Photodetector

Abstract

To provide a photo-detector capable of reducing the thickness and optical loss while maintaining the function of a metalens as a lens.SOLUTION: A photo-detector 4 includes a photodetector element 6 having a surface 6a and including a plurality of avalanche photodiodes APD arranged along the surface 6a, and a plurality of metalens portions 8 arranged on the surface 6a so as to correspond to the plurality of avalanche photodiodes APD. From among the plurality of avalanche photodiodes APD and the plurality of metalens portions 8, in the corresponding one avalanche photodiode APD and one metalens portion 8, the one metalens portion 8 includes a plurality of metalens 9 arranged along the surface 6a.SELECTED DRAWING: Figure 10

Description

[Technical Field]

[0001] The present invention relates to a photodetector. [Background technology]

[0002] Non-Patent Document 1 describes a photodetector including a photodetector element including a plurality of light-receiving regions and a plurality of metalenses arranged on the plurality of light-receiving regions. Non-Patent Document 1 proposes improving the light detection efficiency of the photodetector element by increasing the transmittance and light-collection efficiency of each metalense and by increasing the focal depth of each metalense. [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] E. Mikheeva and 12 others, “CMOS-compatibleall-dielectric metalens for improving pixel photodetector arrays”, APL Photonics 5, 116105 (2020), submitted: July 17, 2020, online publication date: November 13, 2020 Summary of the Invention [Problem to be solved by the invention]

[0004] From the viewpoints of thinning the photodetector and reducing optical loss, it is desirable to position each metalens close to the surface of the photodetector. However, in the photodetector described in Non-Patent Document 1, one metalens corresponds to one light-receiving region, and therefore if the distance from one metalens to the surface of the photodetector is made too small, the numerical aperture of one metalens becomes too large, which could impair the function of the metalens as a lens and increase stray light.

[0005] An object of the present invention is to provide a photodetector that can be made thinner and have reduced optical loss while maintaining the lens function of a metalens. [Means for solving the problem]

[0006] The photodetector of the present invention comprises a photodetector element having a surface and including a plurality of light-receiving regions arranged along the surface, and a plurality of metalens sections arranged on the surface to correspond to the plurality of light-receiving regions, wherein, among the plurality of light-receiving regions and the plurality of metalens sections, in one corresponding light-receiving region and one metalens section, the one metalens section includes a plurality of metalenses arranged along the surface.

[0007] In the photodetector of the present invention, multiple metalenses correspond to one light receiving region. This allows the numerical aperture of each metalense to be reasonably set by adjusting the area of ​​each metalense according to the distance, even when the distance from each metalens section to the surface of the photodetector element is reduced. Furthermore, because the distance from each metalens section to the surface of the photodetector element can be reduced, robustness against the angle of incidence of incident light can be improved. Therefore, the photodetector of the present invention can be made thinner and have reduced optical loss while maintaining the lens function of the metalens.

[0008] In the photodetector of the present invention, the photodetecting element may further include separation regions separating each of the plurality of light-receiving regions, and the plurality of metalenses in each corresponding light-receiving region and metalens portion may be configured to focus light within the corresponding light-receiving region. This makes it possible to more reliably reduce optical loss while suppressing crosstalk between adjacent light-receiving regions.

[0009] In the photodetector of the present invention, the isolation region may be a trench, which makes it possible to easily and reliably prevent crosstalk from occurring between adjacent light-receiving regions.

[0010] The photodetector of the present invention may further include a light transmitting layer disposed between the surface and the plurality of metalens portions, which allows the distance from each metalens portion to the surface of the photodetector to be adjusted, thereby more appropriately setting the numerical aperture of each metalens.

[0011] In the photodetector of the present invention, the light transmitting layer may be formed directly on the surface, and the multiple metalens portions may be formed directly on the light transmitting layer. This reduces the number of interfaces between the metalens portion and the light receiving region, thereby reducing optical loss due to reflection at the interfaces, etc.

[0012] In a photodetector of the present invention, in a corresponding one light-receiving region and one metalens section, one metalens section may have a first metalens and multiple second metalens as the multiple metalenses, the area of ​​the first metalens being larger than the area of ​​each of the multiple second metalens, and the multiple second metalens being arranged to surround the first metalens. This makes it possible to reduce the number of multiple metalens corresponding to one light-receiving region while maintaining the lens function of the metalens.

