Patent Application
20240305895
The present disclosure relates to an imaging device and a camera system.
There have conventionally been known photoelectric conversion image sensors. For example, there has been widespread use of CMOS (complementary metal-oxide semiconductor) image sensors having photodiodes. Features of the CMOS image sensors include low power consumption and pixel-by-pixel accessibility. In general, the CMOS image sensors adopt, as a signal readout method, a so-called rolling shutter method by which exposures and signal charge readouts are performed in sequence for each separate row of a pixel array.
In the rolling shutter method, the starts and ends of exposures vary from one row of the pixel array to another. Therefore, imaging an object moving at high speed may give a distorted image of the object, or using the flash may result in a difference in brightness within an image. Under such circumstances, there is demand for a so-called global shutter function with which to start and end exposures at the same time for all pixels in the pixel array.
For example, Japanese Patent No. 6202512 discloses a method for, in a stacked image sensor whose circuit components and photoelectric converters are separate from each other, achieving a global shutter function by changing a voltage that is supplied to the photoelectric converters and thereby controlling the migration of signal charge from the photoelectric converters to charge storage regions.
Further, U.S. Pat. No. 9,277,146 discloses a technology that makes it possible to, by stacking a plurality of photoelectric converters, take out signals representing each separate color and that makes it possible to, by connecting circuits separately to each of the photoelectric converters, individually control how the signals are read out.
Further, Japanese Unexamined Patent Application Publication No. 2019-186738 discloses a technology for, by stacking photoelectric conversion layers for the purpose of imaging visible light and near-infrared radiation, taking out signals separately from each of the photoelectric conversion layers.
Further, U.S. Patent Application Publication No. 2003/0059103 discloses, for example, an inspection method that involves the use of visible light and near-infrared radiation.
In one general aspect, the techniques disclosed here feature an imaging device including a first pixel and a second pixel. The first pixel includes a first photoelectric converter that generates first signal charge by photoelectric conversion and that has sensitivity to a first wavelength range that is invisible and a first signal detection circuit connected to the first photoelectric converter. The second pixel includes a second photoelectric converter that generates second signal charge by photoelectric conversion and that has sensitivity to a second wavelength range and a second signal detection circuit connected to the second photoelectric converter. An exposure period of the second photoelectric converter does not overlap a light-emitting period of light based on lighting, the light being incident on the first photoelectric converter and having a luminescence peak in the first wavelength range. A readout period during which the second signal detection circuit reads out the second signal charge does not overlap the light-emitting period.
In one general aspect, the techniques disclosed here feature a camera system including the imaging device and a lighting device that emits light having a luminescence peak in the first wavelength range. The lighting device does not emit the light in the exposure period of the second photoelectric converter.
Additional benefits and advantages of the disclosed embodiments will become apparent from the specification and drawings. The benefits and/or advantages may be individually obtained by the various embodiments and features of the specification and drawings, which need not all be provided in order to obtain one or more of such benefits and/or advantages.
Prior to a specific description of an embodiment of the present disclosure, an underlying knowledge forming the basis of an aspect of the present disclosure is described. The inventors found the following problems in an imaging device including a plurality of photoelectric converters.
In a case where an imaging device includes a plurality of photoelectric converters, an image of invisible light can be acquired by the plurality of photoelectric converters including a photoelectric converter having sensitivity to an invisible wavelength range. An image of invisible light is useful in crime prevention, inspection, or other uses, as it may give information that cannot be confirmed with visible light. Meanwhile, in a case where an image is taken of light in the invisible wavelength range, ambient light may be insufficient in intensity, and for example, an image is taken of reflected light produced by illuminating the subject with invisible illuminating light emitted by a lighting device. However, in a case where the invisible illuminating light is used, the invisible illuminating light also falls on one of the plurality of photoelectric converters that is not used to take an image of the invisible illuminating light. As a result of that, the photoelectric converter that is not used to take an image of the invisible illuminating light effects unintended photoelectric conversion to cause image quality degradation. For example, in a case where an imaging device includes a photoelectric converter having sensitivity to a near-infrared wavelength region and a photoelectric converter having sensitivity to a visible light wavelength region, near-infrared illuminating light also falls on the photoelectric converter having sensitivity to the visible light wavelength region. Since the near-infrared illuminating light often has a component of a visible light wavelength such as red as part thereof, the near-infrared illuminating light effects photoelectric conversion also in the photoelectric converter having sensitivity to the visible light wavelength region. This results in a change in the amount of signal charge that is generated by the photoelectric converter having sensitivity to the visible light wavelength region, causing degradation, such as a color shift, in the image quality of the image taken.
The present disclosure was made on the basis of such findings and provides an imaging device that has a plurality of photoelectric converters including a photoelectric converter having sensitivity to an invisible wavelength range and that can reduce image quality degradation due to invisible illuminating light and a camera system. The following gives a detailed description.
As a brief overview of the present disclosure, the following gives examples of an imaging device and a camera system according to the present disclosure.
An imaging device according to a first aspect of the present disclosure includes a first pixel and a second pixel. The first pixel includes a first photoelectric converter that generates first signal charge by photoelectric conversion and that has sensitivity to a first wavelength range that is invisible and a first signal detection circuit connected to the first photoelectric converter. The second pixel includes a second photoelectric converter that generates second signal charge by photoelectric conversion and that has sensitivity to a second wavelength range and a second signal detection circuit connected to the second photoelectric converter. An exposure period of the second photoelectric converter does not overlap a light-emitting period of light based on lighting, the light being incident on the first photoelectric converter and having a luminescence peak in the first wavelength range. A readout period during which the second signal detection circuit reads out the second signal charge does not overlap the light-emitting period.
In such an imaging device, light having a luminescence peak in the first wavelength range for imaging with the first photoelectric converter tends to effect unintended photoelectric conversion in the second photoelectric converter. Since the exposure period of the second photoelectric converter does not overlap a light-emitting period of light having a luminescence peak in the first wavelength range, the light does not cause the second photoelectric converter to generate unintended signal charge even in a case where the light has a component that affects photoelectric conversion of the second photoelectric converter. This makes it possible to reduce image quality degradation.
Further, for example, an imaging device according to a second aspect of the present disclosure may be directed to the imaging device according to the first aspect, wherein the first pixel and the second pixel may be effective pixels.
This makes it possible to reduce the influence of the aforementioned unintended photoelectric conversion in the effective pixels, which directly affect output signals.
Further, for example, an imaging device according to a third aspect of the present disclosure may be directed to the imaging device according to the first or second aspect, wherein the first photoelectric converter and the second photoelectric converter may be stacked.
This makes it possible to place a plurality of photoelectric converters in the same photosensitive region. This makes it possible to increase the number of pixels even in a case where signals corresponding to multiple rays of light are outputted, making it possible to improve image quality.
Further, for example, an imaging device according to a fourth aspect of the present disclosure may be directed to the imaging device according to any one of the first to third aspects, further including at least one voltage supply circuit. The first photoelectric converter and the second photoelectric converter may each include a pixel electrode, a counter electrode that faces the pixel electrode, and a photoelectric conversion layer located between the pixel electrode and the counter electrode. The sensitivity of at least one selected from the group consisting of the first photoelectric converter and the second photoelectric converter may be able to be changed by changing of a voltage that the at least one voltage supply circuit applies between the pixel electrode and the counter electrode.
This makes it possible to adjust sensitivity during imaging with at least one of the first photoelectric converter and the second photoelectric converter simply by changing of the applied voltage.
Further, for example, an imaging device according to a fifth aspect of the present disclosure may be directed to the imaging device according to the fourth aspect, wherein at least one selected from the group consisting of the first photoelectric converter and the second photoelectric converter may be driven by a global shutter method by which an exposure period is defined by the changing of the voltage that the at least one voltage supply circuit applies between the pixel electrode and the counter electrode.
This makes it possible to reduce distortions in an image of a rapidly moving object during imaging with at least one of the first photoelectric converter and the second photoelectric converter.
Further, for example, an imaging device according to a sixth aspect of the present disclosure may be directed to the imaging device according to the fourth aspect, wherein each of the first photoelectric converter and the second photoelectric converter may be driven by a global shutter method by which an exposure period is defined by the changing of the voltage that the at least one voltage supply circuit applies between the pixel electrode and the counter electrode.
This makes it possible to reduce distortions in an image of a rapidly moving object during imaging with each of the first photoelectric converter and the second photoelectric converter.
Further, for example, an imaging device according to a seventh aspect of the present disclosure may be directed to the imaging device according to any one of the first to sixth aspects, further including a third photoelectric converter and a third signal detection circuit connected to the third photoelectric converter.
This makes it possible to increase the number of types of signal that can be acquired by each photoelectric converter. For example, in a case where there are provided three photoelectric converters separately having sensitivity to red, green, and blue wavelength regions, it becomes possible to easily acquire a color image. Further, in a case where the imaging device is provided with four photoelectric converters separately having sensitivity to red, green, blue, and near-infrared wavelength regions, a color image and a near-infrared image can be easily acquired.
Further, for example, an imaging device according to an eighth aspect of the present disclosure may be directed to the imaging device according to any one of the first to seventh aspects, wherein the first wavelength range may be a range of wavelengths in a near-infrared wavelength region, and the second wavelength range may be a range of wavelengths in a visible light wavelength region.
This makes it possible to acquire a visible light image and a near-infrared image with one imaging device.
Further, for example, an imaging device according to a ninth aspect of the present disclosure may be directed to the imaging device according to the eighth aspect, wherein an exposure period of the first photoelectric converter may be shorter than the exposure period of the second photoelectric converter.
This makes it possible to shorten an exposure period in which to acquire a near-infrared image. A photoelectric converter having sensitivity to the near-infrared wavelength region tends to produce a dark current due to thermal excitation, as the photoelectric converter is made of a photoelectric conversion material having a narrow bandgap. The shortening of an exposure period in which to acquire a near-infrared image reduces the influence of a dark current even in a case where a dark current tends to be produced, making it possible to reduce degradation in image quality.
Further, for example, an imaging device according to a tenth aspect of the present disclosure may be directed to the imaging device according to any one of the first to seventh aspects, wherein the first wavelength range may be a range of wavelengths in an ultraviolet wavelength region, and the second wavelength range may be a range of wavelengths in a visible light wavelength region.
This makes it possible to acquire a visible light image and an ultraviolet image with one imaging device.
Further, for example, an imaging device according to an eleventh aspect of the present disclosure may be directed to the imaging device according to any one of the first to seventh aspects, wherein the first wavelength range and the second wavelength range may be each a range of wavelengths in a near-infrared wavelength region.
This makes it possible to acquire, with one imaging device, images corresponding to different wavelengths of near-infrared radiation.
Further, for example, an imaging device according to a twelfth aspect of the present disclosure may be directed to the imaging device according to any one of the first to eleventh aspects, wherein the second photoelectric converter may include a silicon photodiode.
This makes it possible to make the imaging device simple in configuration.
Further, a camera system according to a thirteenth aspect of the present disclosure includes the imaging device according to any one of the first to twelfth aspects and a lighting device that emits light having a luminescence peak in the first wavelength range. The lighting device does not emit the light in the exposure period of the second photoelectric converter.
As a result of this, the light emitted by the lighting device does not fall on the second photoelectric converter in the exposure period of the second photoelectric converter, so that the light does not cause the second photoelectric converter to generate unintended signal charge. This prevents light having a luminescence peak in the first wavelength range from affecting the output of an image taken with the second photoelectric converter, making it possible to reduce image quality degradation.
Further, for example, a camera system according to a fourteenth aspect of the present disclosure may be directed to the camera system according to the thirteenth aspect, wherein the lighting device may emit the light in a period overlapping an exposure period of the first photoelectric converter.
