Photodetection device and method for driving photodetector

Abstract

A light detection device, wherein a control unit executes a first charge transfer process of applying a potential to a transfer gate electrode so that the potential of an area directly below the transfer gate electrode becomes lower than the potential of a charge generation area and thereby transferring the charges generated in the charge generation area to a charge accumulation area, and a first readout process of reading out the amount of charges accumulated in the charge accumulation area. In the first charge transfer process, the control unit applies a potential to an overflow gate electrode so that the potential of an area directly below the overflow gate electrode becomes lower than the potential of the charge generation area.

Description

[Technical field]

[0001] One aspect of the present disclosure relates to a light detection device including a light sensor and a method for driving the light sensor. [Background technology]

[0002] Patent Document 1 describes an optical sensor that includes a photodiode that generates charge in response to incident light, a floating region that accumulates the charge from the photodiode, and a storage capacitance element that accumulates the charge that overflows from the floating region. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2005 / 083790 Summary of the Invention [Problem to be solved by the invention]

[0004] In the optical sensor described in Patent Document 1, the charge overflowing from the floating region can be stored in the storage capacitance element, but when the charge accumulates in the floating region to the extent that it overflows into the storage capacitance element, a part of the charge remains in the photodiode. In this case, the light detection accuracy may be reduced due to the charge remaining in the photodiode. In particular, when the optical sensor has a gating function that detects only light arriving at a specific timing, rather than detecting light throughout a certain period, if the above situation occurs, the charge remaining in the photodiode in one period may be read out as the charge generated in another period, and the amount of charge generated at a specific timing may not be detected accurately.

[0005] An object of one aspect of the present disclosure is to provide a light detection device and a method for driving a light sensor that can improve detection accuracy. [Means for solving the problem]

[0006] A photodetection device according to one aspect of the present disclosure includes a photosensor and a control unit that controls the photosensor. The photosensor has a charge generation region that generates charge in response to incident light, a charge accumulation region, an overflow region, a transfer gate electrode arranged on a region between the charge generation region and the charge accumulation region, and an overflow gate electrode arranged on a region between the charge accumulation region and the overflow region. The control unit performs a first charge transfer process to transfer charges generated in the charge generation region to the charge accumulation region by applying a potential to the transfer gate electrode so that the potential of the region directly below the transfer gate electrode is lower than the potential of the charge generation region, and a first readout process to read out the amount of charge accumulated in the charge accumulation region after the first charge transfer process. In the first charge transfer process, a potential is applied to the overflow gate electrode so that the potential of the region directly below the overflow gate electrode is lower than the potential of the charge generation region.

[0007] In this photodetection device, the photosensor has an overflow region and an overflow gate electrode disposed on a region between the charge accumulation region and the overflow region. This allows the charge overflowing from the charge accumulation region to be accumulated in the overflow region, and saturation of the accumulation capacity can be suppressed. Furthermore, during execution of a first charge transfer process for transferring the charge generated in the charge generation region to the charge accumulation region, the potential of the region directly below the overflow gate electrode is made lower than the potential of the charge generation region. This makes it possible to suppress the charge from remaining in the charge generation region even if the charge is accumulated in the charge accumulation region to the extent that it overflows into the overflow region. Therefore, this photodetection device can improve detection accuracy.

[0008] The control unit may execute the first readout process after executing the first charge transfer process multiple times, which can improve the S / N ratio.

[0009] The charge generation region may include an avalanche multiplication region. In this case, avalanche multiplication can be induced in the charge generation region, and the detection sensitivity of the photosensor can be increased. On the other hand, when the charge generation region includes an avalanche multiplication region, the amount of generated charge becomes extremely large. In this photodetector, even in such a case, saturation of the storage capacitance can be sufficiently suppressed, and residual charge in the charge generation region can be sufficiently suppressed.

[0010] The control unit may execute, after the first readout process, a second charge transfer process for transferring the charges accumulated in the charge accumulation region to the overflow region by applying a potential to the overflow gate electrode so that the potential of the region directly below the overflow gate electrode is reduced, and a second readout process for reading out the total amount of charge accumulated in the charge accumulation region and the overflow region after the second charge transfer process. In this case, not only the amount of charge accumulated in the charge accumulation region is read out in the first readout process, but also the total amount of charge accumulated in the charge accumulation region and the overflow region is read out in the second readout process, thereby improving the detection accuracy of the amount of charge.

[0011] The photosensor may further include an unwanted charge discharge region and an unwanted charge transfer gate electrode disposed on a region between the charge generation region and the unwanted charge discharge region, and the control unit may perform an unwanted charge transfer process to transfer the charges generated in the charge generation region to the unwanted charge discharge region by applying a potential to the unwanted charge transfer gate electrode so that the potential of the region directly below the unwanted charge transfer gate electrode becomes lower than the potential of the charge generation region during a period other than the period during which the first charge transfer process is performed. In this case, the charges generated in the charge generation region during a period other than the period during which the first charge transfer process is performed can be transferred to the unwanted charge discharge region, and the remaining charge in the charge generation region can be further suppressed.

[0012] The light detection device according to one aspect of the present disclosure may further include a light source that emits detection light, and the control unit may execute a first charge transfer process during a period in which the detection light reflected by the object is incident on the charge generation region. In this case, the amount of charge generated in the charge generation region during the period in which the detection light reflected by the object is incident on the charge generation region can be accurately detected.

[0013] The photodetector according to one aspect of the present disclosure further includes a photogate electrode disposed on the charge generation region, and the control unit may apply potentials to the photogate electrode and the overflow gate electrode in the first charge transfer process such that the potential of the region directly below the transfer gate electrode is lower than the potential of the charge generation region and the potential of the region directly below the overflow gate electrode is lower than the potential of the charge generation region. In this case, the height of the potential can be adjusted with high precision.

[0014] The overflow region may have a charge storage capacity larger than the charge storage capacity of the charge storage region, in which case saturation of the storage capacity can be effectively suppressed.

