JP7087018B2 - Photodetector and subject detection system using it - Google Patents

Description

An embodiment of the present invention relates to a photodetector and a subject detection system using the photodetector.

In an optical detection element such as an avalanche photodiode or a silicon photomultiplier (hereinafter, also referred to as SiPM), the temperature dependence of the photon detection efficiency (also referred to as PDE) is large. For this reason, when using outdoors such as in-vehicle applications, it is necessary to keep the temperature of the chip constant by using a chip temperature monitor such as a thermistor and a Pelche element or a heater, which increases the size of the device and consumes power. Increases. Further, the temperature monitor formed by the chip different from the photodetection element main body has low reproduction accuracy of the actual device temperature, which causes a decrease in the temperature correction accuracy.

The photon detection efficiency of SiPM is expressed by the product of the device aperture ratio S, the photoelectric conversion efficiency η, and the avalanche probability Pav. Of these, the avalanche probability _Pav , which has a large effect on temperature characteristics, is empirically
It can be expressed as P _av = P ₀ × (1-exp (-a × V _ov )). Here, P ₀ is a constant that does not depend on temperature, and a is a constant that is caused by the device structure. Further, the voltage V _ov uses the breakdown voltage V _bd of the device and the drive voltage V _op of the device.
V _ov = V _op -V _bd
It is expressed as.

As a result, when the drive voltage V _op is constant, the breakdown voltage V _bd fluctuates, so that the voltage V _ov fluctuates, the avalanche probability P _av fluctuates, and the temperature dependence of the photon detection efficiency occurs. Therefore, in order to suppress the temperature dependence of the photon detection efficiency, it is necessary to correct the temperature dependence of the breakdown voltage _Vbd .

In general, the breakdown voltage _Vbd of the photodetector (photodetector) shows a substantially linear variation with respect to the device temperature, and it can be seen that the temperature can be corrected. However, the influence of the variation of the breakdown voltage _Vbd between the devices cannot be ignored. Therefore, when the number of pixels is increased as in SiPM, it is necessary to correct the variation in the breakdown voltage _Vbd for each pixel.

Japanese Unexamined Patent Publication No. 2013-16638

The present embodiment provides a photodetector capable of suppressing temperature fluctuations in photon detection efficiency and a subject detection system using the photodetector.

The photodetector according to the present embodiment is provided with a pixel provided with at least one avalanche photodiode, a voltage source for applying a drive voltage to the pixel, and a light-shielding portion on the upper surface, and a reverse voltage lower than the breakdown voltage is generated. The drive voltage is controlled based on a temperature detection unit having a diode to be applied and a temperature detection element for detecting information on the temperature of the pixel, and information on the temperature of the pixel detected by the temperature detection unit. It has a control unit.

The circuit diagram which shows the photodetector by 1st Embodiment. The figure which shows the relationship between the reverse voltage of a photodiode and the reverse dark current. The figure which shows the relationship between the breakdown voltage value of an avalanche photodiode and the reverse saturation dark current of a photodiode. The figure explaining the method of performing the environmental temperature correction in the photodetector of 1st Embodiment. The figure explaining the method of performing the environmental temperature correction in the photodetector of the 1st modification of 1st Embodiment. The circuit diagram which shows the photodetector by the 2nd modification of 1st Embodiment. The circuit diagram which shows the photodetector by the 3rd modification of 1st Embodiment. 8 (a) and 8 (b) are a plan view and a cross-sectional view showing a manufacturing process of the photodetector according to the first embodiment. 9 (a) and 9 (b) are a plan view and a cross-sectional view showing a manufacturing process of the photodetector according to the first embodiment. 10 (a) and 10 (b) are a plan view and a cross-sectional view showing a manufacturing process of the photodetector according to the first embodiment. 11 (a) and 11 (b) are a plan view and a cross-sectional view showing a manufacturing process of the photodetector according to the first embodiment. 12 (a) and 12 (b) are a plan view and a cross-sectional view showing a manufacturing process of the photodetector according to the first embodiment. 13 (a) and 13 (b) are a plan view and a cross-sectional view showing a manufacturing process of the photodetector according to the first embodiment. 14 (a) is a plan view of a silicon photomultiplier (SiPM), and FIG. 14 (b) is a plan view showing pixels. The circuit diagram which shows the photodetector by 2nd Embodiment. The figure which shows the pulse-like signal potential induced by a pixel when a photon is input to the pixel of the photodetector of 2nd Embodiment. The figure which shows the switching characteristic of the enhancement type NaCl transistor and the depletion type polyclonal transistor _Tpi used in the photodetector of the second embodiment. The figure which shows the circuit related to the temperature correction in the photodetector of the 3rd Embodiment. The figure which shows the correlation with the cell temperature and the dark pulse signal detection rate. The block diagram which shows the long-distance subject detection system by 4th Embodiment.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(First Embodiment)
FIG. 1 shows a circuit block diagram of the photodetector according to the first embodiment. The photodetector 1 of the first embodiment has a plurality of photodetection pixels Pic ₁ to Pic _n arranged in a linear array, and each pixel Pic _i (i = 1, ..., N) is common. It is connected to the power supply _VCOM . In this embodiment, for example, _68V is applied as the power supply VCOM. Each pixel Pic _i (i = 1, ..., N) includes an optical signal detection unit 2 and a device temperature detection unit 3.