This makes it possible to use the first photoelectric converter to take an image of the light emitted by the lighting device, thus making it possible to improve the image quality of the image taken.
Further, an imaging device according to a fifteenth aspect of the present disclosure includes a first pixel and a second pixel. The first pixel includes a first photoelectric converter that generates first signal charge by photoelectric conversion and that has sensitivity to a first wavelength range that is invisible and a first signal detection circuit connected to the first photoelectric converter. The second pixel includes a second photoelectric converter that generates second signal charge by photoelectric conversion and that has sensitivity to a second wavelength range and a second signal detection circuit connected to the second photoelectric converter. An exposure period of the second photoelectric converter does not overlap a light-emitting period of light based on lighting, the light being incident on the first photoelectric converter and having a luminescence peak in the first wavelength range. The first photoelectric converter and the second photoelectric converter are stacked.
The following describes the present embodiment in concrete terms with reference to the drawings.
It should be noted that the embodiments to be described below each illustrate a comprehensive and specific example. The numerical values, shapes, materials, constituent elements, placement and topology of constituent elements, steps, orders of steps, or other features that are shown in the following embodiments are just a few examples and are not intended to limit the present disclosure. Further, those of the constituent elements in the following embodiments which are not recited in an independent claim are described as optional constituent elements. Further, the drawings are not necessarily strict illustrations. Further, in the drawings, substantially the same components are given the same reference signs, and a repeated description may be omitted or simplified.
Further, terms used herein to show the way in which elements are interrelated, terms used herein to show the shape of an element, and ranges of numerical values used herein are not expressions that represent only exact meanings but expressions that are meant to also encompass substantially equivalent ranges, e.g. differences of approximately several percent.
Further, the terms “above” and “below” used herein do not refer to an upward direction (upward in a vertical direction) and a downward direction (downward in a vertical direction) in absolute space recognition, but are used as terms that are defined by a relative positional relationship on the basis of an order of stacking in a stack configuration. Specifically, the term “above” refers to a light receiving side of an imaging device, and the term “below” refers to a side of the imaging device that faces away from the light receiving side. It should be noted that terms such as “above” and “below” are used solely to designate the mutual placement of members and are not intended to limit the attitude of the imaging device during use. Further, the terms “above” and “below” are applied not only in a case where two constituent elements are placed at a spacing from each other and another constituent element is present between the two constituent elements, but also in a case where two constituent elements are placed in close contact with each other and the two constituent elements touch each other.
The following describes an imaging device according to the present embodiment and a camera system including an imaging device and a lighting device according to the present embodiment.
First, the camera system according to the present embodiment is described.
As shown in
The camera system 1 is configured such that illuminating light 602 emitted by the lighting device 200 is reflected off a subject 600. Reflected light 604 produced by the illuminating light 602 being reflected off the subject 600 is taken out as an electrical signal for imaging by being converted into electric charge by a photoelectric converter of the imaging device 100.
Although, in the example shown in
The imaging device 100 converts light falling on the camera system 1 into an electric signal and outputs an image (image signal). The imaging device 100 includes a first photoelectric converter 13a and a second photoelectric converter 13b. The first photoelectric converter 13a and the second photoelectric converter 13b are each for example a photoelectric conversion element. On the first photoelectric converter 13a and the second photoelectric converter 13b, for example, light based on lighting falls. In the example shown in
The first photoelectric converter 13a and the second photoelectric converter 13b have sensitivity to wavelength ranges differing from each other. The first photoelectric converter 13a has sensitivity to a first wavelength range that is invisible. The second photoelectric converter 13b has sensitivity to a second wavelength range. The configuration of the imaging device 100 will be described in detail later. Having sensitivity to a certain wavelength herein means having an external quantum efficiency of 1% or higher at a certain wavelength.
The lighting device 200 illuminates the subject with the illuminating light. The lighting device 200 produces, as the illuminating light, light having a luminescence peak in a first wavelength range to which at least the first photoelectric converter 13a has sensitivity. The lighting device 200 includes, for example, a first light source 210a and a second light source 210b.
The first light source 210a emits, for example, light containing a component having a wavelength in at least part of the first wavelength range to which the first photoelectric converter 13a has sensitivity. The first light source 210a emits, for example, light having a luminescence peak in the first wavelength range.
The second light source 210b emits, for example, light containing a component having a wavelength in at least part of the second wavelength range to which the second photoelectric converter 13b has sensitivity. The second light source 210b emits, for example, light having a luminescence peak in the second wavelength range.
Types of light source that are used as the first light source 210a and the second light source 210b are not limited to particular types, provided the light sources can emit light of desired wavelengths. The first light source 210a and the second light source 210b are each for example a halogen light source, an LED (light-emitting diode) light source, an organic EL (electroluminescence) light source, a laser diode light source, or other light sources. Further, with the first light source 210a and the second light source 210b, a plurality of light sources differing in luminous wavelength from each other may be combined for use.
The first wavelength range is an invisible wavelength range as mentioned above and, for example, is a wavelength range included in an ultraviolet wavelength region or a near-infrared wavelength region. This makes it possible to use the first photoelectric converter 13a to take an image based on invisible light such as ultraviolet radiation or near-infrared radiation, thus making it possible to acquire an image that is useful in crime prevention, inspection, or other uses. Further, the second wavelength range is for example a wavelength range included in any of the ultraviolet wavelength region, a visible light wavelength region, and the near-infrared wavelength region. Further, the first photoelectric converter 13a may have sensitivity to a wavelength outside the first wavelength range. Further, the second photoelectric converter 13b may have sensitivity to a wavelength outside the second wavelength range.
As specific examples, the first wavelength range is a range of wavelengths in the near-infrared wavelength region, and the second wavelength range is a range of wavelengths in the visible light wavelength region. Therefore, the first light source 210a emits light having a luminescence peak in the near-infrared wavelength region. Further, the second light source 210b emits light having a luminescence peak in the visible light wavelength region. In this case, the light emitted by the first light source 210a is converted by the first photoelectric converter 13a, which has sensitivity to the near-infrared wavelength region, and taken out as an electrical signal for imaging. Further, the light emitted by the second light source 210b is converted by the second photoelectric converter 13b, which has sensitivity to the visible light wavelength region, and taken out as an electrical signal for imaging. This allows the imaging device 100 to separately take out signals corresponding to visible light and near-infrared radiation. This makes it possible, for example, to acquire a visible light image and a near-infrared image.
The near-infrared wavelength region herein refers, for example, to a region of wavelengths longer than or equal to 680 nm and shorter than or equal to 3000 nm. The near-infrared wavelength region may refer to a region of wavelengths longer than or equal to 700 nm and shorter than or equal to 2000 nm, or may refer to a region of wavelengths longer than or equal to 700 nm and shorter than or equal to 1600 nm. Further, the visible light wavelength region refers, for example, to a region of wavelengths longer than or equal to 380 nm and shorter than 680 nm. Further, the ultraviolet wavelength region may refer to a region of wavelengths longer than or equal to 100 nm and shorter than 380 nm, or may refer to a region of wavelengths longer than or equal to 200 nm and shorter than 380 nm. All electromagnetic waves including visible light, infrared radiation, and ultraviolet radiation are herein expressed as “light” for convenience.
Further, for example, the first wavelength range may be a range of wavelengths in the ultraviolet wavelength region, and the second wavelength range may be a range of wavelengths in the visible light wavelength region. This allows the imaging device 100 to separately take out signals corresponding to visible light and ultraviolet radiation. This makes it possible, for example, to acquire a visible light image and an ultraviolet image.
Further, for example, the first wavelength range and the second wavelength range may each be a range of wavelengths in the near-infrared wavelength region. This allows the imaging device 100 to separately take out signals corresponding to near-infrared radiation of different wavelengths. This makes it possible, for example, to acquire two types of near-infrared image of different wavelengths. For example, by generating a difference image using such two types of near-infrared image, a near-infrared image less influenced by ambient light or moisture absorption can be obtained.
Further, in a case where at least one of the first wavelength range and the second wavelength range is a range of wavelengths in the near-infrared wavelength region, the at least one may be a range of wavelengths longer than or equal to 820 nm and shorter than or equal to 980 nm. This makes it possible to use, as a light source of the lighting device 200, which emits the illuminating light, an inexpensive LED light source having a luminescence peak at a wavelength longer than or equal to 820 nm and shorter than or equal to 980 nm.
It should be noted that the number of light sources that the lighting device 200 has is not limited to 2 but may be 1 or may be larger than or equal to 3. For example, the lighting device 200 may be configured to include only the first light source 210a as a light source. In this case, for example, the second photoelectric converter 13b converts, into electric charge, reflected light produced by ambient light or light from an external light source being reflected off the subject. Further, the first light source 210a and the second light source 210b do not need to be provided in one lighting device, and the camera system 1 may include a plurality of lighting devices including a lighting device having the first light source 210a and a lighting device including the second light source 210b. Further, the camera system 1 does not need to include the lighting device 200.
The controller 300 is a control circuit that controls how the imaging device 100 and the lighting device 200 operate. The controller 300 for example outputs various types of driving signal to the imaging device 100 and the lighting device 200. The controller 300 is implemented, for example, by a microcomputer. Functions of the controller 300 may be implemented by a combination of a general-purpose processing circuit and software, or may be implemented by hardware specialized in such processing.
Further, at least some of the functions of the controller 300, e.g. a function of controlling how the imaging device 100 is driven, may be included in the imaging device 100. That is, the controller 300 may be provided as a control circuit or other circuits in the imaging device 100. Therefore, the after-mentioned peripheral circuits and pixels of the imaging device 100 may be driven under the control of a controller 300 provided outside the imaging device 100, or may be driven under the control of a control circuit (controller 300) provided in the imaging device 100.
Next, the imaging device according to the present embodiment is described in detail.
As shown in
The first photoelectric converter 13a and the second photoelectric converter 13b are sacked above the semiconductor substrate 20. This makes it possible to place a plurality of photoelectric converters in the same photosensitive region. This makes it possible to increase the number of pixels even in a case where signals corresponding to multiple rays of light are outputted, making it possible to improve image quality. Although
Further, the first photoelectric converter 13a and the second photoelectric converter 13b may both have sensitivity to at least any of visible light, near-infrared radiation, infrared radiation, and ultraviolet radiation. Further, for example, a Bayer color filter array may be provided above a second photoelectric converter 13b having sensitivity to the entire visible light wavelength region, and each pixel provided in the second photoelectric converter 13b may output, according to a corresponding color filter, a pixel signal corresponding to the intensity of red, blue, or green light. Further, for example, each pixel provided in a first photoelectric converter 13a having sensitivity to the near-infrared wavelength region may output a pixel signal corresponding to the intensity of near-infrared radiation. This gives a color image corresponding to signal charge of the second photoelectric converter 13b and a near-infrared image corresponding to signal charge of the first photoelectric converter 13a.
In the example shown in
Next, a circuit configuration of the imaging device 100 according to the present embodiment is described.
As shown in
The peripheral circuits for example drive the pixel array PA and acquire an image based on signal charge generated by the first photoelectric converters 13a and the second photoelectric converters 13b. The peripheral circuits include, for example, a voltage supply circuit 32a, a reset voltage source 34a, a vertical scanning circuit 36a, column signal processing circuits 37a, and a horizontal signal readout circuit 38a that are connected to the pixels 10a, a voltage source connected to a power wire 40a, or other circuits. Further, the peripheral circuits include, for example, a voltage supply circuit 32b, a reset voltage source 34b, a vertical scanning circuit 36b, column signal processing circuits 37b, and a horizontal signal readout circuit 38b that are connected to the pixels 10b, a voltage source connected to a power wire 40b, or other circuits. Further, the imaging device 100 may include, as circuits included in the peripheral circuits, control circuits that control how peripheral circuits other than those of the imaging device 100 are driven.
