Light detection device

Abstract

The first terminal (61) is connected to the first electrode (11a) of the APD (11). The first and second circuit portions (64, 65) are connected in parallel to each other to the second electrode (11b) of the APD (11). The second terminal (62) is connected to the second electrode (11b) via the first circuit portion (64). The third terminal is connected to the second electrode (11b) via the second circuit portion (65). The first switch (66), the resistor (68), the second electrode (11b), and the second terminal (62) are connected in series to each other. The second switch (67) and the capacitor (69) are connected in parallel to each other to the second electrode (11b). The second switch (67), the second electrode (11b), and the third terminal (63) are connected in series to each other. The TIA (71) is connected in series to the capacitor (69) and is connected to the second electrode (11b) via the capacitor (69).

Description

Technical Field

[0001] This invention relates to a light detection device. Background Technology

[0002] A light detection device with multiple light-receiving areas is known (e.g., Patent Document 1). In Patent Document 1, a field-effect transistor is connected in series with a photodiode forming the light-receiving area. The energizing state of the photodiode is switched using a switch employing this field-effect transistor. As a result, the photodiode used is selected.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2018-44923 Summary of the Invention

[0006] The problem that the invention aims to solve

[0007] When using an avalanche photodiode as the photodiode to form the light-receiving area, a bias voltage is applied to the avalanche photodiode. When light is incident on the avalanche photodiode under the applied bias voltage, the avalanche photodiode multiplies and outputs electrons corresponding to the incident light. At this time, the avalanche photodiode heats up. The higher the bias voltage, the greater the heat generated by the avalanche photodiode. The more avalanche photodiodes in the photodetector, the greater the heat generated by the photodetector. In photodetectors using multiple avalanche photodiodes, there is a concern that the detection accuracy may decrease due to the heat generated by each avalanche photodiode. Depending on the number of avalanche photodiodes in the photodetector, the value of the bias voltage, and the amount of incident light, there is also a concern that the photodetector may be damaged due to the aforementioned heat.

[0008] Even when the light for measuring the target object is not incident, the avalanche photodiode can still generate heat due to the incidence of ambient light such as sunlight. Therefore, it is considered to suppress this heat generation by stopping the application of a bias voltage to the avalanche photodiode when the light for measuring the target object is not incident. For example, in the light detection device described in Patent Document 1, the application of a bias voltage to the photodiode is stopped by disconnecting the electrical connection to the photodiode that forms the light-receiving area. Specifically, a switch connected in series with the photodiode is switched between an on state and an off state. In the on state where the switch is on, a bias voltage is applied to the avalanche photodiode. In the off state where the switch is off, no bias voltage is applied to the avalanche photodiode.

[0009] In this photodetector, a voltage corresponding to the bias voltage applied to the avalanche photodiode is applied to the readout circuit that reads the signal from the avalanche photodiode. Therefore, even if the aforementioned heat generation is suppressed, there is still a concern that the readout circuit of the photodetector may be damaged due to the potential fluctuations applied to the readout circuit corresponding to the switching between the on and off states of the switch.

[0010] The object of the various aspects of the present invention is to provide a light detection device capable of suppressing the heating of avalanche photodiodes caused by incident light and the damage to the readout circuit corresponding to voltage fluctuations.

[0011] Technical means to solve the problem

[0012] One aspect of the light detection device of the present invention includes a plurality of light detection units, each having a light-receiving area. Each light detection unit has an avalanche photodiode, a first terminal, first and second circuit sections, a second terminal, and a third terminal. The avalanche photodiode has first and second electrodes and forms a light-receiving area. The first terminal is connected to the first electrode. A first potential is applied to the first terminal. The first and second circuit sections are connected in parallel to the second electrode. The second terminal is connected to the second electrode via the first circuit section. A second potential is applied to the second terminal. The third terminal is connected to the second electrode via the second circuit section. A third potential is applied to the third terminal. In each light detection unit, the first circuit section includes a first switch and a resistor, and the second circuit section includes a second switch, a capacitor, and a readout circuit. The first switch switches the connection state between the second electrode and the second terminal. The first switch, the resistor, the second electrode, and the second terminal are connected in series. The second switch switches the connection state between the second electrode and the third terminal. The readout circuit includes a transimpedance amplifier. The second switch and capacitor are connected in parallel to the second electrode. The second switch, the second electrode, and the third terminal are connected in series. The transimpedance amplifier is connected in series with the capacitor and connected to the second electrode via the capacitor. The absolute value of the potential difference between the first and third potentials is less than the absolute value of the potential difference between the first and second potentials.

[0013] In one of the above methods, the first terminal is connected to the first electrode of the avalanche photodiode. A first switch toggles the connection between the second electrode of the avalanche photodiode and the second terminal. A second switch toggles the connection between the second electrode of the avalanche photodiode and the third terminal. Therefore, this photodetector can switch the bias voltage applied to the avalanche photodiode from the potential difference between the first potential applied to the first terminal and the second potential applied to the second terminal to the potential difference between the first potential applied to the first terminal and the third potential applied to the third terminal. As a result, heating of the avalanche photodiode caused by light incidence and damage to the readout circuit corresponding to voltage fluctuations are suppressed.

[0014] In one of the above methods, in each photodetector unit, the first switch can also be connected to the second electrode via a resistor. In this case, the effect caused by the parasitic capacitance generated in the first switch is reduced.

[0015] In one of the above embodiments, the photodetector may further include a switch control unit that controls the connection state of the first and second switches based on the timing of photodetection in each photodetector unit. In this case, the photodetector can switch the bias voltage to the avalanche photodiode based on whether it is time to perform photodetection.

[0016] In one of the above methods, the switch control unit can also connect the second electrode to the third terminal while the first switch disconnects the connection between the second electrode and the second terminal. In this case, the light detection device can discharge the generated current to the third terminal when ambient light is incident on the avalanche photodiode that is not detecting the light of the object being measured. As a result, damage to the readout circuit is suppressed.

[0017] In one of the above methods, the switch control unit can also disconnect the connection between the second electrode and the third terminal by the second switch while the first switch is connected to the second electrode and the second terminal. In this case, the heating of the resistor is suppressed.

[0018] In one of the above embodiments, the photodetector may further include an irradiation unit for irradiating light. The switch control unit may also control the energizing state of the first and second switches based on the timing of light irradiation from the irradiation unit. In this case, the photodetector can more reliably determine whether it is time to perform photodetection. As a result, the photodetector can more accurately switch the bias voltage to the avalanche photodiode based on whether it is time to perform photodetection.

[0019] Another aspect of the light detection device of the present invention includes multiple light detection units, each having a light-receiving area. Each light detection unit includes an avalanche photodiode, a first terminal, first and second circuit sections, a second terminal, and a third terminal. The avalanche photodiode has first and second electrodes and forms a light-receiving area. The first terminal is connected to the first electrode. A first potential is applied to the first terminal. The first and second circuit sections are connected in parallel to the second electrode. The second terminal is connected to the second electrode via the first circuit section. A second potential is applied to the second terminal. The third terminal is connected to the second electrode via the second circuit section. A third potential is applied to the third terminal. In each light detection unit, the first circuit section includes a switch and a resistor, and the second circuit section includes a diode, a capacitor, and a readout circuit. The switch switches the connection state between the second electrode and the second terminal. The switch, resistor, second electrode, and second terminal are connected in series. The readout circuit includes a transimpedance amplifier. The diode and capacitor are connected in parallel to the second electrode. The diode has a third electrode and a fourth electrode. The third electrode has the same polarity as the first electrode of the avalanche photodiode. The fourth electrode has the same polarity as the second electrode of the avalanche photodiode. The third electrode is connected to the third terminal. The fourth electrode is connected to the second electrode. The anode of the diode is connected to the third terminal. The transimpedance amplifier is connected in series with a capacitor and is connected to the second electrode via the capacitor. The absolute value of the potential difference between the first and third potentials is less than the absolute value of the potential difference between the first and second potentials.