[0015] A method for driving a photosensor according to one aspect of the present disclosure is a method for driving a photosensor, the photosensor comprising a charge generation region that generates charges in response to incident light, a charge accumulation region, an overflow region, a transfer gate electrode arranged on a region between the charge generation region and the charge accumulation region, and an overflow gate electrode arranged on a region between the charge accumulation region and the overflow region, the method for driving the photosensor includes a charge transfer step of transferring charges generated in the charge generation region to the charge accumulation region by applying a potential to the transfer gate electrode so that the potential of the region directly below the transfer gate electrode is lower than the potential of the charge generation region, and a readout step of reading out the amount of charge accumulated in the charge accumulation region after the charge transfer step, and in the charge transfer step, a potential is applied to the overflow gate electrode so that the potential of the region directly below the overflow gate electrode is lower than the potential of the charge generation region.

[0016] In this method for driving a photosensor, the photosensor has an overflow region and an overflow gate electrode disposed on a region between the charge accumulation region and the overflow region. This allows the charge overflowing from the charge accumulation region to be accumulated in the overflow region, and saturation of the accumulation capacitance can be suppressed. Furthermore, during the execution of a charge transfer step for transferring the charge generated in the charge generation region to the charge accumulation region, the potential of the region directly below the overflow gate electrode is made lower than the potential of the charge generation region. This makes it possible to suppress the charge from remaining in the charge generation region even if the charge is accumulated in the charge accumulation region to the extent that it overflows into the overflow region. Therefore, this method for driving a photosensor can improve detection accuracy. Effect of the Invention

[0017] According to one aspect of the present disclosure, it is possible to provide a light detection device and a method for driving a light sensor that can improve detection accuracy. [Brief description of the drawings]

[0018] [Figure 1] 1 is a configuration diagram of a distance measuring device according to a first embodiment. [Diagram 2] FIG. 2 is a plan view of a pixel portion of the distance measuring sensor. [Diagram 3] FIG. 3 is a cross-sectional view taken along line III-III shown in FIG. 2. [Figure 4] FIG. 2 is a circuit diagram of a distance measuring sensor. [Diagram 5] 4 is a timing chart showing an example of the operation of the distance measuring sensor. [Figure 6] 13(a) to 13(d) are potential distribution diagrams for explaining an example of the operation of the distance measuring sensor. [Figure 7] 4 is a timing chart showing an example of the operation of an image sensor according to a comparative example. [Figure 8] 6(a) to 6(d) are potential distribution diagrams for explaining an example of operation of an image sensor according to a comparative example. [Figure 9]FIG. 11 is a plan view of a portion of a distance measuring sensor according to a first modified example. [Figure 10] 10 is a timing chart showing an example of the operation of the distance measuring sensor according to the first modified example. [Figure 11] FIG. 11 is a plan view of a portion of a distance measuring sensor according to a second modified example. [Figure 12] 13 is a timing chart showing an example of the operation of the distance measuring sensor according to the second modified example. [Figure 13] FIG. 13 is a circuit diagram of a distance measuring sensor according to a third modified example. [Figure 14] FIG. 11 is a configuration diagram of a light detection device according to a second embodiment. [Figure 15] FIG. 11 is a plan view of a portion of an image sensor according to a second embodiment. [Figure 16] 10 is a timing chart showing an example of the operation of the image sensor according to the second embodiment. [Figure 17] 13 is a diagram for explaining a gating function of the photodetector according to the second embodiment. FIG. [Figure 18] 10 is a timing chart showing an example of the operation of the image sensor according to the modified example of the second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] Hereinafter, an embodiment of the present disclosure will be described in detail with reference to the drawings. In the following description, the same or corresponding elements are designated by the same reference numerals, and duplicated description will be omitted. [First embodiment] [Configuration of distance measuring device]

[0020] 1, the distance measuring device (light detection device) 1 includes a light source 2, a distance measuring sensor (distance measuring image sensor, light sensor) 10A, a signal processing unit 3, a control unit 4, and a display unit 5. The distance measuring device 1 is a device that obtains a distance image of an object OJ (an image including information on a distance d to the object OJ) using an indirect TOF method.

[0021] The light source 2 emits pulsed light (detection light) L. The light source 2 is, for example, an infrared LED. The pulsed light L is, for example, near-infrared light, and the frequency of the pulsed light L is, for example, 10 kHz or more. The distance measurement sensor 10A detects the pulsed light L emitted from the light source 2 and reflected by the object OJ. The distance measurement sensor 10A is configured by monolithically forming a pixel unit 11 and a CMOS readout circuit unit 12 on a semiconductor substrate (for example, a silicon substrate). The distance measurement sensor 10A is mounted on a signal processing unit 3.

[0022] The signal processing unit 3 controls the pixel unit 11 and CMOS readout circuit unit 12 of the distance measurement sensor 10A. The signal processing unit 3 performs predetermined processing on the signal output from the distance measurement sensor 10A to generate a detection signal. The control unit 4 controls the light source 2 and the signal processing unit 3. The control unit 4 generates a distance image of the object OJ based on the detection signal output from the signal processing unit 3. The display unit 5 displays the distance image of the object OJ generated by the control unit 4. [Distance sensor configuration]

[0023] As shown in FIG. 2 and FIG. 3, the distance measurement sensor 10A includes a semiconductor layer 20 and an electrode layer 40 in the pixel section 11. The semiconductor layer 20 has a first surface 20a and a second surface 20b. The first surface 20a is a surface on one side in the thickness direction of the semiconductor layer 20. The second surface 20b is a surface on the other side in the thickness direction of the semiconductor layer 20. The electrode layer 40 is provided on the first surface 20a of the semiconductor layer 20. The semiconductor layer 20 and the electrode layer 40 configure a plurality of pixels 11a arranged along the first surface 20a. In the distance measurement sensor 10A, the plurality of pixels 11a are two-dimensionally arranged along the first surface 20a. Hereinafter, the thickness direction of the semiconductor layer 20 is referred to as the Z direction, a direction perpendicular to the Z direction is referred to as the X direction, and a direction perpendicular to both the Z direction and the X direction is referred to as the Y direction. In addition, one side in the Z direction is referred to as the first side, and the other side in the Z direction (opposite to the first side) is referred to as the second side. In addition, in Fig. 2, the arrangement of charge accumulation regions P1 to P4, overflow regions Q1 to Q4, unnecessary charge discharge region R, photogate electrodes PG, transfer gate electrodes TX1 to TX4, overflow gate electrodes OV1 to OV4, and unnecessary charge transfer gate electrodes RG, which will be described later, is shown typically, and other elements are omitted as appropriate.

