Light detection device and ranging system

Abstract

[Problem] To improve reliability by preventing thermal runaway by efficiently exhausting heat when performing photoelectric conversion using germanium as a main material. [Solution] A light detection device (1) comprising: a first semiconductor layer (2) that is mainly composed of silicon; a second semiconductor layer (3) that is laminated on the first semiconductor layer (2) and that mainly comprises germanium; a photoelectric conversion unit (4) disposed on a part of the second semiconductor layer (3) and the first semiconductor layer (2); and a heat dissipation member (5) that is disposed on the second semiconductor layer (3) and that dissipates heat generated by the photoelectric conversion unit (4).

Description

Photodetection device and ranging system

[0001] The present disclosure relates to a photodetection device and a ranging system.

[0002] Silicon photonics has attracted attention for transmitting and receiving data at high speed and with high efficiency. In silicon photonics, a germanium photodiode (hereinafter referred to as GePD) having excellent sensitivity is used as a photoelectric conversion element that converts an optical signal into an electrical signal.

[0003] When an optical signal is continuously incident, the GePD causes self-heating, and dark current is generated. As the dark current increases, the temperature further rises, and when the temperature exceeds a certain threshold, thermal destruction due to thermal runaway occurs. As described above, existing GePDs have a risk of thermal runaway, and there are concerns from the viewpoint of reliability.

[0004] Technologies for countermeasures against heat generation of photodiodes have been proposed (see Patent Documents 1 and 2). Patent Document 1 describes that a heat sink is connected to an optical integrated circuit substrate, and heat generated in the optical integrated circuit substrate is dissipated through the heat sink. Patent Document 2 describes that a substrate of an optical integrated circuit and an optical waveguide are arranged on a carrier, an opening is provided in the substrate, and heat generated by heat-generating components of the optical integrated circuit is discharged from the back surface of the carrier through the opening.

[0005] Japanese Patent No. 6260167, Japanese Patent No. 6530706

[0006] However, Patent Documents 1 and 2 do not explicitly state that GePD is used as a photoelectric conversion element, and according to the descriptions in Patent Documents 1 and 2, efficient heat dissipation focusing on the structure of GePD cannot be achieved.

[0007] Therefore, the present disclosure provides a photodetection device and a ranging system capable of preventing thermal runaway and improving reliability by performing efficient heat dissipation when performing photoelectric conversion using germanium as a main material.

[0008] To solve the above problems, the present disclosure provides a photodetector comprising: a first semiconductor layer mainly made of silicon; a second semiconductor layer mainly made of germanium, laminated on the first semiconductor layer; a photoelectric conversion unit disposed on a part of the first semiconductor layer and the second semiconductor layer; and a heat dissipation member disposed on the second semiconductor layer for dissipating heat generated in the photoelectric conversion unit.

[0009] The device may also include a first wiring layer positioned above the second semiconductor layer and in contact with the heat dissipation member, and a first contact member that provides electrical conductivity between the photoelectric conversion unit and the first wiring layer.

[0010] The photoelectric conversion unit comprises a second wiring layer positioned above the first wiring layer, and a second contact member that provides electrical conductivity between the first wiring layer and the second wiring layer, wherein the heat generated in the photoelectric conversion unit may be dissipated through the heat dissipation member, the first wiring layer, the second contact member, and the second wiring layer.

[0011] The heat dissipation member, the first wiring layer, the second wiring layer, the first contact member, or the second contact member may contain at least one of copper (Cu), aluminum (Al), zinc (Zn), or iron (Fe).

[0012] The photoelectric conversion unit may be arranged in part of the first semiconductor layer and the second semiconductor layer, and the heat dissipation member may be arranged on the second semiconductor layer at a distance from the photoelectric conversion unit.

[0013] The upper surface of the second semiconductor layer may include grooves along the location where the photoelectric conversion unit is positioned, where the heat dissipation member is placed.

[0014] The width of the groove in the short direction is greater than the width of the heat dissipation member in the short direction, the height of the groove is lower than the height of the heat dissipation member, and a part of the side surface of the heat dissipation member may be positioned in the groove.

[0015] The groove portion may be slit-shaped or dot-shaped.

[0016] Two grooves are arranged on both sides in the short direction of the photoelectric conversion portion, which is positioned on the upper surface of the second semiconductor layer, and the two grooves extend in the longitudinal direction of the photoelectric conversion portion. Two heat dissipation members may be arranged in the two grooves.

[0017] The two grooves and the two heat dissipation members may be arranged symmetrically with respect to the photoelectric conversion unit.

[0018] Two or more grooves are arranged on each of the short-side sides of the photoelectric conversion portion that is placed on the upper surface of the second semiconductor layer, the two or more grooves extend in the longitudinal direction of the photoelectric conversion portion, and two or more heat dissipation members may be arranged in the two or more grooves.

[0019] The two or more grooves and the two or more heat dissipation members, which are arranged on each of the two or more sides in the short direction of the photoelectric conversion unit, may be arranged symmetrically with respect to the photoelectric conversion unit.

[0020] The second semiconductor layer may include a metal layer laminated on the side of the second semiconductor layer opposite to the first semiconductor layer.

[0021] The heat generated in the photoelectric conversion unit may be dissipated through the heat dissipation member, as well as through the second semiconductor layer, the first semiconductor layer, and the metal layer.

[0022] The metal layer may contain at least one of copper (Cu), aluminum (Al), zinc (Zn), or iron (Fe).

[0023] The metal layer may be in the shape of a solid pattern, a slit pattern, or a dot pattern.

[0024] The second semiconductor layer is an intrinsic germanium layer, the photoelectric conversion portion is a germanium region of a first conductivity type, and the first semiconductor layer may be of a second conductivity type different from that of the germanium region.

[0025] The second semiconductor layer is an intrinsic germanium layer, and the first semiconductor layer may have a silicon region of a first conductivity type, an intrinsic silicon region, and a silicon region of a second conductivity type arranged sequentially in the planar direction.

