Light-receiving element, and distance-measuring device

Abstract

Disclosed is a light-receiving element that, by using a simple configuration, is capable of suppressing the influence of light that is not to be measured. The light-receiving element has a light-receiving element array in which a plurality of light-receiving elements are two-dimensionally arrayed. The light-receiving element measures the elapsed time from a reference time point to detection of the incidence of light on the plurality of light-receiving elements, and determines the final elapsed time on the basis of the plurality of measured elapsed times. Each of the plurality of light-receiving elements has: a plurality of photoelectric conversion elements having adjacent photoelectric conversion regions; and a non-sensitive region that is for incident light and is provided between the light-receiving elements that are adjacent.

Description

Light-receiving element and distance measuring device

[0001] This disclosure relates to a light-receiving element and a distance measuring device.

[0002] A distance measurement method called the Time-Of-Flight (TOF) method is known, which measures the distance to an object that reflects light based on the time (TOF) from the time light is shone on the object until the reflected light is detected.

[0003] To accurately measure distance using the TOF method, it is important to correctly detect the reflected light from the irradiated light. For example, in Patent Document 1, an aperture is placed in front of the light-receiving element to suppress the incidence of ambient light and other light unrelated to the measurement target onto the light-receiving element.

[0004] Japanese Patent Publication No. 2019-215324

[0005] However, when an aperture is used, precise alignment with the photodetector is necessary. This alignment is particularly difficult when multiple photodetectors are used. Furthermore, a configuration with an aperture is disadvantageous in terms of miniaturization and cost.

[0006] In some embodiments, this disclosure provides a light-receiving element and a distance measuring device that can suppress the influence of light outside the measurement target with a simple configuration.

[0007] In one embodiment, the present disclosure provides a photodetector array having a plurality of photodetectors arranged in two dimensions, a measuring means for measuring the elapsed time from a reference time until the incidence of light on the plurality of photodetectors is detected, and a determining means for determining the final elapsed time based on the measured elapsed times, wherein each of the plurality of photodetectors has a plurality of photoelectric conversion elements having adjacent photoelectric conversion regions, and an insensitive region to incident light provided between adjacent photodetectors.

[0008] According to some embodiments of this disclosure, it is possible to provide a light-receiving element and a distance measuring device that can suppress the influence of light outside the measurement target with a simple configuration.

[0009] Other features and advantages of the technical ideas derived from this disclosure will become apparent from the following description with reference to the attached drawings. In the attached drawings, the same or similar components are given the same reference numeral.

[0010] The attached drawings are included in the specification and constitute a part thereof, illustrating embodiments in this disclosure and used to explain the technical ideas derived from this disclosure together with their descriptions. Block diagram showing an example of the functional configuration of a distance measuring device according to an embodiment Schematic diagram relating to an example of the configuration of the light-emitting unit in Figure 1 Schematic diagram relating to an example of the configuration of the measurement unit in Figure 1 Equivalent circuit diagram of pixels in a photodetector array according to an embodiment Diagram showing an example of the arrangement of subpixels on the light-receiving surface of a pixel Diagram showing an example of the configuration of microlenses corresponding to a pixel Cross-sectional view A-A' of Figure 3 Diagram for explaining the conjugate relationship between the light-emitting array and the photodetector array in a distance measuring device according to an embodiment Diagram schematically showing rays near the light-emitting element Diagram schematically showing rays near a pixel Diagram for explaining the relationship between an image formed on an object in an embodiment and the position in which the reflected light of the image enters the photodetector array Diagram showing an example of the arrangement of subpixels in a pixel according to a modified example of an embodiment Cross-sectional view A-A' of Figure 10 Diagram for explaining the relationship between an image formed on an object in a modified example and the position in which the reflected light of the image enters the photodetector array Diagram for explaining an example of a subpixel that is disabled in a modified example

[0011] The embodiments will be described in detail below with reference to the attached drawings. Note that the following embodiments do not limit the scope of the claims. While the embodiments describe multiple features, not all of these features are necessary, and the features may be combined in any way. Furthermore, in the attached drawings, identical or similar configurations are given the same reference numerals, and redundant descriptions are omitted.

[0012] (Overall configuration of the rangefinder)

[0013] Figure 1 is a block diagram showing an example of the functional configuration of a distance measuring device according to an embodiment. The distance measuring device 100 includes a light-emitting unit 110, a measurement unit 120, an image-side telecentric lens 130, an overall control unit 140, and a beam splitter 150.