[0024] Each pixel 11a has a semiconductor region 21, an avalanche multiplication region 22, a charge distribution region 23, a first charge accumulation region P1, a second charge accumulation region P2, a third charge accumulation region P3, a fourth charge accumulation region P4, a first overflow region Q1, a second overflow region Q2, a third overflow region Q3, a fourth overflow region Q4, two unnecessary charge discharge regions R, a well region 31, and a barrier region 32 in a semiconductor layer 20. Each of the regions 21 to 23, P1 to P4, Q1 to Q4, R, 31, and 32 is formed by carrying out various processes (e.g., etching, film formation, impurity injection, etc.) on a semiconductor substrate (e.g., a silicon substrate).

[0025] The semiconductor region 21 is a p-type (first conductivity type) region and is provided along the second surface 20b of the semiconductor layer 20. The semiconductor region 21 functions as a light absorption region (photoelectric conversion region). As an example, the semiconductor region 21 has a size of 1×10 15 cm -3 It is a p-type region having the following carrier concentration, and its thickness is about 10 μm. Note that the avalanche multiplication region 22 and the like also function as a light absorption region (photoelectric conversion region).

[0026] The avalanche multiplication region 22 includes a first multiplication region 22a and a second multiplication region 22b. The first multiplication region 22a is a p-type region, and is formed on the first side of the semiconductor region 21 in the semiconductor layer 20. As an example, the first multiplication region 22a has a dopant concentration of 1×10 16 cm -3 The second multiplication region 22b is a p-type region having a carrier concentration of 1×10 or more and a thickness of about 1 μm. The second multiplication region 22b is an n-type (second conductivity type) region, and is formed on the first side of the first multiplication region 22a in the semiconductor layer 20. As an example, the second multiplication region 22b has a carrier concentration of 1×10 16 cm -3 The avalanche multiplication region 22 is an n-type region having a carrier concentration of 1 μm or more, and has a thickness of about 1 μm. The first multiplication region 22a and the second multiplication region 22b form a pn junction. The avalanche multiplication region 22 is a region that causes avalanche multiplication. When a predetermined reverse bias is applied, the electric field strength generated in the avalanche multiplication region 22 is, for example, 3×10 5 ~4×10 5 V / cm.

[0027] The charge distributing region 23 is an n-type region and is formed on the first side of the second multiplication region 22b in the semiconductor layer 20. As an example, the charge distributing region 23 has a capacitance of 5×10 15 ~1×10 16 cm -3 The n-type region has a carrier concentration of about 1 μm and a thickness of about 1 μm.

[0028] Each of the charge accumulation regions P1 to P4 is an n-type region, and is formed on the first side of the second multiplication region 22b in the semiconductor layer 20. Each of the charge accumulation regions P1 to P4 is connected to the charge distribution region 23. As an example, each of the first charge accumulation regions P1 to P4 has a charge distribution region 23 of 1×10 18 cm -3 It is an n-type region having a carrier concentration of 1000 or more and a thickness of about 0.2 μm.

[0029] Each of the overflow regions Q1 to Q4 is an n-type region and is formed on the first side of the second multiplication region 22b in the semiconductor layer 20. The charge storage capacity of the first overflow region Q1 is larger than that of the first charge storage region P1. The charge storage capacity of the second overflow region Q2 is larger than that of the second charge storage region P2. The charge storage capacity of the third overflow region Q3 is larger than that of the third charge storage region P3. The charge storage capacity of the fourth overflow region Q4 is larger than that of the fourth charge storage region P4. For example, the charge storage capacities of the charge storage regions P1 to P4 are equal to each other, and the charge storage capacities of the overflow regions Q1 to Q4 are equal to each other. While the PN junction capacitance is used in the charge storage regions P1 to P4, the overflow regions Q1 to Q4 are provided with additional capacitance, so that the storage capacity is larger than that of the charge storage regions P1 to P4. Examples of the capacitance to be added include a MIM (Metal Insulator Metal) capacitance, a MOS capacitance, a trench capacitance, and a PIP capacitance.

[0030] Each of the unwanted charge discharging regions R is an n-type region, and is formed on a first side of the second multiplication region 22b in the semiconductor layer 20. Each of the unwanted charge discharging regions R is connected to the charge distributing region 23. The unwanted charge discharging region R has a configuration similar to that of, for example, the charge accumulation regions P1 to P4.

[0031] The well region 31 is a p-type region, and is formed on the first side of the second multiplication region 22b in the semiconductor layer 20. The well region 31 surrounds the charge distribution region 23 when viewed from the Z direction. The well region 31 configures a plurality of readout circuits (e.g., source follower amplifiers, reset transistors, etc.). The plurality of readout circuits are electrically connected to the charge accumulation regions P1 to P4 and the overflow regions Q1 to Q4, respectively. As an example, the well region 31 has a capacitance of 1×10 16 ~5×10 17 cm -3 The p-type region has a carrier concentration of about 1 μm and a thickness of about 1 μm.

[0032] The barrier region 32 is an n-type region and is formed between the second multiplication region 22b and the well region 31 in the semiconductor layer 20. The barrier region 32 includes the well region 31 when viewed from the Z direction. That is, the well region 31 is located within the barrier region 32 when viewed from the Z direction. The barrier region 32 surrounds the charge distribution region 23. The concentration of n-type impurities in the barrier region 32 is higher than the concentration of n-type impurities in the second multiplication region 22b. As an example, the barrier region 32 is an n-type region having a carrier concentration ranging from the carrier concentration of the second multiplication region 22b to about twice the carrier concentration of the second multiplication region 22b, and has a thickness of about 1 μm. Since the barrier region 32 is formed between the second multiplication region 22b and the well region 31, even if a depletion layer formed in the avalanche multiplication region 22 spreads toward the well region 31 due to application of a high voltage to the avalanche multiplication region 22, the depletion layer is prevented from reaching the well region 31. In other words, it is possible to prevent a current from flowing between the avalanche multiplication region 22 and the well region 31 due to the depletion layer reaching the well region 31.

[0033] Here, the positional relationship between the regions will be described. The first charge accumulation region P1 faces the second charge accumulation region P2 in the X direction, sandwiching the charge distribution region 23 therebetween. The first overflow region Q1 is disposed on the opposite side of the first charge accumulation region P1 to the charge distribution region 23. The second overflow region Q2 is disposed on the opposite side of the second charge accumulation region P2 to the charge distribution region 23.