[0020] In the other embodiment described above, terminal 1 is connected to the first electrode of the avalanche photodiode. A switch toggles the connection between the second electrode of the avalanche photodiode and terminal 2. The fourth electrode of the diode is connected to the second electrode, and the third electrode of the diode is connected to terminal 3. The fourth electrode has the same polarity as the second electrode. The third electrode has the same polarity as the first electrode. Therefore, this photodetector can switch the bias voltage of the avalanche photodiode from the potential difference between the first potential applied to terminal 1 and the second potential applied to terminal 2 to the potential difference between the first potential applied to terminal 1 and the third potential applied to terminal 3. As a result, heating of the avalanche photodiode caused by light incidence and damage to the readout circuit corresponding to voltage fluctuations are suppressed.

[0021] In the other embodiment described above, the switch in the photodetector unit can also be connected to the second electrode via a resistor. In this case, the effect caused by the parasitic capacitance generated in the switch is reduced.

[0022] In the above-described embodiments, the transimpedance amplifier can also be incorporated into the CMOS logic integrated circuit. When the transimpedance amplifier is incorporated into the CMOS logic integrated circuit, it can operate at a relatively high speed. However, the operating voltage range of the CMOS logic integrated circuit is limited. With the above-described structure, the voltage applied to the CMOS logic integrated circuit can be kept within the operating voltage range, and the bias voltage applied to the avalanche photodiode can be varied. Therefore, the operating speed of the transimpedance amplifier can be improved, and heat generation in the avalanche photodiode and damage to the readout circuit corresponding to voltage fluctuations can be suppressed.

[0023] In the other approach described above, the resistor can also have an impedance greater than the input impedance of the second circuit section. In this case, the signal from the avalanche photodiode can be transmitted to the transimpedance amplifier more accurately.

[0024] In the other embodiment described above, the potential difference between the first and second potentials and the potential difference between the first and third potentials can also be included within the operating voltage range of the transimpedance amplifier. In this case, a simple structure can be used to improve the operating speed of the transimpedance amplifier and suppress the heating of the avalanche photodiode and the damage to the readout circuit corresponding to voltage fluctuations.

[0025] Another aspect of the optical detection device of the present invention includes multiple optical detection units. Each optical detection unit has an avalanche photodiode, a first terminal, first and second circuit sections, a second terminal, and a third terminal. The avalanche photodiode has first and second electrodes. The first terminal is connected to the first electrode. The first and second circuit sections are connected to the second electrode in parallel. The second terminal is connected to the second electrode via the first circuit section. The third terminal is connected to the second electrode via the second circuit section. In each optical detection unit, the first circuit section includes a first switch and a resistor, and the second circuit section includes a second switch, a capacitor, and a readout circuit. The first switch switches the connection state between the second electrode and the second terminal. The first switch, the resistor, the second electrode, and the second terminal are connected in series. The second switch switches the connection state between the second electrode and the third terminal. The readout circuit includes a transimpedance amplifier. The second switch and the capacitor are connected to the second electrode in parallel. The second switch, the second electrode, and the third terminal are connected in series. The transimpedance amplifier is connected in series with the capacitor and connected to the second electrode via the capacitor.

[0026] In another embodiment described above, the first terminal is connected to the first electrode of the avalanche photodiode. A first switch toggles the connection between the second electrode of the avalanche photodiode and the second terminal. A second switch toggles the connection between the second electrode of the avalanche photodiode and the third terminal. Therefore, this photodetector can switch the bias voltage applied to the avalanche photodiode from the potential difference between the potential applied to the first terminal and the potential applied to the second terminal to the potential difference between the potential applied to the first terminal and the potential applied to the third terminal. As a result, heating of the avalanche photodiode caused by light incidence and damage to the readout circuit corresponding to voltage fluctuations are suppressed.

[0027] Another aspect of the optical detection device of the present invention includes a plurality of optical detection units. Each optical detection unit has an avalanche photodiode, a first terminal, first and second circuit sections, a second terminal, and a third terminal. The avalanche photodiode has a first and a second electrode. The first terminal is connected to the first electrode. The first and second circuit sections are connected to the second electrode in parallel. The second terminal is connected to the second electrode via the first circuit section. The third terminal is connected to the second electrode via the second circuit section. In each optical detection unit, the first circuit section includes a switch and a resistor, and the second circuit section includes a diode, a capacitor, and a readout circuit. The switch toggles the connection state between the second electrode and the second terminal. The switch, resistor, second electrode, and second terminal are connected in series. The readout circuit includes a transimpedance amplifier. The diode and capacitor are connected to the second electrode in parallel. The diode has a third and a fourth electrode. The third electrode has the same polarity as the first electrode of the avalanche photodiode. The fourth electrode has the same polarity as the second electrode of the avalanche photodiode. The third electrode is connected to the third terminal. The fourth electrode is connected to the second electrode. The transimpedance amplifier is connected in series with the capacitor and is connected to the second electrode via the capacitor.

[0028] In another embodiment described above, terminal 1 is connected to the first electrode of the avalanche photodiode. A switch toggles the connection between the second electrode of the avalanche photodiode and terminal 2. The cathode of the diode is connected to the second electrode, and the anode of the diode is connected to terminal 3. Therefore, this photodetector can switch the bias voltage applied to the avalanche photodiode from the potential difference between the potential applied to terminal 1 and terminal 2 to the potential difference between the potential applied to terminal 1 and terminal 3. As a result, heating of the avalanche photodiode caused by light incidence and damage to the readout circuit corresponding to voltage fluctuations are suppressed.

[0029] The effects of the invention

[0030] Various embodiments of the present invention can provide a light detection device that suppresses the heating of avalanche photodiodes caused by light incidence and the damage to the readout circuit corresponding to voltage fluctuations. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the light detection device of this embodiment.

[0032] Figure 2 This is a schematic diagram of the light-receiving part of a light detection device.

[0033] Figure 3 This is a magnified view of the part that receives light.

[0034] Figure 4 This is a cross-sectional view of the light-receiving part.

[0035] Figure 5 This is a diagram illustrating the circuitry of the light detection unit.

[0036] Figure 6 It is a timing diagram of the control signals of different optical detection units.

[0037] Figure 7 This is a diagram illustrating the characteristics of an avalanche photodiode.

[0038] Figure 8 This is a circuit diagram illustrating a modified example of the light detection unit of this embodiment.

[0039] Figure 9 This is a circuit diagram illustrating a modified example of the light detection unit of this embodiment. Detailed Implementation

[0040] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. Furthermore, in the description, the same symbols are used for the same elements or elements having the same function, and repeated descriptions are omitted.

[0041] First, refer to Figure 1 The structure of the optical detection device in this embodiment will be explained. Figure 1 This is a schematic diagram showing the structure of the light detection device in this embodiment.

[0042] The light detection device 1 determines the distance to the object being measured by detecting light emitted from it. The light detection device 1, for example, constitutes a LiDAR (Light Detection and Ranging) device. The light detection device 1 includes an illumination unit 2, a light receiving unit 3, and lenses L1 and L2. The illumination unit 2 has a light source 2a. The illumination unit 2 is illuminated by a laser B1, for example, from the light source 2a. The laser B1 emitted from the illumination unit 2 passes through the lens L1 and, for example, illuminates the object α. The light reflected from the object α passes through the lens L2 and is incident on the light receiving unit 3 as the object light B2. The light receiving unit 3 detects the incident object light B2. In addition to the object light B2, ambient light B3 is also incident on the light receiving unit 3. The ambient light B3 is, for example, sunlight.