[0013] In the photodetector of the present invention, for one corresponding light-receiving region and one corresponding metalens portion, the distance from one metalens portion to the surface of one light-receiving region is defined as T (μm), and the area of ​​one metalens portion is defined as S (μm 2 ) T is 1.0S 0.5 This allows the distance from the metalens section to the surface of one light receiving region to be sufficiently small relative to the size of the metalens section, making it possible to further reduce the thickness and optical loss. [Effects of the Invention]

[0014] According to the present invention, it is possible to provide a photodetector that can be made thinner and have reduced optical loss while maintaining the function of a metalens as a lens. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a configuration diagram of a PET device according to an embodiment. [Figure 2] FIG. 2 is a configuration diagram of the radiation detection device shown in FIG. [Figure 3] FIG. 3 is a side view of the radiation detector shown in FIG. 2. [Figure 4] FIG. 4 is a plan view of the photodetector element shown in FIG. 3. [Figure 5] FIG. 4 is a circuit diagram of the photodetector shown in FIG. 3. [Figure 6] FIG. 5 is a plan view of a portion of the photodetector element shown in FIG. 4. [Figure 7] 5 is a cross-sectional view of a portion of the photodetector element shown in FIG. 4. [Figure 8] FIG. 5 is a bottom view of the photodetector element shown in FIG. 4. [Figure 9] FIG. 4 is a plan view of a portion of the photodetector shown in FIG. 3. [Figure 10] 10 is a cross-sectional view of a portion of the photodetector taken along line XX shown in FIG. 9. [Figure 11] 10 is a graph showing the calculation results of the electric field strength of the photodetectors of the comparative example and the example, and a graph showing the intensity distribution on the surface of the light receiving region. [Figure 12] FIG. 10 is a cross-sectional view of a portion of a modified photodetector. [Figure 13] FIG. 10 is a bottom view of a modified example of the photodetector element. [Figure 14] 13 is a cross-sectional view of a portion of the photodetector taken along line XIII-XIII shown in FIG. 12. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In each drawing, the same or corresponding parts are designated by the same reference numerals, and redundant explanations will be omitted.

[0017] As shown in FIG. 1, the PET device 1 includes a cradle 101, a gantry 102, a control device 103, and a drive motor 104. The cradle 101 is arranged to pass through an opening of the gantry 102. A subject 105 is placed on the cradle 101. The control device 103 controls the drive motor 104 using a drive motor control signal. This causes the cradle 101 on which the subject 105 is placed to move, changing the position of the subject 105 relative to the opening of the gantry 102. The drive motor 104 may be configured to move the gantry 102, or may be configured to move both the cradle 101 and the gantry 102.

[0018] The gantry 102 has a plurality of radiation detection devices 106. The plurality of radiation detection devices 106 are arranged along the direction in which the opening of the gantry 102 penetrates. Each radiation detection device 106 surrounds the opening of the gantry 102. The control device 103 inputs a control signal for controlling each radiation detection device 106 to the gantry 102. The gantry 102 outputs a detection signal detected by each radiation detection device 106 to the control device 103.

[0019] As shown in FIG. 2, the radiation detection device 106 includes a plurality of radiation detectors 2. The plurality of radiation detectors 2 are arranged in a ring shape to surround the opening of the gantry 102. A radioisotope (positron-emitting nuclide) that emits positrons is injected into the subject 105. The positrons combine with negatrons in the subject 105 to generate annihilation gamma rays. The annihilation gamma rays are emitted in opposite directions from a position P of the radioisotope in the subject 105. As a result, the annihilation gamma rays are detected by a pair of radiation detectors 2 that face each other across the position P. The control device 103 identifies the position P based on the difference in the time of flight of the annihilation gamma rays and generates an image (tomographic image) related to internal information of the subject 105. In other words, the PET device 1 is a TOF-PET device.

[0020] As shown in Fig. 3, the radiation detector 2 includes a plurality of radiation detection units 2A. The plurality of radiation detection units 2A are arranged in a matrix with the X-axis direction and the Y-axis direction as the row and column directions. Each radiation detection unit 2A includes a scintillator (light emitter) 3 and a photodetector 4. In Fig. 3, the Z-axis direction is the radial direction of the ring (see Fig. 2) on which the plurality of radiation detectors 2 are arranged, the X-axis direction is the tangential direction of the ring, and the Y-axis direction is the direction perpendicular to the Z-axis and X-axis directions.

