Light-receiving element, and distance-measuring device

Abstract

The present disclosure relates to a light-receiving element and a distance-measuring device with which it is possible to calculate an accurate distance measurement value even in a pixel at the boundary portion of spot light. This light-receiving element comprises a pixel array unit having a pixel group composed of 4 pixels arranged 2 × 2, the pixel array unit receiving reflected light resulting from irradiation light reflected by a subject at light-receiving timings of which the phase is shifted by 0°, 90°, 180°, and 270° with respect to the irradiation timing of irradiation light emitted from a prescribed light source at a prescribed modulation frequency. The pixel array unit has a first inter-pixel separation unit for separating a semiconductor layer up to at least a portion in the depth direction of the semiconductor layer at a pixel boundary part between adjacent pixel groups, and either has a second inter-pixel separation unit of a different type from the first inter-pixel separation unit, or has neither the first inter-pixel separation unit nor the second inter-pixel separation unit, at a pixel boundary part between adjacent pixels within the pixel group. The present technology can be applied to, e.g., a distance-measuring device that measures the distance to a subject.

Description

Light-receiving element and distance measuring device

[0001] The present disclosure relates to a light-receiving element and a distance measuring device, and particularly to a light-receiving element and a distance measuring device capable of calculating an accurate distance measurement value even for pixels at the boundary portion of a spot light.

[0002] As a distance measuring method in a distance measuring module, an indirect ToF method (Indirect Time of Flight) is generally known. In this indirect ToF method, the time from when pattern light is irradiated toward an object until it is received as reflected light is detected as a phase difference, and the distance to the object is calculated based on this phase difference.

[0003] As a light-receiving element of a distance measuring module, for example, in Patent Document 1, by providing an inter-pixel trench portion that digs into a semiconductor substrate from the back side in the substrate depth direction to a predetermined depth to separate adjacent pixels at the pixel boundary portion, it is possible to prevent incident light from penetrating into an adjacent pixel and confine it within its own pixel, and also prevent leakage of incident light from adjacent pixels. A light-receiving element having such a pixel structure is disclosed.

[0004] Japanese Patent Publication No. 2022-549577

[0005] When an inter-pixel trench portion is provided at the pixel boundary portion of each pixel, when the irradiation light irradiated onto an object is a spot light, in the pixels at the boundary portion of the spot light, the amount of light received varies depending on the pixel, and an accurate distance measurement value may not be able to be calculated.

[0006] The present disclosure has been made in view of such a situation, and enables an accurate distance measurement value to be calculated even for pixels at the boundary portion of a spot light.

[0007] The first aspect of the present disclosure includes a pixel array having a 2x2 array of 4 pixels that receives reflected light reflected by a subject at light receiving timings shifted by 0°, 90°, 180°, and 270° in phase with respect to the irradiation timing of irradiation light irradiated from a predetermined light source at a predetermined modulation frequency, wherein the pixel array has a first inter-pixel separation portion at the pixel boundary between adjacent pixel groups that separates the semiconductor layer to at least a portion of the depth direction of the semiconductor layer, and the pixel boundary between adjacent pixels within the pixel group has a second inter-pixel separation portion of a different type from the first inter-pixel separation portion, or is configured not to have either the first inter-pixel separation portion or the second inter-pixel separation portion.

[0008] A distance measuring device according to a second aspect of the present disclosure comprises a predetermined light source that irradiates an object with illumination light at a predetermined modulation frequency, and a light-receiving element that receives reflected light from the object, wherein the light-receiving element includes a pixel array section having a 2x2 array of 4 pixels that receives the reflected light at reception timings shifted by 0°, 90°, 180°, and 270° in phase with respect to the illumination timing of the illumination light, wherein the pixel array section has a first inter-pixel separation section at the pixel boundary between adjacent pixel groups that separates the semiconductor layer to at least a portion of the depth direction of the semiconductor layer, and the pixel boundary between adjacent pixels within the pixel group has a second inter-pixel separation section of a different type from the first inter-pixel separation section, or is configured to have neither the first inter-pixel separation section nor the second inter-pixel separation section.

[0009] In the first and second aspects of this disclosure, a pixel array is provided with a 2x2 array of 4 pixels that receive reflected light reflected by a subject at light receiving timings shifted by 0°, 90°, 180°, and 270° in phase with respect to the irradiation timing of irradiation light irradiated from a predetermined light source at a predetermined modulation frequency. The pixel array is provided with a first inter-pixel separation section at the pixel boundary between adjacent pixel groups, separating the semiconductor layer to at least a portion of the depth direction of the semiconductor layer. The pixel boundary between adjacent pixels within a pixel group is either a second inter-pixel separation section of a different type from the first inter-pixel separation section, or a configuration in which neither the first nor the second inter-pixel separation section is present.

[0010] The light-receiving element and the distance measuring device may be independent devices or modules incorporated into other devices.

[0011] This figure shows a schematic configuration example of a distance measuring device to which this technology is applied. This is a block diagram showing a configuration example of the light-receiving element in Figure 1. This figure shows a functional arrangement example of pixels in the pixel array section. This figure shows an arrangement example of the first modulation frequency and the second modulation frequency. This figure shows an arrangement example of the first modulation frequency and the second modulation frequency. This figure shows a detailed circuit configuration example of a pixel. This figure explains the emission of illumination light and the driving of the pixel. This figure explains the exposure period at each phase of 0°, 90°, 180°, and 270°. This is a time chart showing an example of pixel driving in the pixel array section. This figure explains the calculation of distance measurement values ​​based on Dual Freq operation. This figure explains the calculation of distance measurement values ​​based on Dual Freq operation. This is a time chart showing another example of pixel driving in the pixel array section. This is a cross-sectional view showing a first configuration example of a pixel. This is a plan view showing a first configuration example of a pixel. This figure explains the effect of the first configuration example of a pixel. This figure explains the effect of the inter-pixel separation section. This is a cross-sectional view showing a modified example of the first configuration example of a pixel. This is a cross-sectional view showing a second configuration example of a pixel. This is a plan view showing a second configuration example of a pixel. This is a plan view showing a second example of pixel configuration. This is a cross-sectional view showing a first modified example of the second example of pixel configuration. This is a cross-sectional view showing a second modified example of the second example of pixel configuration. This is a cross-sectional view showing a third example of pixel configuration. This is a plan view showing a third example of pixel configuration. This is a cross-sectional view showing a fourth example of pixel configuration. This is a plan view showing a fourth example of pixel configuration.

[0012] The following describes the embodiments for implementing this technology (hereinafter referred to as "embodiments") with reference to the attached drawings. The explanation will proceed in the following order: 1. Example of distance measuring device configuration 2. Example of light receiving element configuration 3. Calculation process of distance measurement value 4. First pixel configuration example 5. Modification of the first configuration example 6. Second pixel configuration example 7. Modification of the second configuration example 8. Third pixel configuration example 9. Fourth pixel configuration example 10. Summary of the first to fourth pixel configuration examples

[0013] In the drawings referenced in the following explanation, identical or similar parts are denoted by the same or similar reference numerals, thereby omitting redundant explanations as appropriate. The drawings are schematic, and the relationship between thickness and planar dimensions, the ratio of the thickness of each layer, etc., may differ from the actual figures. Furthermore, there may be parts where the dimensional relationships and ratios differ between drawings.

[0014] Furthermore, the definitions of directions such as up and down in the following explanation are merely for explanatory convenience and do not limit the technical concept of this disclosure. For example, if an object is rotated 90° and observed, up and down will be converted to left and right and read accordingly, and if it is rotated 180° and observed, up and down will be inverted and read accordingly.

[0015] This technology can be applied to all types of photodetectors that have a pixel array section in which pixels are arranged in a matrix in two dimensions, and that convert incident light into photoelectric light to output a pixel signal corresponding to the amount of light. The light to be detected may be light in the visible light region including wavelengths such as R (Red), G (Green), and B (Blu), or it may be light in the invisible light region such as infrared light. Alternatively, it may be light from both the visible and invisible light regions. The photodetector can be used as a solid-state imaging device that generates and outputs an imaging signal corresponding to the amount of incident light, or as a light-receiving device (distance sensor) in a distance measuring device that receives light (reflected light) reflected from an object after infrared light has been irradiated as active light, and measures the distance to the subject using a direct ToF (Time of Flight) or indirect ToF (Time of Flight) method. Below, we will describe an example in which this technology is applied to a distance measuring device that includes a light-receiving device that receives light reflected from an object after infrared light has been irradiated as active light, and measures the distance to the subject using an indirect ToF (Time of Flight) method.

[0016] <1. Example of Rangefinder Configuration> Figure 1 shows a schematic example of a rangefinder configuration to which this technology is applied.

[0017] The distance measuring device 1 in Figure 1 comprises a control device 11, a light receiving device 12, and an illumination device 13. The light receiving device 12 comprises a light receiving element 31 and a lens 32. The illumination device 13 comprises an LD 21 and a light-emitting unit 22.

[0018] The control device 11 is a device that controls the operation of the entire distance measuring device 1. The control device 11 supplies a measurement request to the light receiving device 12, specifying the operating mode. The control device 11 also acquires measurement data generated by the light receiving device 12 based on the results received by the light receiving device 12 in response to the measurement request. The control device 11 is not part of the configuration of the distance measuring device 1, but may be provided outside the distance measuring device 1, for example, as the control unit of a host device into which the distance measuring device 1 is incorporated.

[0019] Here, the control device 11 can specify to the light receiving device 12 an operating mode, which includes a distance measurement mode that measures the distance to an object using an indirect Time-of-Flight (TOF) method, and a 2D image capture mode that generates a two-dimensional brightness image. The indirect ToF method of distance measurement is a method of distance measurement that detects the time of flight from the moment the irradiated light is emitted to the moment the reflected light is received as a phase difference, and calculates the distance to the object. The 2D image capture mode is a mode that outputs a two-dimensional brightness image according to the amount of light received, like a normal image sensor. The distance measuring device 1 also has multiple distance measurement modes. Details of the distance measurement modes will be described later.

[0020] When a measurement request is supplied from the control device 11, the light-receiving element 31 of the light-receiving device 12 supplies a light-emitting pulse to the LD 21 under the control of the control unit 51 (see Figure 2, described later), causing the light-emitting unit 22 to emit illumination light. The light-receiving element 31 then receives reflected light from subjects such as objects 41 and 42 through the lens 32. The lens 32 forms an image of the reflected light from the subjects as incident light on the light-receiving surface of the light-receiving element 31. The configuration of the lens 32 is arbitrary; for example, it is possible to configure the lens 32 using multiple lens groups.

[0021] The light emission pulse is a timing signal that serves as a reference for the light emission operation of the light emission unit 22 and the light receiving operation of the light receiving element 31. For example, it is a pulse signal that alternates between on (high) and off (low). For example, the light receiving element 31 generates a pulse signal with modulation frequency Fmod 1 in the first period, and then generates a pulse signal with modulation frequency Fmod 2, which is different from modulation frequency Fmod 1, in the second period. Modulation frequency Fmod 1 is a low-frequency frequency, for example, 20 MHz. On the other hand, modulation frequency Fmod 2 is a high-frequency frequency, for example, 100 MHz. The distance measurement accuracy on the Fmod 1 side corresponds to, for example, 7.5 [m] for 360 degrees. On the other hand, the distance measurement accuracy on the Fmod 2 side corresponds to, for example, 1.5 [m] for 360 degrees. In other words, when generating a single depth image, distance measurement using a pulse signal with modulation frequency Fmod1 (Coarse Depth) and distance measurement using a pulse signal with modulation frequency Fmod2 (Fine Depth) are performed. In the following, modulation frequency Fmod1 will be referred to as the first modulation frequency Fmod1, and modulation frequency Fmod2 will be referred to as the second modulation frequency Fmod2.