[0034] The third charge accumulation region P3 faces the fourth charge accumulation region P4 in the X direction, sandwiching the charge distribution region 23 therebetween. The third overflow region Q3 is disposed on the opposite side of the charge distribution region 23 with respect to the third charge accumulation region P3. The fourth overflow region Q4 is disposed on the opposite side of the charge distribution region 23 with respect to the fourth charge accumulation region P4. The first charge accumulation region P1 and the fourth charge accumulation region P4 are aligned in the Y direction. The second charge accumulation region P2 and the third charge accumulation region P3 are aligned in the Y direction. The first overflow region Q1 and the fourth overflow region Q4 are aligned in the Y direction. The second overflow region Q2 and the third overflow region Q3 are aligned in the Y direction. The two unnecessary charge discharge regions R face each other in the Y direction, sandwiching the charge distribution region 23 therebetween.

[0035] Each pixel 11a has a photogate electrode PG, a first transfer gate electrode TX1, a second transfer gate electrode TX2, a third transfer gate electrode TX3, a fourth transfer gate electrode TX4, a first overflow gate electrode OV1, a second overflow gate electrode OV2, a third overflow gate electrode OV3, a fourth overflow gate electrode OV4, and two unnecessary charge transfer gate electrodes RG in the electrode layer 40. The gate electrodes PG, TX1 to TX4, OV1 to OV4, and RG are formed on the first surface 20a of the semiconductor layer 20 via an insulating film 41. The insulating film 41 is, for example, a silicon nitride film, a silicon oxide film, or the like.

[0036] The photogate electrode PG is disposed on the charge distribution region 23. The photogate electrode PG is formed of a material (e.g., polysilicon) having electrical conductivity and optical transparency. As an example, the photogate electrode PG has a rectangular shape having two sides facing each other in the X direction and two sides facing each other in the Y direction when viewed from the Z direction. Of the semiconductor region 21, the avalanche multiplication region 22, and the charge distribution region 23, the region directly below the photogate electrode PG functions as a charge generation region 24 that generates charges in response to incident light. In other words, the photogate electrode PG is disposed on the charge generation region 24. In the charge generation region 24, the charges generated in the semiconductor region 21 are multiplied in the avalanche multiplication region 22 and distributed in the charge distribution region 23. Unlike the embodiment, when the pulsed light L is incident on the semiconductor layer 20 from the counter electrode 50 side (in the case of backside incidence), the photogate electrode PG may not have optical transparency. The region directly below the photogate electrode PG is a region that overlaps with the photogate electrode PG when viewed from the Z direction. This also applies to the other gate electrodes TX1 to TX4, OV1 to OV4, and RG.

[0037] The first transfer gate electrode TX1 is disposed on a region between the charge generation region 24 and the first charge storage region P1 in the charge distribution region 23. The second transfer gate electrode TX2 is disposed on a region between the charge generation region 24 and the second charge storage region P2 in the charge distribution region 23. The third transfer gate electrode TX3 is disposed on a region between the charge generation region 24 and the third charge storage region P3 in the charge distribution region 23. The fourth transfer gate electrode TX4 is disposed on a region between the charge generation region 24 and the fourth charge storage region P4 in the charge distribution region 23.

[0038] Each of the transfer gate electrodes TX1 to TX4 is made of a conductive material (e.g., polysilicon). As an example, each of the transfer gate electrodes TX1 to TX4 has a rectangular shape having two sides facing each other in the X direction and two sides facing each other in the Y direction when viewed from the Z direction.

[0039] The first overflow gate electrode OV1 is disposed on a region between the first charge storage region P1 and the first overflow region Q1 in the well region 31. The second overflow gate electrode OV2 is disposed on a region between the second charge storage region P2 and the second overflow region Q2 in the well region 31. The third overflow gate electrode OV3 is disposed on a region between the third charge storage region P3 and the third overflow region Q3 in the well region 31. The fourth overflow gate electrode OV4 is disposed on a region between the fourth charge storage region P4 and the fourth overflow region Q4 in the well region 31.

[0040] Each of the overflow gate electrodes OV1 to OV4 is made of a conductive material (e.g., polysilicon). As an example, each of the overflow gate electrodes OV1 to OV4 has a rectangular shape having two sides facing each other in the X direction and two sides facing each other in the Y direction when viewed from the Z direction.

[0041] One of the unnecessary charge transfer gate electrodes RG is disposed on a region between the charge generating region 24 in the charge distribution region 23 and one of the pair of unnecessary charge discharging regions R. The other of the unnecessary charge transfer gate electrodes RG is disposed on a region between the charge generating region 24 in the charge distribution region 23 and the other of the pair of unnecessary charge discharging regions R. Each unnecessary charge transfer gate electrode RG is formed of a conductive material (e.g., polysilicon). As an example, each unnecessary charge transfer gate electrode RG has a rectangular shape when viewed from the Z direction, having two sides facing each other in the X direction and two sides facing each other in the Y direction.

[0042] The distance measuring sensor 10A further includes a counter electrode 50 and a wiring layer 60 in the pixel section 11. The counter electrode 50 is provided on the second surface 20b of the semiconductor layer 20. The counter electrode 50 includes a plurality of pixels 11a when viewed from the Z direction. The counter electrode 50 faces the electrode layer 40 in the Z direction. The counter electrode 50 is formed of, for example, a metal material. The wiring layer 60 is provided on the first surface 20a of the semiconductor layer 20 so as to cover the electrode layer 40. The wiring layer 60 is electrically connected to each pixel 11a and the CMOS readout circuit section 12 (see FIG. 1). A light incident opening 60a is formed in a portion of the wiring layer 60 facing the photogate electrode PG of each pixel 11a.

[0043] An example of the circuit configuration of each pixel 11a is shown in Fig. 4. As shown in Fig. 4, each pixel 11a has a plurality of (four in this example) reset transistors RST connected to the overflow regions Q1 to Q4, respectively, and a plurality of (four in this example) selection transistors SEL used to select the pixel 11a. [Distance sensor driving method]

[0044] An operation example of the distance measurement sensor 10A will be described with reference to Figures 5 and 6. The following operation is realized by the control unit 4 controlling the driving of the distance measurement sensor 10A. In each pixel 11a of the distance measurement sensor 10A, a negative voltage (e.g., -50V) is applied to the counter electrode 50 with respect to the potential of the photogate electrode PG (i.e., a reverse bias is applied to the pn junction formed in the avalanche multiplication region 22), and a charge of 3 x 10 is applied to the avalanche multiplication region 22. 5 ~4×10 5 In this state, when pulsed light L is incident on the semiconductor layer 20 through the light incident opening 60a and the photogate electrode PG, electrons generated by absorption of the pulsed light L are multiplied in the avalanche multiplication region 22 and move at high speed to the charge distribution region 23.