[0026] A distance measuring system may be applied that includes the above-described light detection device and a distance measuring device that detects the distance of an object based on the electrical signal converted photoelectrically by the photoelectric conversion unit.

[0027] The device includes a transmitting and receiving device that emits frequency-modulated light and receives light whose phase has been changed by reflection from an object, and the transmitting and receiving device may also include the light detection device.

[0028] A cross-sectional view of the photodetector according to the first embodiment. A plan view of the photodetector according to the first embodiment. A perspective view of the photodetector according to the first embodiment. A diagram showing the heat dissipation path of the heat generated in the photoelectric conversion unit with arrow lines. A diagram explaining the operation of the GePD, which is a photodetector according to this embodiment. A cross-sectional view of the photodetector according to the second embodiment. A cross-sectional view of the photodetector according to the third embodiment. A cross-sectional view of the photodetector according to the fourth embodiment. A cross-sectional view of the photodetector according to the fifth embodiment. A cross-sectional view of the manufacturing process of the photodetector according to the first embodiment shown in Figure 1. A cross-sectional view of the process following Figure 10A. A cross-sectional view of the process following Figure 10B. A cross-sectional view of the process following Figure 10C. A cross-sectional view of the process following Figure 10D. A cross-sectional view of the process following Figure 10E. A cross-sectional view of the process following Figure 10F. A cross-sectional view of the process following Figure 10G. A cross-sectional view of the process following Figure 10H. A block diagram showing the schematic configuration of an FMCW type distance measuring system equipped with a photodetector according to any of the first to fifth embodiments. A block diagram showing the internal configuration of the detector. A block diagram showing an example of the schematic configuration of a vehicle control system. An explanatory diagram showing an example of the installation location of the external information detection unit and the imaging unit.

[0029] Embodiments of the light detection device and distance measuring system will be described below with reference to the drawings. While the main components of the light detection device and distance measuring system will be described below, there may be components and functions not shown or described. The following description does not exclude any components or functions not shown or described.

[0030] (First Embodiment) Figure 1 is a cross-sectional view of the photodetector 1 according to the first embodiment, and Figure 2 is a plan view of the photodetector 1 according to the first embodiment. Figure 1 is a cross-sectional view taken along line A-A in Figure 2. The photodetector 1 according to the first embodiment is a germanium photodiode (GePD).

[0031] As shown in Figures 1 and 2, the photodetector 1 according to the first embodiment comprises a silicon layer (first semiconductor layer) 2, an intrinsic germanium layer (second semiconductor layer) 3, a photoelectric conversion unit 4, and a heat sink (heat dissipation member) 5.

[0032] The silicon layer 2 is a first semiconductor layer primarily made of silicon. By implanting P-type impurity ions into the silicon layer 2, a P-type silicon region 2a and a high-concentration P-type silicon region 2b are provided. More specifically, as shown in Figure 2, the high-concentration P-type silicon regions 2b are arranged on both sides of the P-type silicon region 2a in the short direction. The P-type silicon region 2a functions as the anode of the GePD.

[0033] In the intrinsic germanium layer 3, which is placed on top of the silicon layer 2, N-type germanium regions (N-Ge) 3a are formed by implanting N-type impurity ions. The N-type germanium regions 3a function as the cathode of the GePD. Thus, the intrinsic germanium layer 3 is a second semiconductor layer with germanium as its main material.

[0034] The photoelectric conversion unit 4 is located in a portion of the silicon layer 2 and the intrinsic germanium layer 3. More specifically, the photoelectric conversion unit 4 has an N-type germanium region 3a located in a portion of the intrinsic germanium layer 3 and a P-type silicon region 2a located in a portion of the silicon layer 2.

[0035] The heat sink 5 is placed on top of the intrinsic germanium layer 3. The heat sink 5 is a heat sink that dissipates the heat generated in the photoelectric conversion unit 4. For example, the heat sink 5 is placed on top of the intrinsic germanium layer 3, spaced apart from the photoelectric conversion unit 4.

[0036] A groove 3b is positioned on the upper surface of the intrinsic germanium layer 3. As shown in Figure 2, the groove 3b is positioned on both sides of the photoelectric conversion unit 4 in the short direction and along the longitudinal direction of the photoelectric conversion unit 4. The width of the groove 3b is slightly larger than the width of the heat sink 5 in the short direction, and the depth of the groove 3b is lower than the height of the heat sink 5. Therefore, the lower side of the heat sink 5 is positioned in the groove 3b, and the upper side of the heat sink 5 is positioned above the groove 3b.

[0037] In this way, by positioning the lower side of the heat sink 5 in the groove 3b, a portion of the side and bottom surface of the heat sink 5 are positioned opposite the intrinsic germanium layer 3, allowing the heat from the intrinsic germanium layer 3 to be efficiently transferred to the heat sink 5.

[0038] Furthermore, a silicon oxide layer 6 is placed in the gap between the groove 3b of the intrinsic germanium layer 3 and the side and bottom surfaces of the heat sink 5. Although the thermal conductivity of the silicon oxide layer 6 is lower than that of the intrinsic germanium layer 3 and the heat sink 5, the silicon oxide layer 6 placed in the gap of the groove 3b is sufficiently thin, so the heat from the intrinsic germanium layer 3 is efficiently transferred to the heat sink 5 via the silicon oxide layer 6.

[0039] As shown in Figure 2, the P-type silicon region 2a, the high-concentration P-type silicon region 2b, the photoelectric conversion unit 4, and the heat sink 5 are all, for example, elongated in shape. Multiple contacts 7 are arranged on the upper surfaces of the high-concentration P-type silicon region 2b and the photoelectric conversion unit 4. These contacts 7 extend upward and are connected to the first wiring layer (1-MT) 8. The upper surface of the heat sink 5 is in contact with the first wiring layer 8. The intrinsic germanium layer 3, the contacts 7, and the heat sink 5 are covered with a silicon oxide layer 6.