[0014] The light-emitting unit 110 includes a light source unit 113 and a light source control unit 114. The light source unit 113 includes a light-emitting element array 111 in which a plurality of light-emitting elements are arranged in a two-dimensional array, and a light-emitting element drive unit 112.

[0015] The measurement unit 120 includes a photodetector array 121 in which multiple photodetectors are arranged in a two-dimensional array, a TDC (Time-to-Digital Converter) array section 122, a signal processing section 123, a measurement control section 124, and a row selection circuit 125.

[0016] The beam splitter 150 has a half mirror 151 that transmits a portion of the incident light and reflects a portion of it. The beam splitter 150 is arranged such that the half mirror 151 reflects light from the light-emitting element array 111 towards the image-side telecentric lens 130 and transmits light from the image-side telecentric lens 130 to the light-receiving element array 121.

[0017] The optical bandpass filter 160 is positioned between the beam splitter 150 and the photodetector array 121, and passes light within a predetermined wavelength band that includes the wavelength of light emitted by the light-emitting element array 111, while reflecting or absorbing light of other wavelengths.

[0018] When the light-emitting element array 111 in the light source unit 113 emits light, the emitted light is incident on the half mirror 151 of the beam splitter 150. The light reflected by the half mirror 151 is projected into the outside space via the image-side telecentric lens 130.

[0019] Light projected into the external space is partially reflected when it reaches an object in the external space. A portion of the reflected light then enters the image-side telecentric lens 130. The image-side telecentric lens 130 converts the light incident from the external space into rays parallel to the optical axis and outputs them to the beam splitter 150. The half-mirror 151 of the beam splitter 150 transmits a portion of the light incident through the image-side telecentric lens 130. The transmitted light enters the photodetector array 121 via the optical bandpass filter 160.

[0020] The TDC array unit 122 measures the time (TOF) from when the light-emitting element array 111 emits light until the reflected light is detected by the light-receiving element array 121. The TDC array unit 122 measures the TOF for each light-receiving element included in the light-receiving element array 121. In addition, during distance measurement, the light-emitting element array 111 is made to emit light multiple times, and the TOF is measured for each emission.

[0021] The signal processing unit 123 statistically processes the TOF measured for each emission and for each photodetector to suppress the influence of noise components such as ambient light and dark count included in the measured values, as well as the influence of noise from measurement circuits such as the TDC array unit 122, and to determine the final TOF. For example, the signal processing unit 123 can generate a TOF histogram and determine the TOF value based on the frequency distribution, thereby determining a TOF that suppresses the influence of ambient light and noise.

[0022] The Time of Flight (TOF) determined by the signal processing unit 123 is output to the overall control unit 140 via the measurement control unit 124. The overall control unit 140 can calculate the distance L between the distance measuring device 100 and the object reflecting the light by substituting the TOF obtained from the measurement unit 120 into the following equation (1). In equation (1), c is the speed of light. Alternatively, the measurement control unit 124 may calculate the distance L. L = TOF × c / 2 ... (1)

[0023] (Light-emitting unit) An example of the configuration of the light-emitting unit 110 will be further explained with reference to Figure 2. Figure 2 is a schematic diagram showing an example of the configuration of the light-emitting unit 110, with particular attention paid to the configuration of the light-emitting element array 111.

[0024] The light-emitting element array 111 has a plurality of light-emitting elements 201 arranged in a two-dimensional array on a substrate. The light-emitting elements 201 may be, for example, vertical cavity surface-emitting laser (VCSEL) elements. The light-emitting elements 201 may also be other light-emitting elements such as end-face-emitting laser elements or LEDs (light-emitting diodes). The plurality of light-emitting elements 201 constituting the light-emitting element array 111 may be arranged on multiple substrates. The light-emitting element array 111 may be, for example, a configuration in which a plurality of substrates (laser bars) in which a plurality of light-emitting elements 201 are arranged in one dimension are lined up (laser bar stack), or a configuration in which a plurality of light-emitting elements 201 are arranged two-dimensionally on a single substrate.

[0025] The emission wavelengths of the multiple light-emitting elements 201 may be the same. In this embodiment, as an example, the multiple light-emitting elements 201 are assumed to have the same wavelength within the near-infrared band. However, in reality, there may be variations in wavelength due to manufacturing errors, tolerances, etc.