[0022] When the operating mode is distance measurement mode, the light-receiving element 31 generates a depth image containing distance information to the subject based on the reflected light reception result and outputs it to the control device 11 as measurement data. On the other hand, when the operating mode is 2D image capture mode, the light-receiving device 12 generates a brightness image of the subject based on the reflected light reception result and outputs it to the control device 11 as measurement data. The specific configuration of the light-receiving element 31 will be described in detail in Figure 2 and subsequent figures.

[0023] The LD21 of the lighting device 13 is, for example, a laser driver that drives the light-emitting unit 22. Based on the light-emitting pulse from the photodetector 31, the light-emitting unit 22 drives the light-emitting unit 22 and outputs AC-modulated light as irradiation light. AC-modulated light is light whose brightness (luminescence) is modulated at a predetermined modulation frequency Fmod (for example, 20 MHz). The light-emitting unit 22 has a light source such as a VCSEL LED (Vertical Cavity Surface Emitting Laser LED) and emits irradiation light when the LD21 is driven. In the first period, the light-emitting unit 22 irradiates AC-modulated light with a first modulation frequency Fmod1, and in the second period, it irradiates AC-modulated light with a second modulation frequency Fmod2. For the irradiation light, for example, infrared light (IR light) with a wavelength in the range of approximately 850 nm to 940 nm is used.

[0024] <2. Example of light-receiving element configuration> Figure 2 is a block diagram showing an example of the configuration of the light-receiving element 31 in Figure 1.

[0025] The light-receiving element 31 is composed of a control unit 51, a pixel array unit 52, a pulse generation circuit 53, a tap drive unit 54, a vertical drive unit 55, a column processing unit 56, a horizontal drive unit 57, a signal processing unit 58, and an output unit 59.

[0026] The control unit 51 controls the operation of the entire photodetector 31. For example, the control unit 51 acquires the operation mode and measurement request supplied from the control device 11 via an input unit (not shown). The control unit 51 also instructs the pulse generation circuit 53 to generate an emission pulse with a predetermined modulation frequency Fmod according to the operation mode. The control unit 51 supplies control signals to the tap drive unit 54, vertical drive unit 55, column processing unit 56, horizontal drive unit 57, etc., to perform operations according to the operation mode. Specifically, the control unit 51 sets and controls the charge accumulation time in the pixel array unit 52, the readout period of the accumulated charge, the irradiation time of the irradiation light using the pulse generation circuit 53, and the switching period for switching the modulation frequency Fmod of the irradiation light. Furthermore, the control unit 51 instructs the signal processing unit 58 to perform predetermined signal processing according to the operation mode, such as generation processing to generate a depth image (distance image) that calculates distance measurement values ​​based on multiple phase differences and stores them as pixel values, and generation processing of a brightness image.

[0027] <Example of Pixel Arrangement by Function> Multiple pixels 61 are arranged in a matrix in the pixel array section 52. Although the configuration of the pixels 61 in this embodiment is the same, it is possible to make the functions of the pixels different by different driving signals via the tap driving section 54.

[0028] Figure 3 shows an example of the functional arrangement of pixels 61 in the pixel array section 52. As shown in Figure 3, the pixels 61 in the pixel array section 52 are controlled so that the light reception frequency processed by each pixel 61 differs every two rows. For example, the top two rows of pixels 61 process measurement light with a first modulation frequency Fmod1 = 20 MHz. That is, the top two rows of pixels 61 receive and process 20 MHz measurement light with high and low levels of illuminance.

[0029] Furthermore, the next two rows of pixels 61 process the measurement light with a second modulation frequency Fmod2 = 100 MHz. That is, the next two rows of pixels 61 receive and process 100 MHz measurement light with high and low levels of illuminance.

[0030] Furthermore, each pixel 61 that processes the measurement light with the first modulation frequency Fmod1 = 20 MHz will have a combination of four adjacent pixels, for example, in a 2x2 arrangement, when calculating the distance value. In Figure 3, the combination of "0" and "180" corresponds to the measurement pixels corresponding to phases of 0 and 180 degrees, and the combination of "90" and "270" corresponds to the measurement pixels corresponding to phases of 90 and 270 degrees.

[0031] Similarly, each pixel 61 that processes the measurement light at the second modulation frequency Fmod2 = 100 MHz will have a combination of four adjacent pixels, for example, vertically and horizontally, which will be used when calculating the distance measurement value. In Figure 3, the combination of "0" and "180" corresponds to the measurement pixels corresponding to phases of 0 and 180 degrees, and the combination of "90" and "270" corresponds to the measurement pixels corresponding to phases of 90 and 270 degrees.

[0032] As shown in Figure 4, among the multiple pixels 61 of the pixel array section 52, the four pixels adjacent vertically and horizontally that are used in the calculation of distance values ​​when processing measurement light with a first modulation frequency Fmod1 = 20 MHz are referred to as pixels 61A, 61B, 61C, and 61D. In the two rows where measurement light with a second modulation frequency Fmod2 = 100 MHz is processed, the four pixels 61A, 61B, 61C, and 61D are repeatedly arranged in the row direction.

[0033] Similarly, when processing the measurement light with the second modulation frequency Fmod2 = 100 MHz and calculating the distance value, the four adjacent pixels in a 2x2 arrangement, one above the other and one below the other, are referred to as pixels 61a, 61b, 61c, and 61d. In the two rows where the measurement light with the second modulation frequency Fmod2 = 100 MHz is processed, the four pixels 61a, 61b, 61c, and 61d are repeatedly arranged in the row direction.

[0034] Note that these arrangement examples are just examples and are not limited to them. Figure 5 shows an example arrangement of a pixel group that processes measurement light with a first modulation frequency Fmod1 = 20 MHz and a pixel group that processes measurement light with a second modulation frequency Fmod2 = 100 MHz.

[0035] In Figure 5, the pixel group 110 consists of four pixels, 61A, 61B, 61C, and 61D, which process measurement light with a first modulation frequency Fmod1 = 20 MHz, and the pixel group 112 consists of four pixels, 61a, 61b, 61c, and 61d, which process measurement light with a second modulation frequency Fmod2 = 100 MHz.

[0036] Figure 5A shows the arrangement shown in Figure 4, which is an example of a horizontal stripe arrangement in which pixel group 110 and pixel group 112 are repeatedly arranged in the row direction.

[0037] Figure 5B shows an example of a checkerboard arrangement in which pixel group 110 and pixel group 112 are arranged in a checkerboard pattern.

[0038] Figure 5C shows an example of a vertical stripe arrangement in which pixel group 110 and pixel group 112 are repeatedly arranged in the column direction.

[0039] As described above, the arrangement of the pixel group 110, which processes the measurement light with the first modulation frequency Fmod1 = 20 MHz, and the pixel group 112, which processes the measurement light with the second modulation frequency Fmod2 = 100 MHz, can be arbitrary. Furthermore, within the pixel groups 110 and 112, the arrangement of the pixels 61 corresponding to phases 0 and 180 degrees and the pixels 61 corresponding to phases 90 and 270 degrees can be swapped.

[0040] Returning to the explanation of Figure 4, pixel 61 distributes the charge obtained by photoelectric conversion of the received reflected light to two taps (charge storage units) 73A and 73B that store the charge, using two transfer transistors 72A and B. The taps (charge storage units) 73A and 73B in pixels 61A, 61B, 61C, and 61D correspond to the first charge storage units that store the charge obtained by photoelectric conversion of the reflected light. Furthermore, the taps (charge storage units) 73A and 73B in pixels 61a, 61b, 61c, and 61d correspond to the second charge storage units that store the charge obtained by photoelectric conversion of the reflected light.

[0041] Pixels 61A, 61B, 61C, and 61D receive reflected light via tap 73A at reception timings shifted by 0°, 90°, 180°, and 270° relative to the irradiation timing of the first modulated frequency Fmod1, and accumulate charge. More specifically, pixel 61A receives light with a phase of 0° relative to the irradiation timing of the irradiation light, pixel 61B receives light with a phase of 90° relative to the irradiation timing of the irradiation light, pixel 61C receives light with a phase of 180° relative to the irradiation timing of the irradiation light, and pixel 61D receives light with a phase of 270° relative to the irradiation timing of the irradiation light, and so on, receiving reflected light with different phases for each of the four pixels and accumulating charge.

[0042] Note that the phases of 0°, 90°, 180°, or 270° refer to the phase at tap 73A, which is the first tap of pixel 61, unless otherwise specified. Since tap 73B, which is the second tap, has the inverted phase of the first tap, when the phase of the first tap is 0°, 90°, 180°, or 270°, the phase of the second tap is 180°, 270°, 0°, or 90°, respectively. Also, tap 73A is sometimes referred to as the first tap, and tap 73B is sometimes referred to as the second tap.

[0043] Similarly, pixels 61a, 61b, 61c, and 61d receive reflected light via tap 73A (first tap) at reception timings shifted by 0°, 90°, 180°, and 270° in phase relative to the irradiation timing of the illumination light of the second modulation frequency Fmod2. More specifically, pixel 61a receives light with a phase of 0° relative to the irradiation timing of the illumination light, pixel 61b receives light with a phase of 90°, pixel 61c receives light with a phase of 180°, and pixel 61d receives light with a phase of 270°, and so on, receiving reflected light with different phases for each of the four pixels. In Figure 3, the "0" and "180" and "90" and "270" arranged vertically within each pixel 61 correspond to the phase of the first tap in the upper row and the phase of the second tap in the lower row. In this way, the four adjacent pixels 61A, 61B, 61C, 61D and pixels 61a, 61b, 61c, 61d arranged two-dimensionally in the pixel array 52 can simultaneously generate light-receiving signals with different phases by changing the phase relative to the irradiation timing of the irradiated light for each position of pixel 61. In this way, signal charges can be accumulated in the taps 73A, 73B of the four adjacent pixels 61A, 61B, 61C, 61D and pixels 61a, 61b, 61c, 61d in the pixel array 52. ​​As a result, the phase information at the first modulation frequency Fmod1 required for long-distance measurement and the phase information at the second modulation frequency Fmod2 required for high-precision distance measurement can be read out together in a series of readout sequences in a single readout. In this embodiment, after measurement at each pixel 61A, 61B, 61C, and 61D, a sequence process is performed to measure at each pixel 61a, 61b, 61c, and 61d and read the data all at once, but the embodiment is not limited to this.

[0044] Referring again to FIG. 2, in the pixel array unit 52, pixel drive lines 63 are wired along the horizontal direction for each pixel row, and two vertical signal lines 64A and 64B are wired along the vertical direction for each pixel column. The pixel drive line 63 transmits a drive signal for driving when reading the detection signal VSL from each pixel 61. In FIG. 2, the pixel drive line 63 is shown as a single wiring, but it is not limited to one. One end of the pixel drive line 63 is connected to the output end corresponding to each pixel row of the vertical drive unit 55. The vertical signal line 64A is a signal line for transmitting the detection signal VSLA of the first tap to the column processing unit 56, and the vertical signal line 64B is a signal line for transmitting the detection signal VSLB of the second tap to the column processing unit 56.

[0045] The pulse generation circuit 53 generates a light emission pulse with a predetermined modulation frequency Fmod in accordance with the control of the control unit 51 and outputs it to the LD21 of the lighting device 13. As described above, the first modulation frequency Fmod1 of the light emission pulse is set to 20 MHz, and the second modulation frequency Fmod2 is set to 100 MHz. Note that this modulation frequency is an example and is not limited to this numerical value.