The optical signal detection unit 2 of each pixel Pic _i (i = 1, ..., N) detects an optical pulse signal of an avalanche photodiode APD _i , a quench resistor Rq _i , and an avalanche photodiode APD _i operating in Geiger mode. It has an output unit _Vsigi to output. The cathode of the avalanche photodiode APD _i is connected to the power supply Vcom, the anode is connected to one end of the quench resistance Rq _i , and the output unit Vsig _i is connected to the other end of the quench resistance Rq _i . That is, the avalanche photodiode APD _i , the quench resistance Rq _i , and the output unit Vsig _i are connected in series. The output unit Vsig _i is fixed to the ground potential through an external readout circuit (not shown).

From the avalanche photodiode APD _i (i = 1, ..., N), the incident photons are photoelectrically converted, and an avalanche-amplified high-speed pulse of several tens of nanoseconds is output from the optical pulse signal output unit Vsig _i . To. At this time, since the multiplication factor that determines the intensity of the optical signal and the pulse time constant that affects the sensor insensitivity time are proportional to the parasitic capacitance, it is desirable to avoid an increase in the parasitic capacitance due to the addition of a temperature compensation mechanism or the like.

Therefore, in the present embodiment, the device temperature detection unit 3 is newly added to each pixel Pic _i (i = 1, ..., N). The device temperature detection unit 3 detects the temperature of the substrate (not shown) on which the pixels are formed, and the light-shielded photodiode PD _i operating in the reverse saturation region and the photodiode PD _i It is provided with a voltage application unit _{Pi for applying an operating voltage and a terminal 10 i for} outputting device temperature information V _Ti . The avalanche photodiode APD _i (i = 1, ..., N) and the photodiode PD _i are formed using the same planar pattern shape and process process, and the photodiode PD _i is an avalanche photodiode for each pixel. It was placed close to the APD _i . That is, the photodiode PD _i and the avalanche photodiode APD _i have almost the same structure.
As will be described later, a light-shielding film (reference numeral 614 of FIGS. 13 (a) and 13 (b)) is formed above each photodiode PD _i (i = 1, ..., N).

FIG. 2 shows the results of measuring the reverse voltage dependence of the reverse dark current of the photodiode PD _i (i = 1, ..., N). As can be seen from FIG. 2, the photodiode PD _i (i = 1, ..., N) has characteristics equivalent to the current-voltage characteristics and temperature dependence of the avalanche photodiode APD _i . That is, the characteristics of the avalanche photodiode APD _i can be reproduced by the characteristics of the photodiode PD _i (i = 1, ..., N).

Further, in the first embodiment shown in FIG. 1, the voltage application unit Pi for applying the operating voltage of the photodiode PD _i ( _i = 1, ..., N) is set between the power supply _VCOM and the ground potential. , It is realized by using the capacity division by the capacity C ₁ and the capacity C ₂ . That is, the bias voltage Vpd applied to the photodiode PD _i (i = 1, ..., N) is
Vpd = C ₁ / (C ₁ + C ₂ ) × V _COM . In the present embodiment, since C ₁ = 10 pF, C ₂ = 1 pF, and V _COM = 68 V, the bias voltage Vpd is 62 V, which is a reverse saturation voltage that does not exceed the breakdown voltage Vbd.