[0026] When a VCSEL element is used as the light-emitting element 201, for example, by using a GaAs-based material, an emission wavelength in the near-infrared region can be realized. In this case, the dielectric multilayer film that forms the DBR (distributed reflection) mirror constituting the VCSEL can be made of two thin films made of materials with different refractive indices stacked alternately and periodically (GaAs / AlGaAs).

[0027] Furthermore, multiple VCSEL elements arranged in a one-dimensional array in the row direction have a common anode electrode in addition to their individual cathode electrodes, and these electrodes are connected to the corresponding drive circuits 202. By operating only a specific drive circuit 202 of the light-emitting element drive unit 112, only the VCSEL elements located in the corresponding specific row can be made to emit light.

[0028] The light-emitting element array 111 further includes a microlens array 220. The microlens array 220 has a configuration in which a plurality of microlenses 221, each corresponding to one light-emitting element 201, are arranged in a two-times manner. Each microlens 221 focuses the light emitted by the corresponding light-emitting element 201. In this embodiment, the microlenses 221 constituting the microlens array 220 are arranged in a one-to-one correspondence with each light-emitting element 201.

[0029] (Measurement Unit) Figure 3 is a schematic diagram showing an example of the configuration of the measurement unit 120, with particular attention paid to an example of the configuration of the photodetector array 121. The photodetector array 121 has a configuration in which pixels 301, which act as photodetectors, are arranged in two dimensions. As will be described later, each pixel 301 has a photoelectric conversion region that is divided into multiple parts. Note that the term "pixel" in this embodiment is a convenient designation and differs from pixels in general image sensors. The pixels 301 in this embodiment are used to detect the incidence of light and do not output a signal corresponding to the amount of light received during the exposure period. Each pixel 301 is connected to one row selection signal line 303 and one output line 304.

[0030] The row selection circuit 125 has a plurality of row selection signal lines 303 for selecting a plurality of pixels 301 arranged two-dimensionally on the photodetector array 121 on a row-by-row basis. Similarly, the TDC array unit 122 has a plurality of output lines 304 provided for each column of the plurality of pixels 301 arranged two-dimensionally on the photodetector array 121. For the pixel row selected by the row selection circuit 125, the TDC array unit 122 can read the output from the pixels 301 of the selected row by sequentially scanning the plurality of output lines 304.

[0031] Figure 4 is a circuit diagram showing an example configuration of a pixel 301. The pixel 301 has four SPADs (Single Photon Avalanche Diodes) 401, which are photoelectric conversion elements, four load transistors 402, four inverters 403, an output circuit 404, a row selection pulse line 303, and an output line 304. In the following description, a combination of interconnected SPADs 401, load transistors 402, and inverters 403 will be referred to as a sub-pixel 405. Each sub-pixel 405 has its own photoelectric conversion region and can independently detect incident light.

[0032] The reason for dividing a single pixel 301 into multiple subpixels 405 is that if two or more photons are incident on the same photoelectric conversion region during the measurement period, the time of flow (TOF) cannot be accurately measured. By dividing a single pixel 301 into multiple subpixels 405, that is, by dividing the photoelectric conversion region into multiple parts, the probability of multiple photons being incident on the same photoelectric conversion region during the measurement period can be reduced. In addition, since the TOF can be measured for each subpixel, the number of measurement samples per pixel 301 can be increased, which is advantageous in statistical processing to suppress the effects of ambient light and other factors.

[0033] Furthermore, as will be described later, the individual light-emitting elements 201 arranged in the light-emitting element array 111 and the individual pixels 301 arranged in the light-receiving element array 121 are arranged in a conjugate relationship. Therefore, when light emitted from a certain light-emitting element 201 is specularly reflected by an object, it is incident on the center of the corresponding pixel 301. For this reason, the sub-pixels 405 are arranged so that their photoelectric conversion regions receive light incident on the center and surrounding area of ​​the pixel 301. As will be described in detail later, multiple sub-pixels are arranged so that the center of the photoelectric conversion region of the entire sub-pixel is equal to the center of the pixel 301.