[0043] Next, refer to Figure 2 and Figure 3 Explain the structure of the light-receiving part 3. Figure 2 This is a schematic diagram of the light-receiving part 3 of the light detection device. Figure 3 This is a magnified view of part 3, the light-receiving section.

[0044] The light-receiving part 3 includes a light-detecting substrate 5 and a circuit element 7. The light-detecting substrate 5 and the circuit element 7 are bonded to each other. In this embodiment, the light-detecting substrate 5 and the circuit element 7 are opposite to each other. In this embodiment, the relative direction of the light-detecting substrate 5 and the circuit element 7 corresponds to the Z-axis direction. Viewed from the Z-axis direction, the light-detecting substrate 5 and the circuit element 7 are rectangular shapes extending in the XY-axis direction, respectively. The light-detecting substrate 5 and the circuit element 7 are interconnected. In this specification, "connection" refers to electrical conduction unless otherwise specified, including not only direct connections but also indirect connections via other components. "Connection" also includes structures that temporarily electrically separate elements by providing switches or the like between different elements. "Bonding" refers to physical connection regardless of whether there is an electrical connection, including not only direct connections but also indirect connections via other components.

[0045] Circuit element 7 includes integrated circuit C. In this embodiment, circuit element 7 includes only one integrated circuit C. Circuit element 7 may also include multiple integrated circuits C. Integrated circuit C is a CMOS logic integrated circuit. Circuit element 7 processes the signal output from the photodetector substrate 5 in integrated circuit C. The operating voltage of integrated circuit C is, for example, below 20V.

[0046] The circuit element 7 has a port portion 12. The port portion 12 includes multiple electrodes. The photodetector substrate 5 and the circuit element 7 operate according to the voltage applied to the port portion 12. The circuit element 7 processes the signal output from the photodetector substrate 5 and outputs the processed signal from the port portion 12 to the outside of the circuit element 7.

[0047] The photodetector substrate 5 and circuit element 7 include a plurality of signal output units U. In this embodiment, the plurality of signal output units U are arranged in two dimensions along the XY axis. In a variation of this embodiment, the plurality of signal output units U may also be arranged in a row. Figure 3 As shown, the light-receiving unit 3 includes multiple light detection units 15. Each signal output unit U includes multiple light detection units 15. As a variation of this embodiment, each signal output unit U may also include only one light detection unit 15.

[0048] In this embodiment, the light-receiving unit 3 performs light detection at different times for each signal output unit U. As a variation of this embodiment, the light-receiving unit 3 may also perform light detection at different times for each column or row of the signal output units U. Alternatively, the light-receiving unit 3 may perform light detection at the same time in all signal output units U. Multiple light detection units 15 included in one signal output unit U perform light detection at the same time.

[0049] Each light detection unit 15 has a light-receiving area R. The light-receiving section 3 detects light incident on each light-receiving area R. The light detection substrate 5 converts the light incident on the light-receiving area R into electrons and transmits the signal corresponding to the electrons to the circuit element 7. In this embodiment, each light-receiving area R is formed by one avalanche photodiode 11. Hereinafter, the "avalanche photodiode" will be referred to as "APD". Each APD 11 is included in the light detection substrate 5. Each APD 11 is connected to the circuit element 7.

[0050] Each photodetector unit 15 has multiple signal processing units P that process signals output from at least one APD 11. Each signal processing unit P is included in a circuit element 7. Each signal processing unit P is included in an integrated circuit C. In this embodiment, one integrated circuit C includes multiple signal processing units P. The circuit element 7 performs processing related to the signals transmitted from the photodetector substrate 5 in each signal processing unit P.

[0051] Each APD11 forming the light-receiving area R is connected to the signal processing unit P corresponding to each APD11. In this embodiment, as... Figure 3 As shown, one signal processing unit P corresponds to one light-receiving area R. One APD 11 is connected to one signal processing unit P through one protrusion B. In other words, the signal processing unit P and the APD 11 are connected in a one-to-one relationship.

[0052] Next, refer to Figure 4 Here is an example that details the structure of the light-receiving part 3. Figure 4 This is a cross-sectional view of the light-receiving part. In this embodiment, the light-receiving part 3 is a back-incident type semiconductor light detection device.

[0053] In addition to the photodetector substrate 5 and the circuit element 7, the light-receiving section 3 also includes a glass substrate 8 and a mounting substrate 9. In this embodiment, the surface parallel to each main surface of the photodetector substrate 5, the circuit element 7, the glass substrate 8, and the mounting substrate 9 corresponds to the XY-axis plane, and the direction orthogonal to each main surface corresponds to the Z-axis direction. The glass substrate 8 is opposite to the photodetector substrate 5. The photodetector substrate 5 is disposed between the circuit element 7 and the glass substrate 8. The mounting substrate 9 is opposite to the circuit element 7. The circuit element 7 is disposed between the photodetector substrate 5 and the mounting substrate 9.

[0054] The photodetector substrate 5 has a semiconductor substrate 10 that is rectangular in shape when viewed from above. The semiconductor substrate 10 is made of Si and is a P-type semiconductor substrate. The semiconductor substrate 10 has a main surface 10a and a main surface 10b that are opposite to each other. The main surface 10a is the light incident surface onto the semiconductor substrate 10.

[0055] Circuit element 7 has two opposing main surfaces 7a and 7b. Circuit element 7 is rectangular in shape when viewed from above. Light detection substrate 5 is connected to circuit element 7. Main surfaces 7a and 7b are opposite to each other. Light detection substrate 5 and circuit element 7 are bonded by adhesive layer IA. Adhesive layer IA is insulating. Light detection substrate 5 and circuit element 7 are physically and electrically connected by multiple bumps B. The main surfaces 7a and 7b of circuit element 7 are larger than the main surfaces 10a and 10b of semiconductor substrate 10. Viewed from the Z-axis, the edge of circuit element 7 surrounds the edge of light detection substrate 5.

[0056] The glass substrate 8 has two opposing main surfaces, 8a and 8b. The glass substrate 8 is rectangular in shape when viewed from above. Main surface 8b is opposite to main surface 10a of the semiconductor substrate 10. Main surfaces 8a and 8b are flat. The glass substrate 8 is optically bonded to the photodetector substrate 5 using an optical adhesive OA. The glass substrate 8 can also be formed directly on the photodetector substrate 5.

[0057] The mounting substrate 9 has two main surfaces 9a and 9b that are opposite to each other. Main surface 9a is opposite to the main surface 7b of the circuit element 7. Main surface 9a of the mounting substrate 9 is larger than the main surfaces 8a and 8b of the circuit element 7. Viewed from the Z-axis direction, the edge of the mounting substrate 9 surrounds the edge of the circuit element 7. The circuit element 7 and the mounting substrate 9 are connected by a bonding line W. The mounting substrate 9 is connected to the port portion 12 via the bonding line W.

[0058] The semiconductor substrate 10 has a plurality of APDs 11. The plurality of APDs 11 are arranged in a row-and-column two-dimensional configuration when viewed along the Z-axis. Each APD 11 forms a light-receiving region R on its main surface 10a. In addition to the APDs 11, the semiconductor substrate 10 also has peripheral carrier absorption sections 13. A portion of the peripheral carrier absorption sections 13 is located between adjacent APDs 11 when viewed along the Z-axis. The peripheral carrier absorption sections 13 are arranged in a lattice pattern when viewed along the Z-axis. The peripheral carrier absorption sections 13 surround the APDs 11. The peripheral carrier absorption sections 13 are regions that absorb peripheral carriers.