The pixels 10a and the pixels 10b are for example effective pixels. The effective pixels here are pixels that are actually used for outputting an image or pixels that are used for sensing, and do not include optically black pixels and dummy pixels that are used for measuring dark noise.
The circuit configuration of the pixels 10a shown in
Each pixel 10a has a first photoelectric converter 13a and a signal detection circuit 14a. Each pixel 10b has a second photoelectric converter 13b and a signal detection circuit 14b. As will be described later with reference to the drawings, the first photoelectric converter 13a and the second photoelectric converter 13b each have a photoelectric conversion layer sandwiched between two electrodes facing each other and generate signal charge upon receiving incident light. The first photoelectric converter 13a does not need to be an element that is independent in its entirety for each pixel 10a, and for example, a portion of the first photoelectric converter 13a may lie astride a plurality of pixels 10a. Further, the second photoelectric converter 13b does not need to be an element that is independent in its entirety for each pixel 10b, and for example, a portion of the second photoelectric converter 13b may lie astride a plurality of pixels 10b.
The signal detection circuit 14a is a circuit that detects signal charge generated by the first photoelectric converter 13a. The signal detection circuit 14b is a circuit that detects signal charge generated by the second photoelectric converter 13b. In this example, the signal detection circuit 14a includes a signal detection transistor 24a and an address transistor 26a. Further, the signal detection circuit 14b includes a signal detection transistor 24b and an address transistor 26b. The signal detection transistors 24a and 24b and the address transistors 26a and 26b are each for example a field-effect transistor (FET), and for example, as the signal detection transistors 24a and 24b and the address transistors 26a and 26b, N-channel MOSFETs (metal-oxide semiconductor field-effect transistors) are illustrated here. Each transistor such as the signal detection transistors 24a and 24b, the address transistors 26a and 26b, and the after-mentioned reset transistors 28a and 28b has a control terminal, an input terminal, and an output terminal. The control terminal is for example a gate. The input terminal is one of a drain and a source, and is for example a drain. The output terminal is the other of a drain and a source, and is for example a source.
As schematically shown in
The first photoelectric converter 13a of each pixel 10a further has a connection to a sensitivity control line 42a. In the configuration illustrated in
The voltage supply circuit 32a supplies a voltage to the first photoelectric converter 13a. Specifically, the voltage supply circuit 32a supplies a predetermined voltage to the first photoelectric converter 13a via the sensitivity control line 42a during operation of the imaging device 100. The voltage supply circuit 32b supplies a voltage to the second photoelectric converter 13b. Specifically, the voltage supply circuit 32b supplies a predetermined voltage to the second photoelectric converter 13b via the sensitivity control line 42b during operation of the imaging device 100. The voltage supply circuits 32a and 32b are not limited to particular power circuits but may be circuits that generate predetermined voltages or may be circuits that convert voltages supplied from other power supplies into predetermined voltages. As will be described in detail later, by switching, between a plurality of voltages differing from each other, the voltage that is supplied from the voltage supply circuit 32a to the first photoelectric converter 13a, the start and end of storage of signal charge from the first photoelectric converter 13a into the charge storage node 41a are controlled. Further, by switching, between a plurality of voltages differing from each other, the voltage that is supplied from the voltage supply circuit 32b to the second photoelectric converter 13b, the start and end of storage of signal charge from the second photoelectric converter 13b into the charge storage node 41b are controlled. In other words, in the present embodiment, an electronic shutter operation is executed by switching the voltage that is supplied from the voltage supply circuit 32a to the first photoelectric converter 13a and the voltage that is supplied from the voltage supply circuit 32b to the second photoelectric converter 13b. An example of operation of the imaging device 100 will be described later.
Each pixel 10a has a connection to the power wire 40a, which supplies a power supply voltage VDD. Each pixel 10b has a connection to the power wire 40b, which supplies the power supply voltage VDD. As shown in
To the output terminal of the signal detection transistor 24a, the input terminal of the address transistor 26a is connected. The output terminal of the address transistor 26a is connected to one of a plurality of vertical signal lines 47a placed separately for each of the rows of pixels 10a in the pixel array PA. The control terminal of the address transistor 26a is connected to an address control line 46a, and by controlling the potential of the address control line 46a, an output from the signal detection transistor 24a can be selectively read out to a corresponding one of the vertical signal lines 47a.
Further, to the output terminal of the signal detection transistor 24b, the input terminal of the address transistor 26b is connected. The output terminal of the address transistor 26b is connected to one of a plurality of vertical signal lines 47b placed separately for each of the rows of pixels 10b in the pixel array PA. The control terminal of the address transistor 26b is connected to an address control line 46b, and by controlling the potential of the address control line 46b, an output from the signal detection transistor 24b can be selectively read out to a corresponding one of the vertical signal lines 47b.
In the example shown in
The vertical signal lines 47a are main signal lines through which pixel signals from the plurality of pixels 10a of the pixel array PA are transmitted to the peripheral circuits. To the vertical signal lines 47a, the column signal processing circuits 37a are connected. Further, the vertical signal lines 47b are main signal lines through which pixel signals from the plurality of pixels 10b of the pixel array PA are transmitted to the peripheral circuits. To the vertical signal lines 47b, the column signal processing circuits 37b are connected. A column signal processing circuit is also called “row signal storage circuit”. The column signal processing circuits 37a and 37b each perform noise suppression signal processing typified by correlated double sampling and analog-to-digital conversion (AD conversion). As shown in
The horizontal signal readout circuit 38a sequentially reads out signals from the plurality of column signal processing circuits 37a to a horizontal common signal line 49a. Further, the horizontal signal readout circuit 38b sequentially reads out signals from the plurality of column signal processing circuits 37b to a horizontal common signal line 49b.
In the configuration illustrated in
As shown in
In this example, the reset voltage line 44a, which supplies the reset voltage Vr to the reset transistor 28a, is connected to the reset voltage source 34a. Further, the reset voltage line 44b, which supplies the reset voltage Vr to the reset transistor 28b, is connected to the reset voltage source 34b. A reset voltage source is also called “reset voltage supply circuit”. The reset voltage sources 34a and 34b need only be configured to be able to supply the predetermined reset voltage Vr to the reset voltage lines 44a and 44b during operation of the imaging device 100 and, as is the case with the aforementioned voltage supply circuits 32a and 32b, are not limited to particular power circuits. Each of the voltage supply circuits 32a and 32b and the reset voltage sources 34a and 34b may be a portion of a single voltage supply circuit, or may be an independent and separate voltage supply circuit. It should be noted that either or both of the voltage supply circuit 32a and the reset voltage source 34a may be a portion of the vertical scanning circuit 36a. Alternatively, a sensitivity control voltage from the voltage supply circuit 32a and/or the reset voltage Vr from the reset voltage source 34a may be supplied to each pixel 10a via the vertical scanning circuit 36a. Further, either or both of the voltage supply circuit 32b and the reset voltage source 34b may be a portion of the vertical scanning circuit 36b. Alternatively, a sensitivity control voltage from the voltage supply circuit 32b and/or the reset voltage Vr from the reset voltage source 34b may be supplied to each pixel 10b via the vertical scanning circuit 36b.
It is also possible to use the power supply voltage VDD of the signal detection circuits 14a and 14b as the reset voltage Vr. In this case, commonality may be achieved between a voltage supply circuit (not illustrated in
Next, a cross-section structure of pixels of the imaging device 100 according to the present embodiment is described.
Further, in
The semiconductor substrate 20 has impurity regions 26s, 24s, 24d, 28d, and 28s and a device isolation region 20t that provides electrical isolation between pixels. The impurity regions 26s, 24s, 24d, 28d, and 28s here are N-type regions. Further, the device isolation region 20t is also provided between the impurity region 24d and the impurity region 28d. The device isolation region 20t is formed, for example, by performing ion implantation of an acceptor under predetermined implantation conditions.
The impurity regions 26s, 24s, 24d, 28d, and 28s are for example diffusion layers formed in the semiconductor substrate 20. As schematically shown in
Similarly, the address transistors 26a and 26b each include the impurity regions 26s and 24s and a gate electrode 26g connected to the address control line 46a or 46b (see
The reset transistors 28a and 28b each include the impurity regions 28d and 28s and a gate electrode 28g connected to the reset control line 48a or 48b (sec
An interlayer insulating layer 50 is placed over the semiconductor substrate 20 so as to cover the signal detection transistors 24a and 24b, the address transistors 26a and 26b, and the reset transistors 28a and 28b. The interlayer insulating layer 50 is made, for example, of an insulating material such as silicon oxide. As shown in
The aforementioned first photoelectric converter 13a and the aforementioned second photoelectric converter 13b are placed over the interlayer insulating layer 50. In other words, in the present embodiment, the plurality of pixels 10a and the plurality of pixels 10b, which constitute the pixel array PA (see
In the present embodiment, light falls on the first photoelectric converter 13a and the second photoelectric converter 13b from above the first photoelectric converter 13a and the second photoelectric converter 13b, i.e. from a side opposite to the semiconductor substrate 20.
The first photoelectric converter 13a includes a pixel electrode 11a, a counter electrode 12a, and a photoelectric conversion layer 15a placed between the pixel electrode 11a and the counter electrode 12a. In this example, the counter electrode 12a and the photoelectric conversion layer 15a are formed across the plurality of pixels 10a. On the other hand, the pixel electrode 11a is provided for each pixel 10a and, by being spatially isolated from the pixel electrode 11a of an adjacent pixel 10a, is electrically isolated from the pixel electrode 11a of the adjacent pixel 10a.
The second photoelectric converter 13b includes a pixel electrode 11b, a counter electrode 12b, and a photoelectric conversion layer 15b placed between the pixel electrode 11b and the counter electrode 12b. In this example, the counter electrode 12b and the photoelectric conversion layer 15b are formed across the plurality of pixels 10b. On the other hand, the pixel electrode 11b is provided for each pixel 10b and, by being spatially isolated from the pixel electrode 11b of an adjacent pixel 10b, is electrically isolated from the pixel electrode 11b of the adjacent pixel 10b.
The second photoelectric converter 13b is stacked above the first photoelectric converter 13a via an insulating layer 62. On the first photoelectric converter 13a, light having passed through the second photoelectric converter 13b and the insulating layer 62 falls. The second photoelectric converter 13b and the insulating layer 62 allow passage of at least part of light of wavelengths to which the first photoelectric converter 13a has sensitivity. Thus, light falling on the first photoelectric converter 13a passes through the second photoelectric converter 13b. Light falling on the imaging device 100 falls on both the first photoelectric converter 13a and the second photoelectric converter 13b. Therefore, even if light of a wavelength range to which one of the first photoelectric converter 13a and the second photoelectric converter 13b has sensitivity falls on the imaging device 100, the light may affect the other photoelectric converter.
Above the second photoelectric converter 13b, a sealing layer, a color filter, a microlens, or other components may be further provided.
The pixel electrode 11a is an electrode for reading out signal charge generated by the first photoelectric converter 13a. There is at least one pixel electrode 11a for each pixel 10a. The pixel electrode 11a is electrically connected to the gate electrode 24g of the signal detection transistor 24a and the impurity region 28d. The pixel electrode 11b is an electrode for reading out signal charge generated by the second photoelectric converter 13b. There is at least one pixel electrode 11b for each pixel 10b. The pixel electrode 11b is electrically connected to the gate electrode 24g of the signal detection transistor 24b and the impurity region 28d. Further, the pixel electrode 11b is placed on a side of the photoelectric conversion layer 15b that faces the first photoelectric converter 13a.