[0034] As will be described later using Figure 6, the SPAD 401 has a light-receiving region (photoelectric conversion region) 621 and an avalanche region 622. When light (photons) is incident on the SPAD 401, it is photoelectrically converted in the light-receiving region 621, generating electrons and holes. The positively charged holes are discharged through the anode electrode Vbd. The negatively charged electrons (signal charges) move through the light-receiving region 621 toward the avalanche region 622 due to an electric field set so that the potential decreases toward the avalanche region 622. When the signal charges reach the avalanche region 622, the strong electric field of the avalanche region 622 induces avalanche breakdown, generating an avalanche current.

[0035] When no avalanche current is generated, the voltage of the anode electrode Vbd is set so that a reverse bias greater than or equal to the breakdown voltage is applied to the avalanche region 622 of SPAD 401. At this time, no current flows through the load transistor 402, so the cathode potential Vc of SPAD 401 is close to the power supply voltage Vdd, and the output signal of inverter 403 is "0".

[0036] When an avalanche current is generated, the cathode potential Vc of SPAD 401 drops, and the output of inverter 403 changes from "0" to "1". As the cathode potential Vc of SPAD 401 decreases, the reverse bias applied to SPAD 401 decreases, and when the reverse bias falls below the breakdown voltage, no avalanche current is generated. Hereafter, the operation that returns to a state where no avalanche current is generated will be referred to as the quench operation.

[0037] Subsequently, when the load transistor 402 conducts and a hole current flows from Vdd to the cathode of SPAD 401, the cathode potential Vc of SPAD 401 rises, the output of inverter 403 returns from "1" to "0", and the system returns to the state before the photon incident. In this way, the output of SPAD 401 changes temporarily with each photon incident.

[0038] Pixels 301 selected (connected) by the row selection signal line 303 (where the potential of the connected row selection signal line 303 is at the "on" level) are controlled such that the output of the inverter 403 is output to the output line 304. On the other hand, pixels 301 not selected (connected) by the row selection signal line 303 (where the potential of the connected row selection signal line 303 is at the "off" level) are controlled such that the output of the inverter 403 is disconnected from the output line 304. Therefore, it is possible to detect only the light incident on the pixels 301 belonging to a specific row selected by the row selection circuit 125 via the row selection signal line 303. Thus, the outputs of the pixels 301 belonging to the row selected by the row selection circuit 125 are output to the TDC array unit 122 as digital signals with low delay.

[0039] One TDC is provided for each column in the TDC array unit 122, and based on the output of the corresponding pixel 301, the elapsed time (TOF) from the light emission time (reference time) of the light emission unit 110 until a signal is detected at the pixel 301 is measured. The TOF measured for each pixel 301 by the TDC array unit 122 is transmitted to the signal processing unit 123. The reference time is notified to the measurement unit 120 from, for example, the overall control unit 140 or the light emission unit 110 at each light emission timing of the light emission unit 110. Alternatively, the light emission unit 110 and the measurement unit 120 may be synchronized based on the same clock, and a predetermined light emission timing may be used as the reference time.

[0040] For example, from the TOF detected while sequentially selecting one row at a time for the pixels 301 included in the light receiving element array 121, the signal processing unit 123 determines one TOF as described above. The determined TOF is substituted into Equation (1) by the measurement control unit 124 or the overall control unit 140 and converted into distance information.

[0041] FIG. 5A is a diagram schematically showing the configuration of the light receiving surfaces of pixels 301 corresponding to two rows by two columns among the plurality of pixels 301 included in the light receiving element array 121. FIG. 5B is a top view showing a configuration example of the microlenses provided on the light receiving surface of the pixel 301. FIG. 6 is a diagram schematically showing the A - A' cross section of FIG. 5. For convenience, reference numerals are attached only to the pixels on the left side in FIG. 6.

[0042] In this embodiment, the pixel 301 is formed across both the light-receiving element substrate 600 and the logic substrate laminated on the light-receiving substrate 600, and is configured to receive light from the side opposite to the wiring layer. That is, the light-receiving element array 121 has a configuration of a so-called back-illumination type. The light-receiving element substrate 600 is a semiconductor substrate made of, for example, silicon (Si), and has an optical layer 610, a semiconductor layer 620, and a wiring layer 630. The logic substrate laminated under the light-receiving substrate 600 has a wiring layer 640 and a semiconductor layer (not shown).