[0045] When generating a distance image of the object OJ (see FIG. 1), first, a reset process (reset step) is executed in which a reset voltage is applied to each reset transistor RST of each pixel 11a. The reset voltage is a positive voltage with respect to the potential of the photogate electrode PG. As a result, the charges accumulated in the charge accumulation regions P1 to P4 and the overflow regions Q1 to Q4 are discharged to the outside, and the charge accumulation regions P1 to P4 and the overflow regions Q1 to Q4 are no longer accumulated (time T1, FIG. 6(a)). The charges are discharged to the outside via, for example, a readout circuit constituted by the well region 31 and the like, and the wiring layer 60. The operation will be described below with a focus on one selected pixel 11a.

[0046] After the reset process, charges are accumulated in the charge accumulation regions P1 to P4 and the overflow regions Q1 to Q4 during the accumulation period T2 (FIG. 6(b)). During the accumulation period T2, charge transfer signals having mutually different phases are applied to the transfer gate electrodes TX1 to TX4. This executes a charge distribution process (charge distribution step) in which the charges generated in the charge generation region 24 are distributed among the charge accumulation regions P1 to P4.

[0047] As an example, the charge transfer signal applied to the first transfer gate electrode TX1 is a voltage signal in which positive and negative voltages are alternately repeated with respect to the potential of the photogate electrode PG, and is a voltage signal having the same period, pulse width, and phase as the intensity signal of the pulsed light L emitted from the light source 2 (see FIG. 1). The charge transfer signals applied to the second transfer gate electrode TX2, the third transfer gate electrode TX3, and the fourth transfer gate electrode TX4 are voltage signals identical to the pulse voltage signal applied to the first transfer gate electrode TX1, except that their phases are shifted by 90°, 180°, and 270°, respectively.

[0048] In the first period in which a positive voltage is applied to the first transfer gate electrode TX1, the potential φ TX1 is the potential φ in the region (charge generating region 24) directly below the photogate electrode PG. PGIn other words, in the first period, the potential φ TX1 is the potential φ PG A potential is applied to the photogate electrode PG and the first transfer gate electrode TX1 so that the potential φ is lower than the potential φ when a positive voltage is applied to the first transfer gate electrode TX1. This causes the charges generated in the charge generation region 24 to be transferred to the first charge accumulation region P1 (first charge transfer process, first charge transfer step). In FIG. 6(b), the potential φ when a positive voltage is applied to the first transfer gate electrode TX1 is TX1 is indicated by a dashed line, and the potential φ TX1 is indicated by a solid line. Moreover, the charges stored in the first charge storage region P1 and the first overflow region Q1 are indicated by hatching.

[0049] In addition, when adjusting the magnitude of the potential in the region immediately below the gate electrode, the magnitude of the potential applied to the gate electrode may be adjusted, or alternatively or in addition, the carrier concentration in the region immediately below the gate electrode may be adjusted. PG is set to a predetermined height by adjusting the carrier concentration, the photogate electrode PG does not need to be provided. In this case, the above-mentioned negative voltage does not necessarily need to be applied.

[0050] In the first period, a negative voltage is applied to the second to fourth transfer gate electrodes TX2 to TX4, and the potential φ TX2 , the potential φ of the region immediately below the third transfer gate electrode TX3 TX3 , and the potential φ TX4 But the potential φ PG As a result, a potential barrier is generated between the charge generation region 24 and the second to fourth charge storage regions P2 to P4, and the charges generated in the charge generation region 24 are not transferred to the second to fourth charge storage regions P2 to P4. In other words, in the first period, each potential φ TX2 ,φ TX3 and φTX4 is the potential φ PG A potential is applied to the photogate electrode PG and the second to fourth transfer gate electrodes TX2 to TX4 so that the potential becomes higher than .

[0051] Furthermore, in the first period, the potential φ OV1 is the potential φ of the region (charge generating region 24) directly below the photogate electrode PG. PG In other words, the potential applied to the first overflow gate electrode OV1 in the first period is lower than the potential φ OV1 is the potential φ PG 6(b), even if the first charge accumulation region P1 is saturated with charges, the charges overflowing from the first charge accumulation region P1 flow into the first overflow region Q1 and are accumulated in the first overflow region Q1.

[0052] In the second period in which a positive voltage is applied to the second transfer gate electrode TX2, the potential φ TX2 is the potential φ in the region (charge generating region 24) directly below the photogate electrode PG. PG In other words, in the second period, the potential φ TX2 is the potential φ PG A potential is applied to the photogate electrode PG and the second transfer gate electrode TX2 so that the potential φ is lower than the potential φ. This causes the charges generated in the charge generation region 24 to be transferred to the second charge accumulation region P2 (first charge transfer process, first charge transfer step). In the second period, each potential φ TX1 ,φ TX3 and φ TX4 is the potential φ PG A potential is applied to the photogate electrode PG and the first, third and fourth transfer gate electrodes TX1, TX3 and TX4 so that the potential becomes higher than .

[0053] Furthermore, in the second period, the potential φ OV2 is the potential φ of the region (charge generating region 24) directly below the photogate electrode PG. PG A potential is applied to the photogate electrode PG and the second overflow gate electrode OV2 so that the potential Vout is lower than Vout 1. As a result, even if the second charge accumulation region P2 is saturated with charges, the charges overflowing from the second charge accumulation region P2 flow into the second overflow region Q2 and are accumulated in the second overflow region Q2.

[0054] In the third period in which a positive voltage is applied to the third transfer gate electrode TX3, the potential φ TX3 is the potential φ in the region (charge generating region 24) directly below the photogate electrode PG. PG In other words, in the third period, the potential φ TX3 is the potential φ PG A potential is applied to the photogate electrode PG and the third transfer gate electrode TX3 so that the potential φ is lower than the potential φ. This causes the charges generated in the charge generation region 24 to be transferred to the third charge accumulation region P3 (first charge transfer process, first charge transfer step). In the third period, each potential φ TX1 ,φ TX2 and φ TX4 is the potential φ PG A potential is applied to the photogate electrode PG and the first, second and fourth transfer gate electrodes TX1, TX2 and TX4 so that the potential becomes higher than .