The counter electrode 12a is placed opposite the pixel electrode 11a with the photoelectric conversion layer 15a sandwiched therebetween. The counter electrode 12a is placed, for example, on a side of the photoelectric conversion layer 15a on which light falls. Accordingly, on the photoelectric conversion layer 15a, light having passed through the counter electrode 12a falls. Further, the counter electrode 12a is placed, for example, on a side of the photoelectric conversion layer 15a that faces the second photoelectric converter 13b. Therefore, the first photoelectric converter 13a and the second photoelectric converter 13b are stacked so that the counter electrode 12a and the pixel electrode 11b face each other. The counter electrode 12a and the pixel electrode 11b are adjacent to each other via the insulating layer 62.
The counter electrode 12b is placed opposite the pixel electrode 11b with the photoelectric conversion layer 15b sandwiched therebetween. The counter electrode 12b is placed, for example, on a side of the photoelectric conversion layer 15b on which light falls. Accordingly, on the photoelectric conversion layer 15b, light having passed through the counter electrode 12b falls.
The pixel electrode 11b, the counter electrode 12a, and the counter electrode 12b are for example transparent electrodes made of a transparent conducting material. The term “transparent” herein means transmitting at least part of light in a wavelength range to be detected, and it is not essential to transmit light across the whole wavelength range of visible light. For example, the counter electrode 12b allows passage of at least part of light of wavelengths to which the first photoelectric converter 13a has sensitivity and at least part of light of wavelengths to which the second photoelectric converter 13b has sensitivity. Further, for example, the pixel electrode 11b and the counter electrode 12a allow passage of at least part of light of wavelengths to which the first photoelectric converter 13a has sensitivity.
The transparent electrodes may be made, for example, of a transparent conducting oxide (TCO) such as ITO, IZO, AZO, FTO, SnO2, TiO2, or ZnO2.
The pixel electrode 11a is made of a conducting material. The conducting material is for example a metal such as aluminum or copper, a metal nitride, or polysilicon rendered conductive by being doped with an impurity.
The pixel electrode 11a may be a light-blocking electrode. For example, a sufficient light blocking effect may be achieved by forming, as the pixel electrode 11a, a TaN electrode whose thickness is 100 nm. When the pixel electrode 11a is a light-blocking electrode, light having passed through the photoelectric conversion layer 15a may be inhibited from falling on the channel region or impurity regions of a transistor formed in the semiconductor substrate 20 (in this example, at least any of the signal detection transistors 24a and 24b, the address transistors 26a and 26b, and the reset transistors 28a and 28b). The aforementioned wiring layers 56a and 56b may be utilized to form light-blocking films in the interlayer insulating layer 50. By inhibiting light from falling on the channel region of a transistor formed in the semiconductor substrate 20, a shift in the characteristic of the transistor (e.g. a fluctuation in threshold voltage) or other changes may be inhibited. Further, by inhibiting light from falling on an impurity region formed in the semiconductor substrate 20, noise contamination by unintended photoelectric conversion in the impurity region may be inhibited. Thus, inhibiting light from falling on the semiconductor substrate 20 contributes to improvement in reliability of the imaging device 100. It should be noted that the pixel electrode 11a may be a transparent electrode.
It should be noted that the pixel electrode 11a and the counter electrode 12a may swap with each other the positions where they are in when they are placed as shown in
Further, the pixel electrode 11b and the counter electrode 12b may swap with each other the positions where they are in when they are placed as shown in
Further, the first photoelectric converter 13a and the second photoelectric converter 13b may swap with each other the positions where they are in when they are placed as shown in
The photoelectric conversion layers 15a and 15b each generate a hole-electron pair upon receiving incident light. The photoelectric conversion layers 15a and 15b are each made, for example, of an organic material. Further, the photoelectric conversion layers 15a and 15b may each have a structure in which a plurality of layers are stacked. Specific examples of the materials of which the photoelectric conversion layers 15a and 15b are made will be described later.
As described with reference to
As will be described in detail later, the voltage supply circuits 32a and 32b each supply, to the counter electrode 12a or 12b, voltages differing from each other between an exposure period and a non-exposure period. The term “exposure period” herein means a period in which to store, in charge storage regions or other regions, signal charge that is either positive or negative charge generated by photoelectric conversion of the first photoelectric converter 13a and the second photoelectric converter 13b, and may be called “charge storage period”. Further, the term “non-exposure period” means a period during operation of the imaging device excluding an exposure period. It should be noted that the “non-exposure period” is not limited to a period during which light is blocked from falling on the first photoelectric converter 13a or the second photoelectric converter 13b, but may include a period during which the first photoelectric converter 13a or the second photoelectric converter 13b is illuminated with light. Further, the “non-exposure period” includes a period in which signal charge is unintentionally stored in a charge storage region due to the occurrence of parasitic sensitivity.
Further, the “non-exposure period” includes a “readout period” and a “reset period”. The “readout period” is a period in which signals corresponding to the amounts of signal charge generated by the first photoelectric converter 13a and the second photoelectric converter 13b (i.e. the amounts of signal charge stored in the charge storage regions) are read out by the signal detection circuits 14a and 14b, respectively. The “reset period” is a period in which to reset the potentials of the charge storage regions in which to store the signal charge generated by the first photoelectric converter 13a and the second photoelectric converter 13b. Specifically, in the “reset period”, the potentials of the charge storage regions are reset to the reset voltage Vr.
Further, in the present embodiment, the “exposure period”, the “non-exposure period”, the “readout period”, and the “reset period” are defined for each of the pixels 10a and 10b. Since, in the pixel 10a, a signal corresponding to the amount of signal charge generated by the first photoelectric converter 13a is read out, the “exposure period”, the “non-exposure period”, the “readout period”, and the “reset period” of the pixel 10a can also be said to be an “exposure period”, a “non-exposure period”, a “readout period”, and a “reset period” of the first photoelectric converter 13a. Since, in the pixel 10b, a signal corresponding to the amount of signal charge generated by the second photoelectric converter 13b is read out, the “exposure period”, the “non-exposure period”, the “readout period”, and the “reset period” of the pixel 10b can also be said to be an “exposure period”, a “non-exposure period”, a “readout period”, and a “reset period” of the second photoelectric converter 13b. Each of these periods will be described in detail later.
By controlling the potential of the counter electrode 12a in relation to the potential of the pixel electrode 11a, either the hole or electron of a hole-electron pair generated in the photoelectric conversion layer 15a by photoelectric conversion can be collected as signal charge by the pixel electrode 11a. For example, in a case where the hole is utilized as signal charge, the hole can be selectively collected by the pixel electrode 11a by making the counter electrode 12a higher in potential than the pixel electrode 11a. Further, by controlling the potential of the counter electrode 12b in relation to the potential of the pixel electrode 11b, either the hole or electron of a hole-electron pair generated in the photoelectric conversion layer 15b by photoelectric conversion can be collected as signal charge by the pixel electrode 11b. For example, in a case where the hole is utilized as signal charge, the hole can be selectively collected by the pixel electrode 11b by making the counter electrode 12b higher in potential than the pixel electrode 11b. The following illustrates a case where the hole is utilized as signal charge. Of course, it is also possible to utilize the electron as signal charge. In this case, the counter electrode 12a is made lower in potential than the pixel electrode 11a, and the counter electrode 12b is made lower in potential than the pixel electrode 11b.
In the presence of the application of an appropriate bias voltage between the counter electrode 12a and the pixel electrode 11a, the pixel electrode 11a, which faces the counter electrode 12a, collects either positive or negative charge generated by photoelectric conversion in the photoelectric conversion layer 15a. Further, in the presence of the application of an appropriate bias voltage between the counter electrode 12b and the pixel electrode 11b, the pixel electrode 11b, which faces the counter electrode 12b, collects either positive or negative charge generated by photoelectric conversion in the photoelectric conversion layer 15b.
In the imaging device 100, the insulating layer 62 is provided between the first photoelectric converter 13a and the second photoelectric converter 13b. The insulating layer 62 electrically isolates the first photoelectric converter 13a and the second photoelectric converter 13b from each other. In the example shown in
As schematically shown in
Further, the pixel electrode 11b is connected to the gate electrode 24g of the signal detection transistor 24b via the plug 52b, a wire 53b, and a contact plug 54b. In other words, the gate of the signal detection transistor 24b has an electrical connection to the pixel electrode 11b. The plug 52b penetrates the first photoelectric converter 13a and the insulating layer 62. The plug 52b, the wire 53b, and the contact plug 54b constitute at least part of the charge storage node 41b (see
The plugs 52a and 52b, the wires 53a and 53b, and the contact plugs 54a, 54b, 55a, and 55b are each made of a conducting material. For example, the plugs 52a and 52b and the wires 53a and 53b are each made of a metal such as copper. Further, for example, the contact plugs 54a, 54b, 55a, and 55b are each made of polysilicon rendered conductive by being doped with an impurity. It should be noted that the plugs 52a and 52b, the wires 53a and 53b, and the contact plugs 54a, 54b, 55a, and 55b may be made of the same material as one another or may be made of different materials from one another.
Further, an insulating coating 61b is formed around the plug 52b. The insulating coating 61b is located between the plug 52b and the first photoelectric converter 13a. The plug 52b and the first photoelectric converter 13a are not in contact with each other but electrically insulated from each other by the insulating coating 61b. The insulating coating 61b is made, for example, an insulating material such as silicon oxide or silicon nitride.
The collection of signal charge by the pixel electrode 11a causes a voltage corresponding to the amount of signal charge stored in the charge storage region of the pixel 10a to be applied to the gate of the signal detection transistor 24a. The signal detection transistor 24a amplifies this voltage. The voltage amplified by the signal detection transistor 24a is selectively read out as a signal voltage via the address transistor 26a. Further, the collection of signal charge by the pixel electrode 11b causes a voltage corresponding to the amount of signal charge stored in the charge storage region of the pixel 10b to be applied to the gate of the signal detection transistor 24b. The voltage amplified by the signal detection transistor 24b is selectively read out as a signal voltage via the address transistor 26b.
It should be noted that the number of photoelectric converters that the imaging device 100 includes is not limited to particular numbers, provided it is larger than or equal to 2. An imaging device according to the present embodiment may include three or more photoelectric converters.
As shown in
The photoelectric converters 13c and 13d are stacked above the first photoelectric converter 13a and the second photoelectric converter 13b. Specifically, in the imaging device 110, the first photoelectric converter 13a, the second photoelectric converter 13b, the photoelectric converter 13c, and the photoelectric converter 13d are stacked in this order from below. It should be noted that the photoelectric converters may be stacked in any order.
The first photoelectric converter 13a, the second photoelectric converter 13b, the photoelectric converter 13c, and the photoelectric converter 13d for example have sensitivity to wavelength ranges differing from one another.
An insulating layer 62a is placed between the second photoelectric converter 13b and the photoelectric converter 13c. The second photoelectric converter 13b and the photoelectric converter 13c are electrically insulated from each other by the insulating layer 62a.
An insulating layer 62b is placed between the photoelectric converter 13c and the photoelectric converter 13d. The photoelectric converter 13c and the photoelectric converter 13d are electrically insulated from each other by the insulating layer 62b.
The photoelectric converter 13c has a pixel electrode 11c, a counter electrode 12c placed opposite the pixel electrode 11c, and a photoelectric conversion layer 15c placed between the pixel electrode 11c and the counter electrode 12c.