FIG. 3 shows the value of the breakdown voltage Vbd corresponding to the change of the device temperature of the avalanche photodiode APD _i (i = 1, ..., N) and the reverse saturation dark current Ir (reverse saturation dark current Ir) of the photodiode PD _i . The relationship of A / mm ² ) is shown. As can be seen from FIG. 3, the reverse saturated dark current Ir changes exponentially according to the change of the breakdown voltage Vbd. Therefore, by monitoring the reverse saturation dark current Ir of the photodiode PD _i (i = 1, ..., N), information on the temperature fluctuation of the breakdown voltage Vbd of the avalanche photodiode APD _i can be obtained. I understand. That is, by detecting the reverse dark current Ir, the device temperature information can be read out by a general read-out circuit.

In the first embodiment shown in FIG. 1, a current-voltage conversion amplifier AMP _i that receives a reverse dark current Ir of a photodiode PD _i in each pixel Pic _i (i = 1, ..., N), and a pixel selection circuit. It has a configuration in which the switch SW _i is further added. One end of the switch SW _i (i = 1, ..., N) is connected to the terminal 10 _i , and the other end is connected to the input terminal of the current-voltage conversion amplifier AMP _i . With this configuration, device temperature information is acquired. As a reading method, the device temperature information may be read out as a charge by integrating the reverse dark current of the photodiode PD _i (i = 1, ..., N) for a certain period of time. It's not something to get caught up in.

FIG. 4 is a diagram illustrating a method of performing environmental temperature _{correction using the device temperature information VT1 output} from the terminal 101 of the pixel Pic ₁ . In the present embodiment, the voltage control unit 20 is further provided. The device temperature information VT1 output from the pixel _{Pic 1} is input to the voltage control unit 20 outside the chip. The voltage control unit 20 stores a correlation _table between the device temperature information VT1 and the drive voltage Vop. The device temperature information VT1 is converted into a drive voltage Vop according to this correlation _table in the voltage control unit 20, and is output to the high voltage power supply _VCOM as a conversion signal. As a result, since the drive voltage Vop is corrected according to the temperature fluctuation of the break voltage Vbd, the drive voltage Vov becomes constant regardless of the device temperature, and the temperature fluctuation of the photon detection efficiency is suppressed. In FIG. 4, _a method of performing environmental temperature correction using the device temperature information _VT1 output from the terminal 101 of the pixel Pic ₁ has been described, but the same applies to other pixels.

(First modification)
A first modification of the first embodiment will be described with reference to FIG. FIG. 5 is an explanatory diagram of a method of performing environmental temperature correction using the device temperature information _VT1 in the photodetector of the first modification.

In this first modification, as shown in FIG. 5, an electronic cooler 32 for keeping the temperature of the SiPM chip 30 constant and a control unit 35 for controlling the electronic cooler 32 are further provided. .. The device temperature information VT1 to _VTn output from the _SiPM chip 30 is input to the control unit 35 and converted into a temperature control signal of the electronic cooler 32. As a result, the temperature of the SiPM chip 30 is kept constant by the electronic cooler 32, and the temperature fluctuation of the photon detection efficiency due to the fluctuation of the environmental temperature is suppressed.

Further, the method for applying the bias voltage Vpd is not limited to the method by capacitance division by the capacitance C1 and the capacitance _C2 , and may be replaced with _a dedicated voltage source that gives a value in a range not exceeding the breakdown voltage Vbd. good.

(Second modification)
FIG. 6 shows a photodetector according to a second modification of the first embodiment. The photodetector of this second modification is used, for example, when the number of pixels is large and there is no room for wiring. In the first embodiment shown in FIG. 1, the current-voltage conversion amplifier AMP _i (i) provided for each pixel. = 1, ..., N) has a configuration in which one current-voltage conversion amplifier AMP is changed. That is, the current-voltage conversion amplifier AMP is connected to the terminal 10 _i of each pixel Pic _i via the switch SW _i (i = 1, ..., N). A pixel selection unit 40, which is arranged outside the chip and sends a pixel selection signal to a switch corresponding to the selected pixel to turn it on, is newly added. For example, when the pixel to be selected is the pixel Pic ₁ , a pixel selection signal is sent to the switch SW ₁ to turn on the switch SW ₁ .