[0021] The scintillator 3 is disposed on the center side (hereinafter referred to as the "light incident side") of the opening of the gantry 102 relative to the photodetector 4 (see FIG. 2). The scintillator 3 emits light (fluorescence) when annihilation gamma rays are incident on it. 2-x Y x SiO5:Ce(LYSO), gadolinium aluminum gallium garnet (GAGG), NaI(TI), Pr:LuAG, LaBr2, LaBr3, and (Lu x Tb 1-x-y Ce y )3AlO 12 (i.e., LuTAG) wherein the composition ratio x is in the range of 0.5 to 1.5, and the composition ratio y is in the range of 0.01 to 0.15.

[0022] The photodetector 4 detects light emitted by the scintillator 3. The photodetector 4 has a wiring substrate 5, a photodetecting element 6, a planarizing film 7, and multiple metalens units 8. The wiring substrate 5 is shared by multiple photodetectors 4. The wiring substrate 5, the photodetecting element 6, the planarizing film 7, and the metalens unit 8 are arranged in this order from the side opposite the scintillator 3. In other words, the scintillator 3 is arranged on the side opposite the photodetecting element 6 with respect to the metalens unit 8. The scintillator 3 is bonded to the photodetector 4 with a light-transmitting adhesive.

[0023] As shown in FIG. 4, the photodetector element 6 has a plurality of photodetector units 10 arranged two-dimensionally and a common electrode E3. As an example, the photodetector element 6 has a rectangular shape when viewed from the Z-axis direction. The plurality of photodetector units 10 are arranged in a matrix with the X-axis and Y-axis directions as row and column directions. The common electrode E3 is located at the center of the photodetector element 6 when viewed from the Z-axis direction. The common electrode E3 collects charges generated in each photodetector unit 10. In other words, the photodetector element 6 is a SiPM having a plurality of SPADs (photodetector units 10). Note that, although FIG. 4 illustrates the plurality of photodetector units 10 only in the regions at both ends of the photodetector element 6, the plurality of photodetector units 10 are formed throughout the entire photodetector element 6 except for the common electrode E3.

[0024] 5, each photodetector unit 10 includes an avalanche photodiode APD and a quenching resistor R1. One end of the quenching resistor R1 is electrically connected to the anode of the avalanche photodiode APD, and the other end of the quenching resistor R1 is electrically connected to a common electrode E3 via a readout wiring TL of the photodetector element 6. That is, the multiple photodetector units 10 are connected in parallel, and in each photodetector unit 10, the avalanche photodiode APD and the quenching resistor R1 are directly connected. In the photodetector element 6, each avalanche photodiode APD is operated in Geiger mode. In Geiger mode, a reverse voltage (reverse bias voltage) greater than the breakdown voltage of the avalanche photodiode APD is applied to the avalanche photodiode APD. That is, a potential V1 is applied to the anode of the avalanche photodiode APD, and a potential V2 that is positive with respect to the potential V1 is applied to the cathode of the avalanche photodiode APD. The polarities of these potentials are relative, and for example, either one of the potentials may be the ground potential.

[0025] A signal processing unit SP is provided on the wiring board 5. The signal processing unit SP processes signals output from each photodetection element 6, with each photodetection element 6 serving as a channel. The signal processing unit SP outputs the processed signals (detection signals) to the control device 103 (see FIG. 1). The signal processing unit SP constitutes, for example, an ASIC (Application Specific Integrated Circuit). The signal processing unit SP may include a CMOS circuit that converts the signals output from each photodetection element 6 into digital pulses.

[0026] 6, in the photodetector element 6, the readout wiring TL includes a plurality of signal lines TL1 and a plurality of signal lines TL2. As an example, each signal line TL1 extends in the Y-axis direction between avalanche photodiodes APD adjacent to each other in the X-axis direction, and each signal line TL2 extends in the X-axis direction between avalanche photodiodes APD adjacent to each other in the Y-axis direction. The plurality of signal lines TL1 and the plurality of signal lines TL2 extend in a lattice pattern so as to be connected to each other at their intersections, and are electrically connected to a common electrode E3.