[0043] In FIG. 5, the insensitive region 501 is a region configured not to have sensitivity to incident light by the microlens 612 and the light-shielding layer 611. Not having sensitivity to incident light means that no charge is generated even if light is incident on the insensitive region 501, or even if charge is generated, the charge does not flow into the sub-pixel. Note that the light-shielding layer 611 is not essential, but by providing the light-shielding layer 611, the sensitivity of the insensitive region 501 to incident light can be more surely eliminated. Here, the insensitive region 501 is provided so as to surround a square region along the outer edge of the light-receiving region 621 of the sub-pixel, but may be provided so as to surround a region of another shape such as a circle according to the outer edge shape of the light-receiving region 621 of the sub-pixel.

[0044] Further, although the light-shielding layer 611 is formed along the outer edge of the light-receiving region 621 of the sub-pixel, it may be provided so as to cover a part of the light-receiving region 621 from the outside so as to reduce the effective light-receiving region 621 of the sub-pixel. Thereby, the number of photons incident on the sub-pixel can be suppressed.

[0045] There are no insensitive regions between the light-receiving regions 621 of the four subpixels (SPAD401) formed in each of the pixels 301. The subpixels are arranged in a vertical and horizontal arrangement of two in the center of the pixel 301. The four light-receiving regions 621 provided in the same pixel 301 are separated by a separation region 623. The separation region 623 is formed of a semiconductor into which impurities have been implanted so that its potential is higher than that of the light-receiving region 621. By separating the light-receiving regions 621 of adjacent subpixels with a PN junction (separation region 623) that forms a potential barrier, the charge generated by light incident on the separation region 623 is detected in one of the subpixels adjacent to the separation region 623. Furthermore, since the light-receiving region 621 of the subpixel is a division of the light-receiving region of the pixel 301, the overall center of the light-receiving region 621 of the subpixel is equal to the center 330 of the pixel 301.

[0046] Furthermore, in the example shown in Figure 6, the insensitive region 501 has a light-receiving region. However, a charge discharge region 626 is provided so that the charge generated by the light incident on the insensitive region 501 is discharged without being detected by the subpixel. Even when light passes through the light-shielding layer 611 and is incident on the semiconductor region 620 of the light-receiving element substrate 600, the charge converted photoelectrically within the charge discharge region 626 is discharged and not detected by the subpixel. The same is true even when there is no light-shielding layer 611.

[0047] Furthermore, an insulating region 625 is positioned between the light-receiving region 621 and the charge-discharging region 626 to suppress the movement of charge between the light-receiving region 621 and the charge-discharging region 626. The insulating region 625 is composed of, for example, SiO and is called Deep Trench Isolation (DTI). In addition, a region 624 is provided between the light-receiving region 621 and the insulating region 625, in which impurities are implanted to create a high potential and many holes, thereby suppressing dark counts caused by the interface between the insulating region 625 and the light-receiving region 621.

[0048] Each subpixel has a load transistor 402, inverter 403, and output circuit 404, which are located in the semiconductor region (not shown) of the logic board, and the row selection signal line 303 and output line 304 are located in the wiring layer 640 of the logic board.

[0049] The microlenses 612 that constitute the microlens array provided in the optical layer 610 have a configuration in which microlenses for each subpixel with the same curvature are combined. Specifically, as shown in Figure 5B, for a pixel 301 having four subpixels 401, the four microlenses 612 are combined in such an arrangement that the optical axis centers are eccentric toward the center 330 of the pixel 301 (or the center of the photoelectric conversion region of the entire subpixel 401).

[0050] By configuring the microlenses 612 corresponding to each individual pixel in this way, it becomes possible to reliably detect light incident on the center of the pixel 301 in one of the subpixels. Furthermore, the curvature of the microlenses 612 can be reduced while suppressing its height. However, the microlenses 612 may have other configurations. Due to the image-side telecentric lens 130, light parallel to the optical axis is incident on the microlenses 612. The light focused by the microlenses 612 is then incident on the center 330 of the pixel 301 or its vicinity, among the four light-receiving regions 621. Therefore, the time it takes for the charge generated by photoelectric conversion in the subpixels 401 to reach the avalanche region 622 becomes approximately equal among the subpixels 401, reducing measurement time errors.

[0051] Furthermore, in the microlens array, the microlens 612 is configured such that its outer edge 627 does not extend beyond the outer edge of the light-receiving area 621 of the subpixel. This is to prevent light that should not be incident on the subpixel from being incident on by the microlens 612. Also, in the microlens array, the portion 628 where the microlens 612 is not provided is configured to be flat.