[0046] Further, the pulse generation circuit 53 generates drive signals GDA and GDB corresponding to the light emission pulse with the modulation frequency Fmod and supplies them to the tap drive unit 54. The drive signal GDA is a drive signal for transferring the charge generated in the photoelectric conversion unit of each pixel 61 to the first tap, and the drive signal GDB is a drive signal for transferring the charge generated in the photoelectric conversion unit of each pixel 61 to the second tap. In the present embodiment, for example, the drive signal GDA and the drive signal GDB are signals in which the phase of one is inverted with respect to the other.

[0047] The tap driving unit 54 generates driving signals GDA' and GDB' for each pixel 61 by distributing the two driving signals GDA and GDB supplied from the pulse generation circuit 53, and supplies them to each pixel 61 of the pixel array unit 52. The tap driving unit 54 controls the charge distribution to the two taps of each pixel 61 by supplying the driving signals GDA' and GDB' in units of pixel columns of the pixel array unit 52. That is, the driving signals GDA' and GDB' are a combination of pulse signals having phases of [0 deg] and [180 deg] with a frequency of 20 MHz at the first modulation frequency Fmod1, or a combination of pulse signals having phases of [90 deg] and [270 deg] with a frequency of 20 MHz. That is, the combined pulse signal having phases of [0 deg] and [180 deg] is supplied to pixels 61A and 61C (see FIG. 4), and the combined pulse signal having phases of [90 deg] and [270 deg] is supplied to pixels 61B and 61D (see FIG. 4).

[0048] Similarly, the driving signals GDA' and GDB' are a combination of pulse signals having phases of [0 deg] and [180 deg] with a frequency of 100 MHz at the second modulation frequency Fmod2, or a combination of pulse signals having phases of [90 deg] and [270 deg] with a frequency of 100 MHz. That is, the combined pulse signal having phases of [0 deg] and [180 deg] is supplied to pixels 61a and 61c (see FIG. 4), and the combined pulse signal having phases of [90 deg] and [270 deg] is supplied to pixels 61b and 61d (see FIG. 4).

[0049] The vertical driving unit 55 is composed of a shift register, an address decoder, etc., and is a pixel driving unit that drives each pixel 61 of the pixel array unit 52 all at once or in units of rows via pixel driving lines 63 wired horizontally for each pixel row. The detection signals VSLA and VSLB output from each pixel 61 of the pixel row selected and scanned by the vertical driving unit 55 are supplied as pixel signals to the column processing unit 56 through the vertical signal lines 64A or �4B.

[0050] The column processing unit 56 performs predetermined signal processing on the pixel signals input from each pixel 61 of the selected row via the vertical signal line 64A or 64B for each pixel column of the pixel array unit 52, and temporarily holds the pixel signals after signal processing. For example, the column processing unit 56 performs AD (analog-to-digital) conversion of the pixel signals as signal processing.

[0051] The horizontal drive unit 57 is composed of a shift register, an address decoder, and the like, and sequentially selects the unit circuits corresponding to the pixel rows of the column processing unit 56. Through this selective scanning by the horizontal drive unit 57, the pixel signals processed by the column processing unit 56 are sequentially output to the signal processing unit 58.

[0052] The signal processing unit 58 has a predetermined arithmetic processing function and performs predetermined arithmetic processing on the pixel signal output from the column processing unit 56 as necessary, and outputs it to the control device 11 (Figure 1) via the output unit 59.

[0053] For example, when the operating mode is distance measurement mode, the signal processing unit 58 calculates the distance to the subject based on the pixel data (detection signals VSLA and VSLB) for each tap of each pixel 61 supplied from the column processing unit 56, and generates a depth image in which the distance value is stored as the pixel value of each pixel.

[0054] For example, when the operating mode is 2D image capture mode, the signal processing unit 58 generates a brightness image of the subject based on the pixel data for each tap of each pixel 61 supplied from the column processing unit 56. Details of the signal processing unit 58 will be described later.

[0055] The output unit 59 is configured with a predetermined communication interface such as MIPI (Mobile Industry Processor Interface), and outputs depth images and brightness images, which are the calculation processing results of the signal processing unit 58, to the control device 11 as measurement data.

[0056] The light-receiving element 31, configured as described above, performs light-receiving operations in the operating mode specified by the control device 11. When the distance measurement mode is specified as the operating mode, the light-receiving element 31 switches the modulation frequency Fmod of the light emission pulse to two types of modulation frequencies: a first modulation frequency Fmod1 for low-speed driving and a second modulation frequency Fmod2 for high-speed driving, and performs light-receiving operations, generating and outputting a depth image. When the 2D image capture mode is specified as the operating mode, the light-receiving element 31 generates and outputs a luminance image of the subject. In the 2D image capture mode, the illumination light may be emitted at a predetermined modulation frequency Fmod, similar to the distance measurement mode, or it may not be emitted. If the illumination light is not emitted, the output of the light emission pulse to the illumination device 13 is stopped. In this embodiment, it will be explained that the illumination light is emitted at a second modulation frequency Fmod2 for low-speed driving and light is received. Note that the modulation frequency Fmod used when emitting illumination light in 2D image capture mode does not need to be the same as any of the modulation frequencies Fmod used when operating in distance measurement mode.

[0057] <Example of Pixel Circuit Configuration> Figure 6 shows a detailed example of the circuit configuration of pixel 61.

[0058] The pixel 61 in Figure 6 is equipped with a photoelectric conversion element 71 as a photoelectric conversion unit. The pixel 61 also has two transfer transistors 72, two FD (floating diffusion region) 73, two FD gate transistors 74, two amplification transistors 75, two reset transistors 76, and two selection transistors 77, corresponding to two taps. That is, the pixel 61 has transfer transistors 72A and 72B, FDs 73A and 73B, FD gate transistors 74A and 74B, amplification transistors 75A and 75B, reset transistors 76A and 76B, and selection transistors 77A and 77B, where elements with the designation A are elements on the first tap side and elements with the designation B are elements on the second tap side. Furthermore, FDs 73A and 73B correspond to two taps that store the charge generated by the photoelectric conversion element 71. The pixel 61 also has a charge discharge transistor 78. Each transistor included in the pixel 61 is composed of an N-type MOSFET.

[0059] The photoelectric conversion element 71 is composed of, for example, a photodiode, and generates and stores an electric charge corresponding to the amount of reflected light received.

[0060] When the drive signal GDA' supplied to the gate electrode becomes active (High), the transfer transistor 72A becomes conductive in response, thereby transferring the charge stored in the photoelectric conversion element 71 to FD73A. When the drive signal GDB' supplied to the gate electrode becomes active (High), the transfer transistor 72B becomes conductive in response, thereby transferring the charge stored in the photoelectric conversion element 71 to FD73B.

[0061] FD73A is a charge storage unit of the first tap that temporarily stores and holds the charge transferred from the photoelectric conversion element 71. FD73B is a charge storage unit of the second tap that temporarily stores and holds the charge transferred from the photoelectric conversion element 71.

[0062] FD gate transistor 74A conducts when the FD drive signal FDG supplied to its gate electrode becomes active, thereby connecting the additional capacitance between FD gate transistor 74A and reset transistor 76A to FD 73A. FD gate transistor 74B conducts when the FD drive signal FDG supplied to its gate electrode becomes active, thereby connecting the additional capacitance between FD gate transistor 74B and reset transistor 76B to FD 73B. The stored capacitance can be changed by dynamically controlling the on / off state of FD gate transistor 74 according to the amount of incident light. In Figure 6, for simplification, there is a single FD drive signal line 81, and the FD drive signal FDG is shared by FD gate transistors 74A and 74B. However, in reality, FD drive signal lines 81 are provided individually for each of the FD gate transistors 74A and 74B, and their on / off states are controlled so that they operate exclusively.

[0063] The amplifying transistor 75A is connected to a constant current source (not shown) by having its source electrode connected to the vertical signal line 64A via the selection transistor 77A, thereby forming a source follower circuit. The amplifying transistor 75B is connected to a constant current source (not shown) by having its source electrode connected to the vertical signal line 64B via the selection transistor 77B, thereby forming a source follower circuit.

[0064] Reset transistor 76A resets the potential of FD 73A by becoming conductive in response to the active reset drive signal RST supplied to its gate electrode. Reset transistor 76B resets the potential of FD 73B by becoming conductive in response to the active reset drive signal RST supplied to its gate electrode. When reset transistors 76A and 76B are active, FD gate transistors 74A and 74B are also simultaneously active. In Figure 6, for simplification, there is only one reset drive signal line 82, and the reset drive signal RST is shared by reset transistors 76A and 76B. However, in reality, the reset drive signal line 82 is provided separately for each of the reset transistors 76A and 76B, and their on / off states are controlled so that they operate exclusively. A predetermined drain voltage RSTDRAIN is supplied to the drains of reset transistors 76A and 76B.

[0065] The selection transistor 77A is connected between the amplification transistor 75A and the vertical signal line 64A. When the selection signal SEL supplied to the gate electrode becomes active, it conducts and outputs the detection signal VSLA output from the amplification transistor 75A to the vertical signal line 64A. The selection transistor 77B is connected between the amplification transistor 75B and the vertical signal line 64B. When the selection signal SEL supplied to the gate electrode becomes active, it conducts and outputs the detection signal VSLB output from the amplification transistor 75B to the vertical signal line 64B. In Figure 6, for simplification, there is only one selection signal line 83, and the selection signal SEL is shared by the selection transistors 77A and 77B. However, in reality, the selection signal line 83 is provided separately for each of the selection transistors 77A and 77B, and each is controlled to operate exclusively on or off.

[0066] The charge discharge transistor 78 becomes conductive in response to the discharge drive signal OFG supplied to the gate electrode via the discharge drive signal line 84, thereby discharging the charge accumulated in the photoelectric conversion element 71.

[0067] <Explanation of Pixel Operation and Pixel Signals> Figure 7 is a diagram illustrating the emission of light and the driving of pixels. Referring to Figure 7, an example of the operation of pixel 61A will be explained. Here, the driving signal GDA' and the driving signal GDB' are examples of combinations of pulse signals having phases of [0 deg] and [180 deg].

[0068] The horizontal axis represents time, and from top to bottom, the graphs show the emitted light, the reflected light, the drive signal GDA' with a phase of 0 degrees, and the drive signal GDB' with a phase of 180 degrees. The emitted light is, for example, light corresponding to an emission pulse with a first modulation frequency Fmod1, where high levels indicate high luminosity and low levels indicate low luminosity. The reflected light is the light that returns from object 41 with a time delay ΔT from the emitted light.

[0069] The drive signal GDA' is a gate signal supplied to the transfer transistor 72A, and the drive signal GDB' is a gate signal supplied to the transfer transistor 72B.

[0070] First, a reset operation is performed at pixel 61A to reset the charge of pixel 61 before light reception occurs. Specifically, the FD gate transistors 74A and 74B and reset transistors 76A and 76B are turned on, the accumulated charge of FD 73A and 73B is discharged, and the charge discharge transistor 78 is turned on, the accumulated charge of photoelectric conversion element 71 is discharged.

[0071] After the accumulated charge is discharged, light reception begins at the first modulation frequency Fmod1. Specifically, as shown in Figure 7, the light-emitting unit 22 outputs illumination light that is modulated to repeatedly switch on and off for an illumination time T, and the reflected light is received by the photoelectric conversion element 71 after a delay time ΔT corresponding to the distance to the subject. One period of the illumination light (=2T) is 1 / Fmod1. In addition, the drive signal GDA' controls the on / off state of the transfer transistor 72A, and the drive signal GDB' controls the on / off state of the transfer transistor 72B. The drive signal GDA' is, for example, a signal with the same phase as the illumination light, and the drive signal GDB' has the inverted phase of the drive signal GDA'.