In the second modification, the method described in the first modification may be used as the method for correcting the environmental temperature.

(Third modification example)
FIG. 7 shows a photodetector according to a third modification of the first embodiment. The light detection device of the third modification is the light detection device of the first embodiment shown in FIG. ₁ , and each pixel Pic _i (i ₌ 2, ... ·, The device temperature detection unit 3 is deleted from n-1), and each is based on the device temperature information _{VT1 and the device temperature information VTn detected} by the device temperature detection unit 3 of the pixel Pick ₁ and the pixel Pick _n . The device temperature information V _Ti of the pixel Pic _i (i = 2, ..., N-1) is determined.

For example, as a first example, the device temperature information V _Ti of each pixel Pic _i (i = 2, ..., N-1) is the average value of the device temperature information _{VT1 and the device temperature information VTn ,} that is, V _Ti =. It may be ( _{VT1 + VTn )} / 2. In this case, the measurement variation can be suppressed by using the output average of the device temperature detection unit 3.

Further, as a second example, the device temperature information V _Ti of each pixel Pic _i (i = 2, ..., N-1) can be given by a linear approximation of _{VT1 and VTn .} That is, V _Ti = i × ( _VT1 -V _Tn ) / n + V _Tn
May be. In this case, the temperature distribution in the linear array can be accurately reflected.

In this third modification, the method described in the first modification or the second modification may be used as the method for correcting the environmental temperature.

(Production method)
Next, a method of manufacturing the photodetector according to the first embodiment will be described with reference to FIGS. 8 (a) to 13 (b). 8 (a), 9 (a), 10 (a), 11 (a), 12 (a), and 13 (a) show plan views in each manufacturing process, and FIGS. 8 (b) and 9 (b) show. ), 10 (b), 11 (b), 12 (b), 13 (b) show cross-sectional views in each manufacturing process. These cross-sectional views are cross-sectional views cut along the cutting lines AA shown in the corresponding plan views.

As shown in FIGS. 8 (a) and 8 (b), the light detection device of the first embodiment is mounted on a single crystal N-type silicon substrate 600 doped with antimony at a concentration of 2.0 × 10 ¹⁸ / cm ³ . A wafer prepared by epi-growth of a boron-doped silicon epitaxial layer 601 at a concentration of 1.0 × 10 ¹⁵ / cm ³ to a thickness of 3 μm is prepared.

Next, as shown in FIGS. 9 (a) and 9 (b), a resist pattern 602 defining an element region is formed by using a lithography process, and boron is used as a mask at an acceleration voltage of 2.4 MeV. Ion implantation is performed under the condition of a dose amount of 2.0 × 10 ¹² / ^cm3 to form a deep P-type layer 603.

Next, as shown in FIGS. 10 (a) and 10 (b), using a pattern (not shown) in which the element separation region 604 serves as an aperture mask, phosphorus is accelerated by an acceleration voltage of 150 keV and a dose amount of 1.0 × 10. The device separation diffusion layer 605 is formed by ion implantation under the condition of ¹² / ^cm3 . Subsequently, the element separation structure 606 is formed on the surface of the silicon epitaxial layer 601 by using the LOCOS (Local Oxidation) method by using a normal LSI manufacturing process. The oxidation step carried out at this time activates the P-type layer 603 and the device separation / diffusion layer 605.

Next, as shown in FIGS. 11A and 11B, a deep N-type diffusion layer 607 for pixel separation is formed so as to penetrate the epi layer 601 and reach the N-type substrate 600. Subsequently, a photoresist film 608 having a thickness of 0.2 μm is formed into a film by a CVD (Chemical Vapor Deposition) method, and processed into a predetermined shape by lithography and RIE (Reactive Ion Etching) method. It is advisable to inject, for example, boron into the polysilicon film 608 with an acceleration voltage of 20 keV and a dose amount of about 1.0 × 10 ¹⁵ / cm ³ so that a predetermined resistance can be obtained.