[0040] Multiple contacts 9 are arranged on the first wiring layer 8, and these contacts 9 are connected to the second wiring layer (2-MT) ​​10. The first wiring layer 8, the second wiring layer 10, and the contacts 9 are covered with an insulating layer (e.g., a silicon oxide layer) 11.

[0041] In FIG. 1, the structure above the second wiring layer 10 is omitted, but a contact and a third wiring layer may be disposed above the second wiring layer 10.

[0042] There are no particular limitations on the materials of the heat sink 5, the first wiring layer 8, the second wiring layer 10, and the contacts 7, 9, but the material contains at least one of copper (Cu), aluminum (Al), zinc (Zn), or iron (Fe), for example.

[0043] A metal layer 12 is disposed on the surface of the silicon layer 2 opposite the contact surface with the intrinsic germanium layer 3. As will be described later, the metal layer 12 can dissipate heat generated by the photoelectric conversion unit 4. There are no particular limitations on the material of the metal layer 12, but the material contains at least one of copper (Cu), aluminum (Al), zinc (Zn), or iron (Fe), for example.

[0044] In the plan view of FIG. 2, illustration of the first wiring layer 8, the contact 7, and the second wiring layer 10 of FIG. 1 is omitted. As can be understood from FIG. 2, two heat sinks 5 and two high-concentration P-type silicon regions 2b are disposed on both sides in the widthwise direction of the N-type germanium region 3a constituting the photoelectric conversion unit 4, and have a symmetrical structure with respect to the photoelectric conversion unit 4. This enables uniform heat dissipation of heat generated by the photoelectric conversion unit 4 on both sides in the widthwise direction of the photoelectric conversion unit 4.

[0045] FIG. 3 is a perspective view of the photodetection device 1 according to the first embodiment. Although omitted in FIGS. 1 and 2, the photodetection device 1 according to the first embodiment includes an optical waveguide 17 connected to a side surface of the P-type silicon region 2a. Light incident on the P-type silicon region 2a via the optical waveguide 17 is converted into electric charges by the photoelectric conversion unit 4, and a photocurrent corresponding to the converted charge amount flows.

[0046] The thermal resistance Rth (K / W) of each part of the photodetection device 1 of FIG. 1 is represented by the following formula (1).

[0047] Rth=δ / (λA) ...(1) In formula (1), δ is the width (m), λ is the thermal conductivity (W / m·K), and A is the heat transfer area (m 2 ).

[0048] The heatsink 5, made of copper (Cu), has a thermal conductivity of approximately 398 W / m·K, while tungsten, a typical material for contacts 7, has a thermal conductivity of 178 W / m·K. Therefore, a large portion of the heat generated in the photoelectric conversion unit 4 is transferred by the heatsink 5.

[0049] Figure 4 shows the heat dissipation paths for the heat generated in the photoelectric conversion unit 4, indicated by arrows. The heat generated in the photoelectric conversion unit 4 is dissipated through a first heat dissipation path PT1, which flows from the intrinsic germanium layer 3 to the heat sink 5, the first wiring layer 8, the contact 9, and the second wiring layer 10, and a second heat dissipation path PT2, which flows from the P-type silicon region 2a to the metal layer 12.

[0050] Figure 2 shows an example in which a slit-shaped groove 3b extending along the longitudinal direction of the photoelectric conversion unit 4 is provided on the upper surface of the intrinsic germanium layer 3. However, multiple dot-shaped grooves 3b arranged along the longitudinal direction of the photoelectric conversion unit 4 may also be provided. If multiple dot-shaped grooves 3b are provided, a heat sink 5 having multiple columnar fins that match the size of the grooves 3b may be provided.

[0051] Figure 5 is a diagram illustrating the operation of the GePD, which is a photodetector 1 according to this embodiment. With a reverse bias voltage applied between the N-type germanium region 3a and the P-type silicon region 2a, an optical signal is incident on the P-type silicon region 2a from the optical waveguide 17. The incident light is photoelectrically converted in the photoelectric conversion unit 4 to generate an electric charge. The voltage in the N-type germanium region 3a decreases according to the amount of charge generated. The amount of voltage drop in the N-type germanium region 3a represents the light intensity.

[0052] Thus, in the first embodiment, since the heat sink 5 is placed near the N-type germanium region 3a which constitutes a part of the photoelectric conversion unit 4, the heat generated in the photoelectric conversion unit 4 can be efficiently dissipated through the heat sink 5, and thermal runaway of the photodetector 1 can be prevented.

[0053] (Second Embodiment) In order to efficiently transfer the heat transferred from the photoelectric conversion unit 4 to the intrinsic germanium layer 3 via the heat sink 5, it is desirable to maximize the surface area between the intrinsic germanium layer 3 and the heat sink 5.

[0054] Figure 6 is a cross-sectional view of a photodetector 1a according to a second embodiment. Two or more grooves 3b are arranged on each side of the photoelectric conversion unit 4 in the short direction on the upper surface of the intrinsic germanium layer 3. The heat sink 5 has two or more fins 5a that engage with the two or more grooves 3b. The width of each groove 3b is slightly larger than the width of the fins 5a, and the depth of the grooves 3b is lower than the height of the heat sink 5. As a result, the lower side of each fin 5a is positioned in the corresponding groove 3b. The two or more grooves 3b and two or more fins 5a arranged on each side of the photoelectric conversion unit 4 in the short direction in Figure 6 are arranged symmetrically with respect to the photoelectric conversion unit 4.

[0055] In the second embodiment, the area of ​​contact between the intrinsic germanium layer 3 and the heat sink 5 can be increased, allowing heat from the intrinsic germanium region to be efficiently transferred to the heat sink 5.

[0056] In the second embodiment as well, the groove 3b may be slit-shaped or dot-shaped. The shape of the fins 5a of the heat sink 5 needs to be changed to match the shape of the groove 3b.