[0072] Accordingly, in Figure 7, the charge generated when the photoelectric conversion element 71 receives reflected light is transferred to FD 73A while the transfer transistor 72A is ON according to the drive signal GDA', and is transferred to FD 73B while the transfer transistor 72B is ON according to the drive signal GDB'. As a result, during a predetermined period in which irradiation with irradiation light for irradiation time T is performed periodically, the charge transferred via transfer transistor 72A is sequentially accumulated in FD 73A, and the charge transferred via transfer transistor 72B is sequentially accumulated in FD 73B. When FD gate transistors 74A and 74B are ON, the charge is also accumulated in the additional capacitor.

[0073] As described above, the pixel 61 distributes the charge generated by the reflected light received by the photoelectric conversion element 71 to the first tap (FD73A) and the second tap (FD73B) according to the delay time ΔT, and outputs the detection signal VSLA for the first tap and the detection signal VSLB for the second tap, respectively. When the FD gate transistors 74A and 74B are on, the charge is also stored in the additional capacitor.

[0074] Pixel 61B is a combination of pulse signals with phases of [90 degrees] and [270 degrees], where the [90 degrees] drive signal GDA' is T / 2 phase behind the [0 degrees] drive signal GDA', and the [270 degrees] drive signal GDA' is T+T / 2 phase behind the [0 degrees] drive signal GDA'. Similarly, pixel 61C is a combination of pulse signals with phases of [180 degrees] and [0 degrees], where the [180 degrees] drive signal GDA' is T phase behind the [0 degrees] drive signal GDA', and the [0 degrees] drive signal GDA' is in phase with the [0 degrees] drive signal GDA'. Similarly, pixel 61D is a combination of pulse signals with phases of [270 deg] and [90 deg], where the [270 deg] drive signal GDA' is T+T / 2 phase behind the [0 deg] drive signal GDA', and the [90 deg] drive signal GDA' is T / 2 phase behind the [0 deg] drive signal GDA'. The subsequent operation is the same as that of pixel 61A, so a detailed explanation of the operation example is omitted. Similarly, pixels 61a, 61b, 61c, and 61d differ from pixels 61A, 61B, 61C, and 61D in that one period of the irradiated light (=2T) is 1 / Fmod2. The operation descriptions for each are the same as those for pixels 61A, 61B, 61C, and 61D, so they are omitted.

[0075] <3. Calculation of distance values> Next, with reference to Figures 8 to 12, the calculation of distance values, which are distance information to the subject, by the signal processing unit 58 will be explained.

[0076] Figure 8 shows the exposure periods for the first tap of pixels 61A, 61B, 61C, and 61D at phases of 0°, 90°, 180°, and 270°, arranged in a way that makes the phase difference easy to understand. From top to bottom, it shows the illuminated light, the reflected light, and the exposure periods for the first tap of pixels 61A, 61B, 61C, and 61D: GDA_0, GDA_90, GDA_180, and GDA_270.

[0077] As shown in Figure 8, at the first tap, the detection signal VSLA obtained by receiving light at the same phase as the irradiated light (phase 0°) is referred to as detection signal A0, the detection signal VSLA obtained by receiving light at a phase shifted by 90 degrees from the irradiated light (phase 90°) is referred to as detection signal A90, the detection signal VSLA obtained by receiving light at a phase shifted by 180 degrees from the irradiated light (phase 180°) is referred to as detection signal A180, and the detection signal VSLA obtained by receiving light at a phase shifted by 270 degrees from the irradiated light (phase 270°) is referred to as detection signal A270.

[0078] Furthermore, although not shown in the diagram, in the second tap, the detection signal VSLB obtained by receiving light at the same phase as the irradiated light (phase 0°) is referred to as detection signal B0, the detection signal VSLB obtained by receiving light at a phase shifted by 90 degrees from the irradiated light (phase 90°) is referred to as detection signal B90, the detection signal VSLB obtained by receiving light at a phase shifted by 180 degrees from the irradiated light (phase 180°) is referred to as detection signal B180, and the detection signal VSLB obtained by receiving light at a phase shifted by 270 degrees from the irradiated light (phase 270°) is referred to as detection signal B270.

[0079] The signal processing unit 58 calculates the distance value d according to the following equations (1) to (3). That is, in the indirect ToF method, the signal processing unit 58 determines the distance value d by the following equation (1): d = (c × ΔT) / 2 = (c × η) / 4πf ・・・・・・・(1) In equation (1), c is the speed of light, ΔT is the delay time, and f is the modulation frequency of light Fmod. Also, in equation (1), η represents the phase difference [rad] of the reflected light and is expressed by the following equation (2): η = Arctan(Q / I) ・・・・・・・(2) η can take values ​​in the range of 0 or more and less than 2π.

[0080] In equation (2), I and Q are calculated using the detection signals A0 to A270 and B0 to B270 obtained by setting the phases to 0°, 90°, 180°, and 270°, and then calculated in the following equation (3). I and Q are signals obtained by assuming that the brightness change of the irradiated light is a sine wave and converting the phase of the sine wave from polar coordinates to a Cartesian coordinate system (IQ plane).

[0081] I=c0-c180=(A0-B0)-(A180-B180) Q=c90-c270=(A90-B90)-(A270-B270) ・・・・・・・・・(3)

[0082] The signal processing unit 58 calculates the reliability Cf using the following equation (4): Cf = Sqrt(I × I + Q × Q) ・・・・・・・(4) Sqrt(I × I + Q × Q) represents the square root of "I × I + Q × Q".

[0083] The level of confidence Cf is calculated as: Integ time of pixel 61 × Duty cycle of the light source × Reflectance of the subject. As can be seen from equation (4), confidence Cf corresponds to the magnitude of the reflected light received by pixels 61A, 61B, 61C, and 61D, i.e., the luminance information (luminance value).

[0084] Figure 9 is a time chart showing an example of driving pixels 61 of the pixel array section 52. In Figure 9, from top to bottom, the light emission intensity of the light source, the driving state, the GDA1 signal, the GDB1 signal, the OFG1 signal, the GDA2 signal, the GDB2 signal, and the OFG2 signal are shown. The horizontal axis represents time. The light emission intensity of the light source, the GDA1 signal, the GDB1 signal, the OFG1 signal, the GDA2 signal, the GDB2 signal, and the OFG2 signal represent high-level and low-level signals, respectively. The GDA1 signal, the GDB1 signal, and the OFG1 signal are the GDA signal, the GDB signal, and the OFG signal when the modulation frequency Fmod of the light emission pulse is the first modulation frequency Fmod1. The GDA2, GDB2, and OFG2 signals are the GDA, GDB, and OFG signals when the modulation frequency Fmod of the light emission pulse is the second modulation frequency Fmod2. Note that the phases of the GDA1 and GDB1 signals differ in pixels 61A, 61B, 61C, and 61D, respectively, and the phases of the GDA2 and GDB2 signals differ in pixels 61a, 61b, 61c, and 61d, respectively, respectively. However, in Figure 9, for the sake of simplicity, a single set of signals is shown as a representative example.

[0085] The light-receiving element 31 generates the final distance measurement value to be output based on a first phase difference η1 calculated by receiving reflected light with a first modulation frequency Fmod1 = 20 MHz during one frame period, and a second phase difference η2 calculated by receiving reflected light with a second modulation frequency Fmod2 = 100 MHz.

[0086] As shown in Figure 9, at time T0, light emission at the first modulation frequency Fmod1 = 20 MHz begins, and pixels 61A, 61B, 61C, and 61D enter a charge accumulation state (Integration 1). That is, a low-level OFG1 signal is applied to the gate of the charge discharge transistor 78 in pixels 61A, 61B, 61C, and 61D. As a result, the photoelectric conversion elements 71 in pixels 61A, 61B, 61C, and 61D begin photoelectric conversion.

[0087] At this time, the gates of the transfer transistors 72A and 72B of pixels 61A, 61B, 61C, and 61D are supplied with phase-inverted GDA1 and GDB1 signals at 20 MHz, respectively. As a result, in pixels 61A, 61B, 61C, and 61D, the charge corresponding to the potential of the photoelectric conversion element 71 is distributed at 20 MHz to the first tap FD73A and the second tap FD73B.

[0088] On the other hand, a high-level OFG2 signal is applied to the gates of the charge discharge transistors 78 in pixels 61a, 61b, 61c, and 61d. As a result, the potential VDD is applied to the cathodes of the photoelectric conversion elements 71 in pixels 61a, 61b, 61c, and 61d, maintaining the initial state. Similarly, low-level signals are supplied to the gates of the transfer transistors 72A and 72B in pixels 61a, 61b, 61c, and 61d, maintaining the disconnected state.

[0089] At time T1, a high-level OFG1 signal is applied to the gates of the charge discharge transistors 78 in pixels 61A, 61B, 61C, and 61D, and the potential VDD is applied to the cathodes of the photoelectric conversion elements 71, returning to the initial state and ending the charge accumulation state (Integration 1). Also, T / 2 hours before time T1, low-level signals are supplied to the gates of the transfer transistors 72A and 72B in pixels 61A, 61B, 61C, and 61D, resulting in a disconnected state. These states are maintained until time T4.

[0090] At time T2, the blanking period of the light-emitting unit 22 ends, and light emission at the second modulation frequency Fmod2 = 100 MHz begins, causing pixels 61a, 61b, 61c, and 61d to enter a charge accumulation state (Integration 2). That is, a low-level OFG2 signal is applied to the gates of the charge discharge transistors 78 in pixels 61a, 61b, 61c, and 61d. As a result, the photoelectric conversion elements 71 in pixels 61a, 61b, 61c, and 61d begin photoelectric conversion.

[0091] At this time, the gates of the transfer transistors 72A and 72B of pixels 61a, 61b, 61c, and 61d are supplied with phase-inverted GDA2 and GDB2 signals at 100 MHz, respectively. As a result, in pixels 61a, 61b, 61c, and 61d, the charge corresponding to the potential of the photoelectric conversion element 71 is distributed at 100 MHz to the first tap FD73A and the second tap FD73B.

[0092] At time T3, a high-level OFG2 signal is applied to the gates of the charge discharge transistors 78 in pixels 61a, 61b, 61c, and 61d, and the potential VDD is applied to the cathode of the photoelectric conversion element 71, returning to the initial state and ending the charge accumulation state (Integration 2). T / 2 hours before time T3, low-level signals are supplied to the gates of the transfer transistors 72A and 72B in pixels 61a, 61b, 61c, and 61d, resulting in disconnection. These states are maintained until time T4.

[0093] Furthermore, at time T3, high-level selection signals SEL are sequentially or simultaneously supplied to the selection transistors 77A and 77B of pixels 61A, 61B, 61C, and 61D, and to pixels 61a, 61b, 61c, and 61d, and the stored charge is read out. In this way, the stored charge of pixels 61A, 61B, 61C, and 61D, and pixels 61a, 61b, 61c, and 61d is read out during the data readout period from time T3 to time T4. Note that the period from time T0 to time T1 and the period from time T2 to time T3 are set to, for example, 0.1 to 1 ms. Also, the period from time T1 to time T2 is set to, for example, 0.1 ms, and the data readout period from time T3 to time T4 is set to, for example, 5 ms. As can be seen from this, the data readout period from time T3 to time T4 accounts for a large proportion of the processing time when generating distance information, for example, about 80%. Furthermore, since the data at the first modulation frequency Fmod1 = 20 MHz is relatively more robust to distance-phase noise than the data at the second modulation frequency Fmod2 = 100 MHz, stable Dual Freq operation becomes possible by acquiring low-frequency data first, followed by high-frequency data. In addition, each pixel 61 performs signal charge distribution only when it is desired to receive reflected light from object 41, and the charge discharge transistor 78 is kept in a conductive state during other periods. This discharges signal charges generated by ambient light from sunlight or other distance measuring sensors, thereby minimizing the degradation of distance measurement accuracy caused by ambient light.