Next, as shown in FIGS. 12 (a) and 12 (b), a shallow P-type layer 610 for forming an ohmic contact between the silicon epi layer 601 and the metal electrode 613 in the device region, for example, an acceleration voltage of boron. It is formed by ion implantation under the conditions of 40 keV and a dose amount of 1.0 × 10 ¹⁴ / cm ³ , and then activating it. Subsequently, the insulating film layer 611 is formed with a thickness of 0.8 μm by the CVD method, and the contact hole 612 is formed by the lithography and the RIE method.

Next, as shown in FIGS. 13 (a) and 13 (b), the aluminum electrode 613 is formed to have a thickness of 0.8 μm by a sputtering method, and is processed into a predetermined shape by a lithography and RIE method. At this time, the aluminum electrode on the photodiode PD region of the device temperature detection unit 3 is used as the light-shielding film 614. Finally, Ti / Au is formed as a common electrode Vcom on the back surface of the N-type substrate 600.

As described above, the avalanche photodiode 617 of the photodetection unit 2 and the photodiode 616 of the temperature detection unit 3 can be manufactured.

The above has described the case of a photodetector in which an avalanche photodiode is arranged in a one-dimensional array, but a cell having a quench resistor connected in series with the avalanche photodiode is arranged in a two-dimensional array. It is also applicable to a silicon photodiode (SiPM) having one pixel. A plan view of the silicon photomultiplier (SiPM) is shown in FIG. 14 (a), and 90 ₁₁ to 90 ₃₃ arranged in a 3 × 3 array are shown in FIG. 14 (b). In each pixel 90 _ij (i, j = 1, ..., 3), as shown in FIG. 14 (b), the central region of the pixel is set as the photodetector 1001 in order to improve the light detection efficiency, and the periphery of the pixel is set as the photodetector 1001. It is desirable that the element in the region is the photodiode PD of the temperature detection unit 1002. Further, the device _temperature information VT is amplified and averaged by connecting the outputs of the photodiode PDs arranged in the pixel peripheral region in parallel as the temperature detection unit 1002, so that the device temperature information VT can be read out more accurately. ..

As described above, according to the first embodiment and its modifications, it is possible to provide a photodetector capable of suppressing temperature fluctuations in photon detection efficiency.

(Second Embodiment)
A circuit diagram of the photodetector according to the second embodiment is shown in FIG. The photodetector 1 of the second embodiment has a plurality of pixels and has a circuit configuration capable of reading device temperature information for each pixel and each photodetection timing.

The photodetector 1 of the second embodiment has a plurality of pixels Pic ₁ to Pic _n , and each pixel Pic _i (i = 1, ..., N) has a photodetector 2 and device temperature information detection. It has a part 3 and. An enhancement type NaCl transistor Tn _i and a depletion type FIGURE transistor Tp _i are connected in series to the terminal 10 _i that outputs the device temperature information V _Ti of the pixel Pic _i (i = 1, ..., N) to connect an inverter. Configure. The source electrode of the transistor Tp _i (i = 1, ..., N) receives a common reset potential Vrst.

The optical pulse signal output unit Vsig _i (i = 1, ..., N) is input to the current-voltage conversion amplifier AMP _i and converted into a voltage pulse, and this voltage pulse is applied to the terminal 15 _i . The gate electrodes of the transistor Tn _i ( _i = 1, ..., N ₎ and the transistor Tpi are connected to the terminal _15i , and the output of the inverter consisting of the transistor Tn _i and the transistor Tpi is the device temperature information common potential line Vt. Be connected.