[0052] (Relationship between light emission and light reception) The process from when the light emitted from the light-emitting element array 111 is emitted to the outside by the image-side telecentric lens 130, until the reflected light reaches the light-receiving element array 121, will be explained using Figures 7 to 9.

[0053] Figure 7 is a schematic diagram showing the relationship between light emission and light reception in the distance measuring device 100. The light-emitting element array 111 and the light-receiving element array 121 are conjugate via the half-mirror 151 of the beam splitter 150, and the individual light-emitting elements 201 and individual pixels 301 are also conjugate. Note that in Figure 7, the number of rows in the light-emitting element array 111 and the light-receiving element array 121 is set to 8, but this is merely an example.

[0054] The row numbers of the light-emitting element array 111 are assigned starting with row 1, where the row with the smallest Yv value in the XvYvZv coordinate system shown in Figure 7 is 1, and increasing by one each time. Similarly, the row numbers of the light-receiving element array 121 are assigned starting with row 1, where the row with the smallest Y value in the XYZ coordinate system shown in Figure 7 is 1, and increasing by one each time. Furthermore, light-emitting elements 201 and pixels 301 belonging to the same row number are arranged to have a conjugate relationship.

[0055] In Figure 7, as an example, the conjugate relationship between row number 1 and row number 2 of the light-emitting element array 111 and the light-receiving element array 121 is shown by optical paths 701 and 702. 701 is the optical path of the light emitted from the light-emitting element 201 belonging to row number 1, and 702 is the optical path of the light emitted from the light-emitting element 201 belonging to row number 1.

[0056] The light emitted from the light-emitting element 201 belonging to row number 1 is projected into the outside space via the beam splitter 150 and the image-side telecentric lens 130. Of the light reflected by objects in the outside space, the light with an angle close to specular reflection is incident on the image-side telecentric lens 130 and, via the beam splitter 150, is incident on the pixel 301 belonging to row number 1 of the photodetector array 121. Similarly, the light emitted from the light-emitting element 201 belonging to row number 2 is incident on the pixel 301 belonging to row number 2 of the photodetector array 121.

[0057] Figure 8A schematically illustrates the light rays near the light-emitting element 201 in Figure 7, and Figure 8B schematically illustrates the light rays near the pixel 301 in Figure 7. The position of the photodetector array 121 in the Z-axis direction is determined such that the microlens 612 is positioned at position 801 where parallel light rays incident on the afocal system composed of the microlens array 220 and the image-side telecentric lens 130 converge. Position 801 is determined from the focal lengths of the microlens 221 and the image-side telecentric lens 130.

[0058] The ray 811 in Figure 8A is a ray emitted from the light-emitting element 201, and the ray 812 in Figure 8B is a ray that has been reflected back by an object in the external space after the ray 811 was reflected.

[0059] Figure 9 schematically shows the relationship between the position of light projected by the image-side telecentric lens 130 onto an object in the external space and the position of reflected light incident on the photodetector array 121. Here, nine pixels of the photodetector array 121, consisting of three horizontal and three vertical pixels, are shown.

[0060] The region 902 on the object is approximately proportional to the light-receiving region of the pixel 301 of the light-receiving element array 121. Since the microlens array 220 of the light-emitting element array 111 and the image-side telecentric lens 130 constitute an afocal system, the size d of the image formed on the object by light emitted from one light-emitting element 201 is approximately proportional to the light-receiving region of the pixel 301 of the light-receiving element array 121. ｂ This is expressed by the following equation (2): d b =( pf L ) / f M ... (2) Here, p is the light-emitting diameter of the light-emitting element 201, f M The focal length of the microlens 221 is f L This is the focal length of the image-side telecentric lens 130.

[0061] If there is no object at close range that reflects the light projected from the rangefinder, the light emitted by each light-emitting element 201 will form an image on the object at spaced-apart positions, and the size of the image will be smaller than the light-receiving area of ​​the pixel 301.

[0062] In addition to the light projected from the rangefinder 100, ambient light such as light from other light sources in the external space and reflected light from surrounding objects may be projected onto the object. By selecting the emission wavelength of the light-emitting element 201 to be different from the wavelength of general ambient light, much of the ambient light that directly or indirectly enters the image-side telecentric lens 130 is removed by the optical bandpass filter 160.

[0063] However, ambient light incident on the image-side telecentric lens 130 that has a wavelength equal to or close to the emission wavelength of the light-emitting element 201 cannot be removed by the optical bandpass filter 160 and therefore enters the photodetector array 121.