[0094] Referring to Figures 10 and 11, the calculation of the distance measurement value based on the Dual Freq operation of the first modulation frequency Fmod1 and the second modulation frequency Fmod2 will be explained.

[0095] In indirect Time-of-Flight (TOF) distance measurement, aliasing occurs. Specifically, in indirect TOF distance measurement, the phase difference is detected and converted into distance. Therefore, the maximum measurement range is determined according to the modulation frequency Fmod of the light-emitting unit 22, and when the maximum measurement distance is exceeded, the detected phase difference starts again from zero. As a result, for example, when the modulation frequency Fmod is 100 MHz, it is impossible to distinguish between 1.5 m and 3 m. For this reason, it is necessary to perform distance measurement with multiple modulation frequencies Fmod, such as 100 MHz and 20 MHz.

[0096] The signal processing unit 58 generates a final distance information, which is a distance value (Distance), using the distance values ​​of the pixel group 110 that processes measurement light with a first modulation frequency Fmod1 = 20 MHz and the distance values ​​of the pixel group 112 that processes measurement light with a second modulation frequency Fmod2 = 100 MHz.

[0097] In Figure 10, pixel groups Grm and n are shown as pixel groups Grm and n, respectively, to indicate the pixel group Grm that processes the measurement light with a first modulation frequency Fmod1 = 20 MHz, or the pixel group Grm that processes the measurement light with a second modulation frequency Fmod2 = 100 MHz. Here, m represents a column in the pixel group Gr unit, and n represents a row in the pixel group Gr unit. In Figure 10B, when n is an even number, it corresponds to pixels 61A, 61B, 61C, and 61D, and when n is an odd number, it corresponds to pixels 61a, 61b, 61c, and 61d.

[0098] The signals read from pixels 61A, 61B, 61C, and 61D are converted into digital signals (A0, A90, A180, A270) and (B0, B90, B180, B270). The signal processing unit 58 calculates a first distance value (Coarse Depth) φm,n (where n is an even number) for each pixel 61A, 61B, 61C, and 61D according to equation (1). Then, the signal processing unit 58 calculates a confidence level Cfm,n (where n is an even number) according to equation (4).

[0099] On the other hand, the signals read from pixels 61a, 61b, 61c, and 61d are converted into digital signals (A0, A90, A180, A270) and (B0, B90, B180, B270). The signal processing unit 58 calculates a second distance value (Fine Depth) Φm,n (where n is an odd number) for each pixel 61a, 61b, 61c, and 61d according to equation (1). Then, the signal processing unit 58 calculates a confidence level Cfm,n (where n is an odd number) according to equation (4).

[0100] As shown in Figure 10B, the signal processing unit 58 generates the distance measurement value of the pixel group Grm,n using, for example, the distance values ​​of the upper and lower pixel groups Grm,n-1 and Grm,n+1.

[0101] Figure 11 schematically illustrates the calculation method for distance values ​​using a first distance value (Coarse Depth) and a second distance value (Fine Depth). The horizontal axis represents the distance value (Distance), and the vertical axis represents the first distance value (Coarse Depth) and the second distance value (Fine Depth).

[0102] For example, when calculating the distance value of a pixel group Grm,n (where n is an even number), the values ​​of φm,n (where n is an even number), Φm,n-1, and Φm,n+1 are used. φm,n (where n is an even number) determines which period the second distance value belongs to. In Figure 11, the repetition period is the second period, and the second distance value is calculated as (Φm,n-1 + Φm,n+1) / 2.

[0103] As described above, the first distance value (Coarse Depth) corresponds to 7.5 [m] for 360 degrees (1 period), and the distance measurement accuracy of the second distance value (Fine Depth) corresponds to, for example, 1.5 [m] for 360 degrees (1 period). In other words, in Figure 11, the repetition period is the second period, and 1.5 [m] + (Φm, n - 1 + Φm, n + 1) / 2 is the distance measurement value for the pixel group Grm, n (where n is an even number).

[0104] Furthermore, for example, when calculating the distance value of a pixel group Grm,n (where n is odd), the values ​​of Φm,n (where n is odd), φm,n-1, and φm,n+1 are used. The period in which the second distance value is obtained is determined by (φm,n-1 + φm,n+1) / 2. In Figure 11, it is the second period, and the second distance value is determined by Φm,n (where n is odd). In other words, in Figure 11, the repetition period is the second period, and 1.5[m] + Φm,n (where n is odd) is the measured distance value of the pixel group Grm,n (where n is odd). In this way, the signal processing unit 58 generates the final distance measurement value to be output based on the first phase difference η1 (see equation (1)) obtained based on the signals of pixels 61A, 61B, 61C, and 61D in one frame period, the second phase difference η2 (see equation (1)) obtained based on the signals of pixels 61a, 61b, 61c, and 61d, and the repetition period of the second phase difference η2.

[0105] In the above example, as shown in Figure 5, a pixel group 110 that processes measurement light with a first modulation frequency Fmod1 = 20 MHz and a pixel group 112 that processes measurement light with a second modulation frequency Fmod2 = 100 MHz are appropriately arranged within the pixel array unit 52 to perform de-aliasing processing. However, all pixels 61 in the pixel array unit 52 may be driven with a single modulation frequency Fmod. For example, the pixel array unit 52 may be driven only with the first modulation frequency Fmod1 = 20 MHz by arranging the pixel group 110 of pixels 61A, 61B, 61C, and 61D in a repeating matrix direction. Alternatively, if the measurement range of the distance measuring device 1 is limited to 1.5 [m], the pixel array section 52 may be driven only at the second modulation frequency Fmod2 = 100 MHz, with the pixel array section 52 arranged in a repeating matrix configuration of the pixel group 112 of pixels 61a, 61b, 61c, and 61d.

[0106] Alternatively, as shown in Figure 12, for each pixel 61 of the pixel array 52, the accumulation and reading of frame t0 using a first modulation frequency Fmod1 = 20 MHz and the accumulation and reading of frame t1 using a second modulation frequency Fmod2 may be performed sequentially with different frame periods, and the final output distance value may be generated based on the first phase difference η1 and the second phase difference η2 obtained over the two frame periods. In the operation shown in Figure 12, after the accumulation and reading of one frame t0 corresponding to four phases is performed using the first modulation frequency Fmod1, similar to the pixel group 110 of pixels 61A, 61B, 61C, and 61D, the accumulation and reading of one frame t1 corresponding to four phases is performed using the second modulation frequency Fmod2, similar to the pixel group 112 of pixels 61a, 61b, 61c, and 61d.

[0107] In other words, in the pixel array section 52, four pixels adjacent vertically and horizontally constitute a group of pixels used when calculating the distance value, and the phases of the four pixels are a combination of 0°, 90°, 180°, or 270° to calculate the phase difference η.

[0108] <4. First Pixel Configuration Example> A first configuration example of the pixels 61 of the pixel array 52 will be described with reference to Figures 13 and 14.

[0109] Figure 13 is a cross-sectional view of a pixel 61 according to the first configuration example, and Figure 14 is a plan view of a pixel 61 according to the first configuration example. Figure 13 corresponds to the cross-sectional view along the line X-X' in the plan view of Figure 14, and is a cross-sectional view of two adjacent pixels in the row or column direction among the 2x2 four pixels that constitute the pixel group Gr.

[0110] Each pixel 61 of the light-receiving element 31 comprises a semiconductor substrate 241 and a multilayer wiring layer 242 formed on its surface side (lower side in the figure).

[0111] The semiconductor substrate 241 is a semiconductor layer made of, for example, silicon (Si), and is formed with a thickness of, for example, several micrometers. In the semiconductor substrate 241, for example, N-type semiconductor regions 252 are formed on a pixel-by-pixel basis in P-type semiconductor regions 251, thereby forming photodiodes PD on a pixel-by-pixel basis. The photodiodes PD correspond to the photoelectric conversion elements 71 of the pixel 61, and the N-type semiconductor regions 252 are photoelectric conversion regions that convert received reflected light into electric charge (signal charge). The P-type semiconductor regions 251 provided on both the front and back surfaces of the semiconductor substrate 241 also serve as hole charge accumulation regions for suppressing dark current.

[0112] In Figure 13, the upper surface of the semiconductor substrate 241 is the back surface of the semiconductor substrate 241 and is the light incident surface to which light is incident. An anti-reflective film 243 is formed on the upper surface of the back side of the semiconductor substrate 241.

[0113] The anti-reflective coating 243 can be, for example, a laminated structure in which a fixed charge film and an oxide film are laminated, and a high-dielectric constant (High-k) insulating thin film can be used, for example, by the ALD (Atomic Layer Deposition) method. Specifically, hafnium oxide (HfO2), aluminum oxide (Al2O3), titanium oxide (TiO2), STO (Strontium Titan Oxide), etc. can be used. In the example in Figure 13, the anti-reflective coating 243 is composed of a laminated hafnium oxide film 253, an aluminum oxide film 254, and a silicon oxide film 255.

[0114] On the upper surface of the anti-reflective coating 243, at the boundary 244 between adjacent pixels 61 (hereinafter also referred to as the pixel boundary 244), an inter-pixel light-shielding coating 245 is formed to prevent incident light from entering adjacent pixels. The material of the inter-pixel light-shielding coating 245 can be any material that blocks light, and for example, metallic materials such as tungsten (W), aluminum (Al), or copper (Cu) can be used.

[0115] A planarization film 246 is formed on the upper surface of the anti-reflective film 243 and the upper surface of the inter-pixel light-shielding film 245, using an insulating film such as silicon oxide (SiO2), silicon nitride (SiN), or silicon oxynitride (SiON), or an organic material such as resin.

[0116] On the upper surface of the planarization film 246, on-chip lenses 247 are formed on a pixel-by-pixel basis. The on-chip lenses 247 are made of a resin-based material such as styrene resin, acrylic resin, styrene-acrylic copolymer resin, or siloxane resin. The light focused by the on-chip lenses 247 is efficiently incident on the photodiode PD.

[0117] Furthermore, at the pixel boundary portions 244 of the semiconductor substrate 241, inter-pixel isolation portions 261 are formed to separate the semiconductor layer from adjacent pixels. As can be seen from the plan view in Figure 14, the inter-pixel isolation portions 261 are provided in a grid pattern at the pixel boundary portions 244 in units of 2x2 4 pixels that constitute a pixel group Gr. In other words, inter-pixel isolation portions 261 are provided at the pixel boundary portions 244 between adjacent pixel groups Gr, but inter-pixel isolation portions 261 are not provided at the pixel boundary portions 244 between adjacent pixels 61 within a pixel group Gr, and a P-type semiconductor region 251 is formed. As shown in Figure 13, the inter-pixel isolation portions 261 are constructed by embedding a silicon oxide film 255 in a trench dug to a predetermined depth in the substrate depth direction from the back side (on-chip lens 247 side) of the semiconductor substrate 241. The outer periphery of the inter-pixel separation section 261, including its bottom surface and side walls, is covered with a hafnium oxide film 253, which is part of the anti-reflective film 243. The inter-pixel separation section 261 prevents incident light from penetrating to the adjacent pixel 61, confining it within its own pixel, and also prevents incident light from leaking in from the adjacent pixel 61.