[0055] Furthermore, in the third period, the potential φ OV3 is the potential φ of the region (charge generating region 24) directly below the photogate electrode PG. PGA potential is applied to the photogate electrode PG and the third overflow gate electrode OV3 so that the potential Vout is lower than Vout 1. As a result, even if the third charge accumulation region P3 is saturated with charges, the charges overflowing from the third charge accumulation region P3 flow into the third overflow region Q3 and are accumulated in the third overflow region Q3.

[0056] In the fourth period in which a positive voltage is applied to the fourth transfer gate electrode TX4, the potential φ TX4 is the potential φ in the region (charge generating region 24) directly below the photogate electrode PG. PG In other words, in the fourth period, the potential φ TX4 is the potential φ PG A potential is applied to the photogate electrode PG and the fourth transfer gate electrode TX4 so that the potential φ is lower than the potential φ. This causes the charges generated in the charge generation region 24 to be transferred to the fourth charge accumulation region P4 (first charge transfer process, first charge transfer step). In the fourth period, each potential φ TX1 ~φ TX3 is the potential φ PG A potential is applied to the photogate electrode PG and the first to third transfer gate electrodes TX1 to TX3 so that the potential becomes higher than .

[0057] Furthermore, in the fourth period, the potential φ OV4 is the potential φ of the region (charge generating region 24) directly below the photogate electrode PG. PG A potential is applied to the photogate electrode PG and the fourth overflow gate electrode OV4 so that the potential Vout is lower than Vout 1. As a result, even if the fourth charge accumulation region P4 is saturated with charges, the charges overflowing from the fourth charge accumulation region P4 flow into the fourth overflow region Q4 and are accumulated in the fourth overflow region Q4.

[0058] After the charge allocation process in the accumulation period T2, a first readout process (high sensitivity readout process) (first readout step) is executed to read out the amount of charge accumulated in each of the charge accumulation regions P1 to P4 (time T3, FIG. 6(c)). The first readout process is executed after each of the process of transferring the charge generated in the charge generation region 24 to the first charge accumulation region P1, the process of transferring the charge generated in the charge generation region 24 to the second charge accumulation region P2, the process of transferring the charge generated in the charge generation region 24 to the third charge accumulation region P3, and the process of transferring the charge generated in the charge generation region 24 to the fourth charge accumulation region P4 is executed multiple times.

[0059] After the first read process, a voltage higher than the voltage applied in the first period is applied to the first overflow gate electrode OV1 to increase the potential φ of the region immediately below the first overflow gate electrode OV1. OV1 By lowering the potential φ, a charge transfer process (charge transfer step) (second charge transfer process, second charge transfer step) is performed to transfer the charges stored in the first charge storage region P1 to the first overflow region Q1 (FIG. 6(d)). In other words, in the charge transfer process, the potential φ OV1 By applying a potential to the first overflow gate electrode OV1 so that the potential Vcc decreases, the charges stored in the first charge storage region P1 are transferred to the first overflow region Q1.

[0060] Similarly, in the charge transfer process, the potential φ OV2 By applying a potential to the second overflow gate electrode OV2 so that the potential φ in the region immediately below the third overflow gate electrode OV3 is decreased, the charges stored in the second charge storage region P2 are transferred to the second overflow region Q2. OV3 By applying a potential to the third overflow gate electrode OV3 so that the potential φ in the region immediately below the fourth overflow gate electrode OV4 is decreased, the charges stored in the third charge storage region P3 are transferred to the third overflow region Q3. OV4By applying a potential to the fourth overflow gate electrode OV4 so that the potential drops, the charges stored in the fourth charge-storage region P4 are transferred to the fourth overflow region Q4.

[0061] After the charge transfer process, a second readout process (low-sensitivity readout process) (second readout step) is performed to read out the total amount of charge accumulated in the first charge accumulation region P1 and the first overflow region Q1 (time T4, FIG. 6(d)). Similarly, in the second readout process, the total amount of charge accumulated in the second charge accumulation region P2 and the second overflow region Q2 is read out. The total amount of charge accumulated in the third charge accumulation region P3 and the third overflow region Q3 is read out. The total amount of charge accumulated in the fourth charge accumulation region P4 and the fourth overflow region Q4 is read out. After the second readout process, the above-mentioned reset process is performed again (time T1, FIG. 6(a)), and the above-mentioned series of processes are repeatedly performed.

[0062] In addition, in periods other than the first to fourth periods, an unnecessary charge transfer process (unnecessary charge transfer step) is performed to transfer the charges generated in the charge generation region 24 to the unnecessary charge discharging region R. In the unnecessary charge transfer process, a positive voltage is applied to the unnecessary charge transfer gate electrode RG to reduce the potential φ RG is the potential φ in the region (charge generating region 24) directly below the photogate electrode PG. PG In other words, the potential φ RG is the potential φ PG A potential is applied to the photogate electrode PG and the unwanted charge transfer gate electrode RG so that the potential of the unwanted charge transfer gate electrode RG is lower than the potential of the unwanted charge transfer gate electrode RG. This causes the charges generated in the charge generation region 24 to be transferred to the unwanted charge discharge region R. The charges transferred to the unwanted charge discharge region R are discharged to the outside. For example, the unwanted charge discharge region R is connected to a fixed potential, and the charges transferred to the unwanted charge discharge region R are discharged to the outside without going through a readout circuit.