[0057] Thus, in the second embodiment, the number of grooves 3b is increased compared to the first embodiment, and a heat sink 5 with a fin structure that engages with each groove 3b is provided. This allows for a wider surface area between the intrinsic germanium layer 3 and the heat sink 5, thereby improving the heat dissipation effect compared to the first embodiment.

[0058] (Third Embodiment) Figure 7 is a cross-sectional view of the photodetector 1b according to the third embodiment. The photodetector 1b according to the third embodiment differs from the photodetector 1 in that the metal layer 12 in contact with the silicon layer 2 is shaped like a slit or dots. The width of the slits, the number of slits, the diameter of the dots, or the number of dots in the metal layer 12 are arbitrary.

[0059] Figure 7 shows an example in which the solid pattern metal layer 12 of the light detection device 1 according to the first embodiment shown in Figure 1 is made into a slit shape or a dot shape, but the metal layer 12 of the light detection device 1a according to the second embodiment shown in Figure 6 may also be made into a slit shape or a dot shape.

[0060] (Fourth Embodiment) Figure 8 is a cross-sectional view of the photodetector 1c according to the fourth embodiment. The photodetector 1c according to the fourth embodiment is characterized in that the conductivity type of the silicon layer 2 and the conductivity type of the germanium region arranged in a part of the intrinsic germanium layer 3 are reversed compared to Figure 1. Note that the first wiring layer 8, contact 9, and second wiring layer 10 are not shown in Figure 8.

[0061] The silicon layer 2 according to the fourth embodiment has an N-type silicon region 2c and a high-concentration N-type silicon region 2d. The intrinsic germanium layer 3 according to the fourth embodiment has a P-type germanium region 3c.

[0062] The photoelectric conversion unit 4 according to the fourth embodiment has a P-type germanium region 3c that functions as an anode and an N-type silicon region 2c that functions as a cathode.

[0063] As shown in Figure 8, a heat sink 5 is positioned near the P-type germanium region 3c, allowing the heat generated in the photoelectric conversion unit 4 to be efficiently transferred to the heat sink 5.

[0064] The photoelectric conversion unit 4 of the fourth embodiment can be applied not only to the photoelectric conversion unit 4 of the first embodiment, but also to the photoelectric conversion unit 4 of the second and third embodiments.

[0065] (Fifth Embodiment) Figure 9 is a cross-sectional view of a photodetector 1d according to the fifth embodiment. In the fifth embodiment, no impurity ions are implanted in the intrinsic germanium layer 3. Instead, the silicon layer 2 has an intrinsic silicon region 2e, a P-type silicon region 2a, an N-type silicon region 2c, a high-concentration P-type silicon region 2b, and a high-concentration N-type silicon region 2d. Note that the first wiring layer 8, contact 9, and second wiring layer 10 are not shown in Figure 9.

[0066] The intrinsic germanium layer 3 is positioned opposite the intrinsic silicon region 2e, the P-type silicon region 2a, and the N-type silicon region 2c.

[0067] The photoelectric conversion unit 4 according to the fifth embodiment is composed of an intrinsic silicon region 2e, a P-type silicon region 2a, an N-type silicon region 2c, and an intrinsic germanium layer 3.

[0068] A heat sink 5 is placed on the upper surface of the intrinsic germanium layer 3. The heat sink 5 may be provided on the upper surface of the intrinsic germanium layer 3, with a plurality of slit-shaped or dot-shaped grooves 3b and a plurality of fins 5a arranged in the plurality of grooves 3b.

[0069] Thus, in the photodetector 1d according to the fifth embodiment, the step of implanting impurity ions into the intrinsic germanium layer 3 can be omitted. Furthermore, since only one heat sink 5 is required, the structure of the GePD can be simplified compared to the first to fourth embodiments.

[0070] (Example of manufacturing process) Figures 10A to 10I are cross-sectional views showing the manufacturing process of the light detection device 1 according to the first embodiment shown in Figure 1.

[0071] Figure 10A shows the process after implanting N-type impurity ions into the silicon layer 2 to form a P-type silicon region 2a and a high-concentration P-type silicon region 2b. An intrinsic germanium layer 3 is deposited on the P-type silicon region 2a, and N-type impurity ions are implanted from above the intrinsic germanium layer 3 to form an N-type germanium region 3a.

[0072] Next, as shown in Figure 10B, a portion of the upper surface of the intrinsic germanium layer 3 is removed by etching to form a groove 3b on the upper surface of the intrinsic germanium layer 3. The groove 3b is the location for the heat sink 5. The groove 3b is formed so that its width is slightly larger than the width of the heat sink 5.

[0073] Next, as shown in Figure 10C, the top and sides of the intrinsic germanium layer 3 are covered with a silicon oxide layer 6.

[0074] Next, as shown in Figure 10D, a portion of the silicon oxide layer 6 is removed by etching. Here, the silicon oxide layer 6 corresponding to the placement locations of the heat sink 5 and contact 7 is partially removed. As a result, a groove 3b is formed where the heat sink 5 is to be formed, and a trench 13 deeper than the groove 3b is formed where the contact 7 is to be formed.

[0075] Next, as shown in Figure 10E, the material for the heat sink 5 is embedded in the groove 3b. The material for the heat sink 5 is a metal material with high thermal conductivity (for example, copper (Cu)).

[0076] Next, as shown in Figure 10F, the material for the contact 7 is embedded in the trench 13. The material for the contact 7 is a conductive material containing at least one of copper (Cu), aluminum (Al), zinc (Zn), or iron (Fe).

[0077] Although not shown in Figures 10A to 10F, the silicon layer 2 is part of the SOI (Silicon On Insulator) substrate 14. Below the silicon layer 2, a silicon oxide layer 6 called the BOX layer 15 is stacked, and below that, the silicon substrate 16 is placed. The substrate after the process shown in Figure 10F is completed will be referred to as the PD substrate 21 below.