[0118] In the example shown in Figure 13, the silicon oxide film 255, which is the uppermost layer material of the anti-reflective coating 243, is embedded in a trench (groove) carved out from the back side. This simultaneously forms the silicon oxide film 255 on the back side and the inter-pixel separation portion 261. Therefore, the silicon oxide film 255, which is part of the laminated film as the anti-reflective coating 243, and the inter-pixel separation portion 261 are made of the same material, but they do not necessarily have to be the same. The material embedded in the trench (groove) carved out from the back side as the inter-pixel separation portion 261 may be a metallic material such as tungsten (W), aluminum (Al), titanium (Ti), or titanium nitride (TiN).

[0119] On the other hand, on the surface side of the semiconductor substrate 241 on which the multilayer wiring layer 242 is formed, two transfer transistors TRG1 and TRG2 are formed for each photodiode PD formed in each pixel 61. Also on the surface side of the semiconductor substrate 241, floating diffusion regions FD1 and FD2 are formed by a high-density N-type semiconductor region (N-type diffusion region) to serve as charge storage areas for temporarily holding the charge transferred from the photodiode PD. These two transfer transistors TRG1 and TRG2 correspond to transfer transistors 72A and 72B in the equivalent circuit of Figure 6, and floating diffusion regions FD1 and FD2 correspond to FD73A and 73B in the equivalent circuit of Figure 6.

[0120] The multilayer wiring layer 242 is composed of multiple metal films M and interlayer insulating films 262 between them. Figure 13 shows an example in which the metal films M consist of three layers: the first metal film M1 to the third metal film M3.

[0121] In the multilayer wiring layer 242, a reflective film (reflective member) 263 is formed in the region of the first metal film M1, which is closest to the semiconductor substrate 241, located below the photodiode PD formation region. In other words, in a plan view, the region overlaps with at least a portion of the photodiode PD formation region. The reflective film 263 is made of the same material as the other metal wiring 267 of the first metal film M1, such as copper (Cu), aluminum (Al), tungsten (W), titanium (Ti), titanium nitride (TiN), etc.

[0122] The reflective film 263 is incident on the semiconductor substrate 241 from the light incident surface via the on-chip lens 247. It has the function of reflecting infrared light that has passed through the semiconductor substrate 241 without being photoelectrically converted, and re-incidentating it into the semiconductor substrate 241. This reflection function increases the amount of infrared light that is photoelectrically converted within the semiconductor substrate 241, thereby improving the quantum efficiency (QE), that is, the sensitivity of the pixel 61 to infrared light.

[0123] Furthermore, the reflective film 263 is incident on the semiconductor substrate 241 from the light incident surface via the on-chip lens 247. Infrared light that has passed through the semiconductor substrate 241 without being photoelectrically converted is blocked by the first metal film M1 closest to the semiconductor substrate 241, preventing it from passing through to the second metal film M2 and third metal film M3 below it. Therefore, the reflective film 263 can also be said to be a light-shielding film. This light-shielding function prevents infrared light that has passed through the semiconductor substrate 241 without being photoelectrically converted from the first metal film M1 from being scattered by the metal film M below it and incident on nearby pixels. This prevents nearby pixels from mistakenly detecting light.

[0124] Of the metal wiring 267 of the first metal film M1, the metal wiring that is electrically connected to the gate of the transfer transistor TRG1 or TRG2 via the gate contact 266 is referred to as the contact wiring 267.

[0125] In the multilayer wiring layer 242, a wiring capacitance 264 is formed in a predetermined metal film M, for example, the second metal film M2, by forming a comb-like pattern. This wiring capacitance 264 corresponds to the additional capacitance between the FD gate transistor 74A and the reset transistor 76A, as explained in the equivalent circuit of Figure 6. The reflective film 263 and the wiring capacitance 264 may be formed in the same layer (metal film M), but if they are formed in different layers, the wiring capacitance 264 is formed in a layer further from the semiconductor substrate 241 than the reflective film 263. In other words, the reflective film 263 is formed closer to the semiconductor substrate 241 than the wiring capacitance 264.

[0126] As described above, the light-receiving element 31 has a back-illuminated structure in which a semiconductor substrate 241, which is a semiconductor layer, is placed between the on-chip lens 247 and the multilayer wiring layer 242, and incident light is incident on the photodiode PD from the back side on which the on-chip lens 247 is formed.

[0127] Furthermore, each pixel 61 is equipped with two transfer transistors TRG1 and TRG2 for each photodiode PD, and is configured to distribute the charge (electrons) generated by photoelectric conversion in the photodiode PD to the floating diffusion region FD1 or FD2.

[0128] In the first configuration example, the pixels 61 have inter-pixel separation portions 261 formed at the pixel boundary portions 244 of the pixel group Gr units, as shown by arrow E1 in Figure 15, which prevents incident light from penetrating to pixels 61 outside the pixel group Gr units and confines it within the pixel group Gr units, while also preventing leakage of incident light from pixels 61 outside the pixel group Gr units. Furthermore, by providing a reflective film 263 on the metal film M below the photodiode PD formation region, the infrared light that has been transmitted through the semiconductor substrate 241 without being photoelectrically converted within the semiconductor substrate 241 is reflected by the reflective film 263 and re-incidentated into the semiconductor substrate 241.

[0129] On the other hand, within a pixel group Gr unit, as shown by arrow E2 in Figure 15, by not providing an inter-pixel separation portion 261 at the pixel boundary portion 244, incident light is allowed to penetrate to the adjacent pixel 61.

[0130] With the above configuration, the pixel 61 according to the first configuration example can increase the amount of infrared light converted photoelectrically within the semiconductor substrate 241, thereby improving the quantum efficiency (QE), that is, the sensitivity to infrared light.

[0131] Figure 16 illustrates the effect of providing an inter-pixel separation unit 261 for each pixel group Gr.

[0132] The light emitted by the light-emitting unit 22 toward the subject can be, for example, planar light or spotlight. Planar light can illuminate a wide area, but because the light intensity is dispersed, objects at a distance cannot be measured (the measurement range is short). In contrast, spotlight allows for a higher density of light power due to its spot shape (circular shape), enabling measurement over longer distances and suppressing the effects of multipath interference, thus improving accuracy. However, when spotlight is used as the illumination, the amount of light received differs from pixel to pixel at the boundary of the spotlight, in other words, at the outer edge of the spotlight, which may prevent the calculation of an accurate distance value.

[0133] Figure 16A is a schematic diagram showing the state in which spot light is received by the pixel array section 52.

[0134] In Figure 16A, we focus on pixel group 301, which is a 2x2 pixel group Gr located at the boundary of the spot light 302 reflected from the subject. In Figure 16A, the pixel 61 labeled "I" corresponds to the measurement pixel corresponding to the phase 0, 180 degree combination in Figure 3, and the pixel 61 labeled "Q" corresponds to the measurement pixel corresponding to the phase 90, 270 degree combination in Figure 3.

[0135] If the pixel structure of each pixel 61 in the pixel array 52 is such that a pixel separation unit 261 is provided for each pixel, as shown in Figure 16B, then the amount of light received by each pixel 61 in the pixel group 301, which is the combination used to calculate the distance value, will differ. In Figure 16B, "5", "6", "10", and "7" represent the magnitude of the amount of light received by pixels 61A, 61B, 61C, and 61D, with values ​​ranging from "0" to "10". In this way, when the amount of light received differs among pixels 61, the indirect Time-of-Flight (TOF) distance measurement method, which calculates the distance value by calculating the ratio of the amount of light received, cannot calculate accurate distance values ​​and distance measurement values.

[0136] In contrast, the pixel structure of the light-receiving element 31, as described above, does not have an inter-pixel separation section 261 at the pixel boundary 244 within a pixel group Gr unit, but only at the pixel boundary 244 between adjacent pixel groups Gr. In this case, since incident light penetrates to adjacent pixels 61 within the pixel group 301, the amount of light received by pixels 61A, 61B, 61C, and 61D becomes roughly equal, as shown in C of Figure 16, with values ​​of "7", "7", "7", and "7". Therefore, according to the first configuration example of the light-receiving element 31, the amount of light received by each pixel 61 can be evenly distributed within the pixel group Gr at the boundary of the spot light, and accurate distance values ​​and distance measurement values ​​can be calculated.

[0137] <5. Modified Example of the First Configuration> Figure 17 is a cross-sectional view showing a modified example of the first configuration shown in Figure 13.

[0138] In Figure 17, parts corresponding to the first configuration example shown in Figure 13 are denoted by the same reference numerals, and explanations of those parts are omitted as appropriate.

[0139] In the modified example shown in Figure 17, the difference is that the inter-pixel isolation portion 261, which is a DTI (Deep Trench Isolation) formed by carving out from the back side (on-chip lens 247 side) of the semiconductor substrate 241 in the first configuration example in Figure 13, is replaced with an inter-pixel isolation portion 271 that penetrates the semiconductor substrate 241; otherwise, it is the same.

[0140] The inter-pixel separation section 271 is formed by creating a trench on the back side (on-chip lens 247 side) or front side of the semiconductor substrate 241, penetrating to the opposite substrate surface, and embedding a silicon oxide film 255, which is the uppermost layer material of the anti-reflective coating 243, inside the trench. The material embedded in the trench as the inter-pixel separation section 271 may be an insulating film such as the silicon oxide film 255, or a metallic material such as tungsten (W), aluminum (Al), titanium (Ti), or titanium nitride (TiN).

[0141] By forming such an inter-pixel separation section 271, adjacent pixels can be electrically completely separated. This prevents incident light from penetrating to pixels 61 outside the pixel group Gr unit, confining it within the pixel group Gr unit, and also enhances the function of preventing leakage of incident light from pixels 61 outside the pixel group Gr unit.

[0142] Therefore, even in the modified version of the first configuration example, the amount of infrared light photoelectrically converted within the semiconductor substrate 241 can be increased, thereby improving the quantum efficiency, that is, the sensitivity of the pixels 61 to infrared light. Furthermore, the amount of light received by each pixel 61 can be evenly distributed in the pixel group Gr at the boundary of the spot light, allowing for the calculation of accurate distance values.

[0143] <6. Second Pixel Configuration Example> Figure 18 is a cross-sectional view of a pixel 61 according to the second configuration example.

[0144] In Figure 18, parts corresponding to the first configuration example shown in Figure 13 are denoted by the same reference numerals, and their descriptions are omitted as appropriate.

[0145] In the second configuration example shown in Figure 18, the difference from the first configuration example shown in Figure 13 is that an inter-pixel separation portion 261' is provided at the pixel boundary portion 244 between two pixels 61. In other words, in the second configuration example, among the 2x2 four pixels that make up the pixel group Gr, an inter-pixel separation portion 261' is provided at a part of the pixel boundary portion 244 within the pixel group Gr.

[0146] Figure 19 is a plan view of the pixels 61 in the second configuration example, viewed in units of a pixel group Gr.

[0147] As shown in Figure 19, when viewing the pixels 61 in the second configuration example in a plan view in units of a pixel group Gr, a pixel separation portion 261' is provided in the central part of the cross-shaped pixel boundary portion 244 within the pixel group Gr, which consists of 4 pixels arranged in a 2x2 grid. The cross-sectional view along the line X-X' in the plan view of Figure 19 corresponds to Figure 18. The cross-sectional view along the line Y-Y' in the plan view of Figure 19 is the same as that in Figure 13 of the first configuration example.

[0148] Alternatively, the configuration shown in Figure 20 may be adopted, in which a pixel separation portion 261' is provided in a part of the cross-shaped pixel boundary portion 244 within the pixel group Gr.

[0149] Figure 20 is a plan view showing another example of the second configuration example, in which the inter-pixel separation portion 261' is provided in the portion of the cross-shaped pixel boundary portion 244 within the pixel group Gr that is not the central portion. In this case, the cross-sectional view along the line X-X' in the plan view of Figure 20 is the same as that of Figure 13 in the first configuration example, and the cross-sectional view along the line Y-Y' in the plan view of Figure 20 corresponds to Figure 18.