[0027] In each photodetector unit 10, one end of the quenching resistor R1 is connected to the electrode E1, and the other end of the quenching resistor R1 is connected to the signal line TL1. That is, in each photodetector unit 10, one end of the quenching resistor R1 is electrically connected to the anode of the avalanche photodiode APD via the electrode E1, and the other end of the quenching resistor R1 is electrically connected to the common electrode E3 via the readout wiring TL.

[0028] 7, the photodetector element 6 has a semiconductor layer 11. The semiconductor layer 11 is made of N + a first semiconductor region 12 of an N-type (first conductivity type), a first semiconductor region 13 of an N-type (first conductivity type), a plurality of second semiconductor regions 14 of a P-type (second conductivity type), and a plurality of second semiconductor regions 15 of a P-type (second conductivity type). +The semiconductor region 12 includes a semiconductor region (second semiconductor region) 15 of a first conductivity type (second conductivity type). The semiconductor region 13 is formed on the surface of the semiconductor region 12 on the light incident side. A plurality of semiconductor regions 14 are formed in the semiconductor region 13 along the surface 6a of the photodetector element 6. A plurality of semiconductor regions 15 are formed in the semiconductor region 14 along the surface 6a of the photodetector element 6. The impurity concentration of the semiconductor region 12 is higher than the impurity concentration of the semiconductor region 13. The impurity concentration of each semiconductor region 15 is higher than the impurity concentration of each semiconductor region 14.

[0029] In the photodetector element 6, one avalanche photodiode APD is configured by one semiconductor region 15 surrounded by the trench 16, one semiconductor region 14, and the regions of the semiconductor regions 12 and 13 that overlap with the one semiconductor region 15 in the Z-axis direction. + a P-type semiconductor region 12, an N-type semiconductor region 13, a P-type semiconductor region 14 that forms a PN junction with the N-type semiconductor region 13, and a P-type semiconductor region 14 that forms a PN junction with the N-type semiconductor region 13. + and a semiconductor region 15. In this embodiment, each avalanche photodiode APD functions as a light receiving region.

[0030] Trenches 16 are formed on the surface of the semiconductor layer 11 on the light incident side so as to separate the avalanche photodiodes APD. In other words, the trenches 16 are isolation regions that separate the avalanche photodiodes APD, which are light receiving regions. In the trenches 16, for example, an insulating material such as silicon oxide, a metal material such as tungsten, or polysilicon is disposed.

[0031] An insulating layer 17 is formed on the light incident surface of the semiconductor regions 13, 14, and 15. A common electrode E3 and a readout line TL are disposed on the insulating layer 17. The common electrode E3 and the readout line TL are covered with an insulating layer 18. In the photodetecting element 6, the light incident surface of the insulating layer 18 corresponds to the surface 6a of the photodetecting element 6. In each photodetecting unit 10, one end of a quenching resistor R1 (see FIG. 6) is electrically connected to the semiconductor regions 14 and 15 of the avalanche photodiode APD, and the other end of the quenching resistor R1 is electrically connected to the readout line TL.

[0032] A through hole TH is formed in the semiconductor layer 11. An insulating layer 19 is formed on the inner surface of the through hole TH and on the surface of the semiconductor region 12 opposite the light incident side. A through electrode TE is arranged on the inner surface of the through hole TH via the insulating layer 19. The through electrode TE is connected to a common electrode E3 at the opening of the through hole TH on the light incident side. A bump electrode B1 is arranged on the through electrode TE via an under bump metal BM. The through electrode TE and the insulating layer 19 are covered with a passivation film PF. An N-type semiconductor region 1PC is formed in a region surrounding the through hole TH on the light incident side surface of the semiconductor region 12. The semiconductor region 1PC prevents a PN junction formed by the semiconductor region 12 and the semiconductor regions 13 and 14 from reaching the through hole TH.

[0033] 8 , a groove is formed in the passivation film PF so as to surround the through hole TH when viewed from the Z-axis direction, and the semiconductor region 12 is exposed in the groove. A plurality of bump electrodes B2 are disposed on the semiconductor region 12 exposed in the groove. The bump electrode B1 and the plurality of bump electrodes B2 are electrically and physically connected to the wiring substrate 5, which is disposed on the opposite side of the photo-detecting element 6 from the plurality of metalens portions 8. In other words, the photo-detecting element 6 is electrically and physically connected to the wiring substrate 5.

