent inclusive or specific examples. The numerical values, shapes, materials, constituent elements, configurations of constituent elements and connection forms, steps, the order of steps, etc. shown in the following embodiments are examples and are not intended to limit the present disclosure. The various technical solutions described in this specification can be combined with each other as long as no contradiction occurs. In addition, regarding the constituent elements of the following embodiments that are not recorded in the independent claims, they are described as arbitrary constituent elements. In the following description, constituent elements with substantially the same functions are sometimes represented by common reference numerals and the description is omitted. In addition, in order to avoid the drawings becoming overly complicated, the illustration of a part of the elements is sometimes omitted.

[0061] In addition, each figure is a schematic diagram and does not necessarily illustrate the exact figure. Therefore, for example, the scale and the like are not necessarily the same in each figure.

[0062] In addition, in this specification, terms such as "equal" that indicate the relationship between elements, terms such as square or circle that indicate the shape of an element, and numerical ranges do not express strict meanings, but mean essentially the same range, for example, also including differences of several percentage points.

[0063] Furthermore, in this specification, the terms "above" and "below" do not refer to the above (vertically above) and below (vertically below) in absolute spatial recognition, but are used as terms specified by relative positional relationships based on the stacking order in the stacking structure. Specifically, the light-receiving side of the camera device is set to "above", and the side opposite to the light-receiving side is set to "below". In addition, the terms "above" and "below" are only used to specify the relative configuration between components, and are not intended to limit the posture of the camera device when in use. In addition, the terms "above" and "below" are not only applicable to the case where two components are arranged at a distance from each other and there is another component between the two components, but also to the case where two components are arranged in close contact with each other and the two components are connected.

[0064] (Implementation Method)

[0065] [Overall structure]

[0066] First, use Figure 1 The overall structure of the imaging device 100 will be described. Figure 1 It is a schematic diagram showing the structure of an imaging device according to an embodiment.

[0067] like Figure 1 As shown in FIG. 1 , the imaging device 100 includes a plurality of pixels P each including a photoelectric conversion portion supported by a semiconductor substrate 110 in a portion thereof.

[0068] The plurality of pixels P are arranged two-dimensionally on the semiconductor substrate 110 to form a pixel region. The number and arrangement of the pixels P are not limited to Figure 1 The examples shown are arbitrary. For example, by arranging a plurality of pixels P in one dimension, the imaging device 100 can be used as a line sensor.

[0069] As described in detail later with reference to the accompanying drawings, the photoelectric conversion portion of each pixel P has at least a pixel electrode, a light-transmitting counter electrode, and a photoelectric conversion layer sandwiched between the pixel electrode and the counter electrode. The pixel electrode, the counter electrode, and the photoelectric conversion layer are stacked on the semiconductor substrate 110, for example. A plurality of pixel electrodes are arranged in the pixel region, for example, corresponding to each pixel P. In contrast, the counter electrode is provided, for example, in the form of a single electrode layer continuous between a plurality of pixels P. That is, the power supply for supplying voltage to the counter electrode and the supply voltage given by the power supply are, for example, common between a plurality of pixels P. In addition, depending on the resistance value of the counter electrode and the amount of current flowing, there may be a slight difference in potential between a plurality of pixels P. In addition, the electrode layer continuous between a plurality of pixels P may be either one or multiple in one imaging device 100. In the case where the electrode layer continuous between a plurality of pixels P is one in one imaging device, the voltage supplied to the counter electrodes of all pixels P can be controlled by one power supply. When there are a plurality of electrode layers continuous between a plurality of pixels P in one imaging device, for example, when the electrode layer is divided for each row of pixels P, a different voltage can be supplied to the counter electrode for each row. As with the counter electrode, a single continuous photoelectric conversion layer can also be shared among a plurality of pixels P with respect to the photoelectric conversion layer.

[0070] exist Figure 1 In the illustrated configuration, the imaging device 100 includes at least a row scanning circuit 120 connected to each pixel P via a row selection line R, and a detection circuit 130 connected to each pixel P via an output signal line S. The row scanning circuit 120 and the detection circuit 130 are disposed around a pixel region, for example.

[0071] exist Figure 1 In the example shown, a plurality of pixels P are arranged in a matrix of m rows and n columns. m and n represent independent natural numbers. Figure 1 The numbers with subscripts in the numbers of the row selection lines R and the output signal lines S in FIG. 1 represent the rows or columns of pixels P connected to the row selection lines R and the output signal lines S. The row selection lines R (R0 to R1) are connected to the pixel P. m－1 ) is provided in each row from row 0 to row m-1 of a plurality of pixels P, and is electrically connected to one or more pixels P belonging to the same row. Two or more row selection lines R may also be provided in each row. Output signal lines S (S0 to S1) n－1) is arranged in each column from column 0 to column n-1 of a plurality of pixels P, and is electrically connected to the output circuit of one or more pixels P belonging to the same column. As shown in the figure, the output signal lines S are respectively connected to the detection circuit 130. In addition, two or more output signal lines S may be arranged in the same column. In addition, Figure 1 Although not shown in the figure, other wirings such as reset signal lines described later may be provided for each row or column and electrically connected to the pixels P.

[0072] The detection circuit 130 may include, for example, a circuit for performing noise suppression signal processing represented by correlated double sampling, a sample-and-hold circuit, a circuit for performing analog-to-digital conversion, etc. A pixel signal representing an image of a subject is read out as an output of the detection circuit 130 .

[0073] The detection circuit 130 may also have a function of detecting the level of the output signal read from the pixel P via the output signal line S. For example, a reference line to which a predetermined voltage is applied during operation is connected to the detection circuit 130. The detection circuit 130 may, for example, have one or more comparators that output the level of the output signal from the pixel P of each column, that is, the comparison result of the voltage level of each output signal line S and the voltage level of the reference line. The comparison of the voltage level may be performed in the form of analog voltage comparison or in the form of digital value comparison. In addition, the detection circuit 130 may also supply voltage or current to a plurality of pixels P via the output signal line S at a timing when no signal detection is performed.

[0074] exist Figure 1 In the illustrated configuration, the imaging device 100 further includes a control circuit 140 , a voltage supply circuit 150 , and an image processing circuit 160 .

[0075] In addition, Figure 1 In the illustrated structure, the imaging device 100 includes a semiconductor substrate 110 and a substrate 210 different from the semiconductor substrate 110. Figure 1 In the example shown, a plurality of pixels P, a row scanning circuit 120, a detection circuit 130, and a control circuit 140 are formed on a semiconductor substrate 110, and a voltage supply circuit 150 and an image processing circuit 160 are formed on a substrate 210. The semiconductor substrate 110 is electrically connected to the substrate 210. In addition, the semiconductor substrate 110 and the substrate 210 are stacked, for example, in a manner such that the semiconductor substrate 110 is arranged on the upper side. The semiconductor substrate 110 and the substrate 210 are stacked, for example, using a substrate bonding technology. In this way, by forming the image processing circuit 160 on a substrate 210 different from the semiconductor substrate 110 on which the photoelectric conversion layer is stacked, the area of ​​the semiconductor substrate 110 can be reduced. Furthermore, by stacking the semiconductor substrate 110 and the substrate 210, the area of ​​the imaging device 100 can be reduced.