For example, when a photon is input to the pixel Pic ₁ , _a pulse-shaped signal potential is induced in the terminal 151 as shown in FIG. The switching characteristics (Id-Vg curve) of the transistors Tn ₁ and Tp ₁ are set as shown in FIG. When the wave height of the voltage pulse of the terminal 151 exceeds the threshold voltage Vthn ₁ of the transistor Tn ₁ , the transistor Tp ₁ remains OFF and the transistor Tn ₁ turns ON, and the device temperature of the pixel _{Pic 1 is} connected to the common potential line Vt. Information _VT1 is output. Next, when the avalanche pulse generated by the photon generated by the photon incident on the pixel Pic ₁ is terminated by the quenching operation and the peak value of the avalanche pulse becomes equal to or less than the threshold voltage Vthn ₁ of the transistor Tn ₁ , the transistor Tn ₁ is turned off. .. As a result, the common potential line Vt is generated by the parasitic capacitance Cex.
Vex ₁ = Ir ₁ × Δt / Cex
The voltage value Vex ₁ defined in is obtained, and the device temperature information _VT1 of the pixel Pic ₁ is output as a voltage value from the common potential line Vt. At this time, Ir ₁ indicates the reverse saturation dark current of the photodiode PD ₁ for temperature detection, and Δt indicates the time during which the transistor Tn ₁ is turned on, as shown in FIG.

Next, when the avalanche pulse wave height further decreases and becomes equal to or less than the threshold voltage Vthp ₁ of the transistor Tp ₁ , the transistor Tp ₁ is turned ON and the common potential line Vt is reset to the common reset potential Vrst.

With the above configuration, the device temperature information can be read out for each pixel and each light detection timing, and the temperature can be corrected in real time. This makes it possible to suppress temperature fluctuations in photon detection efficiency.

As described above, according to the second embodiment, it is possible to provide a photodetector capable of suppressing temperature fluctuations in photon detection efficiency.

(Third Embodiment)
Next, the photodetector according to the third embodiment will be described. The photodetector of the third embodiment has a different configuration of the device temperature detection unit 3 from the photodetector of the first embodiment shown in FIG. The device temperature detection unit 3 in the third embodiment uses a method of performing temperature correction using a dark output pulse count of a shielded avalanche photodiode operating in the Geiger mode. As described above, in the third embodiment, by using a temperature correction element having the same structure as the APD used for light detection and performing the same bias operation, more accurate temperature correction including variation in the element becomes possible. ..

FIG. 18 shows a circuit related to temperature correction in the photodetector of the third embodiment. The photodetector 1 of the third embodiment includes a plurality of photodetection pixels Pic ₁ to Pic _n and at least one temperature monitor pixel Pic _T. Each pixel Pic _i (i = 1, ..., N) has the same structure as the pixel described in the first embodiment. The temperature monitor pixel Pic _T has the same structure as each pixel Pic _i (i = 1, ..., N) except that a light-shielding film is arranged on the upper part. The photodetection pixels Pic ₁ to Pic _n and the temperature monitor pixel Pic _T are connected to a common power supply Vcom. As shown in FIG. 1, the photodetection pixels Pic ₁ to Pic _n and the temperature monitor pixel Pic _T are similar to the case where the cell in which the avalanche photodiode and the quench resistor are connected in series is shown in FIG. 10 (a), respectively, as shown in FIG. , Has a configuration arranged in an array.
The output units Vsig ₁ to _Vsign of the pixels Pic ₁ to Pic _n output an optical pulse signal and are fixed to the ground potential through an external readout circuit (not shown).

The dark pulse signal output from the temperature monitor pixel Pick _T is input to the current-voltage conversion amplifier AMP through the output terminal Vt, converted into the number of dark pulses per time by the counter 52, and the dark pulse signal detection rate. Is output as. FIG. 19 shows the correlation between the cell temperature and the dark pulse signal detection rate. It can be seen that the dark pulse signal detection rate increases exponentially with temperature and is very sensitive to temperature. Therefore, the accuracy of the temperature monitoring method in this embodiment is very high.

After that, the dark pulse signal detection rate output from the counter 50 is input to the control unit 52, converted into temperature information by the temperature table 53 prepared in advance, and controlled by the power supply circuit for _VCOM control or the electronic cooler. It is fed back to the unit 54.

The dark pulse signal indicating the temperature dependence of the cell is an avalanche pulse due to the thermal excited electrons of silicon used as a substrate, and the number of pulses depends on the cell area or the detection time length. In order to improve the temperature monitor accuracy, it is necessary to secure a statistically sufficient number of events (number of events), and it is necessary to secure a sufficient detection time or a sufficient cell area. It is desirable to increase the cell area of the temperature monitor pixel PicT because the extension of the detection time reduces the real-time property due to the decrease in the frequency of temperature monitoring.