[0078] Next, as shown in Figure 10G, the PD board 21 and the logic board 22 are bonded together. The bonding between the PD board 21 and the logic board 22 is performed using, for example, a CCC (Couper to Couper Connection), vias, bumps, etc.

[0079] Figure 10G shows an example where the cross-sectional structure of Figure 10F is reversed and attached to the logic board 22. Circuits that perform various signal processing on the signals converted photoelectrically by the GePD are mounted on the logic board 22.

[0080] Next, as shown in Figure 10H, the silicon substrate 16 and BOX layer 15 of the SOI substrate 14 are removed to expose the silicon layer 2. Then, as shown in Figure 10I, a metal layer 12 is formed on the upper surface of the silicon layer 2.

[0081] (Distance measuring device) Figure 11 is a block diagram showing the schematic configuration of a FMCW (Frequency Modulated Continuous Wave) type distance measuring system (LiDAR: Light Detection And Ranging) 20 equipped with a light detection device 1 according to any of the first to fifth embodiments.

[0082] The distance measuring system 20 in Figure 11 comprises a PD board 21, a logic board 22, and a light-emitting board 23. These three boards may be stacked, or the PD board 21 and logic board 22 may be stacked and the light-emitting board 23 may be placed separately.

[0083] A laser chip 24 that emits laser light of a predetermined fixed wavelength (for example, 1550 nm) is mounted on the light-emitting substrate 23.

[0084] A modulator 31, a splitter 32, a circulator 33, an antenna 34, a coupler 35, and a detector 36 are mounted on the PD board 21. The detector 36 has an optical detection device 1 according to the first to fifth embodiments.

[0085] The modulator 31 frequency modulates the laser light emitted by the laser chip 24. For example, the modulator 31 modulates the laser light so that the frequency increases linearly over time, and then decreases linearly, to generate a transmission signal. The modulator 31 inputs the generated transmission signal to the splitter 32 via the optical waveguide 17.

[0086] The splitter 32 splits the transmission signal and inputs it to the circulator 33 and the coupler 35.

[0087] The circulator 33 inputs the transmission signal from the splitter 32 to the antenna 34, and also inputs the return signal received by the antenna 34 to the coupler 35. The return signal is a signal that is phase-delayed relative to the transmission signal.

[0088] Antenna 34 radiates the transmission signal from circulator 33 into free space and receives signals from free space.

[0089] The coupler 35 generates a beat signal through the interference between the return signal from the circulator 33 and the transmitted signal from the splitter 32. The frequency of the beat signal changes according to the frequency difference between the transmitted signal and the return signal. The frequency difference changes according to the distance from the antenna 34 to the object 37. Therefore, the distance from the antenna 34 to the object 37 can be estimated based on the frequency of the beat signal.

[0090] The detector 36 extracts a beat signal from the signal propagating from the optical waveguide 17. Figure 12 is a block diagram showing the internal configuration of the detector 36. As shown in Figure 12, the detector 36 includes a first GePD 36a, a second GePD 36b, and a transimpedance amplifier.

[0091] Both the first GePD 36a and the second GePD 36b have the same structure as the photodetector 1 according to the embodiment described above. The first GePD 36a is connected to the optical waveguide 17, and the second GePD 36b is also connected to the optical waveguide 17. The current signal photoelectrically converted by the first GePD 36a and the current signal photoelectrically converted by the second GePD 36b are input to the transimpedance amplifier 36c.

[0092] The transimpedance amplifier 36c converts these current signals to impedance and amplifies them to generate a beat signal, which is a voltage signal.

[0093] The logic board 22 is equipped with a controller 41, a DAC (Digital Analog Converter) 42, an ADC (Analog Digital Converter) 43, and an FFT (Fast Fourier Transform) processing unit 44.

[0094] The controller 41 generates various control signals to control the light-emitting substrate 23 and the PD substrate 21. The DAC 42 converts the control signals generated by the controller 41 into analog signals and transmits them to the light-emitting substrate 23 and the PD substrate 21.

[0095] The ADC 43 performs AD conversion on the beat signal from the detector 36 according to instructions from the controller 41 and inputs it to the FFT processing unit 44. The FFT processing unit 44 performs FFT processing on the digital beat signal from the ADC 43 and derives the frequency of the beat signal based on the power spectrum density generated by the FFT processing.

[0096] The controller 41 outputs power spectrum density information generated by the FFT processing unit 44 according to external control. The controller 41 can also detect the distance to the object 37 based on the power spectrum density information generated by the FFT processing unit 44. In this way, the logic board 22 functions as a distance measuring device.

[0097] <Examples of application to mobile devices> The technology disclosed herein (this technology) can be applied to various products. For example, the technology disclosed herein may be implemented as a device mounted on any type of mobile device such as automobiles, electric vehicles, hybrid electric vehicles, motorcycles, bicycles, personal mobility devices, airplanes, drones, ships, and robots.

[0098] Figure 13 is a block diagram showing a schematic configuration example of a vehicle control system, which is an example of a mobile control system to which the technology described herein may be applied.

[0099] The vehicle control system 12000 comprises a plurality of electronic control units connected via a communication network 12001. In the example shown in Figure 13, the vehicle control system 12000 includes a drive system control unit 12010, a body system control unit 12020, an external information detection unit 12030, an internal information detection unit 12040, and an integrated control unit 12050. The functional configuration of the integrated control unit 12050 is shown in the figure, which includes a microcomputer 12051, an audio / image output unit 12052, and an in-vehicle network interface 12053.

[0100] The drivetrain control unit 12010 controls the operation of devices related to the vehicle's drivetrain according to various programs. For example, the drivetrain control unit 12010 functions as a control device for a drivetrain generating device that generates driving force for the vehicle, such as an internal combustion engine or a drive motor; a drivetrain transmission mechanism that transmits driving force to the wheels; a steering mechanism that adjusts the steering angle of the vehicle; and a braking device that generates braking force for the vehicle.