[0150] In the second configuration example, as described above, an inter-pixel separation section 261' is provided in a part of the cross-shaped pixel boundary section 244 within the pixel group Gr. If the inter-pixel separation section 261 provided in the pixel boundary section 244 between adjacent pixel groups Gr is considered the first inter-pixel separation section, then the inter-pixel separation section 261' provided in the central part of the cross-shaped pixel boundary section 244 within the pixel group Gr, or in the part excluding the central part, is a second inter-pixel separation section of a different type from the first inter-pixel separation section. In Figure 19, the length of the cross-shaped inter-pixel separation section 261', or in Figure 20, the length of the inter-pixel separation section 261' extending from the inter-pixel separation section 261 at the boundary of the pixel group Gr to the central part of the pixel group Gr, may be appropriately set according to the ratio of color mixing of incident light, in other words, the degree of crosstalk of incident light into adjacent pixels. By adjusting the length of the inter-pixel separation section 261', it is possible to adjust the even distribution of the amount of light received by each pixel 61 in the pixel group Gr.

[0151] <7. Modifications of the Second Configuration Example> Figure 21 is a cross-sectional view showing the first modification of the second configuration example.

[0152] The first modified example in Figure 21 is similar to the second configuration example shown in Figure 18 in that a part of the cross-shaped pixel boundary portion 244 within the pixel group Gr is provided with an inter-pixel separation portion 261'. On the other hand, it differs from the second configuration example shown in Figure 18 in that the depth of the inter-pixel separation portion 261' provided in a part of the cross-shaped pixel boundary portion 244 within the pixel group Gr is shallower than the inter-pixel separation portion 261 provided at the boundary portion of the pixel group Gr. Here, the depth of the inter-pixel separation portion 261' represents the depth of the trench dug in the substrate depth direction from the back side (on-chip lens 247 side) of the semiconductor substrate 241.

[0153] Figure 22 is a cross-sectional view showing a second modified example of the second configuration.

[0154] The second modified example in Figure 22 is similar to the second configuration example shown in Figure 18 in that a pixel separation portion 261' is provided in a part of the cross-shaped pixel boundary portion 244 within the pixel group Gr. On the other hand, it differs from the second configuration example shown in Figure 18 in that the width of the pixel separation portion 261' provided in a part of the cross-shaped pixel boundary portion 244 within the pixel group Gr is narrower than the pixel separation portion 261 provided at the boundary portion of the pixel group Gr. Here, the width of the pixel separation portion 261' represents the thickness of the light-shielding wall in the planar direction of the semiconductor substrate 241.

[0155] In the basic structure of the second configuration example shown in Figures 18 to 20, the ratio of color mixing of incident light is appropriately adjusted by adjusting the length of the cross-shaped inter-pixel separation portion 261' within the pixel group Gr, or the length of the inter-pixel separation portion 261' extending from the boundary portion of the pixel group Gr to the central portion. However, as in the first and second modified examples, the ratio of color mixing of incident light may be appropriately adjusted by further differentiating the depth or width of the inter-pixel separation portion 261' from the inter-pixel separation portion 261 at the boundary portion of the pixel group Gr. Both the depth and width of the inter-pixel separation portion 261' may be different from the inter-pixel separation portion 261 at the boundary portion of the pixel group Gr.

[0156] <8. Third Pixel Configuration Example> Figure 23 is a cross-sectional view of a pixel 61 according to the third configuration example.

[0157] In Figure 23, the same reference numerals are used for parts corresponding to the first and second configuration examples described above, and explanations of those parts are omitted as appropriate.

[0158] In the third configuration example shown in Figure 23, an inter-pixel separation portion 261A is provided at the pixel boundary portion 244 between adjacent pixel groups Gr, and an inter-pixel separation portion 261B is provided at the cross-shaped pixel boundary portion 244 within the pixel group Gr. The inter-pixel separation portion 261A at the boundary portion of the pixel group Gr and the inter-pixel separation portion 261B at the cross-shaped portion within the pixel group Gr are formed of different embedding materials. The inter-pixel separation portion 261A corresponds to the first inter-pixel separation portion, and the inter-pixel separation portion 261B corresponds to the second inter-pixel separation portion.

[0159] Figure 24 is a plan view of the pixels 61 in the third configuration example, viewed in units of pixel group Gr.

[0160] The inter-pixel separation portion 261A and the inter-pixel separation portion 261B have different light-shielding performance due to the difference in the materials embedded therein. Specifically, the embedding material is selected so that the light-shielding performance of the inter-pixel separation portion 261A at the boundary of the pixel group Gr is greater than that of the inter-pixel separation portion 261B at the cross-shaped portion. For example, the material embedded in the inter-pixel separation portion 261A at the boundary of the pixel group Gr may be a metallic material such as tungsten (W), aluminum (Al), titanium (Ti), or titanium nitride (TiN). On the other hand, the material embedded in the inter-pixel separation portion 261B at the cross-shaped portion may be an insulating film such as silicon oxide (SiO2), silicon nitride (SiN), or silicon oxynitride (SiON), or an organic material such as resin. For example, by using the same material for the inter-pixel separation portion 261A at the boundary of the pixel group Gr and the inter-pixel light-shielding film 245, the inter-pixel separation portion 261A and the inter-pixel light-shielding film 245 can be formed simultaneously. Furthermore, by using silicon oxide as the material for the cross-shaped inter-pixel separation portion 261B, the silicon oxide film 255, which is the uppermost layer material of the anti-reflective film 243, and the inter-pixel separation portion 261B can be formed simultaneously.

[0161] In the third configuration example, as described above, by using different embedding materials in the inter-pixel separation portion 261A at the boundary of the pixel group Gr and the inter-pixel separation portion 261B in the cross shape, the ratio of color mixing of incident light, that is, the degree of crosstalk of incident light into adjacent pixels within the pixel group Gr, can be appropriately set. This makes it possible to adjust the even distribution of the amount of light received by each pixel 61 in the pixel group Gr.

[0162] In the example described above, the inter-pixel separation section 261B in the cross shape is connected to the inter-pixel separation section 261A at the boundary of the pixel group Gr, so that each of the 2x2 pixels 61 is completely separated by the inter-pixel separation section 261B in the cross shape. However, as shown in Figure 19 or Figure 20, the inter-pixel separation section 261B may not be provided for a part of the cross shape. Also, as shown in Figure 21 or Figure 22, at least one of the depth or width of the inter-pixel separation section 261B may be different from that of the inter-pixel separation section 261A at the boundary of the pixel group Gr.

[0163] <9. Fourth Pixel Configuration Example> Figure 25 is a cross-sectional view of a pixel 61 according to the fourth configuration example.

[0164] In Figure 25, the parts corresponding to the first to third configuration examples described above are denoted by the same reference numerals, and explanations of those parts are omitted as appropriate.

[0165] In the fourth configuration example shown in Figure 25, a moth-eye structure 211 with fine irregularities formed periodically is formed on the back surface of the semiconductor substrate 241, above the photodiode PD formation area. Furthermore, the anti-reflective film 243 formed on the upper surface of the semiconductor substrate 241, corresponding to the moth-eye structure 211, is also formed in a moth-eye structure.

[0166] The moth-eye structure 211 of the semiconductor substrate 241 is configured such that, for example, multiple square pyramidal regions of substantially the same shape and size are regularly arranged (in a grid pattern).

[0167] The moth-eye structure 211 is formed, for example, as an inverted pyramidal structure in which multiple square pyramidal regions with vertices on the photodiode PD side are arranged in a regular pattern. Alternatively, the moth-eye structure 211 may be a forward pyramidal structure in which multiple square pyramidal regions with vertices on the on-chip lens 247 side are arranged in a regular pattern. The size and arrangement of the multiple square pyramids may be randomly formed, not regularly arranged. Furthermore, each concave or convex portion of each square pyramid in the moth-eye structure 211 may have some curvature and a rounded shape. The moth-eye structure 211 only needs to have a structure in which the concave and convex structures are repeated periodically or randomly, and the shape of the concave or convex portions is arbitrary.

[0168] Figure 26 is a plan view of the pixels 61 according to the fourth configuration example, viewed in units of a pixel group Gr. In the example of Figure 26, the moth-eye structure 211 is formed by arranging square pyramidal regions in a 5x5 grid. By forming the moth-eye structure 211 on the light incident surface of the semiconductor substrate 241 as a diffraction structure that diffracts incident light, the abrupt change in refractive index at the substrate interface is mitigated, producing an anti-reflective effect. The moth-eye structure 211 also functions as an optical diffraction section that diffracts light due to its uneven structure.

[0169] Therefore, in the fourth configuration example as well, the amount of infrared light photoelectrically converted within the semiconductor substrate 241 can be increased, thereby improving the quantum efficiency, that is, the sensitivity of the pixels 61 to infrared light. In addition, the amount of light received by each pixel 61 can be evenly distributed in the pixel group Gr at the boundary of the spot light, allowing for the calculation of accurate distance values.

[0170] Furthermore, by providing the moth-eye structure 211, the light incident on the light incident surface of the semiconductor substrate 241 is diffused, thereby reducing the amount of light that passes through to the side of the semiconductor substrate 241 opposite to the light incident surface (the side with the multilayer wiring layer 242), is reflected by the multilayer wiring layer 242, and passes back to the light incident surface (reflected light).

[0171] The fourth configuration example in Figures 25 and 26 is a configuration in which the moth-eye structure 211 is added to the first configuration example described above, but it is also possible to add the moth-eye structure 211 to the second and third configuration examples described above.

[0172] <10. Summary of the First to Fourth Pixel Configuration Examples> The pixel array section 52 has pixel groups (pixel group 110, pixel group 112) consisting of 2x2 four pixels that receive reflected light reflected from the subject at light receiving timings shifted by 0°, 90°, 180°, and 270° in phase with respect to the irradiation timing of the irradiation light irradiated from a predetermined light source of the light-emitting section 22 at a predetermined modulation frequency. The pixel array section 52 has a first inter-pixel separation section at the pixel boundary between adjacent pixel groups that separates the semiconductor layer to at least a part of the depth direction of the semiconductor layer, and a second inter-pixel separation section of a different type from the first inter-pixel separation section at the pixel boundary between adjacent pixels within a pixel group, or a configuration in which neither the first inter-pixel separation section nor the second inter-pixel separation section is present. Configurations having a second pixel separation unit of a different type from the first pixel separation unit are the second and third configuration examples described above, while configurations having neither a first nor a second pixel separation unit are the first and fourth configuration examples described above.

[0173] Because the pixel array portion 52 of the light-receiving element 31 has the aforementioned pixel group, incident light penetrates to adjacent pixels 61 within the pixel group. Therefore, even in the pixel group at the boundary of the spot light, the amount of light received by each pixel 61 within the pixel group can be evenly distributed, and an accurate distance measurement value can be calculated.

[0174] This technology is not limited to the embodiments described above, and various modifications are possible without departing from the spirit of this technology.

[0175] This technology can be applied to a method called the Continuous-Wave method, which is a type of indirect ToF (Time-of-Flight) method that amplitude modulates the light projected onto an object. Furthermore, the structure of the photodiode PD of the photodetector 31 can be applied to photodetectors with a CAPD (Current Assisted Photonic Demodulator) structure, or to gate-type photodetectors that alternately apply pulses to two gates of the photodiode PD, or any other photodetector with a structure that distributes charge to two charge storage units.