[0076] In addition, in the imaging device 100, as long as a plurality of pixels P are formed on the semiconductor substrate 110, the positions where other structures are formed are not particularly limited. The row scanning circuit 120, the detection circuit 130, the control circuit 140, the voltage supply circuit 150, and the image processing circuit 160 may be formed on the semiconductor substrate 110, or may be formed on the substrate 210. Alternatively, in each of the row scanning circuit 120, the detection circuit 130, the control circuit 140, the voltage supply circuit 150, and the image processing circuit 160, a part of the circuit may be formed on the semiconductor substrate 110, and another part of the circuit may be formed on the substrate 210. In addition, each of the row scanning circuit 120, the detection circuit 130, the control circuit 140, the voltage supply circuit 150, and the image processing circuit 160 may be formed in such a manner that at least a part of the circuit is formed on a substrate other than the semiconductor substrate 110 and the substrate 210, and the substrate or the like is electrically connected to the semiconductor substrate 110 and the substrate 210.

[0077] The control circuit 140 receives, for example, command data and a clock from outside the imaging device 100, and controls the entire imaging device 100. The control circuit 140 can be implemented, for example, by a microcontroller including one or more processors and a memory.

[0078] In addition, the control circuit 140 includes, for example, a timing generator, and supplies drive signals to the row scanning circuit 120, the detection circuit 130, the voltage supply circuit 150, and the like. Figure 1 In FIG. 1 , an arrow extending toward the control circuit 140 and an arrow extending from the control circuit 140 schematically represent an input signal to the control circuit 140 and an output signal from the control circuit 140 , respectively.

[0079] The voltage supply circuit 150 is electrically connected to each pixel P, for example, by being connected to a voltage line 151 connected to the counter electrode. The voltage supply circuit 150 supplies a predetermined voltage to the photoelectric conversion unit (specifically, the counter electrode) of each pixel P via the voltage line 151 when the imaging device 100 operates.

[0080] The voltage supply circuit 150 is configured, for example, to be able to switch at least two or more different voltages and apply them to the voltage line 151. The change in the voltage output from the voltage supply circuit 150 may be either step-by-step or continuous. The voltage supply circuit 150 is not limited to a specific power supply circuit, and may be a circuit that converts a voltage supplied from a power supply such as a battery into a prescribed voltage or a circuit that outputs one of a plurality of power supplies, or a circuit that generates a prescribed voltage. The voltage supply circuit 150 may also be a part of the above-mentioned row scanning circuit 120. The voltage supply circuit 150 supplies a voltage in a region where a photocurrent corresponding to a potential difference ΔV between electrodes of the photoelectric conversion unit described later changes linearly to the voltage line 151.

[0081] The image processing circuit 160 is electrically connected to the output of the detection circuit 130. The image processing circuit 160 corrects the signal from the detection circuit 130 and outputs the corrected signal. The image processing circuit 160 can be implemented by, for example, a DSP (Digital Signal Processor), an ISP (Image Signal Processor), an FPGA (Field-Programmable Gate Array), etc. The image processing circuit 160 performs signal processing such as offset addition, offset subtraction, gain correction, white balance correction, noise reduction, Bayer compensation, convolution operation, and edge emphasis. In addition, the image processing circuit 160 performs linear transformation signal processing. The functions of such an image processing circuit 160 can be implemented by a combination of a general processing circuit and software, or by hardware specially designed for such processing.

[0082] The image processing circuit 160 includes, for example, a memory 170. The memory 170 is a memory capable of storing digital information. The memory 170 stores, for example, a transformation table used in a linear transformation process described in detail later. The transformation table is, for example, a table that establishes a correspondence between a value before transformation (input value) and a value after transformation (output value) as a result of the transformation. The memory 170 is, for example, a non-volatile memory, but may also be a volatile memory. Alternatively, the memory 170 may be only a volatile memory by having a function of acquiring and storing data when the power supply to the camera device 100 is turned on. The memory 170 may also be provided in a portion other than the substrate 210 in the form of a chip or a package. In addition, the memory 170 may also be shared by the image processing circuit 160 and the control circuit 140.

[0083] [Exemplary Structure of Pixel P]

[0084] Next, an exemplary structure of the pixel P included in the imaging device 100 will be described.

[0085] Figure 2 It is a diagram showing an exemplary circuit configuration of the imaging device 100 according to the embodiment. Figure 2 from Figure 1 Four pixels P are taken out of the plurality of pixels P included in the pixel region shown and are schematically shown together with a row scanning circuit 120 , a detection circuit 130 , and a voltage supply circuit 150 .

[0086] Each pixel P includes a photoelectric conversion unit 10 and an output circuit 20 electrically connected to the photoelectric conversion unit 10. The photoelectric conversion unit 10 generates signal charges by receiving incident light. The output circuit 20 is a circuit for outputting a signal corresponding to the signal charges generated by the photoelectric conversion unit 10. Figure 2In the illustrated structure, the output circuit 20 includes a signal detection transistor 22, an address transistor 24, and a reset transistor 26. The signal detection transistor 22, the address transistor 24, and the reset transistor 26 are, for example, field effect transistors formed on the semiconductor substrate 110. In the following, unless otherwise specified, an example in which an N-channel MOSFET (Metal Oxide Semiconductor Field Effect Transistor) is used as the transistor is described.

[0087] As in Figure 2 As schematically shown in FIG. 1 , the photoelectric conversion unit 10 includes an opposing electrode 11 as an example of a first electrode, a pixel electrode 12 as an example of a second electrode, and a photoelectric conversion layer 13 sandwiched between the opposing electrode 11 and the pixel electrode 12. The opposing electrode 11 is light-transmissive. In addition, the term "light-transmissive" in this specification means that at least a portion of light of a wavelength that can be absorbed by the photoelectric conversion layer 13 is transmitted, and it is not necessary to transmit light in the entire wavelength range of visible light.

[0088] The photoelectric conversion layer 13 absorbs light and generates signal charges. Specifically, the photoelectric conversion layer 13 receives incident light and generates pairs of holes and electrons. That is, the signal charge is one of the holes and the electrons. The signal charge is captured by the pixel electrode 12 and accumulated in the charge accumulation region including the node FD. For example, when holes are used as signal charges, the holes are captured by the pixel electrode 12. Electrons, which are charges of the opposite polarity to the signal charge, are captured by the counter electrode 11.

[0089] As shown in the figure, the counter electrode 11 of each pixel P is electrically connected to the voltage line 151. Therefore, the voltage supply circuit 150 can apply a voltage to the counter electrodes 11 of the plurality of pixels P at the same time via the voltage line 151. Figure 2 The figure shows that the voltage line 151 is connected to each counter electrode 11 of the plurality of pixels P. However, as described above, the counter electrode 11 of each pixel P is, for example, a single light-transmitting electrode continuous between the plurality of pixels P, and the voltage line 151 does not need to be a wiring line branched into a plurality of lines.