[0101] The body system control unit 12020 controls the operation of various devices mounted on the vehicle body according to various programs. For example, the body system control unit 12020 functions as a control device for a keyless entry system, a smart key system, a power window system, or various lamps such as headlights, reverse lights, brake lights, turn signals, or fog lights. In this case, the body system control unit 12020 may receive radio waves transmitted from a portable device that replaces a key or signals from various switches. The body system control unit 12020 receives these radio waves or signals and controls the vehicle's door lock system, power window system, lamps, etc.

[0102] The external information detection unit 12030 detects information from outside the vehicle equipped with the vehicle control system 12000. For example, an imaging unit 12031 is connected to the external information detection unit 12030. The external information detection unit 12030 causes the imaging unit 12031 to capture images of the outside of the vehicle and receives the captured images. Based on the received images, the external information detection unit 12030 may perform object detection processing such as detecting people, cars, obstacles, signs, or characters on the road surface, or distance detection processing.

[0103] The imaging unit 12031 is a light sensor that receives light and outputs an electrical signal corresponding to the amount of light received. The imaging unit 12031 can output the electrical signal as an image or as distance measurement information. The light received by the imaging unit 12031 may be visible light or invisible light such as infrared light.

[0104] The in-vehicle information detection unit 12040 detects information inside the vehicle. The in-vehicle information detection unit 12040 is connected to, for example, a driver status detection unit 12041 that detects the driver's state. The driver status detection unit 12041 includes, for example, a camera that captures images of the driver, and the in-vehicle information detection unit 12040 may calculate the driver's level of fatigue or concentration, or determine whether the driver is drowsy, based on the detection information input from the driver status detection unit 12041.

[0105] The microcomputer 12051 can calculate control target values ​​for the drive force generator, steering mechanism, or braking device based on information inside and outside the vehicle acquired by the external information detection unit 12030 or the internal information detection unit 12040, and output control commands to the drive system control unit 12010. For example, the microcomputer 12051 can perform cooperative control aimed at realizing ADAS (Advanced Driver Assistance System) functions, including collision avoidance or impact mitigation, following driving based on distance between vehicles, maintaining vehicle speed, vehicle collision warning, or vehicle lane departure warning.

[0106] Furthermore, the microcomputer 12051 can perform cooperative control for purposes such as autonomous driving, where the vehicle drives autonomously without driver intervention, by controlling the drive force generating device, steering mechanism, or braking device, etc., based on information about the vehicle's surroundings acquired by the external information detection unit 12030 or the internal information detection unit 12040.

[0107] Furthermore, the microcomputer 12051 can output control commands to the body system control unit 12020 based on external information acquired by the external information detection unit 12030. For example, the microcomputer 12051 can control the headlights according to the position of a preceding or oncoming vehicle detected by the external information detection unit 12030, and perform coordinated control aimed at reducing glare, such as switching from high beams to low beams.

[0108] The audio-image output unit 12052 transmits at least one of audio and image output signals to an output device capable of visually or audibly notifying information to the vehicle's occupants or to those outside the vehicle. In the example shown in Figure 13, the output devices include an audio speaker 12061, a display unit 12062, and an instrument panel 12063. The display unit 12062 may include, for example, at least one of an onboard display and a head-up display.

[0109] Figure 14 shows an example of the installation position of the imaging unit 12031.

[0110] In Figure 14, the imaging unit 12031 includes imaging units 12101, 12102, 12103, 12104, and 12105.

[0111] The imaging units 12101, 12102, 12103, 12104, and 12105 are installed, for example, on the front nose, side mirrors, rear bumper, back door, and the upper part of the windshield inside the vehicle 12100. The imaging unit 12101 installed on the front nose and the imaging unit 12105 installed on the upper part of the windshield inside the vehicle mainly acquire images of the front of the vehicle 12100. The imaging units 12102 and 12103 installed on the side mirrors mainly acquire images of the sides of the vehicle 12100. The imaging unit 12104 installed on the rear bumper or back door mainly acquires images of the rear of the vehicle 12100. The imaging unit 12105 installed on the upper part of the windshield inside the vehicle is mainly used for detecting preceding vehicles, pedestrians, obstacles, traffic lights, traffic signs, or lanes.

[0112] Figure 14 shows an example of the imaging range of imaging units 12101 to 12104. Imaging range 12111 indicates the imaging range of imaging unit 12101 located on the front nose, imaging ranges 12112 and 12113 indicate the imaging ranges of imaging units 12102 and 12103 located on the side mirrors, respectively, and imaging range 12114 indicates the imaging range of imaging unit 12104 located on the rear bumper or back door. For example, by superimposing the image data captured by imaging units 12101 to 12104, an overhead view image of the vehicle 12100 can be obtained.

[0113] At least one of the imaging units 12101 to 12104 may have a function for acquiring distance information. For example, at least one of the imaging units 12101 to 12104 may be a stereo camera consisting of multiple image sensors, or an image sensor having pixels for phase difference detection.

[0114] For example, the microcomputer 12051, based on distance information obtained from the imaging units 12101 to 12104, can determine the distance to each object within the imaging range 12111 to 12114 and the temporal change of this distance (relative speed to the vehicle 12100). In particular, it can extract the closest object on the vehicle 12100's path that is traveling in approximately the same direction as the vehicle 12100 at a predetermined speed (e.g., 0 km / h or more) as the preceding vehicle. Furthermore, the microcomputer 12051 can set a predetermined distance to be maintained before the preceding vehicle and perform automatic braking control (including follow-and-stop control) and automatic acceleration control (including follow-and-start control), etc. In this way, cooperative control aimed at autonomous driving, where the vehicle drives autonomously without driver intervention, can be performed.