At this time, in SiPM, since quenching occurs due to Geiger mode operation, if the area per cell is increased, the quenching time, that is, the detection dead time is further increased due to the increase in parasitic capacitance. Therefore, it is desirable to increase the number of cells per pixel and secure the frequency of dark pulse generation by increasing the total cell area per pixel.

On the other hand, in the photodetection pixel used for distance measurement by the distance measurement method (Time of Flight method), it is sufficient if the detection timing of the pulse generated by the incident photon can be obtained accurately, and it is not necessary to generate a histogram by integrating the number of events. .. That is, considering the pulse band, it is preferable that the cell parasitic capacitance is low, and the cell area is small as long as the photodetection efficiency can be sufficiently obtained. At the same time, in order to suppress an increase in the chip area, it is desirable to minimize the number of cells of a plurality of photodetected pixels arranged for arraying.

Therefore, in the present embodiment, the optical detection pixels Pic ₁ to Pic _n have a scale of about 100 cells / pixel, the temperature monitor pixel Pic _T has 1000 cells / pixel, and the number of cells of the temperature monitor pixel Pic _T is the optical detection pixel Pic. It was set to 10 times the number of cells from ₁ to _Pixel .

As described above, according to the third embodiment, it is possible to provide a photodetector capable of suppressing temperature fluctuations in photon detection efficiency.

(Fourth Embodiment)
FIG. 20 shows a subject detection system according to the fourth embodiment. The subject detection system 200 of this embodiment includes a light projection unit 210 and a light detection unit 250, projects light from the light projection unit 210 onto the subject 100, is reflected by the subject 100, and returns to the same direction as the irradiation direction. The light detection unit 250 detects the coming reflected light, and by calculating the return time (light flight time), intensity, etc., the distance from the flight time of the light to the subject 100, and the reflectance of the subject 100 from the light intensity. It is a device that estimates such things.

The light projection unit 210 has, for example, a near-infrared light irradiation unit 212 that projects light in the near-infrared region, a light splitting unit 214 that splits the projected light and the reflected light from the subject, for example, a light splitting unit 214 having a beam splitter, and light as a subject. It is provided with an optical scanning unit 216 for two-dimensionally scanning in the horizontal and vertical directions toward 100. The reflected light reflected from the subject 100 and returned in the same direction as the irradiation direction returns to the light scanning unit 216 again, and is guided to the photodetection unit 250 by the light dividing unit 214.

The light detection unit 250 drives a condensing lens 260 that collects light from the light division unit 214, a light detector 264 that detects the intensity of light, and a light detector 264, and emits light from the light detector 264. The near-infrared light irradiation unit 212 uses the drive and read-out circuit 270 to read out the light, the synchronization circuit 272 to obtain the synchronization of the timing of the light projected from the near-infrared light irradiation unit 212, and the synchronization timing from the synchronization circuit 272. It includes a time calculation processing unit 274 that calculates the return time of the light projected from the subject 100, and a data storage unit 276 for accumulating two-dimensional information and time information of the subject 100.

In the fourth embodiment, as the photodetector 264 that detects the near-infrared light reflected by the subject 100, the photodetector 1 of the first to third embodiments or a modification thereof is used. As a result, the subject detection system 200 of the fourth embodiment can provide a subject detection system capable of suppressing temperature fluctuations in photon detection efficiency, as in the first to third embodiments.

Although some embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other embodiments, and various omissions, replacements, and changes can be made without departing from the gist of the invention. These embodiments and variations thereof are included in the scope of the invention described in the claims and the equivalent scope thereof, as are included in the scope and gist of the invention.