[0176] In the example described above, a photodetector was described in which the first conductivity type was P-type and the second conductivity type was N-type, and electrons were used as the signal charge. However, this disclosure can also be applied to a photodetector in which holes are used as the signal charge. That is, the first conductivity type can be N-type and the second conductivity type can be P-type, and the aforementioned semiconductor regions can be composed of semiconductor regions of the opposite conductivity types.

[0177] The technologies described herein, as described in multiple instances, can each be implemented independently, as long as no conflict arises. Of course, any multiple technologies can also be implemented in combination. For example, some or all of the technologies described in one embodiment can be implemented in combination with some or all of the technologies described in another embodiment. Furthermore, some or all of the technologies described above can be implemented in combination with other technologies not described above.

[0178] The effects described herein are merely illustrative and not limiting; other effects may also occur.

[0179] Furthermore, this technology can employ the following configuration: (1) A light-receiving element comprising a pixel array section having a group of 4 pixels in a 2x2 configuration, which receives reflected light reflected by a subject at light-receiving timings shifted by 0°, 90°, 180°, and 270° in phase with respect to the irradiation timing of irradiation light irradiated from a predetermined light source at a predetermined modulation frequency, wherein the pixel array section has a first inter-pixel separation section at the pixel boundary between adjacent pixel groups that separates the semiconductor layer to at least a portion of the depth direction of the semiconductor layer, and the pixel boundary between adjacent pixels within the pixel group has a second inter-pixel separation section of a different type from the first inter-pixel separation section, or a configuration that does not have either the first inter-pixel separation section or the second inter-pixel separation section. (2) The light-receiving element according to (1), further comprising a signal processing unit that calculates a phase difference using the pixel signals of the 2x2 4 pixels that receive the reflected light at light-receiving timings shifted by 0°, 90°, 180°, and 270° in phase, and calculates distance information to the subject. (3) The light-receiving element according to (2), wherein the predetermined light source sequentially emits a first illumination light with a first modulation frequency and a second illumination light with a second modulation frequency different from the first modulation frequency as the predetermined modulation frequency, and the signal processing unit calculates a first phase difference using the pixel signals of the 2x2 4 pixels that receive the reflected light of the first illumination light, calculates a second phase difference using the pixel signals of the 2x2 4 pixels that receive the reflected light of the second illumination light, and calculates distance information to the subject using the first phase difference and the second phase difference. (4) The timing of receiving the reflected light of the first illumination light and the timing of receiving the reflected light of the second illumination light are in different frame periods, and the signal processing unit calculates distance information to the subject using the first phase difference and the second phase difference obtained in two frame periods, as described in (3). (5) The timing of receiving the reflected light of the first illumination light and the timing of receiving the reflected light of the second illumination light are in the same frame period, and the signal processing unit calculates distance information to the subject using the first phase difference and the second phase difference obtained in one frame period, as described in (3).(6) The pixel array portion does not have either the first inter-pixel separation portion or the second inter-pixel separation portion at the pixel boundary between adjacent pixels in the pixel group, and each pixel has a semiconductor region of a different conductivity type than the photoelectric conversion region provided in each pixel, as described in any of (1) to (5). (7) The pixel array portion has the second inter-pixel separation portion at the pixel boundary between adjacent pixels in the pixel group, and the second inter-pixel separation portion is provided in a part of the pixel boundary between adjacent pixels in the pixel group in a plan view, as described in any of (1) to (5). (8) The second inter-pixel separation portion is provided in the central part of the cross-shaped pixel boundary between adjacent pixels in the pixel group in a plan view, as described in (7). (9) The second inter-pixel separation portion is provided in the part of the cross-shaped pixel boundary between adjacent pixels in the pixel group excluding the central part, as described in (7), as described in a plan view. (10) The light-receiving element according to any one of (1) to (5), (7) to (9), wherein the pixel array portion has the second inter-pixel separation portion at the pixel boundary between adjacent pixels in the pixel group, and the second inter-pixel separation portion is provided deeper than the first inter-pixel separation portion. (11) The light-receiving element according to any one of (1) to (5), (7) to (10), wherein the pixel array portion has the second inter-pixel separation portion at the pixel boundary between adjacent pixels in the pixel group, and the second inter-pixel separation portion is provided narrower than the first inter-pixel separation portion. (12) The light-receiving element according to any one of (1) to (5), (7) to (11), wherein the pixel array portion has the second inter-pixel separation portion at the pixel boundary between adjacent pixels in the pixel group, and the first inter-pixel separation portion and the second inter-pixel separation portion are formed of different embedding materials. (13) The pixel is a light-receiving element according to any one of (1) to (5) or (7) to (12) above, having a moth-eye structure on the back side of the semiconductor layer. (14) The first inter-pixel separation portion is a light-receiving element according to any one of (1) to (13) above, penetrating the semiconductor layer in the depth direction to separate the semiconductor layer.(15) A distance measuring device comprising: a predetermined light source that irradiates an object with illumination light at a predetermined modulation frequency; and a light receiving element that receives reflected light from the object after the illumination light has been reflected, wherein the light receiving element comprises a pixel array section having a 2x2 array of 4 pixels that receives the reflected light at reception timings shifted by 0°, 90°, 180°, and 270° in phase with respect to the illumination timing of the illumination light; the pixel array section has a first inter-pixel separation section at the pixel boundary between adjacent pixel groups that separates the semiconductor layer to at least a portion of the depth direction of the semiconductor layer; and the pixel boundary between adjacent pixels within a pixel group has a second inter-pixel separation section of a different type from the first inter-pixel separation section, or is configured not to have either the first inter-pixel separation section or the second inter-pixel separation section.

[0180] 1 Distance measuring device, 11 Control device, 12 Light receiving device, 13 Illumination device, 22 Light-emitting unit, 31 Light-receiving element, 41 Object, 42 Object, 51 Control unit, 52 Pixel array unit, 53 Pulse generation circuit, 54 Tap drive unit, 55 Vertical drive unit, 56 Column processing unit, 57 Horizontal drive unit, 58 Signal processing unit, 59 Output unit, 61 (61A-61D, 61a-61d) Pixel, 63 Pixel drive line, 64A, 64B Vertical signal line, 71 Photoelectric conversion element, 72 (72A, 72B) Transfer transistor, 73A, 73B Tap, 74 (74A, 74B) FD gate transistor, 75 (75A, 75B) Amplifying transistor, 76 (76A, 76B) Reset transistor, 77 (77A, 77B) Selection transistor, 78 Charge discharge transistor, Gr, Grm, n Pixel group, 110 Pixel group, 112 Pixel group, PD Photodiode, 211 Moth-eye structure, 241 Semiconductor substrate, 242 Multilayer wiring layer, 243 Anti-reflective film, 244 Boundary (pixel boundary), 245 Inter-pixel light-shielding film, 246 Planarization film, 247 On-chip lens, 251 P-type semiconductor region, 252 N-type semiconductor region, 253 Hafnium oxide film, 254 Aluminum oxide film, 255 Silicon oxide film, 261 (261A, 261B) Inter-pixel separation region, 262 Interlayer insulating film, 263 Reflective film, 264 Wiring capacitance, 271 pixel separation section, 301 pixel group, 302 spot light

Claims

1. A light-receiving element comprising a pixel array section having a 2x2 arrangement of 4 pixels, which receives reflected light reflected by a subject at light-receiving timings shifted by 0°, 90°, 180°, and 270° in phase with respect to the irradiation timing of irradiation light irradiated from a predetermined light source at a predetermined modulation frequency, wherein the pixel array section has a first inter-pixel separation section at the pixel boundary between adjacent pixel groups that separates the semiconductor layer to at least a portion of the depth direction of the semiconductor layer, and the pixel boundary between adjacent pixels within the pixel group has a second inter-pixel separation section of a different type from the first inter-pixel separation section, or is configured to have neither the first inter-pixel separation section nor the second inter-pixel separation section.

2. The light-receiving element according to claim 1, further comprising a signal processing unit that calculates the phase difference using the pixel signals of the 2x2 4 pixels, which receive the reflected light at light-receiving timings shifted by 0°, 90°, 180°, and 270° in phase, and calculates distance information to the subject.

3. The light-receiving element according to claim 2, wherein the predetermined light source sequentially emits a first illumination light with a first modulation frequency and a second illumination light with a second modulation frequency different from the first modulation frequency as the predetermined modulation frequency, the signal processing unit calculates a first phase difference using the pixel signals of the 2x2 4 pixels that receive the reflected light of the first illumination light, calculates a second phase difference using the pixel signals of the 2x2 4 pixels that receive the reflected light of the second illumination light, and calculates distance information to the subject using the first phase difference and the second phase difference.

4. The light-receiving element according to claim 3, wherein the timing of receiving the reflected light of the first illumination light and the timing of receiving the reflected light of the second illumination light are different frame periods, and the signal processing unit calculates distance information to the subject using the first phase difference and the second phase difference obtained over the two frame periods.

5. The light-receiving element according to claim 3, wherein the timing of receiving the reflected light of the first illumination light and the timing of receiving the reflected light of the second illumination light are within the same frame period, and the signal processing unit calculates distance information to the subject using the first phase difference and the second phase difference obtained in one frame period.

6. The photodetector according to claim 1, wherein the pixel array portion does not have either the first inter-pixel separation portion or the second inter-pixel separation portion at the pixel boundary between adjacent pixels in the pixel group, and has a semiconductor region of a different conductivity type from the photoelectric conversion region provided in each pixel.

7. The light-receiving element according to claim 1, wherein the pixel array portion has the second inter-pixel separation portion at the pixel boundary between adjacent pixels in the pixel group, and the second inter-pixel separation portion is provided in a plan view as part of the pixel boundary between adjacent pixels in the pixel group.

8. The light-receiving element according to claim 7, wherein the second inter-pixel separation portion is provided in the central portion of the cross-shaped pixel boundary between adjacent pixels in the pixel group, in a plan view.

9. The light-receiving element according to claim 7, wherein the second inter-pixel separation portion is provided in a plan view, excluding the central portion of the cross-shaped pixel boundary between adjacent pixels in the pixel group.

10. The light-receiving element according to claim 1, wherein the pixel array portion has a second inter-pixel separation portion at the pixel boundary between adjacent pixels in the pixel group, and the second inter-pixel separation portion is provided to be shallower in depth than the first inter-pixel separation portion.

11. The light-receiving element according to claim 1, wherein the pixel array portion has a second inter-pixel separation portion at the pixel boundary between adjacent pixels in the pixel group, and the second inter-pixel separation portion is provided to be narrower than the first inter-pixel separation portion.

12. The light-receiving element according to claim 1, wherein the pixel array portion has the second inter-pixel separation portion at the pixel boundary between adjacent pixels in the pixel group, and the first inter-pixel separation portion and the second inter-pixel separation portion are formed of different embedding materials.

13. The photodetector according to claim 1, wherein the pixel has a moth-eye structure on the back side of the semiconductor layer.

14. The photodetector according to claim 1, wherein the first inter-pixel separation portion penetrates the semiconductor layer in the depth direction and separates the semiconductor layer.

15. A distance measuring device comprising: a predetermined light source that irradiates an object with illumination light at a predetermined modulation frequency; and a light-receiving element that receives reflected light from the object, wherein the light-receiving element includes a pixel array section having a 2x2 array of 4 pixels that receives the reflected light at reception timings shifted by 0°, 90°, 180°, and 270° in phase with respect to the illumination timing of the illumination light; the pixel array section has a first inter-pixel separation section at the pixel boundary between adjacent pixel groups that separates the semiconductor layer to at least a portion of the depth direction of the semiconductor layer; and the pixel boundary between adjacent pixels within a pixel group has a second inter-pixel separation section of a different type from the first inter-pixel separation section, or is configured not to have either the first inter-pixel separation section or the second inter-pixel separation section.

Images