[0090] On the other hand, the pixel electrode 12 is electrically separated for each pixel P. As shown in the figure, the pixel electrode 12 of each pixel P is connected to the gate of the signal detection transistor 22 of the corresponding output circuit 20 via the node FD. The source of the signal detection transistor 22 is connected to the corresponding output signal line S via the address transistor 24. The drain of the signal detection transistor 22 is connected to the power line 32. When the power line 32 is in operation, for example, a power supply voltage VDD is applied to it, so that it functions as a source follower power supply. By functioning as a source follower power supply through the power line 32, the signal detection transistor 22 amplifies and outputs the potential of the node FD. The power supply voltage VDD is, for example, about 3.3V, but is not particularly limited.

[0091] The gate of the address transistor 24 is connected to a row selection line R. The row scanning circuit 120 controls the voltage level applied to the row selection line R to switch the address transistor 24 on and off, and can read signals from the pixels P belonging to the selected row to the output signal line S.

[0092] exist Figure 2 In the example shown, the output circuit 20 includes a reset transistor 26. One of the drain and source of the reset transistor 26 is connected to the node FD. The node FD electrically connects the photoelectric conversion unit 10 and the gate of the signal detection transistor 22. The other of the drain and source of the reset transistor 26 is connected to a reset voltage line 36. A predetermined reset voltage VRST is applied to the reset voltage line 36 when the imaging device 100 is in operation. As shown in the figure, the reset signal line 38 is connected to the gates of the reset transistors 26 of a plurality of pixels P belonging to the same row, for example.

[0093] exist Figure 2 In the example shown, the reset signal line 38 is connected to the row scanning circuit 120. The row scanning circuit 120 turns on the reset transistor 26 in units of rows of a plurality of pixels P by controlling the voltage level applied to the reset signal line 38. Thus, the potential of the node FD of the pixel P in which the reset transistor 26 is turned on can be reset to VRST.

[0094] When the imaging device 100 is in operation, a predetermined voltage is applied from the voltage supply circuit 150 to the counter electrode 11 via the voltage line 151, thereby generating a potential difference ΔV between the counter electrode 11 and the pixel electrode 12. Here, the voltage supply circuit 150 applies a voltage to the counter electrode 11 such that the potential of the counter electrode 11 is higher than the potential of the pixel electrode 12, with reference to the pixel electrode 12. By making the potential of the counter electrode 11 higher than the potential of the pixel electrode 12, charges with positive polarity, such as holes, among positive charges and negative charges generated in the photoelectric conversion layer 13 by the incidence of light can be collected by the pixel electrode 12 as signal charges. In the following, unless otherwise specified, an example in which holes are used as signal charges is described.

[0095] In the present embodiment, since holes are used as signal charges, if the voltage applied from the voltage supply circuit 150 to the voltage line 151 during exposure is set to V1, V1 is used so that the potential of the opposing electrode 11 is higher than the potential of the pixel electrode 12. In addition, the initial potential of the pixel electrode 12 during exposure is determined by the above-mentioned reset voltage VRST supplied via the reset transistor 26. That is, since the node FD and the pixel electrode 12 have the same potential, the potential difference ΔV between the pixel electrode 12 and the opposing electrode 11 just after reset is (V1-VRST). As described above, in the present embodiment, it is an example of using holes as signal charges, and a specific value of a voltage that becomes (V1-VRST)>0 during the exposure period can be selected for V1. In addition, as the reset voltage VRST, for example, a positive voltage of 0V or near 0V can be used.

[0096] Figure 3 2 is a cross-sectional view schematically showing a cross-sectional structure of one pixel among a plurality of pixels P according to the present embodiment.

[0097] like Figure 3 As shown, the counter electrode 11 of the photoelectric conversion unit 10 is opposed to the pixel electrode 12 via the photoelectric conversion layer 13 and is located above the pixel electrode 12. The counter electrode 11 is, for example, located on the side of the imaging device 100 closer to the pixel electrode 12 than the pixel electrode 12, where light from the subject is incident. The counter electrode 11 is, for example, formed of a transparent conductive material such as ITO (Indium Tin Oxide). As described above, the counter electrode 11 is, for example, provided in the form of a single electrode layer that is continuous across a plurality of pixels P. On the main surface of the counter electrode 11 on the side opposite to the photoelectric conversion layer 13 side, an optical filter 42 such as a color filter, a microlens 44, and a sealing film 46, etc., can be stacked.

[0098] The photoelectric conversion layer 13 located between the counter electrode 11 and the pixel electrode 12 is stacked on the semiconductor substrate 110. With such a structure, the photoelectric conversion unit 10 having photoelectric conversion characteristics described later can be easily formed. The photoelectric conversion layer 13 is formed of, for example, an organic material or an inorganic material such as amorphous silicon. The photoelectric conversion layer 13 receives light incident through the counter electrode 11 and generates excitons by photoelectric conversion, specifically, generates pairs of holes and electrons. The photoelectric conversion layer 13 may also include both a layer composed of an organic material and a layer composed of an inorganic material. In addition, when an organic material is used in the photoelectric conversion layer 13, it may also be set as a layer formed by mixing multiple materials, that is, a bulk heterojunction layer. Like the counter electrode 11, the photoelectric conversion layer 13 is provided in the form of a single photoelectric conversion film that is continuous across multiple pixels P, for example.

[0099] The pixel electrode 12 is located closer to the semiconductor substrate 110 than the photoelectric conversion layer 13, and is electrically separated from the pixel electrodes 12 of other adjacent pixels P by being spatially separated from them. An interlayer insulating layer 50 is provided between adjacent pixel electrodes 12, for example. The pixel electrode 12 is formed of, for example, a metal such as aluminum or copper, a metal nitride, a metal nitride, or polysilicon to which conductivity is imparted by doping with impurities.

[0100] The photoelectric conversion unit 10 may also include a charge blocking layer 14. The charge blocking layer 14 has the function of allowing one of holes and electrons to pass through, while blocking the movement of the other by using a potential barrier. For example, when blocking electrons, a material with a lower electron affinity than the photoelectric conversion layer 13 is selected, and when blocking holes, a material with a higher ionization energy than the photoelectric conversion layer 13 is selected. Figure 3 In the example shown, a charge blocking layer 14 is disposed between the photoelectric conversion layer 13 and the pixel electrode 12. In the present embodiment, the charge blocking layer 14 is an electron blocking layer having a function of blocking electrons of opposite polarity to the signal charge. Although not shown, the photoelectric conversion unit 10 may also have a hole blocking layer having a function of blocking holes as signal charges between the photoelectric conversion layer 13 and the counter electrode 11 in addition to or in place of the charge blocking layer 14.