1 ... Photodetector, 2 ... Optical signal detector, 3 ... Device temperature detector, 10 ₁ to 10 _n ... Terminal, 15 ₁ to 15 _n ... Terminal, 20 ... Voltage control unit, 30 ... SiPM chip, 32 ... Electronic cooler, 35 ... Control unit, 40 ... Pixel selection unit, 90 ₁₁ to 90 ₃₃ ... Pixel, 100 ... Subject, 200 ... Subject detection system, 210 ... Light projection unit, 212 ... Near infrared light irradiation unit, 214 ... Light splitting unit, 216 ... Optical scanning unit 216, 250 ... Light detection Unit 260 ... Condensing diode, 264 ... Photodetector, 270 ... Drive and readout circuit, 272 ... Synchronous circuit, 274 ... Time calculation processing unit, 276 ... Data storage unit 276, 600 ... Single crystal N-type silicon substrate, 601 ... Silicon epitaxial layer, 502 ... Resist pattern, 603 ... P-type layer, 604 ... Element separation region, 605 ... Element separation Diffusion layer, 607 ... N-type diffusion layer 607, 608 ... Polysilicon film, 612 ... Contact hole, 613 ... Metal electrode, 614 ... Light shielding film, 616 ... Photodiode, 617 ... avalanche photodiode, 1001 ... photodetector, 1002 ... temperature detector

Claims (8)

A pixel with at least one avalanche photodiode,
A voltage source that applies a drive voltage to the pixel,
A temperature detector having a light-shielding portion on the upper surface, a photodiode to which a reverse voltage lower than the breakdown voltage is applied, and a temperature detection element for detecting information on the temperature of the pixel, and a temperature detector.
A control unit that controls the drive voltage based on information about the temperature of the pixel detected by the temperature detection unit, and a control unit.
Information about the temperature of the pixel is obtained based on the reverse saturation dark current of the photodiode .
The photodiode is provided with a voltage application unit that applies a reverse voltage lower than the breakdown voltage.
The voltage application unit is a photodetector having at least two capacitances connected in series between the voltage source and a predetermined potential. The plurality of pixels are provided and arranged in a line, and the temperature detecting unit includes first and second temperature detecting elements arranged at both ends of the plurality of pixels arranged in a line.
The photodetector according to claim 1, wherein the temperature detection unit determines the temperature of each of the pixels based on the outputs of the first and second temperature detection elements. A pixel with at least one avalanche photodiode,
A voltage source that applies a drive voltage to the pixel,
A temperature detector having a light-shielding portion on the upper surface, a photodiode to which a reverse voltage lower than the breakdown voltage is applied, and a temperature detection element for detecting information on the temperature of the pixel, and a temperature detector.
A control unit that controls the drive voltage based on information about the temperature of the pixel detected by the temperature detection unit, and a control unit.
Information about the temperature of the pixel is obtained based on the reverse saturation dark current of the photodiode .
The temperature detection unit is a photodetector having a selection unit arranged corresponding to the pixel and operating the temperature detection unit based on an output pulse signal from the avalanche photodiode. The selection unit is an N-channel MOS transistor having a gate terminal for receiving an output pulse signal from the avalanche photodiode, a source terminal, and a drain terminal connected to the output terminal of the temperature detection element, and the avalanche photodiode. A gate terminal that receives an output pulse signal, a source terminal connected to the source terminal of the N-channel MOS transistor, and a P-channel MOS transistor having a drain terminal that receives a predetermined reset potential.
3. The optical detection device according to claim 3 , wherein temperature information is output from the source terminal of the N-channel MOS transistor and the P-channel MOS transistor. The photodetector according to any one of claims 1 to 4 , wherein the photodiode has the same structure as the avalanche photodiode. The photodetector according to any one of claims 1 to 5, further comprising a current-voltage conversion amplifier that receives the reverse saturated dark current of the photodiode. Claims 1, 3 to 6 in which a plurality of the pixels are provided and arranged in a two-dimensional array, and a plurality of the temperature detecting elements are arranged and connected in parallel around the pixels arranged in the two-dimensional array. The light detection device according to any one of the above. The light irradiation unit that projects light, the light division unit that divides the light and the reflected light of the light from the subject, the light scanning unit that scans the projected light toward the subject, and the light division unit. A light detection device that detects the divided reflected light, a drive / readout circuit that drives the light detection device and reads out the intensity of the reflected light from the light detection device, and a drive / readout circuit for light projected from the light irradiation unit. The optical detection device includes a synchronization circuit for obtaining timing synchronization and a time calculation processing unit for calculating the return time of light projected from the light irradiation unit using the synchronization timing from the synchronization circuit. The subject detection system, which is the optical detection device according to any one of Items 1 to 7 .

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