[0064] In this embodiment, for a plurality of pixels 301 arranged two-dimensionally in the light-receiving element array 121, the light-receiving area is limited to the vicinity of the center of the pixel, and a dead zone 501 is provided between adjacent pixels. Therefore, light reflected at positions 903 and 904 on the object corresponding to the dead zone 501 in the light-receiving element array 121 (corresponding to the light ray 813 in Figure 8B) is not detected by the sub-pixels. Because it is reflected and absorbed by the light-shielding curtain 611 or converted into photoelectric light in the charge discharge region 626, it does not affect the TOF measurement.

[0065] Thus, according to this embodiment, ambient light having a wavelength similar to the emission wavelength can be suppressed by the insensitive region 501. Therefore, TOF measurement with suppressed ambient light influence can be achieved without using separate components as in the conventional technology.

[0066] (Modification) In the first embodiment, a dead zone was created by physically limiting the light-receiving area in a pixel. However, a dead zone can also be realized by other methods. As one example of such a modification, this description explains a configuration in which a part of the light-receiving area is effectively made a dead zone by disabling a part of the subpixel (not used for TOF measurement). The differences from the first embodiment will be explained in detail below.

[0067] Figure 10 is a schematic diagram showing the light-receiving area of ​​a 2x2 pixel 301 provided on the light-receiving element array 121. Figure 11 is a schematic diagram showing the B-B' cross section of Figure 10.

[0068] In the first embodiment, sub-pixels (photoelectric conversion regions) are provided at the centers of the light-receiving surfaces of each pixel, and the rest is set as an insensitive region. In this modification, sub-pixels are arranged over the entire light-receiving surface of each pixel. In FIG. 10, the boundaries of pixel 301 are shown by solid lines, and the boundaries between sub-pixels (photoelectric conversion regions) are shown by broken lines. As shown in FIG. 11, sub-pixels are provided instead of the charge discharge regions of the first embodiment. Here, as a typical example, a configuration in which sub-pixels are provided over the entire light-receiving surface of the pixel is shown, but an insensitive region smaller than that of the first embodiment may exist.

[0069] In this modification, a substantial insensitive region is formed by invalidating a part of the sub-pixels. The invalidation of the sub-pixels can be realized by various methods. For example, the anode voltage Vbd may be supplied to each sub-pixel via a separate wiring, and a reverse bias below the breakdown voltage may be applied to the anode electrode of the sub-pixel to be invalidated. Thereby, avalanche amplification does not occur in the sub-pixel. Alternatively, for the sub-pixels to be invalidated, the signal may simply not be read out, or the TOF may not be measured.

[0070] For example, if only the sub-pixels in the central portion of the pixel are made effective, the same effects as those of the first embodiment can be obtained. Also, as an effect peculiar to this modification, it is possible to cope with the deviation that occurs in the conjugate relationship between the light-emitting element array 111 and the light-receiving element array 121 due to causes such as manufacturing errors and changes over time.

[0071] FIG. 12A is a diagram schematically showing the position of the image formed by the emitted light of the light-emitting element 201 on the object in association with the light-receiving regions of the sub-pixels provided in the light-receiving element array 121, similar to FIG. 9. FIG. 12 shows that due to a deviation in the conjugate relationship between the light-emitting element array 111 and the light-receiving element array 121, the imaging position of the image 901 on the object is in the +X Ｏ direction and +Y Ｏ direction.

[0072] As shown in FIG. 7, the coordinates (X Ｏ , Y Ｏ) corresponds to the coordinates (X, Y) on the light-receiving element array 121. Therefore, the reflected light of the image 901 is incident at a position shifted in the +X and +Y directions from the center 330 of the pixel, as shown by 901' in Figure 12B.

[0073] In such cases, the detection of unwanted incident light can be suppressed by disabling the hatched sub-pixels in Figure 12B that are not included in a predetermined size (here, the size of two horizontal and vertical pixels) that includes the incident position 901'. Thus, according to this modification, the position of the effective light-receiving region can be dynamically changed according to the position where the light emitted from the light-emitting element 201 is reflected by an object and incident on a pixel of the light-receiving element array. Therefore, the required precision for the installation positions of the light-emitting element array 111 and the light-receiving element array 121 can be lowered compared to the first embodiment, which is advantageous from a manufacturing standpoint.