[0034] In the photodetector element 6 configured as described above, each avalanche photodiode APD in each photodetector unit 10 is operated in Geiger mode. In this state, when light is incident on each avalanche photodiode APD from the front surface 6a, photoelectric conversion occurs in each avalanche photodiode APD, and photoelectrons (charges) are generated in each avalanche photodiode APD. When photoelectrons are generated, avalanche multiplication occurs in each avalanche photodiode APD, and the amplified electrons (charges) are collected in the common electrode E3 via the semiconductor regions 15 and the quenching resistor R1. The charges collected in the common electrode E3 from each photodetector unit 10 are input as signals to a signal processing unit SP (see FIG. 5) of the wiring substrate 20.

[0035] The semiconductor layer 11 is formed of, for example, Si. In the semiconductor layer 11, P-type impurities are, for example, Group 3 elements such as B, and N-type impurities are, for example, Group 5 elements such as N, P, and As. These impurities are added by, for example, diffusion or ion implantation. The insulating layers 17, 18, and 19 are formed of, for example, SiO2 or SiN. The insulating layers 17, 18, and 19 are formed by, for example, thermal oxidation or sputtering. The electrodes E1 and E3 and the through-electrode TE are formed of, for example, a metal such as aluminum. The electrodes E1 and E3 and the through-electrode TE are formed by, for example, sputtering. The resistivity of the quenching resistor R1 is higher than the resistivity of the electrode E1 and the common electrode E3. The quenching resistor R1 is formed of, for example, polysilicon. The quenching resistor R1 is formed by, for example, CVD (Chemical Vapor Deposition). The material of the quenching resistor R1 may be, for example, SiCr, NiCr, TaNi, FeCr, or the like.

[0036] As shown in FIGS. 3, 9, and 10, multiple metalens units 8 are provided on the planarization film 7. The multiple metalens units 8 are disposed on the surface 6a of the photodetector element 6 via the planarization film 7. When viewed from the Z-axis direction (a direction intersecting the surface 6a), each metalens unit 8 is two-dimensionally arranged so as to overlap with a corresponding avalanche photodiode APD (i.e., each photodetector unit 10). In other words, one metalens unit 8 corresponds to one avalanche photodiode APD (they face each other in the Z-axis direction). Note that FIGS. 9 and 10 only show a portion of the photodetector 4 that corresponds to one photodetector unit 10.

[0037] Each metalens unit 8 has multiple metalenses 9 for one avalanche photodiode APD included in the photodetector unit 10. Each metalens 9 is a metasurface lens formed on the surface 7a of the planarization film 7. The metalens 9 is formed from a metalens material such as a-Si, HfO2, Nb2O5, or TiO2. The metalens 9 is formed, for example, by etching the planarization film 7 to form multiple grooves in the planarization film 7. The multiple metalenses 9 are configured to focus light into the avalanche photodiode APD of a corresponding one of the photodetectors 10.

[0038] The metalens 9 is configured, for example, based on the phase design of a Fresnel lens. The outer diameter of the metalens 9 is, for example, several μm to several tens of μm. The outer diameter of the metalens 9 is designed according to the size of the light detecting unit 10 corresponding to the metalens unit 8 having the metalens 9. The thickness of the metalens unit 8 in the Z-axis direction is, for example, approximately 500 nm. The single period of the metalens unit 8 is equal to or less than the wavelength of the light L, for example, approximately 250 nm.

[0039] The planarization film 7 is disposed between the surface 6a of the photodetector element 6 and the multiple metalens portions 8. The planarization film 7 is a light-transmitting layer formed directly on the surface 6a. The planarization film 7 is formed of, for example, SiO2, GaAs, GaP, Si, SiC, or the like. The planarization film 7 is formed by, for example, thermal oxidation or sputtering. The thickness of the planarization film 7 is, for example, several μm.

[0040] As shown in FIG. 10 , in one avalanche photodiode APD and one metalens portion 8 that face each other in the Z-axis direction, each metalens 9 focuses light L onto the light incident surface of the corresponding avalanche photodiode APD (i.e., the surface 15a of the corresponding semiconductor region 15).