The pixel electrode 11c is connected to the signal detection circuit 14c via a plug 52c or other components. The plug 52c penetrates the first photoelectric converter 13a, the second photoelectric converter 13b, and the insulating layers 62 and 62a. An insulating coating 61c is formed around the plug 52c. The insulating coating 61c is located between the plug 52c and the first photoelectric converter 13a and between the plug 52c and the second photoelectric converter 13b.
The photoelectric converter 13d has a pixel electrode 11d, a counter electrode 12d placed opposite the pixel electrode 11d, and a photoelectric conversion layer 15d placed between the pixel electrode 11d and the counter electrode 12d.
The pixel electrode 11d is connected to the signal detection circuit 14d via a plug 52d or other components. The plug 52d penetrates the first photoelectric converter 13a, the second photoelectric converter 13b, the photoelectric converter 13c, and the insulating layers 62, 62a, and 62b. An insulating coating 61d is formed around the plug 52d. The insulating coating 61d is located between the plug 52d and the first photoelectric converter 13a, between the plug 52d and the second photoelectric converter 13b, and between the plug 52d and the photoelectric converter 13c.
The imaging device 110 makes it possible to increase the number of types of signal that can be acquired by each photoelectric converter. This makes it possible to easily acquire a color image or other images by adjusting wavelengths to which each photoelectric converter has sensitivity.
Thus, even in a case where the imaging device 110 includes three or more photoelectric converters, light falling on the imaging device 110 falls on each photoelectric converter. Therefore, even if light of a wavelength range to which one of the photoelectric converters has sensitivity falls on the imaging device 110, the light may affect another of the photoelectric converters.
Next, the photoelectric conversion layers 15a and 15b according to the present embodiment are described in detail.
As mentioned above, in the first photoelectric converter 13a, by illuminating the photoelectric conversion layer 15a with light and applying a bias voltage between the pixel electrode 11a and the counter electrode 12a, either positive or negative charge generated by photoelectric conversion is collected by the pixel electrode 11a, and the electric charge thus collected can be stored in the charge storage region. By using, in the first photoelectric converter 13a, a photoelectric conversion layer 15a that exhibits a photocurrent characteristic such as that described below and reducing the potential difference between the pixel electrode 11a and the counter electrode 12a to a certain degree, the signal charge already stored in the charge storage region can be inhibited from migrating to the counter electrode 12a via the photoelectric conversion layer 15a. Furthermore, further storage of signal charge into the charge storage region after the reduction of the potential difference may be inhibited. That is, by controlling the magnitude of a bias voltage that is applied to the photoelectric conversion layer 15a, a global shutter function may be achieved without separately providing each of the plurality of pixels with an element such as a transfer transistor as in the case of a technology described in U.S. Patent Application Publication No. 2007/0013798. As for the second photoelectric converter 13b too, a global shutter function may be achieved by operation that is similar to that of the first photoelectric converter 13a. An example of operation in the imaging device 100 will be described later.
The photoelectric conversion layers 15a and 15b each contain, for example, a semiconductor material. In the present embodiment, for example, an organic semiconductor material is used as the semiconductor material.
At least one of the photoelectric conversion layers 15a and 15b contains, for example, tin naphthalocyanine represented by general formula (1) below. In the following, the tin naphthalocyanine represented by general formula (1) below is sometimes simply called “tin naphthalocyanine”.
In general formula (1), R1 to R24 each independently represent a hydrogen atom or a substituent. The substituent is not limited to particular substituents. The substituent may be a deuterium atom, a halogen atom, an alkyl group (including a cycloalkyl group, a bicycloalkyl group, and a tricycloalkyl group), an alkenyl group (including a cycloalkenyl group and a bicycloalkenyl group), an alkynyl group, an aryl group, a heterocyclic group, a cyano group, a hydroxy group, a nitro group, a carboxy group, an alkoxy group, an aryloxy group, a silyloxy group, a heterocyclic oxy group, an acyloxy group, a carbamoyloxy group, an alkoxycarbonyloxy group, an aryloxycarbonyloxy group, an amino group (including an anilino group), an ammonio group, an acylamino group, an aminocarbonylamino group, an alkoxycarbonylamino group, an aryloxycarbonylamino group, a sulfamoylamino group, an alkylsulfonylamino group, an arylsulfonylamino group, a mercapto group, an alkylthio group, an arylthio group, a heterocyclic thio group, a sulfamoyl group, a sulfo group, an alkylsulfinyl group, an arylsulfinyl group, an alkylsulfonyl group, an arylsulfonyl group, an acyl group, an aryloxycarbonyl group, an alkoxycarbonyl group, a carbamoyl group, an arylazo group, a heterocyclic azo group, an imide group, a phosphino group, a phosphinyl group, a phosphinyloxy group, a phosphinylamino group, a phosphono group, a silyl group, a hydrazino group, a ureide group, a boronic acid group (—B(OH)2), a phosphato group (—OPO(OH)2), a sulfato group (—OSO3H), or other publicly-known substituents.
As the tin naphthalocyanine represented by general formula (1) above, a commercially available product may be used. Alternatively, for example, as disclosed in Japanese Unexamined Patent Application Publication No. 2010-232410, the tin naphthalocyanine represented by general formula (1) above may be synthesized with a naphthalene derivative represented by general formula (2) below as a starting material. R25 to R30 in general formula (2) may be substituents that are similar to R1 to R24 in general formula (1).
In the tin naphthalocyanine represented by general formula (1) above, eight or more of R1 to R24 may be hydrogen atoms or deuterium atoms, sixteen of more of R1 to R24 may be hydrogen atoms or deuterium atoms, or all of R1 to R24 may be hydrogen atoms or deuterium atoms from the point of view of ease of control of a molecular aggregation state. Furthermore, tin naphthalocyanine represented by general formula (3) below is advantageous in view of ease of synthesis.
The tin naphthalocyanine represented by general formula (1) above has absorption in a wavelength range of approximately 200 nm to 1100 nm. The tin naphthalocyanine represented by general formula (3) above has an absorption peak at a wavelength of approximately 870 nm as shown in
As can be seen from
As shown in
As shown in
The photoelectric conversion structures 150 and 151 each contain at least one of a p-type semiconductor and an n-type semiconductor.
As shown in
As will be described later, the mixed layers 150m and 151m may each contain at least one of a p-type semiconductor and an n-type semiconductor.
The p-type semiconductor layers 150p and 151p each contain, for example, an organic p-type semiconductor. The n-type semiconductor layers 150n and 15 In each contain, for example, an organic n-type semiconductor. Therefore, the photoelectric conversion structure 150 contains, for example, an organic photoelectric conversion material containing the tin naphthalocyanine represented by general formula (1) above, the organic p-type semiconductor, and the organic n-type semiconductor.
The organic p-type semiconductor is a donor organic semiconductor and, typified mainly by a hole transport organic compound, refers to an electron-donating organic compound. In more particular, the organic p-type semiconductor refers to an organic compound that is lower in ionization potential when two organic materials are used in contact with each other. Accordingly, it is possible to use any electron-donating organic compound as the donor organic compound. Usable examples include metal complexes having, as ligands, a triarylamine compound, a benzidine compound, a pyrazoline compound, a styrylamine compound, a hydrazone compound, a triphenylmethane compound, a carbazole compound, a polysilane compound, a thiophene compound, a phthalocyanine compound, naphthalocyanine compound, a subphthalocyanine compound, a cyanine compound, a merocyanine compound, an oxonol compound, a polyamine compound, an indole compound, a pyrrole compound, a pyrazole compound, a polyarylene compound, a condensed aromatic carbocyclic compound (naphthalene derivative, anthracene derivative, phenanthrene derivative, tetracene derivative, pyrene derivative, perylene derivative, fluoranthene derivative), and a nitrogen-containing heterocyclic compound. The donor organic semiconductor is not limited to this, and an organic material that is lower in ionization potential than an organic material used as the after-mentioned acceptor organic compound may be used as the donor organic semiconductor. The acceptor organic compound is also called “n-type organic compound”. The aforementioned “tin naphthalocyanine” is an example of an organic p-type semiconductor material.
The organic n-type semiconductor is an acceptor organic semiconductor and, typified mainly by an electron transport organic compound, refers to an electron-accepting organic compound. In more particular, the organic n-type semiconductor refers to an organic compound that is higher in ionization potential when two organic compounds are used in contact with each other. Accordingly, it is possible to use any electron-accepting organic compound as the acceptor organic compound. Usable examples include metal complexes having, as ligands, a fullerene, a fullerene derivative, a condensed aromatic carbocyclic compound (naphthalene derivative, anthracene derivative, phenanthrene derivative, tetracene derivative, pyrene derivative, perylene derivative, fluoranthene derivative), a 5- to 7-membered heterocyclic compound containing a nitrogen atom, an oxygen atom, or a sulfur atom (such as pyridine, pyrazine, pyrimidine, pyridazine, triazine, quinoline, quinoxaline, quinazoline, phthalazine, cinnoline, isoquinoline, pteridine, acridine, phenazine, phenanthroline, tetrazole, pyrazole, imidazole, thiazole, oxazole, indazole, benzimidazole, benzotriazole, benzoxazole , benzothiazole, carbazole, purine, triazolopyridazine, triazolopyrimidine, tetrazaindene, oxadiazole, imidazopyridine, pyrrolidine, pyrrolopyridine, thiadiazolopyridine, dibenzazepine, or tribenzazepine), a polyarylene compound, a fluorene compound, a cyclopentadiene compound, a silyl compound, and a nitrogen-containing heterocyclic compound. The acceptor organic semiconductor is not limited to this, and as mentioned above, an organic material that is higher in electron affinity than an organic material used as the donor organic compound may be used as the acceptor organic semiconductor. The donor organic compound is also called “p-type organic compound”.
The mixed layers 150m and 151m may each be, for example, a bulk heterojunction structure layer including an organic p-type semiconductor and an organic n-type semiconductor. In a case where the mixed layers 150m and 151m are formed as layers each having a bulk heterojunction structure, the tin naphthalocyanine represented by general formula (1) above may be used as the organic p-type semiconductor material. As the organic n-type semiconductor material, for example, a fullerene and/or a fullerene derivative may be used.
From the point of view of improving photoelectric conversion efficiency, the material constituting the p-type semiconductor layer 150p may be the same as the p-type semiconductor material contained in the mixed layer 150m. Further, the material constituting the p-type semiconductor layer 151p may be the same as the p-type semiconductor material contained in the mixed layer 151m. Similarly, the material constituting the n-type semiconductor layer 150n may be the same as the n-type semiconductor material contained in the mixed layer 150m. Further, the material constituting the n-type semiconductor layer 15 In may be the same as the n-type semiconductor material contained in the mixed layer 151m. A bulk heterojunction structure is described in detail in Japanese Patent No. 5553727, the entire contents of which are hereby incorporated by reference.
Using appropriate materials depending on the wavelength range to be detected makes it possible to achieve an imaging device having sensitivity to the desired wavelength range. It should be noted that the materials used in the photoelectric conversion layers 15a and 15b are not limited to organic semiconductor materials. At least one of the photoelectric conversion layers 15a and 15b may contain an inorganic semiconductor material such as amorphous silicon or a compound semiconductor as the p-type semiconductor and/or the n-type semiconductor. At least one of the photoelectric conversion layers 15a and 15b may include a layer made of an organic material and a layer made of an inorganic material.