[0059] like Figure 4As shown, the semiconductor substrate 10 includes a semiconductor region 21 and semiconductor layers 31, 32, 33, and 34. Multiple APDs 11 each include a semiconductor region 21 and semiconductor layers 31, 32, and 33. A peripheral carrier absorber 13 includes a semiconductor region 21 and a semiconductor layer 34. The peripheral carrier absorber 13 absorbs carriers located at the periphery of the semiconductor layer 34. That is, the semiconductor layer 34 functions as a peripheral carrier absorber layer that absorbs peripheral carriers.

[0060] Semiconductor region 21 and semiconductor layers 32, 33, and 35 are of a first conductivity type, while semiconductor layers 31 and 34 are of a second conductivity type. Impurities in the semiconductors are added, for example, by diffusion or ion implantation. In this embodiment, the first conductivity type is P-type, and the second conductivity type is N-type. When the semiconductor substrate 10 is based on Si, group 13 elements such as B are used as P-type impurities, and group 15 elements such as P or As are used as N-type impurities. In this embodiment, semiconductor layers 32, 33, and 35 have the same impurity concentration. Semiconductor layers 32, 33, and 35 have a higher impurity concentration than semiconductor region 21.

[0061] Semiconductor region 21 is located on the main surface 10b side of semiconductor substrate 10. Semiconductor region 21 constitutes a part of main surface 10b. Semiconductor region 21 is, for example, P-type.

[0062] Semiconductor layer 31 forms part of main surface 10b. Semiconductor layer 31 is adjacent to and surrounded by semiconductor region 21 when viewed from the Z-axis direction. Semiconductor layer 31 is, for example, N+ type. In this embodiment, semiconductor layer 31 forms a cathode in APD 11.

[0063] Semiconductor layer 32 is located closer to the main surface 10a than semiconductor layer 31. Semiconductor layer 32 is in contact with and surrounded by semiconductor region 21. Semiconductor layer 32 is disposed inside semiconductor region 21. A portion of semiconductor region 21 is disposed between semiconductor layer 31 and semiconductor layer 32. Semiconductor layer 32 is, for example, P-type. Semiconductor layer 32 constitutes the avalanche region of APD 11.

[0064] Semiconductor layer 33 is located closer to the main surface 10a than semiconductor layer 32 and semiconductor region 21. Semiconductor layer 33 constitutes the entire surface of main surface 10a. Semiconductor layer 33 is in contact with semiconductor region 21 on the main surface 10b side. Semiconductor layer 33 is, for example, P+ type. Semiconductor layer 33 constitutes the anode of APD 11.

[0065] Semiconductor layer 34 forms part of main surface 10b. Viewed from the Z-axis, semiconductor layer 34 is in contact with and surrounded by semiconductor region 21. Peripheral carrier absorption section 13 is formed by semiconductor layer 34 and is only in contact with semiconductor region 21 in semiconductor substrate 10. Peripheral carrier absorption section 13 does not contain layers equivalent to avalanche regions. Semiconductor layer 34 is, for example, N+ type.

[0066] A groove 14 is formed on the semiconductor substrate 10. In this embodiment, the groove 14 is located closer to the edge of the semiconductor substrate 10 than the APD 11 when viewed from the Z-axis direction. The groove 14 does not penetrate the semiconductor substrate 10. A semiconductor layer 35 forms the edge of the groove 14 and a portion of the main surface 10b. The semiconductor layer 35 is, for example, of P+ type. The semiconductor layer 35 is in contact with the semiconductor region 21. The semiconductor layer 35 extends from the main surface 10b along the Z-axis direction and is in contact with the semiconductor layer 33. The semiconductor layer 35 constitutes the anode of the APD 11.

[0067] The photodetector substrate 5 further includes an insulating film 41, electrodes 42 and 43, a passivation film 46, and an insulating layer 47. The insulating film 41 is laminated on the main surface 10b of the semiconductor substrate 10. The insulating film 41 is, for example, a silicon oxide film. The electrode 42 is disposed on the insulating film 41. The electrode 43 is disposed on the edge of the insulating film 41 and the trench 14. The passivation film 46 is disposed on the insulating film 41 and the electrodes 42 and 43. The insulating layer 47 is disposed on the passivation film 46, filling the trench 14, thereby forming the photodetector substrate 5 into a cuboid shape.

[0068] Electrode 42 penetrates the insulating film 41 and is connected to the semiconductor layer 31 of APD 11. A portion of electrode 42 is exposed from the passivation film 46, forming the pad electrode 52 of APD 11. Electrode 42 outputs a signal from APD 11 at the pad electrode 52. Electrode 43 is connected to the semiconductor layer 35. A portion of electrode 43 is exposed from the passivation film 46, forming the pad electrode 53 of APD 11. In this embodiment, pad electrode 52 is the cathode pad electrode of APD 11. Pad electrode 53 is the anode pad electrode of APD 11.

[0069] Pad electrodes 52 and 53 are bonded to their respective bumps B. Each APD 11 is connected to one corresponding bump B via pad electrode 52. Multiple APDs 11 are connected to one different bump B. In other words, APDs 11 are connected to bumps B in a one-to-one relationship.

[0070] Next, refer to Figure 5 The circuit structure of each light detection unit 15 in this embodiment is explained. Figure 5 This is a diagram used to illustrate the circuitry of each optical detection unit.

[0071] like Figure 5As shown, each photodetector unit 15 includes an APD 11, a first terminal 61, a second terminal 62, a third terminal 63, a first circuit section 64, and a second circuit section 65. In this embodiment, the APD 11 is included in the photodetector substrate 5. The first terminal 61, the second terminal 62, the third terminal 63, the first circuit section 64, and the second circuit section 65 are included in the circuit element 7. The APD 11 has an electrode 11a and an electrode 11b. Electrode 11a is connected to the first terminal 61. Electrode 11b is connected to the first circuit section 64 and the second circuit section 65. When electrode 11a corresponds to the first electrode, electrode 11b corresponds to the second electrode.

[0072] In this embodiment, electrode 11a is the anode of APD 11. Electrode 11a corresponds to a pad electrode connected to the P-type semiconductor of APD 11. In this embodiment, electrode 11a corresponds to pad electrode 53. Electrode 11b is the cathode of APD 11. Electrode 11b corresponds to a pad electrode connected to the N-type semiconductor of APD 11. In this embodiment, electrode 11b corresponds to pad electrode 52.

[0073] The first circuit section 64 and the second circuit section 65 are connected to the electrode 11b in parallel. The second terminal 62 is connected to the electrode 11b via the first circuit section 64. The third terminal 63 is connected to the electrode 11b via the second circuit section 65.

[0074] The first circuit section 64 includes a switch 66 and a resistor 68. Switch 66 is equivalent to a first switch. Switch 66 switches the connection state between electrode 11b and second terminal 62. Switch 66 switches the connection state between electrode 11b and second terminal 62 by switching between an ON state and an OFF state. An "ON state" refers to the state where multiple interconnected wirings are connected. That is, the ON state is the state of being on (ON). An "OFF state" refers to the state where multiple interconnected wirings are electrically disconnected. That is, the OFF state is the state of being off (OFF). Switch 66, resistor 68, electrode 11b, and second terminal 62 are connected in series. In other words, switch 66 and resistor 68 are connected in series between electrode 11b and second terminal 62. In this embodiment, switch 66 is connected to electrode 11b via resistor 68. Resistor 68 has an impedance greater than the input impedance of the second circuit section 65.