[0041] The distance in the Z-axis direction between the surface of one avalanche photodiode APD on the light incident side (i.e., surface 15a of semiconductor region 15) and metalens portion 8 is defined as T (μm), and the area of ​​metalens portion 8 corresponding to one avalanche photodiode APD is defined as S (μm 2 ), the following equation (1) holds: T≦1.0S 0.5 …(1)

[0042] The area of ​​the metalens portion 8 is, for example, several hundred μm 2 ~several thousand μm 2 Therefore, the distance in the Z-axis direction between the surface on the light incident side of one avalanche photodiode APD and the metalens portion 8 can be set to several tens of μm or less.

[0043] As described above, in the photodetector 4, multiple metalenses 9 correspond to one avalanche photodiode APD. As a result, even if the distance from each metalens portion 8 to the surface 6a of the photodetector element 6 is reduced, the numerical aperture of each metalens 9 can be reasonably set by adjusting the area of ​​each metalens 9 according to that distance. Furthermore, because the distance from each metalens portion 8 to the surface 6a of the photodetector element 6 can be reduced, robustness with respect to the angle of incidence of light L can be improved. Therefore, the photodetector 4 can be made thinner and have reduced optical loss while maintaining the lens function of the metalens 9.

[0044] In the photodetector 4, the photodetecting element 6 includes trenches 16 that separate the avalanche photodiodes APD, and multiple metalenses 9 are configured to focus light into one avalanche photodiode APD in a corresponding one avalanche photodiode APD and one metalens portion 8. This makes it possible to more reliably reduce optical loss while suppressing crosstalk between adjacent avalanche photodiodes APD.

[0045] In the photodetector 4, multiple metalenses 9 are configured to focus light while avoiding the trench 16 in a corresponding one avalanche photodiode APD and one metalens unit 8. In the photodetector 4, since the metalens unit 8 includes multiple metalenses 9, the degree of freedom in phase design is improved, making it easier to design the photodetector 4 so that light is focused while avoiding the trench 16. Furthermore, in the photodetector 4, since the metalens unit 8 includes multiple metalenses 9, the degree of freedom in phase design is improved, making it possible to design the photodetector 4 so that light is focused toward a specific region of the avalanche photodiode APD (e.g., a region of particularly high sensitivity among the light-receiving regions). For example, the metalens 9 can be designed to focus light toward the central region of the avalanche photodiode APD when the avalanche photodiode APD is viewed from the light incident side. The central region of the avalanche photodiode APD refers to a region within the avalanche photodiode APD that has the same center of gravity as the center of gravity of the avalanche photodiode APD when the avalanche photodiode APD is viewed from the light incident side. The central region of the avalanche photodiode APD has, for example, a shape that is substantially similar to the shape of the avalanche photodiode APD. The central region of the avalanche photodiode APD may be a region with particularly high sensitivity among the light receiving regions. This makes it possible to more reliably reduce optical loss while suppressing crosstalk between adjacent avalanche photodiodes APD.

[0046] In the photodetector 4, a planarization film 7 is disposed between the surface 6a of the photodetecting element 6 and the plurality of metalens sections 8. This makes it possible to adjust the distance from each metalens section 8 to the surface 6a of the photodetecting element 6, allowing the numerical aperture of each metalens 9 to be set more appropriately.

[0047] In the photodetector 4, the planarization film 7 is formed directly on the surface 6a of the photodetecting element 6, and multiple metalens portions 8 are formed directly on the planarization film 7. This reduces the number of interfaces between the metalens portions 8 and the avalanche photodiodes APD, making it possible to reduce optical loss due to reflection at the interfaces, etc.

[0048] In the photodetector 4, for one corresponding avalanche photodiode APD and one corresponding metalens section 8, the distance from one metalens section 8 to the surface of the avalanche photodiode APD on the light incident side is defined as T (μm), and the area of ​​one metalens section 8 is defined as S (μm 2 ) T is 1.0S 0.5 This allows the distance from the metalens unit 8 to the surface of the avalanche photodiode APD on the light incident side to be sufficiently small relative to the size of the metalens unit 8, making it possible to further reduce the thickness of the photodetector 4 and optical loss.