[0101] By providing the photoelectric conversion unit 10 with a charge blocking layer 14, the charge injection from the pixel electrode 12 to the photoelectric conversion layer 13 is suppressed, and the dark current is reduced. This effect improves the signal detection accuracy of the imaging device 100, especially the detection accuracy in areas with less light. In addition, the higher the detection accuracy, the better the performance of the imaging device 100, but it can be used without problems when higher detection accuracy is not required. In addition, in the case where a sufficient energy barrier is formed between the photoelectric conversion layer 13 and the electrode material used, the dark current can be reduced even if the charge blocking layer 14 is omitted. In other words, the charge blocking layer 14 is not necessarily indispensable in the imaging device 100, and the photoelectric conversion unit 10 may not have the charge blocking layer 14.

[0102] As the semiconductor substrate 110, a semiconductor substrate containing silicon is used. Here, an example of using a P-type silicon (Si) substrate as the semiconductor substrate 110 is described. The semiconductor substrate 110 may also be an insulating substrate having a semiconductor layer on the surface. The semiconductor substrate 110 may have an impurity region and an element separation region. Although omitted in the figure, the element separation region is provided when, for example, the output circuit 20 provided for each pixel P is electrically separated between the pixels P. Figure 3 The impurity regions 22d, 22s, and 24s shown are, for example, N-type diffusion regions.

[0103] The signal detection transistor 22 includes impurity regions 22d and 22s in the impurity region, a gate insulating layer 22x on the semiconductor substrate 110, and a gate electrode 22g on the gate insulating layer 22x. The impurity region 22d functions as a drain region of the signal detection transistor 22. The impurity region 22s functions as a source region of the signal detection transistor 22. In the illustrated structure, the address transistor 24 shares the impurity region 22s with the signal detection transistor 22. The address transistor 24 includes a gate insulating layer 24x on the semiconductor substrate 110, a gate electrode 24g on the gate insulating layer 24x, and impurity regions 22s and 24s. The impurity region 24s functions as a source region of the address transistor 24.

[0104] Regarding the reset transistor 26 Figure 3 Although not shown in the figure, the semiconductor device 100 also includes an impurity region, a gate insulating layer on the semiconductor substrate 110, and a gate electrode on the gate insulating layer. For example, the reset voltage line 36 described above is connected to one side of the impurity region.

[0105] The power supply line 32 is connected to the impurity region 22d as the drain region of the signal detection transistor 22. The output signal line S is connected to the impurity region 24s as the source region of the address transistor 24. The row selection line R is connected to the gate electrode 24g of the address transistor 24.

[0106] The interlayer insulating layer 50 covers the signal detection transistor 22, the address transistor 24, the reset transistor 26, and other wiring layers and contact portions formed on the semiconductor substrate 110. The photoelectric conversion unit 10 of each pixel P is supported by the interlayer insulating layer 50. The interlayer insulating layer 50 includes a plurality of insulating layers each formed of, for example, silicon oxide, silicon nitride, or a polymer film.

[0107] The node FD includes, for example, the wiring and the contact portion between the gate electrode 22g and the pixel electrode 12. Figure 2 As described above, the node FD is connected to the source or drain of the reset transistor 26. The impurity region that functions as the source or drain of the reset transistor 26 is N-type, and forms a PN junction with the P-well in the semiconductor substrate 110. Therefore, the impurity region functions as a charge storage capacitor that temporarily accumulates holes that are signal charges. The node FD is floating as long as the reset transistor 26 is not turned on, so as the signal charge accumulates in the node FD, the potential of the node FD and the pixel electrode 12 connected to the node FD rises.

[0108] [Exemplary Photoelectric Conversion Characteristics of Photoelectric Conversion Section 10]

[0109] Next, the relationship between the photoelectric conversion characteristics of the photoelectric conversion unit 10 and the voltage supplied from the voltage supply circuit 150 to the voltage line 151 will be described. As described above, unless otherwise specified, an example in which holes are used as signal charges will be described below.

[0110] Figure 4 Schematically shows an example of the photoelectric conversion characteristics of the photoelectric conversion unit 10 according to the present embodiment. Figure 4 The current-voltage characteristics (I-V characteristics) of the photoelectric conversion unit 10 are shown in FIG. Figure 4 In FIG. 1 , the horizontal axis represents the potential difference ΔV between the counter electrode 11 and the pixel electrode 12. In the present embodiment, the potential difference ΔV is equal to, for example, the bias voltage applied between the counter electrode 11 and the pixel electrode 12. In addition, ΔV is assumed to be positive when the potential of the counter electrode 11 is higher than that of the pixel electrode 12. Figure 4 In FIG. 1 , the vertical axis represents the current flowing to the pixel electrode 12 when light is incident on the photoelectric conversion layer 13, that is, the current flowing between the counter electrode 11 and the pixel electrode 12. Hereinafter, this current is referred to as the photocurrent. As long as the incident light amount and the potential difference ΔV are constant, the photocurrent is constant except for the random change factors such as shot noise. In other words, if the potential of the counter electrode 11 or the pixel electrode 12 changes, and the potential difference ΔV changes, the photocurrent changes to a current value corresponding thereto.

[0111] like Figure 4 As shown in the example, in this embodiment, the photocurrent in the photoelectric conversion layer 13 starts to flow at a certain potential difference ΔV or more. In addition, the photocurrent generally increases in a convex curve shape with respect to the increase of the potential difference ΔV between the counter electrode 11 and the pixel electrode 12. Figure 4 The photoelectric conversion unit 10 having the photoelectric conversion characteristics shown can be realized by using, for example, an organic photoelectric conversion material or a combination of an organic photoelectric conversion material and other materials generally used to form the photoelectric conversion layer 13. Alternatively, the photoelectric conversion layer 13 can be formed using an inorganic photoelectric conversion material.

[0112] exist Figure 4 In the example shown, the photocurrent increases in proportion to the potential difference ΔV in a region where the potential difference ΔV is relatively low, and in a region where the potential difference ΔV is relatively high above the region, the photocurrent increases at a lower rate as the potential difference ΔV increases, and increases relatively gently with respect to the potential difference ΔV. In this specification, the voltage range in which the photocurrent increases relatively steeply with respect to the potential difference ΔV between the counter electrode 11 and the pixel electrode 12 is referred to as the first voltage range or linear region, and the voltage range in which the photocurrent increases relatively gently with respect to the potential difference ΔV is referred to as the second voltage range or saturation region.

[0113] In the linear region, the photocurrent flowing between the counter electrode 11 and the pixel electrode 12 changes linearly with respect to the potential difference ΔV, and can be linearly approximated. The linear region is a voltage range after the photocurrent rises in the photocurrent characteristic, and is a voltage range in which the photocurrent flowing between the counter electrode 11 and the pixel electrode 12 changes linearly with respect to the potential difference ΔV. The range of the linear region can be set to a range of potential difference ΔV in which the deviation of the photoelectric conversion characteristic from the linear approximation line is within 10%, for example. That is, in this specification, the linear region is a voltage range in which the photocurrent changes substantially linearly with respect to the potential difference ΔV, and may also include a voltage range in which the photocurrent characteristic deviates from the linear approximation line. In addition, the linear region may be a range of potential difference ΔV in which the deviation of the photoelectric conversion characteristic from the linear approximation line is 5% or less, or a range of potential difference ΔV of 3% or less. In addition, the linear region is, for example, a voltage range in which the photocurrent flowing between the counter electrode 11 and the pixel electrode 12 first changes linearly with respect to the potential difference ΔV when the potential difference ΔV is made higher than the potential difference ΔV at which the photocurrent starts to flow. Furthermore, the linear region is for example Figure 4 The photocurrent characteristics of the example shown include a voltage range of the potential difference ΔV in which the slope of the photocurrent with respect to the potential difference ΔV is the maximum.