While the foregoing has described a photoelectric conversion layer containing tin naphthalocyanine and having sensitivity to the near-infrared wavelength region, the materials contained in the photoelectric conversion layers 15a and 15b are not limited to photoelectric conversion materials for use in the near-infrared wavelength region. For example, by containing subphthalocyanine as the p-type semiconductor and containing a fullerene and/or a fullerene derivative as the n-type semiconductor, the photoelectric conversion layer 15b can be a photoelectric conversion layer having sensitivity to the visible light wavelength region. Further, by containing copper phthalocyanine as the p-type semiconductor and containing the C60 fullerene as the n-type semiconductor, at least one of the photoelectric conversion layers 15a and 15b can be a photoelectric conversion layer having sensitivity to the ultraviolet wavelength region.
Further, the photoelectric conversion layers 15a and 15b are not limited in structure to the aforementioned examples. For example, the photoelectric conversion layer 15a does not need to include at least one of the hole blocking layer 150h, the electron blocking layer 150e, the p-type semiconductor layer 150p, and the n-type semiconductor layer 150n. Further, the photoelectric conversion layer 15b does not need to include at least one of the hole blocking layer 151h, the electron blocking layer 151e, the p-type semiconductor layer 151p, and the n-type semiconductor layer 151n.
Next, the photocurrent characteristics of the photoelectric conversion layers 15a and 15b are described. While the following representatively describes the photocurrent characteristic of the photoelectric conversion layer 15a of the first photoelectric converter 13a, the photoelectric conversion layer 15b of the second photoelectric converter 13b may have a similar photocurrent characteristic. Therefore, the photocurrent characteristic of the photoelectric conversion layer 15b of the second photoelectric converter 13b too may be described by reading “constituent elements such as the first photoelectric converter 13a and peripheral circuits connected to the first photoelectric converter 13a in the following description” as “corresponding constituent elements such as the second photoelectric converter 13b and peripheral circuits connected to the second photoelectric converter 13b”.
As shown in
For example, in a case where the applied bias voltage is switched between two voltage values in the first voltage range, the sensitivity of the first photoelectric converter 13a changes, as the absolute value of the output current density varies. Further, in a case where the applied bias voltage is switched between a voltage value of the first voltage range and a voltage value of the third voltage range, the sensitivity of the first photoelectric converter 13a changes in a similar fashion. Further, in this case, in the presence of the application of a bias voltage of a voltage value of the third voltage range, the sensitivity of the first photoelectric converter 13a is almost zero.
As in the case of the first photoelectric converter 13a, the sensitivity of the second photoelectric converter 13b is able to be changed by changing of a bias voltage that the voltage supply circuit 32b applies to the photoelectric conversion layer 15b.
The first to third voltage ranges may be distinguished from one another by the slopes of lines of the graph of the photocurrent characteristic when linear vertical and horizontal axes are used. For reference, in
Next, an operation example of the imaging device 100 according to the present embodiment is described. The operation example to be described below is specifically an operation example in which the imaging device 100 acquires an image.
More specifically, graph (a), at the top of
The following describes the operation example of the imaging device 100 with reference to
In the acquisition of an image, first, the resetting of the charge storage regions of each pixel 10a and each pixel 10b in the pixel array PA and the reading out of post-reset pixel signals are executed. For example, as shown in
In the resetting of a pixel 10b belonging to the R0_bth row, the address transistor 26b, whose gate is connected to the address control line 46b of the R0_bth row, is turned on by controlling the potential of the address control line 46b, and the reset transistor 28b, whose gate is connected to the reset control line 48b of the R0_bth row, is turned on by controlling the potential of the reset control line 48b. As a result of this, the charge storage node 41b and the reset voltage line 44b become connected to each other, and the reset voltage Vr is supplied to the charge storage region. That is, the potentials of the gate electrode 24g of the signal detection transistor 24b and the pixel electrode 11b of the second photoelectric converter 13b are reset to the reset voltage Vr. After that, a post-reset pixel signal is read out from the pixel 10b of the R0_bth row via the vertical signal line 47b. The pixel signal thus obtained is a pixel signal corresponding to the magnitude of the reset voltage Vr. After the reading out of the pixel signal, the reset transistor 28b and the address transistor 26b are turned off. In a case where a signal corresponding to the amount of signal charge stored in the pixel 10b in the preceding frame is read out, the reading out of a pixel signal may also be performed prior to a reset.
In this example, as shown in
The resetting and reading out of a pixel 10a in the R4_ath to R7_ath rows are performed in a manner similar to the aforementioned pixel 10b. Specifically, with the R4_ath row cited as an example, the address transistor 26a, whose gate is connected to the address control line 46a of the R4_ath row, is turned on by controlling the potential of the address control line 46a, and the reset transistor 28a, whose gate is connected to the reset control line 48a of the R4_ath row, is turned on by controlling the potential of the reset control line 48a. As a result of this, the charge storage node 41a and the reset voltage line 44a become connected to each other, and the reset voltage Vr is supplied to the charge storage region. That is, the potentials of the gate electrode 24g of the signal detection transistor 24a and the pixel electrode 11a of the first photoelectric converter 13a are reset to the reset voltage Vr. After that, a post-reset pixel signal is read out from the pixel 10a of the R4_ath row via the vertical signal line 47a. After the reading out of the pixel signal, the reset transistor 28a and the address transistor 26a are turned off. In a case where a signal corresponding to the amount of signal charge stored in the pixel 10a in the preceding frame is read out, the reading out of a pixel signal may also be performed prior to a reset.
As shown in
In the presence of the application of bias voltages in the third voltage range to the photoelectric conversion layers 15a and 15b, the migration of signal charge from the photoelectric conversion layers 15a and 15b to the charge storage regions hardly occurs. A reason for this is that in the presence of the application of bias voltages in the third voltage range to the photoelectric conversion layers 15a and 15b, most positive and negative charges generated by illumination with light rapidly recombine to disappear before being collected by the pixel electrode 11a or 11b. Accordingly, in the presence of the application of bias voltages in the third voltage range to the photoelectric conversion layers 15a and 15b, the storage of signal charge into the signal charge regions hardly occurs even when light falls on the photoelectric conversion layers 15a and 15b. This reduces the occurrence of unintended sensitivity in a period other than the exposure period. Such unintended sensitivity is also called “parasitic sensitivity”.
With attention focused on a certain row (e.g. the R0_bth row) in chart (g) of
Next, after the end of the resetting of all rows of the pixel array PA and the reading out of pixel signals, exposure periods of the pixels 10a belonging to the R4_ath to R7_ath rows are started in accordance with the horizontal synchronization signal Hss (time t9). In chart (g) of
The voltage supply circuit 32a switches the voltage that is applied to the counter electrode 12a again to the voltage V3_a, whereby the exposure periods of the pixels 10a belonging to the R4_ath to R7_ath rows end (time t14). Thus, in the present embodiment, switching of the voltage that is applied to the counter electrode 12a between the voltage V3_a and the voltage Ve_a enables switching between an exposure period and a non-exposure period. That is, an exposure period is defined by changing of a voltage that the voltage supply circuit 32a applies between the pixel electrode 11a and the counter electrode 12a. As can be seen from
Next, after the end of the exposure periods of the pixels 10a belonging to the R4_ath to R7_ath rows, exposure periods of the pixels 10b belonging to the R0_bth to R3_bth rows are started in accordance with the horizontal synchronization signal Hss (time t15). The exposure periods of the pixels 10b are started by the voltage supply circuit 32b switching the voltage that is applied to the counter electrode 12b to the voltage Ve_b, which is different from the voltage V3_b. The voltage Ve_b is a voltage (e.g. approximately 10 V) that causes the potential difference between the pixel electrode 11b and the counter electrode 12b to fall within the aforementioned first voltage range. By the voltage Ve_b being applied to the counter electrode 12b, signal charge (in the present embodiment, a hole) in the photoelectric conversion layer 15b is collected by the pixel electrode 11b and stored in a charge storage region including a charge storage node 41b.
The voltage supply circuit 32b switches the voltage that is applied to the counter electrode 12b again to the voltage V3_b, whereby the exposure periods of the pixels 10b belonging to the R0_bth to R3_bth rows end (time t29). Thus, in the present embodiment, switching of the voltage that is applied to the counter electrode 12b between the voltage V3_b and the voltage Ve_b enables switching between an exposure period and a non-exposure period. That is, an exposure period is defined by changing of a voltage that the voltage supply circuit 32b applies between the pixel electrode 11b and the counter electrode 12b. As can be seen from
Thus, the operation described here is an example in which driving in the global shutter method is applied to both pixels 10a having first photoelectric converters 13a and pixels 10b having second photoelectric converters 13b in the imaging device 100.
Further, as shown in
Further, the lighting device 200 causes the second light source 210b to emit light during the period from the start (time t15) of an exposure period of a pixel 10b to the end (time t29). That is, the second light source 210b of the lighting device 200 emits light in a period overlapping an exposure period of a pixel 10b including a second photoelectric converter 13b. In this example, a light-emitting period of the second light source 210b and an exposure period of the pixel 10b are the same period. This causes light reflected by the subject reflecting light emitted by the second light source 210b to fall on the first photoelectric converter 13a and the second photoelectric converter 13b during the exposure period of the pixel 10b. Further, the second light source 210b is turned off during a non-exposure period of the pixel 10b.
In the camera system 1, the timing of emission of light by the lighting device 200 is controlled, for example, by the controller 300. The controller 300 for example acquires a signal representing a driving timing of a pixel in the imaging device 100 from the imaging device 100 and controls the emission of light by the lighting device 200 in accordance with the signal thus acquired. Further, the controller 300 may output, to the imaging device 100 and the lighting device 200, a signal that controls the timing of an exposure period in the imaging device 100 and the timing of a light-emitting period in the lighting device 200.
Thus, the lighting device 200 emits light by causing the first light source 210a and the second light source 210b to be lit in conjunction with the respective exposure periods of the pixels 10a and 10b. This causes the subject to be illuminated in an exposure period with illuminating light in a wavelength range to which the first photoelectric converter 13a or the second photoelectric converter 13b has sensitivity, making it possible to improve the image quality of an image that is taken by the imaging device 100. Further, the lighting device 200 does not emit light in the respective non-exposure periods of the pixels 10a and 10b. This makes it possible to achieve increased longevity and energy reduction of the first light source 210a and the second light source 210b.
Further, in the present operation example, as shown in
Further, apart from the above, also in a case where light emitted by a near-infrared light source does not have a component of visible light as part thereof, the second photoelectric converter 13b may generate unintended signal charge. For example, there is a case where the wavelength region to which the second photoelectric converter 13b has sensitivity may extend into part of the near-infrared wavelength region as well as the second wavelength region in the visible light wavelength region. Specifically, for example, there is a case where the second photoelectric converter 13b also has sensitivity to a wavelength range of approximately 680 nm to 720 nm. In this case, even when the first light source 210a emits only near-infrared radiation having a component ranging from 700 nm to 1100 nm, the near-infrared radiation may fall on the second photoelectric converter 13b to effect photoelectric conversion in the second photoelectric converter 13b. Even in such a case, a component of light that affects the photoelectric conversion of the second photoelectric converter 13b is inhibited from falling on the second photoelectric converter 13b to cause the second photoelectric converter 13b to generate unintended signal charge, as the first light source 210a does not emit light in the exposure period of the pixel 10b. This results, for example, in making it possible to inhibit a color shift from occurring in the image taken.
Next, the reading out of signal charge from pixels belonging separately to each row of the pixel array PA is performed in accordance with the horizontal synchronization signal Hss. In this example, the reading out of signal charge from pixels belonging separately to each of the R0_bth to R3_bth and R4_ath to R7_ath rows are executed in sequence on a row-by-row basis from time t31. In the following, the period from selection of a pixel belonging to one row to reselection of a pixel belonging to the row is sometimes called “IV period”. In this example, a period from time t0 to time t31 is equivalent to a 1V period. A 1V period is equivalent, for example, to a one-frame period. Further, a 1V period is equal in length to a cycle of timing of a falling edge (or a rising edge) of the vertical synchronization signal Vss.