[0049] In the photodetector 4, for one corresponding avalanche photodiode APD and one corresponding metalens unit 8, when the distance from one metalens unit 8 to the surface of the avalanche photodiode APD on the light incident side is T (μm) and the outer diameter of one metalens 9 in the metalens unit 8 is D (μm), the light collection angle θ of one metalens 9 is tan -1 (D / 2T). The outer diameter of each of the multiple metalenses 9 in the metalens unit 8 can be adjusted in accordance with the distance from the metalens unit 8 to the surface of the avalanche photodiode APD on the light incident side, making it possible to prevent the collection angle θ of each metalens 9 from becoming too large. This reduces the distance from one metalens unit 8 to the surface of the avalanche photodiode APD on the light incident side, making it possible to suppress the generation of stray light that would otherwise result from an increase in the collection angle of the metalens.

[0050] FIG. 11(a) is a graph showing the calculated electric field strength of a comparative photodetector in which the metalens section includes a single metalens (outer diameter 50 μm) for each corresponding light-receiving region and metalens section, and a graph showing the intensity distribution at the surface of the light-receiving region (Z = 5 μm) for the single metalens. FIG. 11(b) is a graph showing the calculated electric field strength of an example in which the metalens section includes multiple metalens (outer diameter 10 μm) for each corresponding light-receiving region and metalens section, and a graph showing the intensity distribution at the surface of the light-receiving region (Z = 5 μm) for the single metalens of the photodetector. In both the comparative example and example photodetectors, the distance from the metalens to the surface of the light-receiving region was 5 μm, and each metalens was designed to focus light to the center of the metalens (X = 0 μm). The graphs showing the calculated electric field strength in Figures 11(a) and 11(b) are the results of FDTD calculations of the electric field strength in the range from the center (X = 0 μm) of a single metalens to the outer periphery of the metalens when 404 nm light is irradiated perpendicularly onto the light-receiving area. As shown in Figure 11(a), when the metalens section includes a single metalens, no significant difference is observed between the intensity at the center of the metalens and the intensity at positions other than the center of the metalens, confirming the presence of stray light at positions other than the center of the metalens. On the other hand, as shown in Figure 11(b), when the metalens section includes multiple metalenses, a significant difference is observed between the intensity at the center of the metalens and the intensity at positions other than the center of the metalens, demonstrating the suppression of stray light at positions other than the center of the metalens. This is because adjusting the outer diameter of the metalens according to the distance from the metalens to the surface of the light-receiving area prevents the metalens' light collection angle from becoming too large, thereby suppressing the generation of stray light.

[0051] The present invention is not limited to the above embodiment. For example, the planarization film 7 may be an insulating layer covering the readout wiring TL, and the light incident surface of the insulating layer 17 may be the surface 6a of the photodetector element 6. Alternatively, as shown in FIG. 12 , the plurality of metalens units 8 may be disposed on the surface 21a of a light-transmitting substrate 21, and the light-transmitting substrate 21 may be bonded to the surface 6a of the photodetector element 6 via a light-transmitting adhesive layer 22 formed on the surface 6a. The metalens units 8 may be formed on the light-transmitting substrate 21, for example, by forming a film made of a metalens material on the surface 21a of the light-transmitting substrate 21, forming an EB mask layer on the film by EB lithography, and then etching the film and the layer to form the plurality of metalens units 8 on the surface 21a of the light-transmitting substrate 21.

[0052] The thickness of light-transmitting substrate 21 is, for example, several tens of μm to several hundreds of μm. For one corresponding avalanche photodiode APD and one corresponding metalens unit 8, the size of metalens 9 arranged on surface 21a of light-transmitting substrate 21 can be adjusted depending on the distance from metalens unit 8 to the surface of the avalanche photodiode APD on the light incident side.

[0053] 13 and 14, the metalens unit 8 may have a first metalens 91 and a plurality of second metalenses 92 as the plurality of metalenses 9. When viewed in the Z-axis direction, the area of ​​the first metalens 91 is larger than the area of ​​each of the second metalenses 92. When viewed in the Z-axis direction, the plurality of second metalenses 92 are arranged to surround the first metalens 91. This allows the number of metalenses 9 corresponding to one avalanche photodiode APD to be reduced while maintaining the lens function of the metalens 9. The shape, area, arrangement, etc. of each of the plurality of metalenses 9 in the metalens unit 8 do not need to have regularity and / or uniformity and can be designed according to the shape of the light-receiving region, etc. Note that FIGS. 13 and 14 only show a portion of the photodetector 4 corresponding to one photodetector 10.