[0114] In addition, the linear region is a voltage range between the potential difference ΔV at which the photocurrent starts to flow and the saturation region. For example, the linear region is a voltage range between an inflection point in the photocurrent characteristic where the photocurrent starts to flow because the potential difference ΔV becomes larger than zero and the photocurrent starts to flow and an inflection point where the increase ratio of the photocurrent decreases as the potential difference ΔV increases. In addition, the linear region may be a voltage range from the potential difference ΔV at which the photocurrent starts to flow to a potential difference ΔV in a range where the linearity of the photocurrent with respect to the potential difference ΔV is maintained.

[0115] As described above, the linear region of the present embodiment does not include an extremely narrow voltage region such as an extremely small voltage range in the photocurrent characteristics with respect to the potential difference ΔV, that is, an extremely narrow voltage region where the linear approximation line is almost a tangent. Therefore, the voltage range of the linear region has a range of at least 100 mV or more, and may have a range of 500 mV or more, or may have a range of 1 V or more.

[0116] In the saturation region, the photocurrent that flows does not easily increase as the potential difference ΔV increases. In the saturation region, the amount of change in the photocurrent with respect to the potential difference ΔV is smaller than that in the linear region. In addition, in this specification, the saturation region is not a region that includes only the voltage range in which the photocurrent is completely saturated and does not increase even if the potential difference ΔV increases, but a voltage range in which the photocurrent is substantially saturated. In addition, the saturation region is a voltage range of a potential difference ΔV larger than that in the linear region.

[0117] In addition, in the photoelectric conversion characteristics of the photoelectric conversion unit 10, when the potential difference ΔV becomes larger in the negative direction, the same change as the photocurrent on the positive side mentioned above may also occur in the photocurrent in the negative direction, and when electrons are used as signal charges, there may also be a linear region and a saturation region.

[0118] [Operation of the Imaging Device 100]

[0119] Next, the operation of the imaging device 100 will be described. Specifically, the operation of the imaging device 100 in which the signal from the pixel P is corrected by the image processing circuit 160 and then output will be described.

[0120] A signal corresponding to the amount of signal charge generated by the photoelectric conversion section 10 and captured by the pixel electrode 12 during the exposure period of the imaging device 100 is output from the output circuit 20 of each pixel P during the readout period. The detection circuit 130 detects the signal output from the output circuit 20, performs noise suppression signal processing and analog-to-digital conversion on the detected signal, and outputs it to the image processing circuit 160. The detection circuit 130 outputs a signal corresponding to a change in the potential of the pixel electrode 12, which is a change corresponding to the amount of incident light on the photoelectric conversion section 10.

[0121] The voltage supply circuit 150 supplies the voltage V1 such that the potential difference ΔV between the pixel electrode 12 and the counter electrode 11 is within the above-mentioned linear region to the counter electrode 11 via the voltage line 151 during exposure. The voltage V1 is an example of the first voltage. Thus, if light is incident on the photoelectric conversion unit 10, the charge generated by the photoelectric conversion is accumulated at the node FD, and the potential of the pixel electrode 12 rises. As a result, in the linear region, the above-mentioned potential difference ΔV becomes smaller and the photocurrent decreases, and the node FD is not easily saturated, so the dynamic range can be effectively expanded. In addition, when the amount of charge accumulated to the node FD is small, the change in the above-mentioned potential difference ΔV is small, and it can be regarded that the photocurrent is constant, that is, the sensitivity is constant. At this time, the signal output by the detection circuit 130 changes linearly. On the other hand, since the more the signal charge accumulates at the node FD, the less the photoelectric current, the signal output by the detection circuit 130 no longer changes linearly with respect to the incident light amount. Therefore, as described below, the signal output by the detection circuit 130 is corrected by the image processing circuit 160.

[0122] When the potential of the node FD is set to VFD during exposure, VFD can be expressed by the following (Formula 3).

[0123] [Formula 6]

[0124]

[0125] Here, CFD is the capacitance of the node FD, t is the exposure period, and I is the photocurrent. In addition, VRST is the voltage supplied to the node FD via the reset transistor 26 when resetting the potential of the node FD, and has nothing to do with the signal caused by the photoelectric conversion. Therefore, for simplicity, VRST=0 is assumed below.

[0126] In the linear region, the photocurrent is proportional to the potential difference ΔV=V1-VFD. In addition, its proportionality coefficient is, for example, sensitivity, which is proportional to the amount of incident light. That is, if α is set as a constant, the photocurrent I is expressed by the following (Formula 4). In (Formula 4), for simplicity, it is assumed that the slice is 0.

[0127] [Formula 7]

[0128] I=α(V1-VFD)·L (Formula 4)

[0129] Here, L is the light intensity to the photoelectric conversion unit 10. Substituting (Equation 4) into (Equation 3) and solving the differential equation, the following (Equation 5) can be obtained. For simplicity, (Equation 5) is derived assuming that the light intensity L is constant during the exposure period.

[0130] [Formula 8]

[0131]

[0132] The potential VFD represented by the obtained (Formula 5) is a signal component based on the charge after photoelectric conversion, and the detection circuit 130 detects a signal corresponding to the potential VFD from the output circuit 20 of the pixel P. Therefore, it can be seen that by using the imaging device 100 in a manner that causes the potential difference ΔV between the pixel electrode 12 and the counter electrode 11 to operate in a linear region, the signal output of the pixel P is no longer linear with respect to the light intensity L and the exposure time t. In addition, the potential VFD rises due to the accumulation of holes as signal charges, but if it becomes a potential difference ΔV where the photocurrent is 0, it will no longer rise even if light is further incident on the photoelectric conversion unit 10. As a result, the signal detected by the detection circuit 130 reaches the upper limit value. Therefore, if the output value of the output circuit 20 of the pixel P is y, and the maximum value of the output value is ymax, the output value y of the output circuit can be expressed by the following (Formula 6).

[0133] [Formula 9]

[0134]

[0135] Here, if the logarithms of both sides of (Formula 6) are taken and sorted, the following (Formula 7) is obtained.