[0063] 1, when pulsed light L is emitted from the light source 2 and the pulsed light L reflected by the object OJ is detected by the distance measuring sensor 10A, the phase of the intensity signal of the pulsed light L detected by the distance measuring sensor 10A shifts in accordance with the distance d to the object OJ from the phase of the intensity signal of the pulsed light L emitted from the light source 2. Therefore, a distance image of the object OJ can be generated by acquiring, for each pixel 11a, a signal based on the amount of charge accumulated in the charge accumulation regions P1 to P4 and the overflow regions Q1 to Q4 (i.e., the amount of charge read out in the first readout process and the second readout process). [Actions and Effects of the First Embodiment]

[0064] In the distance measuring device 1, the distance measuring sensor 10A has a first overflow region Q1 having a charge storage capacity larger than that of the first charge storage region P1, a second overflow region Q2 having a charge storage capacity larger than that of the second charge storage region P2, a first overflow gate electrode OV1 arranged on a region between the first charge storage region P1 and the first overflow region Q1, and a second overflow gate electrode OV2 arranged on a region between the second charge storage region P2 and the second overflow region Q2. This allows the charge overflowing from the first charge storage region P1 to be stored in the first overflow region Q1, and the charge overflowing from the second charge storage region P2 to be stored in the second overflow region Q2. As a result, saturation of the storage capacity can be suppressed. Furthermore, during the first period in the charge distribution process, the potential φ of the region directly below the first overflow gate electrode OV1 is increased by 100%. OV1 is the potential φ of the charge generating region 24 PG During the second period of the charge distribution process, the potential φ OV2 is the potential φ of the charge generating region 24 PGThis makes it possible to prevent charges from remaining in the charge generation region 24 even when charges are accumulated in the first charge accumulation region P1 to the extent that they overflow into the first overflow region Q1, and when charges are accumulated in the second charge accumulation region P2 to the extent that they overflow into the second overflow region Q2. Therefore, the distance measuring device 1 can improve the accuracy of distance measurement. Also, it is possible to achieve high sensitivity and a wide dynamic range.

[0065] This point will be further described with reference to a comparative example shown in Figures 7 and 8. In the image sensor of the comparative example, the potential φ TX is the potential φ in the region directly below the photogate electrode PG. PG In addition, the potential φ of the region directly below the overflow gate electrode OV is set higher than the potential φ of the region directly below the overflow gate electrode OV throughout the entire accumulation period T2. OV is the potential φ in the region directly under the photogate electrode PG. PG After the accumulation period T2, the potential φ TX is the potential φ in the region (charge generating region) directly below the photogate electrode PG. PG and the charge accumulated in the charge generation region is transferred to the charge accumulation region P. After that, the amount of charge accumulated in the charge accumulation region P is read out (time T3, FIG. 8(c)).

[0066] In the image sensor of the comparative example, the potential φ OV is the potential φ in the region directly under the photogate electrode PG. PG 8(c), when the charge accumulation region P accumulates to the extent that the charge overflows into the overflow region Q, a part of the charge remains in the region (charge generation region) directly below the photogate electrode PG. In this case, the accuracy of distance measurement may be reduced due to the charge remaining in the charge accumulation region.

[0067] In contrast, as described above, in the distance measuring device 1, during the charge distribution process, the potential φ OV1 and the potential φ of the region immediately below the second overflow gate electrode OV2 OV2 is the potential φ of the charge generating region 24 PG This makes it possible to prevent the charges from remaining in the charge generation region 24 even if the charges are accumulated in the first charge accumulation region P1 or the second charge accumulation region P2 to the extent that they overflow into the first overflow region Q1 or the second overflow region Q2.

[0068] The control unit 4 executes a first charge transfer process for transferring the charges generated in the charge generation region 24 to the first charge accumulation region P1 a plurality of times, and then executes a first readout process for reading out the amount of charges accumulated in the charge accumulation region P1. This can improve the S / N ratio.

[0069] The charge generation region 24 includes the avalanche multiplication region 22. In this case, avalanche multiplication can be caused in the charge generation region 24, and the detection sensitivity of the distance measuring sensor 10A can be improved. On the other hand, when the charge generation region 24 includes the avalanche multiplication region 22, the amount of generated charge becomes extremely large. Even in such a case, the distance measuring device 1 can sufficiently suppress saturation of the storage capacitance and sufficiently suppress remaining charge in the charge generation region 24.

[0070] The control unit 4 executes a first readout process for reading out the amount of charge accumulated in the first charge accumulation region P1 and the second charge accumulation region P2, a second charge transfer process for transferring the charge accumulated in the first charge accumulation region P1 to the first overflow region Q1 and transferring the charge accumulated in the second charge accumulation region P2 to the second overflow region Q2, and a second readout process for reading out the total amount of charge accumulated in the first charge accumulation region P1 and the first overflow region Q1 and reading out the total amount of charge accumulated in the second charge accumulation region P2 and the second overflow region Q2. As a result, not only the amount of charge accumulated in the first and second charge accumulation regions P2 is read out in the first readout process, but also the total amount of charge accumulated in the first charge accumulation region P1 and the first overflow region Q1 and the total amount of charge accumulated in the second charge accumulation region P2 and the second overflow region Q2 are read out in the second readout process, so that the detection accuracy of the amount of charge can be improved.

[0071] The control unit 4 executes an unwanted charge transfer process in which the charge generated in the charge generation region 24 is transferred to the unwanted charge discharge region R by the unwanted charge transfer gate electrode RG during a period other than the first and second periods (i.e., a period other than the period in which the first charge transfer process is executed). This makes it possible to transfer the charge generated in the charge generation region 24 during a period other than the first and second periods to the unwanted charge discharge region R, thereby further suppressing the remaining charge in the charge generation region 24. The unwanted charge transfer process is particularly useful in an environment with a lot of disturbance light.

[0072] In the first period, the control unit 4 controls the potential φ TX1 is the potential φ of the region (charge generating region 24) directly below the photogate electrode PG. PG and the potential φ of the region immediately below the first overflow gate electrode OV1. OV1 is the potential φ in the region directly under the photogate electrode PG. PG The control unit 4 applies a potential to the photogate electrode PG and the first transfer gate electrode TX1 so that the potential φ TX2is the potential φ in the region directly under the photogate electrode PG. PG and the potential φ of the region immediately below the second overflow gate electrode OV2. OV2 is the potential φ in the region directly under the photogate electrode PG. PG The control unit 4 applies a potential to the photogate electrode PG and the second transfer gate electrode TX2 so that the potential φ TX3 is the potential φ in the region directly under the photogate electrode PG. PG and the potential φ of the region immediately below the third overflow gate electrode OV3. OV3 is the potential φ in the region directly under the photogate electrode PG. PG The control unit 4 applies a potential to the photogate electrode PG and the third transfer gate electrode TX3 so that the potential φ TX4 is the potential φ in the region directly under the photogate electrode PG. PG and the potential φ OV4 is the potential φ in the region directly under the photogate electrode PG. PG A potential is applied to the photogate electrode PG and the fourth transfer gate electrode TX4 so that the potential is lower than the potential Vp of the photogate electrode PG. This makes it possible to adjust the level of each potential with high precision.