[0054] Furthermore, the photodetecting element 6 as a SiPM having multiple SPADs (photodetecting units 10) may have other configurations, such as a configuration in which the N-type semiconductor region and the P-type semiconductor region are reversed. Furthermore, the photodetecting element 6 may have multiple light-receiving regions having configurations other than avalanche photodiodes APDs. Each metalens 9 may focus light L at a position other than the light-incident surface of the corresponding avalanche photodiode APD. For example, it may focus light L in the depth direction of the light-receiving region (in the direction opposite to the light-incident surface of the avalanche photodiode APD). Each metalens 9 may focus light L, for example, inside the light-receiving region (e.g., within the region of the semiconductor region 15). By having each metalens 9 focus light inside the light-receiving region, the focal length of each metalens 9 can be equal to or greater than the distance T (μm) from the metalens unit 8 to the light-incident surface of the avalanche photodiode APD. Therefore, when the outer diameter of each metalens 9 is D (μm), the light collection angle θ is tan -1 Since the photodiode 6 has a D / 2T structure, the light collection angle can be made smaller than when light is collected on the surface of the light receiving region. This makes it possible to further suppress the generation of stray light. The photodetector element 6 is not limited to a front-illuminated type, but may be a back-illuminated type. The photodetector element 6 may have an isolation region formed of a semiconductor region of a first conductivity type, a semiconductor region of a second conductivity type, a light-shielding film, etc., instead of the trench 16. The photodetector element 6 does not necessarily have an isolation region for isolating each avalanche photodiode APD.

[0055] Furthermore, the detection target of the radiation detector 2 is not limited to annihilation gamma rays, but may be other radiation such as X-rays. Furthermore, in the radiation detector 2, the light-emitting body that emits light in response to incidence of radiation is not limited to the scintillator 3, but may be another light-emitting body such as a Cherenkov radiator. [Explanation of symbols]

[0056] 4...photodetector, 6...photodetecting element, 6a...surface, 7...planarizing film, 8...metalens portion, 9...metalens, 16...trench, 21...light-transmitting substrate, 91...first metalens, 92...second metalens, APD...avalanche photodiode (light-receiving region) L...light.

Claims

1. a photodetector element having a surface and including a plurality of light receiving regions disposed along the surface; a plurality of metalens portions arranged on the surface to correspond to the plurality of light receiving regions; among the plurality of light receiving regions and the plurality of metalens sections, in a corresponding one light receiving region and one metalens section, the one metalens section includes a plurality of metalenses arranged along the surface, In the corresponding one light-receiving region and one metalens section, the one metalens section has a first metalens and a plurality of second metalens as the plurality of metalenses, a photodetector wherein an area of ​​the first metalens is greater than an area of ​​each of the plurality of second metalenses.

2. the photodetector element further includes an isolation region that isolates each of the plurality of light receiving regions; 10. The photodetector of claim 1, wherein, for a corresponding one of the light-receiving regions and one of the metalens portions, the plurality of metalenses are configured to focus light within the one of the light-receiving regions.

3. The photodetector of claim 2 , wherein the isolation region is a trench.

4. 4. The photodetector of claim 1, further comprising a light-transmitting layer disposed between the surface and the plurality of metalens portions.

5. the light-transmitting layer is formed directly on the surface, 5. The photodetector of claim 4, wherein the plurality of metalens portions are formed directly on the light-transmitting layer.

6. An optical detector described in any one of claims 1 to 5, wherein the plurality of second metalenses are arranged to surround the first metalense.

7. For the corresponding one light receiving region and one metalens section, the distance from the one metalens section to the surface of the one light receiving region is defined as T (μm), and the area of ​​the one metalens section is defined as S (μm ２ ) and T is 1.0S ０．５ 7. The photodetector according to claim 1, wherein:

8. 8. The photodetector of claim 1, wherein each of the plurality of metalenses is configured to focus light to a different position within the one light-receiving region.

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