[0136] [Formula 10]

[0137]

[0138] The output value y of the output circuit 20 and the maximum value ymax of the output value described above can be treated as the output value y and the maximum value ymax of the signal output by the detection circuit 130 from the output circuit 20 to the image processing circuit 160. The output value y and the maximum value ymax of the signal output by the detection circuit 130 are, for example, digital values ​​after analog-to-digital conversion. Here, if the left side of (Formula 7) is defined by the output value Y after the conversion, the output value Y after the conversion becomes linear with respect to the exposure time t and the light intensity L as shown on the right side. That is, if the output value y of the signal detected by the original detection circuit 130 is converted into the output value Y according to the left side of (Formula 7), even if the imaging device 100 is operated in such a way that the potential difference ΔV between the pixel electrode 12 and the counter electrode 11 becomes a linear region, the output after the conversion becomes linear with respect to the exposure time t and the light intensity L. In addition, since the exposure time t×light intensity L corresponds to the incident light amount of the photoelectric conversion unit 10, the output after the conversion changes linearly with respect to the incident light amount to the photoelectric conversion unit 10. Therefore, in the present embodiment, the image processing circuit 160 performs conversion processing on the signal output from the detection circuit 130 based on a conversion function represented by the following (Equation 8), for example.

[0139] [Formula 11]

[0140]

[0141] Here, δ is a proportionality constant. In addition, y is an input value of the above-mentioned transformation function, Y is an output value of the above-mentioned transformation function, and ymax can also be said to be the maximum value of the input value of the above-mentioned transformation function.

[0142] The maximum value ymax of the output value output by the detection circuit 130 is, for example, a signal value corresponding to the potential VFD when the node FD is saturated, but may be replaced by a saturated signal value corresponding to the number of output bits of the analog-to-digital conversion performed by the detection circuit 130 .

[0143] The memory 170 may also store a transformation table including the transformation results of the transformation function based on (Formula 8). The memory 170 stores, for example, a plurality of transformation tables corresponding to a plurality of pixels P, respectively. The transformation table is, for example, a transformation table in which the transformation results (transformed output values) are corresponding to all output values ​​of the detection circuit 130. In this case, the image processing circuit 160 corrects the signal based on the transformation table. Specifically, the image processing circuit 160 compares the output value from the detection circuit 130 input with the table value stored in the memory 170, and transforms the output value. Thus, the processing load of the image processing circuit 160 can be reduced.

[0144] The image processing circuit 160 performs correction based on the conversion function represented by such (Formula 8), and the influence of parameters such as temperature change, individual difference of the camera device, and inter-pixel deviation in the pixel area is included in the output value y before the conversion, so the proportional constant δ can be set to a unique value. Therefore, the image processing circuit 160 can simply perform linear correction without considering the influence of the parameter. In addition, in the conversion processing based on (Formula 8), when using the value reference using the LUT, it is no longer necessary to prepare a table according to the number of parameters such as the above-mentioned temperature change, so the memory usage can be reduced.

[0145] As described above, the image processing circuit 160 corrects the signal from the detection circuit 130 based on the transformation function derived from the potential change of the pixel electrode 12 relative to the incident light amount to the photoelectric conversion unit 10 when the potential difference ΔV is in the linear region, so that the output changes linearly with respect to the incident light amount to the photoelectric conversion unit 10. In this way, even when the signal from the detection circuit 130 does not change linearly with respect to the incident light amount to the photoelectric conversion unit 10, the image processing circuit 160 corrects the signal using the transformation function so that the output becomes linear with respect to the incident light amount to the photoelectric conversion unit 10. At this time, the transformation function is derived using the linearity of the photocurrent with respect to the potential difference ΔV, so it is easy to derive and the transformation function itself becomes simple. Therefore, it is possible to realize the imaging device 100 having the image processing circuit 160 that can perform linear correction on the signal in a simple manner with respect to the incident light amount.

[0146] In addition, the voltage supply circuit 150 supplies the voltage V1 such that the potential difference ΔV between the pixel electrode 12 and the opposing electrode 11 is in the above-mentioned linear region to the opposing electrode 11 via the voltage line 151, for example, at the start time of exposure. In addition, the voltage supply circuit 150 may not necessarily apply the voltage V1 such that the potential difference ΔV between the pixel electrode 12 and the opposing electrode 11 is in the above-mentioned linear region to the opposing electrode 11 at the start time of exposure. That is, even if the voltage supply circuit 150 applies the voltage V1 such that the potential difference ΔV between the pixel electrode 12 and the opposing electrode 11 is in the above-mentioned saturation region to the opposing electrode 11 at the start time of exposure, the same effect can be achieved by accumulating the signal charge at the node FD during exposure so that the potential difference ΔV between the pixel electrode 12 and the opposing electrode 11 is changed to the above-mentioned linear region. That is, the voltage supply circuit 150 supplies the voltage V1 to the counter electrode 11 so that the voltage range that the potential difference ΔV between the pixel electrode 12 and the counter electrode 11 can take according to the amount of incident light on the photoelectric conversion unit 10 includes at least a part of the linear region. In addition, for example, the user of the imaging device 100 can switch the voltage V1 supplied by the voltage supply circuit 150 between the voltage V1 such that the potential difference ΔV between the pixel electrode 12 and the counter electrode 11 is in the linear region and the voltage V2 such that the potential difference ΔV is in the saturation region at any timing.

[0147] In addition, the reason why the output of the output circuit 20 is not linear with respect to the incident light amount per exposure time and per unit time, that is, the incident light amount during the exposure period, when the imaging device 100 is operated in a manner such that the potential difference ΔV between the pixel electrode 12 and the counter electrode 11 is in a linear region is that the potential of the node FD rises due to the accumulation of signal charges, and the potential difference ΔV of the photoelectric conversion unit 10 decreases. Therefore, under the conditions of low light intensity or short exposure time, or both, when the output value y of the detection circuit 130 is small, the potential difference ΔV of the photoelectric conversion unit 10 hardly changes, and the reduction of the photocurrent is also small. That is, in this case, the output value y can be regarded as linear with respect to the incident light amount. At this time, the output value Y after the conversion can be regarded as consistent with the output value y before the conversion. Therefore, the proportional constant δ can be obtained by the following (Formula 9) within the range where the output value y of the detection circuit 130 can be regarded as linear with respect to the incident light amount. Assuming that the output value y of the detection circuit 130 is consistent with the output value Y after the conversion, (Formula 9) is derived by transforming (Formula 8).

[0148] [Formula 12]

[0149]

[0150] Figure 5This is a diagram showing the relationship between the ratio of the output value y of the detection circuit 130 to the maximum value ymax of the output value of the detection circuit 130 and the error amount before and after output conversion when the imaging device 100 is operated so that the potential difference ΔV between the pixel electrode 12 and the counter electrode 11 is in the linear region. Figure 5 In FIG. 1 , the horizontal axis represents the ratio of the output value y of the detection circuit 130 to the maximum value ymax of the output value of the detection circuit 130 (hereinafter, also referred to as the output value ratio). Figure 5 In the equation 8, the vertical axis represents the ratio of the difference between the output value converted by the output conversion method and the output value when the output value of the detection circuit 130 is considered to be linear (hereinafter also referred to as conversion error). Figure 5 This is a graph showing the degree to which the output values ​​before and after the conversion based on (Equation 8) match each other with respect to the output value ratio of the detection circuit 130.