[0115] For example, the microcomputer 12051 can use distance information obtained from imaging units 12101 to 12104 to classify and extract three-dimensional object data related to three-dimensional objects, such as motorcycles, passenger cars, large vehicles, pedestrians, utility poles, and other three-dimensional objects, and use this data for automatic obstacle avoidance. For example, the microcomputer 12051 identifies obstacles around the vehicle 12100 into obstacles that are visible to the driver of the vehicle 12100 and obstacles that are difficult to see. The microcomputer 12051 then determines the collision risk, which indicates the degree of risk of collision with each obstacle. If the collision risk is above a set value and there is a possibility of collision, the microcomputer 12051 can provide driving assistance to avoid collisions by outputting a warning to the driver via the audio speaker 12061 or the display unit 12062, or by performing forced deceleration or evasive steering via the drive system control unit 12010.

[0116] At least one of the imaging units 12101 to 12104 may be an infrared camera that detects infrared light. For example, the microcomputer 12051 can recognize pedestrians by determining whether or not pedestrians are present in the images captured by the imaging units 12101 to 12104. Such pedestrian recognition is performed, for example, by a procedure to extract feature points from the images captured by the imaging units 12101 to 12104 as infrared cameras, and a procedure to perform pattern matching on a series of feature points that indicate the contour of an object to determine whether or not it is a pedestrian. When the microcomputer 12051 determines that a pedestrian is present in the images captured by the imaging units 12101 to 12104 and recognizes a pedestrian, the audio-image output unit 12052 controls the display unit 12062 to superimpose a rectangular contour line for emphasis on the recognized pedestrian. The audio-image output unit 12052 may also control the display unit 12062 to display an icon indicating a pedestrian at a desired position.

[0117] The above describes an example of a vehicle control system to which the technology described herein may be applied. The technology described herein may be applied to the external information detection unit 12030, etc., among the configurations described above.

[0118] Furthermore, this technology can take the following configurations: (1) A photodetector comprising: a first semiconductor layer mainly made of silicon; a second semiconductor layer mainly made of germanium laminated on the first semiconductor layer; a photoelectric conversion unit disposed on the first semiconductor layer and a part of the second semiconductor layer; and a heat dissipation member disposed on the second semiconductor layer for dissipating heat generated in the photoelectric conversion unit. (2) The photodetector according to (1), comprising: a first wiring layer disposed above the second semiconductor layer and in contact with the heat dissipation member; and a first contact member for making the photoelectric conversion unit and the first wiring layer electrically conductive. (3) The photodetector according to (2), comprising: a second wiring layer disposed above the first wiring layer; and a second contact member for making the first wiring layer and the second wiring layer electrically conductive, wherein the heat generated in the photoelectric conversion unit is dissipated through the heat dissipation member, the first wiring layer, the second contact member, and the second wiring layer. (4) The photodetector according to (3), wherein the heat dissipation member, the first wiring layer, the second wiring layer, the first contact member, or the second contact member comprises at least one of copper (Cu), aluminum (Al), zinc (Zn), or iron (Fe). (5) The photodetector according to any one of (1) to (4), wherein the photoelectric conversion unit is arranged in part with the first semiconductor layer and the second semiconductor layer, and the heat dissipation member is arranged on the second semiconductor layer at a distance from the photoelectric conversion unit. (6) The photodetector according to (5), further comprising a groove provided along the location of the photoelectric conversion unit on the upper surface of the second semiconductor layer, in which the heat dissipation member is arranged. (7) The photodetector according to (6), wherein the width of the groove in the short direction is greater than the width of the heat dissipation member in the short direction, the height of the groove is lower than the height of the heat dissipation member, and a part of the side surface of the heat dissipation member is arranged in the groove. (8) The light detection device according to (6) or (7), wherein the groove portion is slit-shaped or dot-shaped.(9) The photodetector according to any one of (6) to (8), wherein two grooves are arranged on both sides in the short direction of the photoelectric conversion portion arranged on the upper surface of the second semiconductor layer, the two grooves extend in the longitudinal direction of the photoelectric conversion portion, and two heat dissipation members are arranged in the two grooves. (10) The photodetector according to (9), wherein the two grooves and the two heat dissipation members are arranged symmetrically with respect to the photoelectric conversion portion. (11) The photodetector according to any one of (6) to (8), wherein two or more grooves are arranged on each side in the short direction of the photoelectric conversion portion arranged on the upper surface of the second semiconductor layer, the two or more grooves extend in the longitudinal direction of the photoelectric conversion portion, and two or more heat dissipation members are arranged in the two or more grooves. (12) The photodetector according to (11), wherein the two or more grooves and the two or more heat dissipation members, which are arranged on each of the short sides of the photoelectric conversion unit, are arranged symmetrically with respect to the photoelectric conversion unit. (13) The photodetector according to any one of (1) to (12), further comprising a metal layer laminated on the side of the second semiconductor layer opposite to the first semiconductor layer. (14) The photodetector according to (13), wherein the heat generated in the photoelectric conversion unit is dissipated via the heat dissipation members and also dissipated via the second semiconductor layer, the first semiconductor layer, and the metal layer. (15) The photodetector according to (14), wherein the metal layer comprises at least one of copper (Cu), aluminum (Al), zinc (Zn), or iron (Fe). (16) The photodetector according to (14) or (15), wherein the metal layer is in the shape of a solid pattern, a slit, or a dot. (17) The photodetector according to any one of (1) to (16), wherein the second semiconductor layer is an intrinsic germanium layer, the photoelectric conversion unit is a germanium region of a first conductivity type, and the first semiconductor layer is of a second conductivity type different from the germanium region. (18) The photodetector according to any one of (1) to (4), wherein the second semiconductor layer is an intrinsic germanium layer, and the first semiconductor layer has a silicon region of a first conductivity type, an intrinsic silicon region, and a silicon region of a second conductivity type arranged sequentially in the planar direction.(19) A distance measuring system comprising: a light detection device as described in any one of (1) to (18); and a distance measuring device that detects the distance of an object based on an electrical signal photoelectrically converted by the photoelectric conversion unit. (20) A distance measuring system according to (19), comprising a transmitting and receiving device that emits frequency-modulated light and receives light whose phase has changed due to reflection of the light by an object, wherein the transmitting and receiving device has the light detection device.