[0075] The second circuit section 65 includes a switch 67, a capacitor 69, and a readout circuit 70. Switch 67 is equivalent to a second switch. The readout circuit 70 includes a transimpedance amplifier 71. Hereinafter, the "transimpedance amplifier" will be referred to as "TIA". Switch 67 switches the connection state between electrode 11b and terminal 63. Switch 67 switches the connection state between electrode 11b and terminal 63 by switching between an on and off state. Switch 67 and capacitor 69 are connected in parallel to electrode 11b. Electrode 11b, switch 67, and terminal 63 are connected in series. In other words, switch 67 is inserted between electrode 11b and terminal 63. TIA 71 is connected in series with capacitor 69. TIA 71 is connected to electrode 11b via capacitor 69. Capacitor 69 has an input impedance lower than that of TIA 71. The impedance of resistor 68 is greater than the input impedance of either capacitor 69 or TIA 71.

[0076] Switches 66 and 67 are, for example, field-effect transistors (FETs). Switches 66 and 67 are, for example, MOS-FETs. Switches 66 and 67 switch between on and off states according to the applied voltage.

[0077] In this embodiment, switch 66, resistor 68, switch 67, capacitor 69, and TIA71 are included in one integrated circuit C. Switch 66, resistor 68, switch 67, capacitor 69, and TIA71 may also be included in different integrated circuits. At least TIA71 is included in a CMOS logic integrated circuit.

[0078] The light-receiving unit 3 further includes a switch control unit 75. The switch control unit 75 controls switches 66 and 67 respectively. The switch control unit 75 controls the connection state of switches 66 and 67 based on the timing of light detection in each light detection unit 15. In this embodiment, the switch control unit 75 controls the connection state of switches 66 and 67 based on the timing of laser B1 being irradiated from the irradiation unit 2. The switch control unit 75 switches the on and off states of switch 66.

[0079] The switch control unit 75 may be configured as a computer, for example. This computer includes a CPU (Central Processing Unit), main memory, auxiliary memory, a communication control unit, input devices, and output devices. The switch control unit 75 may be configured as one or more computers, which are composed of this hardware and software such as programs.

[0080] In this embodiment, the switch control unit 75 is disposed on the circuit element 7. As a variation of this embodiment, the switch control unit 75 may also be disposed separately from the circuit element 7 on the mounting substrate 9. As yet another variation of this embodiment, the switch control unit 75 may also be disposed outside the light-receiving part 3.

[0081] Next, refer to Figure 6 and Figure 7 This explains the operation of each light detection unit 15 in this embodiment. Figure 6 It is a timing diagram of the control signals of different optical detection units. Figure 7 This is a diagram representing the characteristics of APD.

[0082] The light-receiving unit 3 causes multiple signal output units U to operate at different times. The switch control unit 75 outputs a control signal instructing light detection to the light detection unit 15 of each signal output unit U. The light detection unit 15 of each signal output unit U operates based on the control signal output from the switch control unit 75. The control signal output from the switch control unit 75 instructs each light detection unit 15 on the timing of light detection. In this embodiment, the control signal is synchronized with the timing of laser B1 emitted from the irradiation unit 2.

[0083] Figure 6 Signals S1, S2, S3, and S4 are represented as control signals output from the switch control unit 75. Signals S1, S2, S3, and S4 have different waveforms. For example, the light receiving unit 3 activates the four groups of signal output units U at different times based on signals S1, S2, S3, and S4 from the switch control unit 75. In this embodiment, each signal output unit U includes multiple light detection units 15. The switch control unit 75 outputs signals with the same waveform to the light detection units 15 included in the same signal output unit U.

[0084] Each signal S1, S2, S3, and S4 is, for example, a high-level or low-level signal. When signals S1, S2, S3, and S4 input to the signal output unit U are at a high level, the light detection unit 15 included in the signal output unit U detects the target light B2. When signals S1, S2, S3, and S4 input to the signal output unit U are at a low level, the light detection unit 15 included in the signal output unit U does not detect the target light B2.

[0085] For example, Figure 6As shown, when signal S1 drops from a high level to a low level, signal S2 rises from a low level to a high level. Consequently, when the light detection unit 15 of the signal output unit U, which receives input signal S1, finishes detecting the target light B2, the light detection unit 15 of the signal output unit U, which receives input signal S2, begins detecting the target light B2. When signal S2 drops from a high level to a low level, signal S3 rises from a low level to a high level. Consequently, when the light detection unit 15 of the signal output unit U, which receives input signal S2, finishes detecting the target light B2, the light detection unit 15 of the signal output unit U, which receives input signal S3, begins detecting the target light B2.

[0086] When the light source B2 is being detected in the light detection unit 15, the switch control unit 75 connects electrode 11b to the second terminal 62 via switch 66 and disconnects electrode 11b from the third terminal 63 via switch 67. When the light source B2 is not being detected in the light detection unit 15, the switch control unit 75 disconnects electrode 11b from the second terminal 62 via switch 66 and connects electrode 11b to the third terminal 63 via switch 67. In other words, when the light source B2 is being detected in the light detection unit 15, the switch control unit 75 makes switch 66 active and switch 67 passive. When the light source B2 is not being detected in the light detection unit 15, the switch control unit 75 makes switch 66 passive and switch 67 active.

[0087] For example, switch 66 is in the ON state when the control signal from switch control unit 75 is high, and in the OFF state when the control signal from switch control unit 75 is low. Switch 67 is in the ON state when the control signal from switch control unit 75 is low, and in the OFF state when the control signal from switch control unit 75 is high.

[0088] A first potential is applied to terminal 61. A second potential is applied to terminal 62. A third potential is applied to terminal 63. A voltage corresponding to the potential difference between the first and third potentials, or a voltage corresponding to the potential difference between the first and second potentials, is applied to APD 11. The absolute value of the potential difference between the first and third potentials is less than the absolute value of the potential difference between the first and second potentials. The potential differences between the first and second potentials and the potential differences between the first and third potentials are within the range of the operating voltage of TIA 71. The potential difference between the first and second potentials is determined according to the multiplication rate set in APD 11. In this embodiment, the first potential is lower than both the second and third potentials, and the third potential is lower than the second potential.

[0089] The voltage applied to APD11 is switched according to the control of the switch control unit 75. When the photodetector unit 15 detects the target light B2, electrode 11b is connected to the second terminal 62 by switch 66, and the connection between electrode 11b and the third terminal 63 is disconnected by switch 67. As a result, a voltage corresponding to the potential difference between the first potential applied to the first terminal 61 and the second potential applied to the second terminal 62 is applied to APD11.

[0090] When the photodetector unit 15 is not detecting the target light B2, the connection between electrode 11b and the second terminal 62 is disconnected by switch 66, and electrode 11b and the third terminal 63 are connected by switch 67. As a result, a voltage corresponding to the potential difference between the first potential applied to the first terminal 61 and the third potential applied to the third terminal 63 is applied to APD 11.

[0091] In this embodiment, -60V is applied to terminal 61, for example, as a first potential. +10V is applied to terminal 62, for example, as a second potential. 0V is applied to terminal 63, for example, as a third potential. In this case, ground may also be connected to terminal 63. When the photodetector 15 detects the target light B2, a voltage of 70V is applied to APD 11 as a bias voltage. When the photodetector 15 does not detect the target light B2, a voltage of 60V is applied to APD 11 as a bias voltage.

[0092] Figure 7 An example illustrating the characteristics of APD11. In Figure 7 In the diagram, the horizontal axis represents the bias voltage of APD11, and the vertical axis represents the gain of APD11. In this case, the gain of APD11 is approximately 24 times when the target light B2 is detected, compared to approximately 16 times when the target light B2 is not detected. Thus, the gain of APD11 is lower when the target light B2 is not detected compared to when it is.