[0151] The range in which the output value y of the detection circuit 130 is considered to be linear with respect to the incident light amount is, for example, a condition in which the conversion error is less than 10%. Figure 5 As can be seen from the figure, the range is a range where the output value y of the detection circuit 130 is 17.5% or less relative to its maximum value ymax. In addition, more preferably, the range where the output value y of the detection circuit 130 is considered to be linear relative to the incident light amount may be a range where the conversion error is 5% or less. In this case, the range is a range where the output value y of the detection circuit 130 is 9.3% or less relative to its maximum value ymax.

[0152] Therefore, the image processing circuit 160 may also calculate the proportional constant δ according to (Formula 9), for example, using an output value y that is less than 10% of the maximum value ymax of the output value. Thus, the proportional constant δ can be simply calculated. The image processing circuit 160, for example, obtains the output value y of one or more signals output by actually driving the pixel P, and calculates the proportional constant δ using the obtained output value y. Thus, the image processing circuit 160 can calculate the proportional constant δ only based on the output value y output from the detection circuit 130, so the calculation of the proportional constant δ can be simplified. When the output values ​​y of a plurality of signals are used, for example, the proportional constant δ calculated based on the respective output values ​​y is averaged.

[0153] In addition, from the perspective of suppressing the influence of reduced accuracy of the output value y due to the influence of noise, etc., the output value y used in the calculation of the proportional constant δ can be greater than 0.5% of the maximum output value ymax, or greater than 1% of the maximum output value ymax.

[0154] The image processing circuit 160 stores the calculated proportional constant δ and / or the conversion result based on (Formula 8) using the calculated proportional constant δ in the memory 170. In addition, the image processing circuit 160 corrects the signal from the detection circuit 130 based on (Formula 8) using the following proportional constant δ, for example, wherein the proportional constant δ is calculated according to (Formula 9) using the output value y that is less than 10% of the maximum value ymax of the output value.

[0155] The proportional constant δ and the conversion result based on (Equation 8) using the proportional constant δ that can be stored in the memory 170 can be updated at any timing. For example, when the power of the camera device 100 is turned on, in operation or in maintenance mode, one or more output values ​​y can be automatically or manually obtained, the proportional constant δ can be recalculated based on the obtained output value y and (Equation 9), and the conversion result of (Equation 8) can be recalculated using the recalculated proportional constant δ. The proportional constant δ and the conversion table value including the conversion result based on (Equation 6) using the proportional constant δ stored in the memory 170 can be updated to the recalculated proportional constant δ and the conversion result. In addition, the calculation method of the proportional constant δ is not limited to the above example, and the proportional constant δ calculated without using the above (Equation 9) can also be used for the correction of the image processing circuit 160. In addition, the proportional constant δ and the conversion table including the conversion result based on (Equation 6) using the proportional constant δ that are not calculated by the image processing circuit 160 but calculated by an external computer or user can also be stored in the memory 170.

[0156] In addition, the memory 170 has a capacity of a bit number greater than the output bit number of the detection circuit 130 as input data to the image processing circuit 160, for example. For example, in the case where the analog-to-digital conversion of the detection circuit 130 is performed with 12 bits, the amount of data after the conversion based on (Equation 8) may become 14 bits or more. Furthermore, if the number of bits below the decimal point is included, the amount of data after the conversion may also become 20 bits or more. The memory 170 has a capacity of a bit number that can store it with sufficient accuracy, for example.

[0157] In this specification, correction of the output value of the signal from the detection circuit 130 based on the conversion function such as the above (Formula 8) is also referred to as linear conversion processing.

[0158] Next, the flow of the signal correction process in the image processing circuit 160 will be described. Figure 6 FIG. 1 is a flowchart showing an example of a process flow performed by the image processing circuit 160. The image processing circuit 160 performs the process of performing the image processing circuit 160 according to the following example: Figure 6 The process exemplarily shown in , corrects the signal output from the detection circuit.

[0159] like Figure 6 As shown, the image processing circuit 160 first performs defect correction on the signal from the detection circuit 130 (step S10). In the defect correction, for example, the signal of an abnormal pixel P that does not output a signal corresponding to the amount of incident light to the photoelectric conversion unit 10 is compensated based on the signals from the pixels P surrounding the abnormal pixel P. For example, the average value of the signals of the surrounding pixels P is set to the signal value of the abnormal pixel P. The abnormal pixel P is, for example, a pixel P that always outputs a value near the upper limit or a value near the lower limit. In the defect correction, the signals of the pixels P other than the abnormal pixel P are not specially processed. In addition, the image processing circuit 160 can also omit the defect correction.

[0160] Next, the image processing circuit 160 performs the above-mentioned linear transformation processing on the signal after the defect correction in step S10 (step S20). In this way, the image processing circuit 160 performs the linear transformation processing when performing defect correction, for example, after the defect correction. Thus, the linear transformation processing is also performed on the signal of the pixel P that is compensated according to the signals of the surrounding pixels P through the defect correction. Therefore, when the image processing circuit 160 performs the linear transformation processing using the transformation function represented by (Formula 8), with respect to the signal of the pixel P after the defect correction, the input value y of the transformation function is the signal value after the defect correction, and with respect to the signal of the pixel P after the defect correction is not performed, the input value y of the transformation function is the signal value output by the detection circuit 130.

[0161] Next, the image processing circuit 160 performs gain correction (step S30) and gamma correction (step S40) on the signal after the linear transformation processing in step S20. In addition, the gain correction is, for example, a color correction such as white balance correction. The gamma correction is a correction used to match the dynamic range on the display of the image. In this way, when the image processing circuit 160 performs gain correction and gamma correction, it performs gain correction and gamma correction after the linear transformation processing. Thus, the linear transformation processing is corrected so that the signal is linearly transformed with respect to the incident light amount to the photoelectric conversion unit 10, so that the gain correction and gamma correction can be correctly performed on the signal after the linear transformation processing. In addition, in the case of the camera device 100 that obtains a monochrome image without providing a color filter, for example, the image processing circuit 160 can omit the gain correction of step S30 such as white balance correction. In addition, regarding the gamma correction, the user of the camera device 100 can also switch on and off at any timing. At this time, if the gamma correction is set to off, the gamma correction of step S40 can be omitted. That is, the image processing circuit 160 may not perform at least one of step S30 and step S40.

[0162] (Other embodiments)

[0163] As mentioned above, although the imaging device and the imaging method according to the present disclosure have been described based on the embodiments, the present disclosure is not limited to these embodiments.

[0164] For example, in the above embodiment, an example of using holes as signal charges is described, but the signal charges may also be electrons. In the case of using electrons as signal charges, the voltage supply circuit 150 applies a voltage to the opposing electrode 11 such that the potential of the opposing electrode 11 is lower than the potential of the pixel electrode 12, with reference to the pixel electrode 12. As a result, the electrons are captured by the pixel electrode 12. In addition, in this case, by making the photoelectric conversion unit 10 have a photoelectric conversion characteristic in which the photocurrent changes linearly with respect to the potential difference ΔV between the opposing electrode 11 and the pixel electrode 12, the image processing circuit 160 can perform signal correction such as the linear conversion process described above.