In the reading out of signal charge from a pixel 10b belonging to the R0_bth row after the end of an exposure period, the address transistor 26b of the R0_bth row is turned on. This causes a pixel signal corresponding to the amount of signal charge stored in the charge storage region of the pixel 10b in the exposure period to be outputted to the vertical signal line 47b. The reading out of the pixel signal may be followed by turning on the reset transistor 28b to perform the resetting of the pixel 10b and, if necessary, the reading out of a post-reset pixel signal. After the reading out of the pixel signal or after the resetting of the pixel 10b, the address transistor 26b and, if necessary, the reset transistor 28b are turned off. The same operation is sequentially executed on a row-by-row basis on pixels 10b belonging separately to each of the R1_bth to R3_bth rows and pixels 10a belonging separately to each of the R4_ath to R7_ath rows.
Readout after the end of an exposure period of a pixel 10a in the R4_ath to R7_ath rows is performed in a manner similar to a pixel 10b. Specifically, with the R4_ath row cited as an example, first, the address transistor 26a of the R4_ath row is turned on. This causes a pixel signal corresponding to the amount of signal charge stored in the charge storage region of the pixel 10a in the exposure period to be outputted to the vertical signal line 47a. The reading out of the pixel signal may be followed by turning on the reset transistor 28a to perform the resetting of the pixel 10a and, if necessary, the reading out of a post-reset pixel signal. After the reading out of the pixel signal or after the resetting of the pixel 10a, the address transistor 26a and, if necessary, the reset transistor 28a are turned off. The same operation is sequentially executed on a row-by-row basis on pixels 10a belonging separately to each of the R5_ath to R7_ath rows.
After the reading out of signal charge from pixels belonging separately to each row of the pixel array PA after the exposure periods has been performed since time t31, signals from which stationary noise has been removed are obtained by taking the differences between signals read out after the exposure periods and signals read out during the period between time t0 and time t8. In a case where resets are performed after the reading out of pixel signals since t31 after the exposure periods, signals from which stationary noise has been removed may be obtained by taking the differences between readouts of pixel signals after the resets and readouts of pixel signals before the resets. In this case, it is not necessary to read out pixel signals after the resets during the period between time t0 and time t8.
In a non-exposure period of a pixel 10a, during which the voltage V3_a is applied to the counter electrode 12a, a bias voltage in the third voltage range is applied to the photoelectric conversion layer 15a of the first photoelectric converter 13a. Further, in a non-exposure period of a pixel 10b, during which the voltage V3_b is applied to the counter electrode 12b, a bias voltage in the third voltage range is applied to the photoelectric conversion layer 15b of the second photoelectric converter 13b. Therefore, the storage of signal charge into the signal charge regions hardly occurs even when light falls on the photoelectric conversion layer 15a and the photoelectric conversion layer 15b. This inhibits the generation of noise attributed to unintended contamination with electric charge.
From the point of view of inhibiting further storage of signal charge into a charge storage region, it is conceivable that an exposure period may be ended by applying, to the counter electrode 12a, a voltage obtained by reversing the polarity of the aforementioned voltage Ve_a. However, simply reversing the polarity of the voltage that is applied to the counter electrode 12a may cause already-stored signal charge to migrate to the counter electrode 12a via the photoelectric conversion layer 15a. The migration of signal charge from the charge storage region to the counter electrode 12a via the photoelectric conversion layer 15a is observed, for example, as a black spot in the image acquired. That is, the migration of signal charge from the charge storage region to the counter electrode 12a via the photoelectric conversion layer 15a can be a factor for negative parasitic sensitivity. The same applies to a case where a voltage obtained by reversing the polarity of the aforementioned voltage Ve_b is applied to the counter electrode 12b.
In the example, since the voltages that are applied to the counter electrodes 12a and 12b are changed again to the voltages V3_a and V3_b, respectively, after the end of exposure periods, bias voltages in the third voltage range are applied to the photoelectric conversion layers 15a and 15b after the storage of signal charge into the charge storage regions. In the presence of the application of bias voltages in the third voltage range, it is possible to inhibit signal charge already stored in a charge storage region from migrating to the counter electrode 12a via the photoelectric conversion layer 15a. Similarly, it is possible to inhibit signal charge already stored in a charge storage region from migrating to the counter electrode 12b via the photoelectric conversion layer 15b. In other words, the application of bias voltages in the third voltage range to the photoelectric conversion layers 15a and 15b makes it possible to retain, in the charge storage regions, signal charge stored during the exposure periods. This makes it possible to reduce the occurrence of negative parasitic sensitivity due to a loss of signal charge from the charge storage regions.
Thus, in the present embodiment, the starts and ends of exposure periods are controlled by the voltage Vb_a, which is applied to the counter electrode 12a, and the voltage Vb_b, which is applied to the counter electrode 12b. That is, the present embodiment makes it possible to achieve a global shutter function without providing a transfer transistor or other components in each pixel 10a or each pixel 10b. The present embodiment, in which an electronic shutter is executed by controlling the voltages Vb_a and Vb_b without transferring signal charge via a transfer transistor, makes faster operation possible. Further, not needing to separately provide a transfer transistor or other components in each pixel 10a or each pixel 10b is advantageous to finer pixels.
As noted above, in the present operation example, the exposure period of the pixel 10b does not overlap a light-emitting period of light from the first light source 210a having a luminescence peak in the first wavelength range, which is invisible and to which the first photoelectric converter 13a has sensitivity. As a result of this, light from the first light source 210a does not affect the photoelectric conversion of the second photoelectric converter 13b. Therefore, an image taken with the second photoelectric converter 13b is outputted in a state where a component of light that affects the photoelectric conversion of the second photoelectric converter 13b is inhibited from falling on the second photoelectric converter 13b to cause the second photoelectric converter 13b to generate unintended signal charge. Therefore, the imaging device 100 can reduce image quality degradation.
Further, in the present operation example, an exposure period of a pixel 10a is shorter than an exposure period of a pixel 10b. For example, in a case where the first photoelectric converter 13a of the pixel 10a has sensitivity to the near-infrared wavelength region, the first photoelectric converter 13a tends to produce a dark current due to thermal excitation, as the first photoelectric converter 13a is made of a photoelectric conversion material having a narrow bandgap. Therefore, when an exposure period of a pixel 10a is shorter than an exposure period of a pixel 10b, it is possible to reduce the influence of a dark current and reduce degradation in image quality. Further, a period of emission of light by the lighting device 200, which emits illuminating light in an exposure period of a pixel 10a, can be shortened. This makes it possible to lower power consumption and increase the longevity of the light sources.
Although, in the present operation example, the reading out and resetting of pixels belonging separately to each of the R0_bth to R3_bth and R4_ath to R7_ath rows are executed in sequence on a row-by-row basis, this is not intended to impose any limitation. The reading out and resetting of the pixels 10b of the R0_bth to R3_bth rows and the reading out and resetting of the pixels 10a of the R4_ath to R7_ath rows may be performed in an overlapping period, provided readout circuits are independently configured.
Further, in the present operation example, a light-emitting period of the first light source 210a and an exposure period of a pixel 10a do not need to be the same period, provided they overlap each other. Similarly, a light-emitting period of the second light source 210b and an exposure period of a pixel 10b do not need to be the same period, provided they overlap each other.
Further, in the present operation example, the second light source 210b does not need to emit light. For example, in a case where the second photoelectric converter 13b has sensitivity to the visible light wavelength region, it is easy to take an image with the second photoelectric converter 13b by means of ambient light.
Further, in the present operation example, the light having a luminescence peak in the first wavelength range, to which the first photoelectric converter 13a has sensitivity, may be emitted from another lighting device or other devices other than the lighting device 200.
Further, in the present operation example, an exposure period of a pixel 10a may be equal to or longer than an exposure period of a pixel 10b.
Further, even in a case where the imaging device 110 is used instead of the imaging device 100, the imaging device 110 operates such that a light-emitting period of the first light source 210a does not overlap an exposure period of a pixel including a photoelectric converter other than the first photoelectric converter 13a.
Next, a comparative example of operation of the imaging device 100 is described.
First, the resetting of the charge storage regions of each pixel 10a and each pixel 10b in the pixel array PA and the reading out of post-reset pixel signals are executed. For example, as shown in
Next, while the resetting of the charge storage regions of each pixel 10a and each pixel 10b in the pixel array PA and the reading out of post-reset pixel signals are being executed, the voltage supply circuit 32b switches the voltage that is applied to the counter electrode 12b to the voltage Ve_b, which is different from the voltage V3_b, whereby exposure periods of the pixels 10b belonging to the R0_bth to R3_bth rows are started (time t5). Further, the second light source 210b starts emitting light at the same time as the start of the exposure periods of the pixels 10b (time t5).
Next, after the end of the resetting of all rows of the pixel array PA and the reading out of pixel signals and during the exposure periods of the pixels 10b, the voltage supply circuit 32a switches the voltage that is applied to the counter electrode 12a to the voltage Ve_a, which is different from the voltage V3_a, in accordance with the horizontal synchronization signal Hss, whereby exposure periods of the pixels 10a belonging to the R4_ath to R7_ath rows are started (time t9). Further, the first light source 210a starts emitting light at the same time as the start of the exposure periods of the pixels 10a (time t9). The time t9, at which the first light source 210a starts emitting light, is in the middle of the exposure periods of the pixels 10b. Therefore, during the exposure periods of the pixels 10b, light from the first light source 210a tends to fall on the second photoelectric converters 13b to cause the second photoelectric converters 13b to generate unintended signal charge.
Further, at the time t9, at which the exposure periods of the pixels 10a are started, the second light source 210b is emitting light. Therefore, during the exposure periods of the pixels 10a, light from the second light source 210b tends to fall on the first photoelectric converters 13a to cause the first photoelectric converters 13a to generate unintended signal charge.
Next, the voltage supply circuit 32b switches the voltage that is applied to the counter electrode 12b again to the voltage V3_b, whereby the exposure periods of the pixels 10b belonging to the R0_bth to R3_bth rows end (time t29). The second light source 210b ends the emission of light at the same time as the end of the exposure periods of the pixels 10b (time t29).
After the end of the exposure periods of the pixels 10b belonging to the R0_bth to R3_bth rows, the reading out of signal charge from pixels belonging separately to each row of the pixel array PA is performed. In this example, the reading out of signal charge from pixels belonging separately to each of the R0_bth to R3_bth and R4_ath to R7_ath rows are executed in sequence on a row-by-row basis from time t31.
Next, the voltage supply circuit 32a switches the voltage that is applied to the counter electrode 12a again to the voltage V3_a, whereby the exposure periods of the pixels 10a belonging to the R4_ath to R7_ath rows end (time t33). Further, the first light source 210a ends the emission of light at the same time as the end of the exposure periods of the pixels 10a (time t33).
Thus, in the comparative example, an exposure period of a pixel 10b overlaps a light-emitting period of the first light source 210a. Therefore, during the exposure period of the pixel 10b, light from the first light source 210a falls on the second photoelectric converter 13b to cause the second photoelectric converter 13b to generate unintended signal charge. This causes degradation in the image quality of an image that is taken with the second photoelectric converter 13b.