[0093] Next, refer to Figure 8 The circuit of each light detection unit 15A in the modified example of this embodiment will be explained. Figure 8 This is a diagram illustrating the circuitry of each photodetector unit 15A in this modified example. This modified example is generally similar to or the same as the embodiment described above. This modified example differs from the embodiment described above by using a diode 80 instead of a switch 67. The following description will focus on the differences between the embodiment described above and this modified example.

[0094] Each photodetector unit 15A has an APD 11, a first terminal 61, a second terminal 62, a third terminal 63, a first circuit section 64, and a second circuit section 65A. Therefore, the photodetector unit 15A differs from the photodetector unit 15 in that the second circuit section 65 is the second circuit section 65A.

[0095] The second circuit section 65A includes a diode 80, a capacitor 69, and a readout circuit 70. The diode 80 has electrodes 81 and 82. Electrode 81 of the diode 80 has the same polarity as electrode 11b of the APD 11. Electrode 82 of the diode 80 has the same polarity as electrode 11a of the APD 11. Electrode 81 of the diode 80 is connected to electrode 11b. Electrode 82 of the diode 80 is connected to a third terminal 63. The diode 80 and capacitor 69 are connected in parallel to electrode 11b. Electrode 11b, diode 80, and third terminal 63 are connected in series. When electrode 81 corresponds to the fourth electrode, electrode 82 corresponds to the third electrode.

[0096] In this embodiment, electrode 81, connected to electrode 11b, is the anode of diode 80. Electrode 82, connected to the third terminal 63, is the cathode of diode 80. As a variation of this embodiment, such as using... Figure 9 In the case of polarity reversal of APD11 as described in the modified example below, the cathode of diode 80 is connected to electrode 11b as electrode 81, and the anode of diode 80 is connected to the third terminal 63 as electrode 82.

[0097] In this variation, switch 66, resistor 68, diode 80, capacitor 69, and TIA71 are included in a single integrated circuit C. Switch 66, resistor 68, diode 80, capacitor 69, and TIA71 can also be included in different integrated circuits. At least TIA71 is included in a CMOS logic integrated circuit.

[0098] A first potential is applied to terminal 61. A second potential is applied to terminal 62. A third potential is applied to terminal 63. The absolute value of the potential difference between the first and third potentials is less than the absolute value of the potential difference between the first and second potentials. The potential differences between the first and second potentials and between the first and third potentials are included in the operating voltage range of TIA71. The potential difference between the first and second potentials is determined according to the multiplication rate set in APD11.

[0099] The voltage applied to APD11 is switched according to the control of the switch control unit 75. When the photodetector unit 15A detects the target light B2, electrode 11b is connected to the second terminal 62 by switch 66. In this embodiment, the first potential is lower than the second and third potentials, and the third potential is lower than the second potential. As a result, a voltage corresponding to the potential difference between the first potential applied to the first terminal 61 and the second potential applied to the second terminal 62 is applied to APD11.

[0100] When the photodetector unit 15A is not detecting the target light B2, the connection between electrode 11b and the second terminal 62 is disconnected by switch 66. In this embodiment, the first potential is lower than the second and third potentials, and the third potential is lower than the second potential. As a result, a voltage corresponding to the potential difference between the first potential applied to the first terminal 61 and the third potential applied to the third terminal 63 is applied to APD 11.

[0101] In this embodiment, -60V is applied to terminal 61, for example, as a first potential. +10V is applied to terminal 62, for example, as a second potential. 0V is applied to terminal 63, for example, as a third potential. In this case, ground can also be connected to terminal 63. When the photodetector 15A detects the target light B2, a voltage of 70V is applied to APD 11 as a bias voltage. When the photodetector 15A does not detect the target light B2, a voltage of 60V is applied to APD 11 as a bias voltage. Thus, in each photodetector 15A, the gain of APD 11 is lower when the target light B2 is not detected compared to when it is.

[0102] Next, refer to Figure 9 The circuit of each light detection unit 15B in the modified example of this embodiment is explained. Figure 9 This is a diagram illustrating the circuitry of each photodetector unit 15B in this modified example. This modified example is generally similar to or the same as the embodiment described above. This modified example differs from the embodiment described above in terms of APD polarity reversal. Hereinafter, the differences between this modified example and the embodiment described above will be described in detail.

[0103] In each photodetector unit 15B, the APD 11 also has electrodes 11a and 11b. Electrode 11a is connected to the first terminal 61. Electrode 11b is connected to the first circuit section 64 and the second circuit section 65. In each photodetector unit 15B, electrode 11a is the cathode of the APD 11. In this modified example, electrode 11a corresponds to a pad electrode connected to the N-type semiconductor of the APD 11. Electrode 11b is the anode of the APD 11. Electrode 11b corresponds to a pad electrode connected to the P-type semiconductor of the APD 11.

[0104] A first potential is applied to terminal 61. A second potential is applied to terminal 62. A third potential is applied to terminal 63. The absolute value of the potential difference between the first and third potentials is less than the absolute value of the potential difference between the first and second potentials. The potential differences between the first and second potentials and between the first and third potentials are included in the range of the operating voltage of TIA71. The potential difference between the first and second potentials is determined according to the multiplication rate set in APD11. In this modified example, the first potential is higher than the second and third potentials, and the third potential is higher than the second potential.

[0105] The voltage applied to APD11 is switched according to the control of the switch control unit 75. When the photodetector unit 15B detects the target light B2, electrode 11b is connected to the second terminal 62 by switch 66, and the connection between electrode 11b and the third terminal 63 is disconnected by switch 67. As a result, a voltage corresponding to the potential difference between the first potential applied to the first terminal 61 and the second potential applied to the second terminal 62 is applied to APD11.

[0106] When the photodetector unit 15B is not detecting the target light B2, the connection between electrode 11b and the second terminal 62 is disconnected by switch 66, and electrode 11b and the third terminal 63 are connected by switch 67. As a result, a voltage corresponding to the potential difference between the first potential applied to the first terminal 61 and the third potential applied to the third terminal 63 is applied to APD 11.

[0107] In this modified example, a +70V voltage is applied to terminal 61, for example, as a first potential. A 0V voltage is applied to terminal 62, for example, as a second potential. A +12V voltage is applied to terminal 63, for example, as a third potential. In this case, a ground wire can also be connected to terminal 62. When the photodetector 15 detects the target light B2, a 70V voltage is applied to APD 11 as a bias voltage. When the photodetector 15 does not detect the target light B2, a 58V voltage is applied to APD 11 as a bias voltage. Thus, in each photodetector 15B, the gain of APD 11 is lower when the target light B2 is not detected compared to when it is.

[0108] Next, the function of the photodetector 1 will be explained. In each photodetector unit 15, 15B, the first terminal 61 is connected to the electrode 11a of the APD 11. Switch 66 switches the connection state between the electrode 11b of the APD 11 and the second terminal 62. Switch 67 switches the connection state between the electrode 11b of the APD 11 and the third terminal 63. Therefore, the photodetector 1 can switch the bias voltage applied to the APD 11 from the potential difference between the first potential applied to the first terminal 61 and the second potential applied to the second terminal 62 to the potential difference between the first potential applied to the first terminal 61 and the third potential applied to the third terminal 63.

[0109] By applying a lower bias voltage to APD11 when light detection is not performed, the heating of APD11 caused by incident ambient light or other ions can be suppressed when light detection is not performed. For example, in the light detection units 15 and 15B of the light detection device 1 described above, if the potential difference between the first and second potentials is lower than the potential difference between the first and third potentials, and if switch 66 is in the off state and switch 67 is in the on state, the bias voltage applied to APD11 is reduced. As a result, the heating of APD11 caused by incident light is suppressed.