[0119] The aspects of this disclosure are not limited to the individual embodiments described above, but include various modifications that a person skilled in the art could conceive, and the effects of this disclosure are not limited to those described above. In other words, various additions, modifications, and partial deletions are possible, as long as they do not depart from the conceptual idea and spirit of this disclosure derived from the claims and their equivalents.

[0120] 1, 1a, 1b, 1c, 1d Photodetector, 2 Silicon layer, 2a P-type silicon region, 2b High-concentration P-type silicon region, 2c N-type silicon region, 2d High-concentration N-type silicon region, 2e Intrinsic silicon region, 3 Intrinsic germanium layer, 3a N-type germanium region, 3b Groove, 3c P-type germanium region, 4 Photoelectric conversion unit, 5 Heat sink, 5a Fin, 6 Silicon oxide layer, 7 Contact, 8 First wiring layer, 9 Contact, 10 Second wiring layer, 11 Insulating layer, 12 Metal layer, 13 Trench, 14 SOI substrate, 15 BOX layer, 16 Silicon substrate, 17 Optical waveguide, 20 Distancing system, 21 PD substrate, 22 Logic substrate, 23 Light-emitting substrate, 24 Laser chip, 31 Modulator, 32 Splitter, 33 Circulator, 34 Antenna, 35 Coupler, 36 Detector, 36a First GePD, 36b Second GePD, 36c Transimpedance Amplifier, 37 Object, 41 Controller, 44 FFT Processing Unit

Claims

1. A photodetector comprising: a first semiconductor layer mainly made of silicon; a second semiconductor layer mainly made of germanium, laminated on the first semiconductor layer; a photoelectric conversion unit disposed on the first semiconductor layer and a part of the second semiconductor layer; and a heat dissipation member disposed on the second semiconductor layer for dissipating heat generated by the photoelectric conversion unit.

2. The photodetector according to claim 1, further comprising: a first wiring layer disposed above the second semiconductor layer and in contact with the heat dissipation member; and a first contact member that provides electrical conductivity between the photoelectric conversion unit and the first wiring layer.

3. The photodetector according to claim 2, further comprising: a second wiring layer disposed above the first wiring layer; and a second contact member that provides electrical conductivity between the first wiring layer and the second wiring layer, wherein the heat generated in the photoelectric conversion unit is dissipated through the heat dissipation member, the first wiring layer, the second contact member, and the second wiring layer.

4. The photodetector according to claim 3, wherein the heat dissipation member, the first wiring layer, the second wiring layer, the first contact member, or the second contact member comprises at least one of copper (Cu), aluminum (Al), zinc (Zn), or iron (Fe).

5. The photodetector according to claim 1, wherein the photoelectric conversion unit is arranged in part of the first semiconductor layer and the second semiconductor layer, and the heat dissipation member is arranged on the second semiconductor layer at a distance from the photoelectric conversion unit.

6. The photodetector according to claim 5, further comprising a groove provided along the location of the photoelectric conversion unit on the upper surface of the second semiconductor layer, wherein the heat dissipation member is arranged.

7. The optical detection device according to claim 6, wherein the width of the groove in the short direction is greater than the width of the heat dissipation member in the short direction, the height of the groove is lower than the height of the heat dissipation member, and a part of the side surface of the heat dissipation member is positioned in the groove.

8. The light detection device according to claim 6, wherein the groove portion is slit-shaped or dot-shaped.

9. The photodetector according to claim 6, wherein two grooves are arranged on both sides in the short direction of the photoelectric conversion portion disposed on the upper surface of the second semiconductor layer, the two grooves extend in the longitudinal direction of the photoelectric conversion portion, and two heat dissipation members are arranged in the two grooves.

10. The photodetector according to claim 9, wherein the two grooves and the two heat dissipation members are arranged symmetrically with respect to the photoelectric conversion unit.

11. The photodetector according to claim 6, wherein two or more grooves are arranged on each of the short sides of the photoelectric conversion portion disposed on the upper surface of the second semiconductor layer, the two or more grooves extend in the longitudinal direction of the photoelectric conversion portion, and two or more heat dissipation members are arranged in the two or more grooves.

12. The photodetector according to claim 11, wherein the two or more grooves and the two or more heat dissipation members, which are arranged on each of the short sides of the photoelectric conversion unit, are arranged symmetrically with respect to the photoelectric conversion unit.

13. The photodetector according to claim 1, further comprising a metal layer laminated on the side of the second semiconductor layer opposite to the first semiconductor layer.

14. The photodetector according to claim 13, wherein the heat generated in the photoelectric conversion unit is dissipated via the heat dissipation member and also dissipated via the second semiconductor layer, the first semiconductor layer, and the metal layer.

15. The photodetector according to claim 14, wherein the metal layer comprises at least one of copper (Cu), aluminum (Al), zinc (Zn), or iron (Fe).

16. The photodetector according to claim 14, wherein the metal layer is in the shape of a solid pattern, a slit, or a dot.

17. The photodetector according to claim 1, wherein the second semiconductor layer is an intrinsic germanium layer, the photoelectric conversion unit is a germanium region of a first conductivity type, and the first semiconductor layer is of a second conductivity type different from that of the germanium region.

18. The photodetector according to claim 1, wherein the second semiconductor layer is an intrinsic germanium layer, and the first semiconductor layer has a silicon region of a first conductivity type, an intrinsic silicon region, and a silicon region of a second conductivity type arranged sequentially in the planar direction.

19. A distance measuring system comprising: a light detection device according to claim 1; and a distance measuring device that detects the distance of an object based on an electrical signal converted photoelectrically by the photoelectric conversion unit.

20. A distance measuring system according to claim 19, comprising a transmitting and receiving device that emits frequency-modulated light and receives light whose phase has been changed by reflection from an object, wherein the transmitting and receiving device has the light detection device.

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