[0165] In addition, for example, in the above-mentioned embodiment, the image processing circuit 160 performs linear transformation processing based on the transformation function represented by the above-mentioned (Formula 8), but the present invention is not limited to this. The transformation function used in the linear transformation processing can also be derived by adding parameters different from the parameters described above and represented by a formula other than (Formula 8).

[0166] In the above embodiment, for example, the image processing circuit 160 performs linear transformation using the transformation table stored in the memory 170, but the present invention is not limited thereto. The image processing circuit 160 may perform linear transformation by processing such as arithmetic processing that does not use the transformation table.

[0167] Furthermore, the imaging device may not include all of the components described in the above embodiments, and may be configured only with components for performing target operations.

[0168] Furthermore, in the above-described embodiment, the processing executed by a specific processing unit such as a control circuit or an image processing circuit may be executed by another processing unit. Furthermore, the order of a plurality of processing may be changed, or a plurality of processing may be executed in parallel.

[0169] In addition, the global or specific aspects of the present disclosure may also be implemented by a system, device, method, integrated circuit, computer program, or a computer-readable CD-ROM or other recording medium. In addition, the present disclosure may also be implemented by any combination of a system, device, method, integrated circuit, computer program, and recording medium.

[0170] For example, the present disclosure may be implemented as an imaging device of the above-mentioned embodiment, or as a processing circuit for an imaging device having the functions of the image processing circuit of the above-mentioned embodiment, or as a signal processing method for an imaging device performed by the image processing circuit of the above-mentioned embodiment, or as a program for causing a computer to execute such a signal processing method, or as a non-temporary recording medium readable by a computer having such a program recorded thereon. In addition, in the present disclosure, the image processing circuit of the above-mentioned embodiment may be implemented as a processing circuit used in a photodetector or the like other than an imaging device.

[0171] In addition, as long as they do not depart from the gist of the present disclosure, various modified forms that can be conceived by those skilled in the art to implement the embodiments and examples, and other forms constructed by combining some of the constituent elements in the embodiments and examples are also included in the scope of the present disclosure.

[0172] Industrial Applicability

[0173] The embodiments of the present disclosure can be applied to light detection devices, image sensors, and the like. For example, the camera device disclosed herein can be used in digital still cameras or digital video cameras such as digital SLR cameras and digital mirrorless SLR cameras. Alternatively, the camera device disclosed herein can be used in various camera systems or sensor systems, such as business cameras for broadcasting purposes, inspection cameras for industrial purposes or object recognition cameras, medical cameras, or surveillance cameras. In addition, by appropriately selecting the material of the photoelectric conversion layer, it is also possible to obtain images using infrared rays. Camera devices that perform shooting using infrared rays can be used, for example, in security cameras, cameras mounted on vehicles, and the like. Vehicle-mounted cameras can be used, for example, as input to a control device for safe driving of a vehicle. Alternatively, vehicle-mounted cameras can be used to assist an operator in driving a vehicle safely.

[0174] Description of symbols

[0175] 10 Photoelectric conversion unit

[0176] 11 Counter electrode

[0177] 12 Pixel Electrode

[0178] 13 Photoelectric conversion layer

[0179] 14 Charge blocking layer

[0180] 20 Output Circuit

[0181] 22 Signal detection transistor

[0182] 24 Address transistors

[0183] 26 Reset transistor

[0184] 32 Power cord

[0185] 36 Reset voltage line

[0186] 38 Reset signal line

[0187] 42 Optical Filters

[0188] 44 Microlens

[0189] 46 Sealing film

[0190] 50 interlayer insulation layer

[0191] 100 Camera Device

[0192] 110 Semiconductor substrate

[0193] 120 line scanning circuit

[0194] 130 Detection circuit

[0195] 140 Control circuit

[0196] 150 Voltage supply circuit

[0197] 151 Voltage line

[0198] 160 Image Processing Circuit

[0199] 170 Memory

[0200] 210 substrate

[0201] FD Node

[0202] P Pixel

[0203] R Row select line

[0204] S Output signal line

Claims

1. A camera device, wherein: have: The photoelectric conversion unit includes a first electrode, a second electrode, and a photoelectric conversion layer between the first electrode and the second electrode, and generates electric charges by receiving light; A voltage supply circuit supplies a first voltage to the first electrode; a detection circuit that outputs a signal corresponding to a change in potential of the second electrode, the change in potential of the second electrode being a change corresponding to an amount of light incident on the photoelectric conversion unit; and The image processing circuit corrects the signal from the detection circuit and outputs the corrected signal. The photoelectric conversion unit has the following photoelectric conversion characteristics: when the potential difference between the first electrode and the second electrode is within a first voltage range, the photocurrent flowing between the first electrode and the second electrode changes linearly with respect to the potential difference, The voltage supply circuit supplies the first voltage to the first electrode so that the voltage range that the potential difference can take according to the amount of incident light to the photoelectric conversion unit includes at least a part of the first voltage range. The image processing circuit corrects the signal based on a transformation function derived from a change in the potential of the second electrode relative to the amount of incident light to the photoelectric conversion unit when the potential difference is within the first voltage range, so that the output changes linearly with respect to the amount of incident light to the photoelectric conversion unit.

2. The imaging device according to claim 1, wherein: The image processing circuit corrects the signal based on the conversion function represented by the following (Formula 1). [Formula 1] Among them, y is the input value of the above transformation function, Y is the output value of the above transformation function, ymax is the maximum value of the input value of the above transformation function, and δ is the proportional constant.

3. The imaging device according to claim 2, wherein: The image processing circuit calculates the δ according to the following (Formula 2) using the y that is less than 10% of the ymax: [Formula 2] 4. The imaging device according to any one of claims 1 to 3, wherein: The image processing circuit includes a memory for storing a table, and the signal is corrected based on the table, wherein the table includes a transformation result based on the transformation function.

5. The imaging device according to any one of claims 1 to 3, wherein: A semiconductor substrate having the above-mentioned photoelectric conversion layer stacked thereon is provided.

6. The imaging device according to claim 5, wherein: A substrate having the above-mentioned image processing circuit formed thereon is provided, The semiconductor substrate and the substrate are stacked.

7. The imaging device according to claim 5, wherein: A substrate having the above-mentioned image processing circuit formed thereon is provided, The semiconductor substrate is electrically connected to the substrate.

8. The imaging device according to any one of claims 1 to 3, wherein: The image processing circuit performs at least one of gain correction and gamma correction after correcting the signal based on the conversion function.

9. A processing circuit, wherein: The input signal is corrected based on the conversion function represented by the following (Formula 1), and the corrected input signal is output. [Formula 3] Among them, y is the input value of the above transformation function, Y is the output value of the above transformation function, ymax is the maximum value of the input value of the above transformation function, and δ is the proportional constant.

10. The processing circuit of claim 9, wherein: A memory for storing a table including transformation results based on the transformation function is provided.

11. The processing circuit according to claim 9 or 10, wherein: Using the above y being 10% or less of the above ymax, the above δ is calculated according to the following (Formula 2): [Formula 4]

Images