[0110] The bias voltage applied to APD11 switches between the potential difference between the first and second potentials and the potential difference between the first and third potentials. Therefore, the variation in the bias voltage of APD11 is smaller compared to the state where a bias voltage is applied to APD11 and the state where no bias voltage is applied to APD11. As a result, fluctuations in the potential applied to the readout circuit 70 are also suppressed, thus suppressing damage to the readout circuit 70.

[0111] In the photodetector unit 15A, terminal 61 is connected to electrode 11a of APD 11. Switch 66 switches the connection state between electrode 11b of APD 11 and terminal 62 of APD 11. Electrode 81 of diode 80 is connected to electrode 11b, and electrode 82 of diode 80 is connected to terminal 63. Electrode 81 has the same polarity as electrode 11b. Electrode 82 has the same polarity as electrode 11a. Therefore, the photodetector 1 switches the bias voltage applied to APD 11 from the potential difference between a first potential applied to terminal 61 and a second potential applied to terminal 62 to the potential difference between a first potential applied to terminal 61 and a third potential applied to terminal 63.

[0112] For example, in the light detection unit 15A of the aforementioned light detection device 1, when the potential difference between the first and second potentials is lower than the potential difference between the first and third potentials, the bias voltage applied to the APD 11 decreases as long as the switch 66 is in the off state. As a result, the heating of the APD 11 caused by the incident light is suppressed. The bias voltage applied to the APD 11 switches between the potential difference between the first and second potentials and the potential difference between the first and third potentials. Therefore, compared to the case where the state of applying a bias voltage to the APD 11 is switched and the state of not applying a bias voltage to the APD 11 is switched, the variation of the bias voltage of the APD 11 is small. As a result, the variation of the potential applied to the readout circuit 70 is also suppressed, thus suppressing damage to the readout circuit 70.

[0113] In each of the photodetector units 15, 15A, and 15B, switch 66 is connected to electrode 11b via resistor 68. In this case, the effect caused by parasitic capacitance generated in switch 66 is reduced.

[0114] In each of the photodetector units 15, 15A, and 15B, the TIA71 is integrated into a CMOS logic integrated circuit. When the TIA71 is integrated into the CMOS logic integrated circuit, the TIA can operate at a relatively high speed. However, the operating voltage range of the CMOS logic integrated circuit is limited. With the above-described structure, the voltage applied to the CMOS logic integrated circuit can be kept within the operating voltage range, and the bias voltage applied to the APD11 can be varied. Therefore, the operating speed of the TIA71 can be improved, and heat generation of the APD11 and damage to the readout circuit 70 corresponding to voltage fluctuations can be suppressed.

[0115] In a structure where switch 66, resistor 68, switch 67, capacitor 69, and TIA71 are all contained within the same CMOS logic integrated circuit, each photodetector unit 15, 15B can operate at a relatively low operating voltage, for example, below 20V. In other words, with switch 66, resistor 68, switch 67, capacitor 69, and TIA71 all contained within the same integrated circuit, TIA71 can operate at a relatively high speed.

[0116] In a structure where switch 66, resistor 68, diode 80, capacitor 69, and TIA71 are all integrated into the same CMOS logic integrated circuit, each photodetector unit 15A can operate at a relatively low operating voltage, for example, below 20V. In other words, with switch 66, resistor 68, diode 80, capacitor 69, and TIA71 all integrated into the same integrated circuit, TIA71 can operate at a relatively high speed.

[0117] In each of the optical detection units 15, 15A, and 15B, resistor 68 has an impedance greater than the input impedance of the second circuit section 65. In this case, the signal from APD11 can be transmitted to TIA71 more accurately.

[0118] In each of the optical detection units 15, 15A, and 15B, the potential difference between the first and second potentials and the potential difference between the first and third potentials can also be included within the operating voltage range of the TIA71. In this case, the operating speed of the TIA71 can be improved using a simple structure, while suppressing the heating of the APD11 and the damage to the readout circuit 70 corresponding to voltage fluctuations.

[0119] The light detection device 1 further includes a switch control unit 75 that controls the connection state of switches 66 and 67 based on the timing of light detection in each light detection unit 15, 15A, 15B. In this case, the light detection device 1 can switch the bias voltage to APD 11 according to whether it is the timing for light detection.

[0120] Relative to each light detection unit 15, 15B, the switch control unit 75 connects electrode 11b to the third terminal 63 via switch 67 when switch 66 disconnects the connection between electrode 11b and the second terminal 62. In this case, the light detection device 1 can discharge the generated current to the third terminal 63 even when ambient light B3 is incident on the APD 11, which is not detecting the target light B2. As a result, damage to the readout circuit 70 is suppressed.

[0121] Relative to each photodetector unit 15, 15B, when switch 66 connects electrode 11b to the second terminal 62, switch control unit 75 causes switch 67 to disconnect electrode 11b from the third terminal 63. In this case, the heating of resistor 68 is suppressed.

[0122] The light detection device 1 may further include an irradiation unit 2 for irradiating light. The switch control unit 75 controls the energization state of switches 66 and 67 according to the timing of light irradiation from the irradiation unit 2. In this case, the light detection device 1 can more reliably determine whether it is time to perform light detection. As a result, the light detection device 1 can more accurately switch the bias voltage to APD 11 according to whether it is time to perform light detection.

[0123] The embodiments and variations of the present invention have been described above, but the present invention is not necessarily limited to the embodiments described above, and various changes can be made without departing from its spirit.

[0124] For example, in the above-described embodiments and variations, APD11 operates in linear mode. However, APD11 can also operate in Geiger mode. In this case, each photodetector unit 15 may further have a quenching circuit connected to APD11. The quenching circuit can be provided either on the photodetector substrate 5 or on the circuit element 7. The quenching circuit can also be integrated with the resistor 68.

[0125] In the above-described embodiments and modifications, the photodetector substrate 5 and the circuit element 7 are arranged separately from each other and opposite to each other in the Z-axis direction. However, the photodetector substrate 5 and the circuit element 7 may also be integrally formed. The photodetector substrate 5 and the circuit element 7 may also be arranged in a direction intersecting the Z-axis direction.

[0126] In the above-described embodiments and variations, the photodetector substrate 5 and the circuit element 7 are connected via bump B. However, the photodetector substrate 5 and the circuit element 7 can also be directly coupled.

[0127] In the above-described embodiments and variations, the switch control unit 75 controls switches 66 and 67 respectively. However, switches 66 and 67 can also be linked. For example, switches 66 and 67 can also be constructed using CMOS.

[0128] In each of the light detection units 15 and 15B, when the target light B2 is detected in the light detection unit 15, the switch control unit 75 turns on switch 66 and turns off switch 67. When the target light B2 is not detected in the light detection unit 15, the switch control unit 75 turns off switch 66 and turns on switch 67. However, when the target light B2 is not detected in the light detection unit 15, both switches 66 and 67 can be turned on. In this case, the bias voltage applied to APD 11 is lower than when switch 66 is on and switch 67 is off. The fluctuation of the bias voltage of APD 11 is smaller than when switching between applying a bias voltage to APD 11 and not applying a bias voltage to APD 11. As a result, the heating of APD 11 caused by light incidence and the damage to the readout circuit 70 corresponding to the potential fluctuation are suppressed. When switch 66 is in the off state and switch 67 is in the on state, the heating of resistor 68 is suppressed compared to the case where both switches 66 and 67 are in the on state.