[0074] (Other Embodiments) For example, in the pixel configuration shown in Figure 10, a light-shielding curtain may be provided in the portion of the pixel excluding the area near the center to achieve the same configuration as the first embodiment.

[0075] Furthermore, although the above-described embodiment described a configuration using a SPAD as the photoelectric conversion element, a general combination of a photodiode and an amplifier may also be used. However, since the time required for charge amplification in a SPAD is much faster than when the charge multiplication of a general photodiode signal is performed using an analog circuit, using a SPAD is advantageous in terms of the measurement accuracy of TOF.

[0076] The technical ideas derived from this disclosure are not limited to the exemplary embodiments disclosed, but are intended to encompass various modifications of the exemplary embodiments, or substitutions with equivalent structures or functions. The scope of the following claims should be interpreted in the broadest way to encompass all such modifications and equivalent structures and functions.

[0077] This application claims priority based on Japanese Patent Application No. 2024-209748, filed on December 2, 2024, and all of its contents are incorporated herein by reference.

Claims

1. A photodetector comprising: a photodetector array in which a plurality of photodetectors are arranged in two dimensions; a measuring means for measuring the elapsed time from a reference time until the incidence of light on the plurality of photodetectors is detected; and a determining means for determining the final elapsed time based on the measured elapsed times, wherein each of the plurality of photodetectors comprises: a plurality of photoelectric conversion elements having adjacent photoelectric conversion regions; and an insensitive region to incident light provided between adjacent photodetectors.

2. The photodetector according to claim 1, wherein the plurality of photoelectric conversion elements are provided on a part of the light-receiving surface of the photodetector.

3. The light-receiving element according to claim 2, wherein the portion of the light-receiving element includes the center of the light-receiving surface.

4. The photodetector according to claim 2 or 3, further comprising a microlens array for focusing light incident on the photodetector array, wherein the microlens array has a microlens for each of the photodetectors formed by combining microlenses corresponding to each of the plurality of photoelectric conversion elements such that the optical axis is eccentric toward the center of the photodetector.

5. The light-receiving element according to any one of claims 1 to 4, further comprising a light-shielding layer provided in the insensitive region.

6. The photodetector according to any one of claims 1 to 5, wherein the plurality of photoelectric conversion elements are SPADs (Single Photon Avalanche Diodes).

7. The photodetector according to claim 6, wherein in each of the plurality of photodetectors, the plurality of photoelectric conversion elements are formed on a semiconductor substrate, and adjacent photoelectric conversion elements are separated by a potential barrier.

8. The photodetector according to claim 6, further comprising an insulating region provided between adjacent photodetectors of the plurality of photodetectors.

9. The photodetector according to claim 6, further comprising a charge discharge region for discharging charge generated by light incident on the insensitive region.

10. A distance measuring device comprising: a light-emitting array in which a plurality of light-emitting elements are arranged in two dimensions; a lens that projects light emitted from the light-emitting array outwards; a light-receiving element according to any one of claims 1 to 9 that receives light incident through the lens; and a calculation means for determining distance based on the final elapsed time.

11. The photodetector according to claim 1, wherein the plurality of photoelectric conversion elements are provided on the entire light-receiving surface of the photodetector, and a portion of the plurality of photoelectric conversion elements are disabled.

12. The photodetector according to claim 11, wherein the photoelectric conversion element is deactivated by the supplied voltage, by the fact that the elapsed time is not measured, by the measured elapsed time not being used to determine the final elapsed time, or by the photoelectric conversion region being shielded from light.

13. The photodetector according to claim 11 or 12, wherein the plurality of photoelectric conversion elements are SPADs (Single Photon Avalanche Diodes).

14. A distance measuring device comprising: a light-emitting array in which a plurality of light-emitting elements are arranged in two dimensions; a lens that projects light emitted from the light-emitting array outwards; a light-receiving element according to any one of claims 11 to 13 that receives light incident through the lens; and a calculation means for determining distance based on the final elapsed time.

15. The distance measuring device according to claim 14, wherein the photoelectric conversion element to be deactivated is determined by the position at which the reflected light of the light projected by the lens enters the light-receiving element.

16. The distance measuring device according to claim 14 or 15, wherein among the plurality of photoelectric conversion elements, any photoelectric conversion element that is not included in a region of a predetermined size that includes the position where the reflected light projected by the lens is incident on the light receiving element is deactivated.

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