For example, in a case where the first wavelength range is a range of wavelengths in a near-infrared wavelength region, the second wavelength range is a range of wavelengths in a visible light wavelength region, and a visible light image and a near-infrared image are acquired by the imaging device 100, a color filter may be provided above the second photoelectric converter 13b. The color filter includes, for example, a color filter that transmits red and near-infrared wavelengths, a color filter that transmits green and near-infrared wavelengths, and a color filter that transmits blue and near-infrared wavelengths. These color filters are arranged, for example, in a Bayer array in the photosensitive region. In this case, the light emitted by the first light source 210a, which has a luminescence peak in the near-infrared wavelength region, may also have a component at a red wavelength. Therefore, when the first light source 210a emits light in an exposure period of the pixel 10b, light from the first light source 210a falls on the second photoelectric converter 13b after passing through the color filter that transmits red and near-infrared wavelengths. As a result of that, the generation of unintended signal charge in the pixel 10b provided with the color filter that transmits red and near-infrared wavelengths causes a color shift to occur in the image taken.
Meanwhile, in the aforementioned operation example of the imaging device 100, an exposure period of a pixel 10b does not overlap a light-emitting period of the first light source 210a. This prevents unintended signal charge from being generated as in the case of the comparative example, making it possible to reduce degradation in the image quality of an image that is taken with the second photoelectric converter 13b.
Although the foregoing had been described with reference to an example in which a color filter is provided, this is not intended to impose any limitation. Even in the absence of a color filter in the imaging device 100, an effect of reducing image quality degradation is brought about, as degradation in image quality occurs regardless of the presence or absence of a color filter.
While the foregoing has described an imaging device and a camera system according to the present disclosure with reference to embodiments, the present disclosure is not intended to be limited to these embodiments. Various modifications conceived of by persons skilled in the art are encompassed in the scope of the present disclosure. Further, constituent elements of different embodiments may be arbitrarily combined without departing from the scope of the present disclosure.
For example, although, in the aforementioned embodiment, the first photoelectric converter 13a and the second photoelectric converter 13b are stacked, this is not intended to impose any limitation. For example, the first photoelectric converter 13a and the second photoelectric converter 13b may be arranged side by side in the same plane above the semiconductor substrate 20.
Further, for example, although, in the foregoing embodiment, the imaging device 100 drives both the pixels 10a and 10b by the global shutter method, this is not intended to impose any limitation. The imaging device 100 may switch the driving of at least either the pixels 10a or 10b from the global shutter method to the rolling shutter method depending on the subject. In the rolling shutter driving of the pixels 10a, the voltage that the voltage supply circuit 32a applies to the counter electrode 12a may be fixed at the voltage Ve_a both in an exposure period and a non-exposure period. In this case, an exposure period can be defined by the time from the timing of a reset of a charge storage region including a charge storage node 41a to a signal readout. Similarly, in the rolling shutter driving of the pixels 10b, the voltage that the voltage supply circuit 32b applies to the counter electrode 12b may be fixed at the voltage Ve_b both in an exposure period and a non-exposure period. In this case, an exposure period can be defined by the time from the timing of a reset of a charge storage region including a charge storage node 41b to a signal readout.
Further, for example, in the foregoing embodiment, the circuits connected to the pixels 10a and the circuits connected to the pixel 10b may be partially shared. For example, at least any of the voltage supply circuits 32a and 32b, the reset voltage sources 34a and 34b, the vertical scanning circuits 36a and 36b, the horizontal signal readout circuits 38a and 38b, and the power wires 40a and 40b may be a single shared circuit connected to both the pixels 10a and 10b.
Further, for example, in the foregoing embodiment, the signal detection circuit 14a and the signal detection circuit 14b may share some circuit element. For example, by having switches or other pieces of equipment capable of switching between connections to the charge storage node 41a and the charge storage node 41b, the signal detection circuit 14a and the signal detection circuit 14b may share a circuit element subsequent to a signal detection transistor or an address transistor.
Further, although, in the foregoing embodiment, the signal detection transistors 24a and 24b, the address transistors 26a and 26b, and the reset transistors 28a and 28b are N-channel MOSFETs, this is not intended to impose any limitation. At least one of the signal detection transistors 24a and 24b, the address transistors 26a and 26b, and the reset transistors 28a and 28b may be a P-channel MOSFET. Further, at least one of the signal detection transistors 24a and 24b, the address transistors 26a and 26b, and the reset transistors 28a and 28b may be not a field-effect transistor but another transistor such as a bipolar transistor.
Further, although, in the foregoing embodiment, the first photoelectric converter 13a and the second photoelectric converter 13b are each configured to have a photoelectric conversion layer sandwiched between a pair of electrodes and a pair of electrodes, this is not intended to impose any limitation. For example, one of the first photoelectric converter 13a and the second photoelectric converter 13b may be configured to have a photodiode provided over the semiconductor substrate 20.
The imaging device 500 according to Modification 2 differs from the imaging device 100 according to the embodiment in that the imaging device 500 includes pixels 510b instead of the pixels 10b and does not include the voltage supply circuit 32b. The pixels 510b are each configured to have a second photoelectric converter 513b and a charge storage node 541b instead of the second photoelectric converter 13b and the charge storage node 41b of a pixel 10b and further have a transfer transistor 25b. In the present modification, each of the pixels 510b is an example of the second pixel.
The imaging device 500 according to Modification 2 is provided in the camera system 1, for example, instead of the imaging device 100.
As shown in
Each pixel 510b has a second photoelectric converter 513b, a signal detection circuit 14b, a transfer transistor 25b, and a reset transistor 28b. As will be described later with reference to the drawings, the second photoelectric converter 513b has a photodiode provided over the semiconductor substrate 20 and generates signal charge upon receiving incident light. The second photoelectric converter 513b has sensitivity, for example, to a range of wavelengths in the visible light wavelength region.
In the pixel 510b, the signal detection circuit 14b detects signal charge generated by the second photoelectric converter 513b.
The transfer transistor 25b may be a field-effect transistor. Unless otherwise noted, the following describes an example in which an N-channel MOSFET is applied as the reset transistor 25b. It should be noted that the transfer transistor 25b may be a P-channel MOSFET. Further, the transfer transistor 25b may be not a field-effect transistor but another transistor such as a bipolar transistor.
As schematically shown in
These transfer control lines 43b are connected to the vertical scanning circuit 36b for each separate pixel row. Accordingly, the vertical scanning circuit 36b applies a predetermined voltage to the transfer control lines 43b, whereby signal charge of the second photoelectric converters 513b of a plurality of pixels 510b arranged in each row can be transferred to the charge storage nodes 541b on a row-by-row basis.
In each of the pixels 510b, the control terminal of the signal detection transistor 24b is connected to the charge storage node 541b. The signal detection transistor 24b amplifies and outputs signal charge transferred from the second photoelectric converter 513b to the charge storage region including the charge storage node 541b.
In each of the pixels 510b, the reset transistor 28b is connected between the reset voltage line 44b and the charge storage node 541b. The control terminal of the reset transistor 28b is connected to a reset control line 48b, and by controlling the potential of the reset control line 48b, the potential of the charge storage node 541b can be reset to the reset voltage Vr. Further, in a case where the transfer transistor 25b is in an on-state, the potential of the second photoelectric converter 513b too is reset at the same time as that of the charge storage node 541b.
Next, a cross-section structure of pixels of the imaging device 500 according to Modification 2 is described.
As shown in
The semiconductor substrate 20 has impurity regions 25d and 513s. The impurity regions 25d and 513s are N-type regions here. The impurity regions 25d and 513s are for example diffusion layers formed in the semiconductor substrate 20.
The second photoelectric converter 513b is for example an embedded silicon photodiode, formed in the semiconductor substrate 20, that includes the impurity region 513s. These impurity regions 513s are provided separately for each of the pixels 510b.
The transfer transistor 25b includes the impurity region 25d, part of the impurity region 513s, and a gate electrode 25g connected to the transfer control line 43b (see
In the imaging device 500, a contact plug 57b and a wire 58b are formed in the interlayer insulating layer 50. The contact plug 57b is made, for example, of polysilicon rendered conductive by being doped with an impurity. The wire 58b is made, for example, of a metal such as copper. The impurity region 25d is connected to a first end of the contact plug 57b. A second end of the contact plug 57b is connected to the wire 58b. The contact plug 57b and the wire 58b constitute part of the charge storage node 541b (see
In the imaging device 500, the first photoelectric converter 13a is stacked above the second photoelectric converter 513b via the interlayer insulating layer 50. The first photoelectric converter 13a overlaps, in a plan view, a charge storage region connected to the second photoelectric converter 513b. It should be noted that the first photoelectric converter 13a and the second photoelectric converter 513b do not need to overlap each other in a plan view.
In the imaging device 500, the pixel electrode 11a of the first photoelectric converter 13a is for example a transparent electrode. Since, in the example shown in
Next, an operation example of the imaging device 500 according to Modification 2 is described. The operation example to be described below is specifically an operation example in which the imaging device 500 acquires an image. A description of the operation example of the imaging device 500 is given with a focus on points of difference from the operation example of the imaging device 100, and a description of common features are omitted or simplified.
In the present operation example, signal readout periods and exposure periods of the pixels 10a are identical in timing to those of the pixels 10a of the operation example of the imaging device 100. Further, in the present operation example, signal readout periods and exposure periods of the pixels 510b are identical in timing to those of the pixels 10b of the operation example of the imaging device 100.
In the present operation example, operation that is similar to that of the operation example of the imaging device 100 described with reference to
Next, the vertical scanning circuit 36b temporarily switches the voltage Vtg, which is applied to the control terminal of the transfer transistor 25b, from the voltage VL to the voltage VH, whereby the exposure period of each of the pixels 510b ends (time t29). As a result of this, the transfer transistor 25b is temporarily turned off, and signal charge stored in the second photoelectric converter 513b is transferred via the transfer transistor 25b to the charge storage region including the charge storage node 541b. From the end of exposure to the signal readout period of the pixel 510b, the reset transistor 28b is off, and the signal charge transferred from the second photoelectric converter 513b to the charge storage region of the pixel 510b and stored in the charge storage region is sequentially read out in the signal readout period of the pixel 510b. Although, in the example shown in
Further, as shown in
Further, the lighting device 200 causes the second light source 210b to emit light during the period from the start (time t15) of an exposure period of a pixel 510b to the end (time t29). That is, the second light source 210b of the lighting device 200 emits light in a period overlapping an exposure period of a pixel 510b including a second photoelectric converter 513b. In this example, a light-emitting period of the second light source 210b and an exposure period of the pixel 510b are the same period. This causes light reflected by the subject reflecting light emitted by the second light source 210b to fall on the first photoelectric converter 13a and the second photoelectric converter 513b during the exposure period of the pixel 510b. Further, the second light source 210b is turned off during a non-exposure period of the pixel 510b.
Further, in the operation example of the imaging device 500 too, as in the operation example of the imaging device 100, the exposure period (from time t15 to time t29) of the pixel 510b does not overlap the light-emitting period (from time t9 to time t14) of the first light source 210a in the lighting device 200. That is, the first light source 210a does not emit light in the exposure period of the pixel 510b. Therefore, light from the first light source 210a does not affect the photoelectric conversion of the second photoelectric converter 513b. As a result of this, a component of light that affects the photoelectric conversion of the second photoelectric converter 513b is inhibited from falling on the second photoelectric converter 513b to cause the second photoelectric converter 513b to generate unintended signal charge. Therefore, the imaging device 500 can reduce image quality degradation.
An imaging device according to the present disclosure is applicable, for example. to an image sensor or other sensors. Further, an imaging device according to the present disclosure can be used in a camera for medical use, a camera for use in a robot, a security camera, a camera that is mounted on a vehicle for use, or other cameras.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2021-196519 | Dec 2021 | JP | national |
| 2022-131170 | Aug 2022 | JP | national |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/JP2022/041784 | Nov 2022 | WO |
| Child | 18664980 | US |