[0129] The above-described modifications can also be combined separately. For example, in each light detection unit 15B, such as light detection unit 15A, a diode 80 can be used instead of switch 67.

[0130] Explanation of symbols

[0131] 1…Photodetector, 2…Illumination unit, 11…Avalanche photodiode, 11a, 11b…Electrodes, 15, 15A, 15B…Photodetector unit, 61…First terminal, 62…Second terminal, 63…Third terminal, 64…First circuit section, 65, 65A…Second circuit section, 66, 67…Switch, 68…Resistor, 69…Capacitor, 70…Readout circuit, 71…Mutual impedance amplifier, 75…Switch control section, 80…Diode, 81, 82…Electrodes, R…Light-receiving area.

Claims

1. A light detection device, characterized in that: Includes multiple light detection units, each with a light-receiving area. Each of the aforementioned optical detection units includes: An avalanche photodiode having first and second electrodes and forming the light-receiving region; The first terminal connected to the first electrode and to which the first potential is applied; The first and second circuit sections are connected in parallel to the second electrode; The second terminal is connected to the second electrode via the first circuit section and is subject to a second potential; and The third terminal is connected to the second electrode via the second circuit section and is subject to the third potential. In each of the aforementioned optical detection units The first circuit section includes a first switch for switching the connection state between the second electrode and the second terminal, and a resistor. The first switch, the resistor, the second electrode, and the second terminal are connected in series. The second circuit section includes a second switch for switching the connection state between the second electrode and the third terminal, a capacitor, and a readout circuit containing a transimpedance amplifier. The second switch and the capacitor are connected in parallel to the second electrode. The second switch, the second electrode, and the third terminal are connected in series. The transimpedance amplifier is connected in series with the capacitor and is connected to the second electrode via the capacitor. The absolute value of the potential difference between the first potential and the third potential is less than the absolute value of the potential difference between the first potential and the second potential.

2. The optical detection device as described in claim 1, characterized in that: In each of the optical detection units, the first switch is connected to the second electrode via the resistor.

3. The optical detection device as described in claim 1, characterized in that: It also includes a switch control unit that controls the connection state based on the first and second switches according to the timing of light detection in each of the light detection units.

4. The optical detection device as described in claim 2, characterized in that: It also includes a switch control unit that controls the connection state based on the first and second switches according to the timing of light detection in each of the light detection units.

5. The optical detection device as described in claim 3, characterized in that: When the first switch disconnects the connection between the second electrode and the second terminal, the switch control unit connects the second electrode and the third terminal via the second switch.

6. The optical detection device as described in claim 4, characterized in that: When the first switch disconnects the connection between the second electrode and the second terminal, the switch control unit connects the second electrode and the third terminal via the second switch.

7. The optical detection device as described in claim 3, characterized in that: The switch control unit causes the second switch to disconnect the connection between the second electrode and the third terminal when the first switch is connected to the second electrode and the second terminal.

8. The optical detection device as described in claim 4, characterized in that: The switch control unit causes the second switch to disconnect the connection between the second electrode and the third terminal when the first switch is connected to the second electrode and the second terminal.

9. The optical detection device as described in claim 5, characterized in that: The switch control unit causes the second switch to disconnect the connection between the second electrode and the third terminal when the first switch is connected to the second electrode and the second terminal.

10. The optical detection device as described in claim 6, characterized in that: The switch control unit causes the second switch to disconnect the connection between the second electrode and the third terminal when the first switch is connected to the second electrode and the second terminal.

11. The optical detection device as described in claim 3, characterized in that: It also includes the irradiation section for irradiating light. The switch control unit controls the energizing state of the first and second switches according to the timing of the light being irradiated from the irradiation unit.

12. The optical detection device as described in claim 4, characterized in that: It also includes the irradiation section for irradiating light. The switch control unit controls the energizing state of the first and second switches according to the timing of the light being irradiated from the irradiation unit.

13. The optical detection device as described in claim 5, characterized in that: It also includes the irradiation section for irradiating light. The switch control unit controls the energizing state of the first and second switches according to the timing of the light being irradiated from the irradiation unit.

14. The optical detection device as described in claim 6, characterized in that: It also includes the irradiation section for irradiating light. The switch control unit controls the energizing state of the first and second switches according to the timing of the light being irradiated from the irradiation unit.

15. The optical detection device as described in claim 7, characterized in that: It also includes the irradiation section for irradiating light. The switch control unit controls the energizing state of the first and second switches according to the timing of the light being irradiated from the irradiation unit.

16. The optical detection device as described in claim 8, characterized in that: It also includes the irradiation section for irradiating light. The switch control unit controls the energizing state of the first and second switches according to the timing of the light being irradiated from the irradiation unit.

17. The optical detection device as described in claim 9, characterized in that: It also includes the irradiation section for irradiating light. The switch control unit controls the energizing state of the first and second switches according to the timing of the light being irradiated from the irradiation unit.

18. The optical detection device as described in claim 10, characterized in that: It also includes the irradiation section for irradiating light. The switch control unit controls the energizing state of the first and second switches according to the timing of the light being irradiated from the irradiation unit.

19. A light detection device, characterized in that: Includes multiple light detection units, each with a light-receiving area. Each of the aforementioned optical detection units includes: An avalanche photodiode having first and second electrodes and forming the light-receiving region; The first terminal connected to the first electrode and to which the first potential is applied; The first and second circuit sections are connected in parallel to the second electrode; The second terminal is connected to the second electrode via the first circuit section and is subject to a second potential; The third terminal is connected to the second electrode via the second circuit section and is subject to the third potential. In each of the aforementioned optical detection units The first circuit section includes a switch for switching the connection state between the second electrode and the second terminal, and a resistor. The switch, the resistor, the second electrode, and the second terminal are connected in series. The second circuit section includes diodes, capacitors, and a readout circuit containing a transimpedance amplifier. The diode and the capacitor are connected in parallel to the second electrode. The diode includes a third electrode having the same polarity as the first electrode of the avalanche photodiode and a fourth electrode having the same polarity as the second electrode of the avalanche photodiode. The third electrode of the diode is connected to the third terminal. The fourth electrode of the diode is connected to the second electrode. The transimpedance amplifier is connected in series with the capacitor and is connected to the second electrode via the capacitor. The absolute value of the potential difference between the first potential and the third potential is less than the absolute value of the potential difference between the first potential and the second potential.

20. The optical detection device as described in claim 19, characterized in that: In each of the aforementioned optical detection units, the switch is connected to the second electrode via the resistor.

21. The light detection device according to any one of claims 1 to 20, characterized in that: The transimpedance amplifier is contained within a CMOS logic integrated circuit.

22. The light detection device according to any one of claims 1 to 20, characterized in that: The resistor has an impedance greater than the input impedance of the second circuit section.

23. The optical detection device as described in claim 21, characterized in that: The resistor has an impedance greater than the input impedance of the second circuit section.

24. The light detection device according to any one of claims 1 to 20, characterized in that: The potential difference between the first potential and the second potential, and the potential difference between the first potential and the third potential, are included in the range of the operating voltage of the transimpedance amplifier.

25. The optical detection device as described in claim 21, characterized in that: The potential difference between the first potential and the second potential, and the potential difference between the first potential and the third potential, are included in the range of the operating voltage of the transimpedance amplifier.

26. The optical detection device as described in claim 22, characterized in that: The potential difference between the first potential and the second potential, and the potential difference between the first potential and the third potential, are included in the range of the operating voltage of the transimpedance amplifier.

27. The optical detection device as described in claim 23, characterized in that: The potential difference between the first potential and the second potential, and the potential difference between the first potential and the third potential, are included in the range of the operating voltage of the transimpedance amplifier.

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