[0073] The distance measuring sensor 10A has not only the first and second charge accumulation regions P1, P2, the first and second overflow regions Q1, Q2, the first and second transfer gate electrodes TX1, TX2, and the first and second overflow gate electrodes OV1, OV2, but also the third and fourth charge accumulation regions P3, P4, the third and fourth overflow regions Q3, Q4, the third and fourth transfer gate electrodes TX3, TX4, and the third and fourth overflow gate electrodes OV3, OV4. In the charge distribution process, the control unit 4 provides charge transfer signals having different phases to the transfer gate electrodes TX1 to TX4, thereby distributing the charges generated in the charge generation region 24 among the charge accumulation regions P1 to P4. This makes it possible to realize charge distribution by the first to fourth transfer gate electrodes TX1 to TX4, and improve the accuracy of distance measurement. [Modification of the first embodiment]

[0074] In the distance measuring sensor 10B according to the first modification shown in FIG. 9, the unnecessary charge discharging region R and the unnecessary charge transfer gate electrode RG are not provided in each pixel unit 11. The third charge accumulation region P3 faces the fourth charge accumulation region P4 in the Y direction via the charge generating region 24 (photogate electrode PG). The distance measuring sensor 10B is driven, for example, as shown in FIG. 10. In this driving method, the unnecessary charge transfer process for transferring the charge generated in the charge generating region 24 to the unnecessary charge discharging region R is not performed. As in the above embodiment, the first modification also makes it possible to suppress saturation of the storage capacitance and the remaining charge in the charge generating region 24, thereby improving the accuracy of distance measurement.

[0075] In the distance measuring sensor 10C according to the second modification shown in FIG. 11, the third and fourth charge accumulation regions P3, P4, the third and fourth overflow regions Q3, Q4, the third and fourth transfer gate electrodes TX3, TX4, and the third and fourth overflow gate electrodes OV3, OV4 are not provided in each pixel section 11. Each pixel section 11 has four unnecessary charge discharge regions R1, R2, R3, R4 and four unnecessary charge transfer gate electrodes RG. The unnecessary charge discharge regions R1, R2 face each other in the X direction via the charge generation region 24 (photogate electrode PG). The unnecessary charge discharge regions R3, R4 face each other in the X direction via the charge generation region 24. The unnecessary charge discharge regions R1, R4 face each other in the Y direction via the first charge accumulation region P1. The unnecessary charge discharge regions R2, R3 face each other in the Y direction via the second charge accumulation region P2.

[0076] The distance measuring sensor 10C is driven, for example, as shown in Fig. 12. In this driving method, in the accumulation period T2, a first period in which a positive voltage is applied to the first transfer gate electrode TX1, a second period in which a positive voltage is applied to the second transfer gate electrode TX2, and a period in which an unnecessary charge transfer process is performed in which charges generated in the charge generation region 24 are transferred to the unnecessary charge discharge region R are repeated in this order. This driving method can also generate a distance image of the object OJ. As in the above embodiment, the second modified example can also suppress saturation of the storage capacitance and residual charges in the charge generation region 24, thereby improving the accuracy of distance measurement.

[0077] As in the third modification shown in Fig. 13, the reset transistor RST may be disposed at a position different from that of the embodiment. In Fig. 13, only a part of the circuit configuration of the pixel 11a is shown. As in the above embodiment, the third modification also makes it possible to suppress saturation of the storage capacitance and residual charge in the charge generation region 24, thereby improving the accuracy of distance measurement. [Second embodiment]

[0078] 14, the light detection device 100 includes a light source 2, an image sensor 10D, a control unit 4, and an optical system 6. The light detection device 100 is configured as a range gate camera equipped with a gating function (shutter function) for detecting light arriving at a predetermined timing (predetermined period). The optical system 6 guides pulsed light L emitted from the light source 2 and reflected by an object OJ to a pixel unit 11 of the image sensor 10D.

[0079] 15, the image sensor 10D differs from the distance measuring sensor 10A described above in that the image sensor 10D does not include the second to fourth charge accumulation regions P2 to P4, the second to fourth overflow regions Q2 to Q4, the second to fourth transfer gate electrodes TX2 to TX4, and the second to fourth overflow gate electrodes OV2 to OV4. In the image sensor 10D, the first charge accumulation region P1 and the unnecessary charge discharge region R are disposed on one side in the X direction with respect to the charge generation region 24 (photogate electrode PG). The first charge accumulation region P1 and the unnecessary charge discharge region R are aligned in the Y direction. The first transfer gate electrode TX1 and the unnecessary charge transfer gate electrode RG are aligned in the Y direction.

[0080] The photodetector 100 is driven, for example, as shown in Fig. 16. In this driving method, instead of the charge distribution process, a first charge transfer process (first charge transfer step) is repeatedly executed in the accumulation period T2 to transfer the charges generated in the charge generation region 24 to the first charge accumulation region P1. As an example, the charge transfer signal applied to the first transfer gate electrode TX1 is a voltage signal in which positive and negative voltages are alternately repeated with respect to the potential of the photogate electrode PG, and is a voltage signal having the same period and pulse width as the intensity signal of the pulsed light L emitted from the light source 2, except that the phase is shifted by a predetermined amount.

[0081] During the period in which a positive voltage is applied to the first transfer gate electrode TX1, the potential φ TX1 is the potential φ in the region (charge generating region 24) directly below the photogate electrode PG. PGIn other words, during this period, the potential φ TX1 is the potential φ PG A potential is applied to the photogate electrode PG and the first transfer gate electrode TX1 so that the potential therebetween is lower than 1. This causes the charges generated in the charge generation region 24 to be transferred to the first charge accumulation region P1.

[0082] On the other hand, during a period in which a negative voltage is applied to the first transfer gate electrode TX1, the potential φ TX1 is the potential φ in the region (charge generating region 24) directly below the photogate electrode PG. PG In other words, during this period, the potential φ TX1 is the potential φ PG A potential is applied to the photogate electrode PG and the first transfer gate electrode TX1 so that the potential between the photogate electrode PG and the first transfer gate electrode TX1 and the first charge accumulation region P1 is higher than the potential between the photogate electrode PG and the first charge accumulation region P1 and the first charge accumulation region P1 is higher than the potential between the photogate electrode PG and the first transfer gate electrode TX1. As a result, a potential barrier is generated between the charge generation region 24 and the first charge accumulation region P1, and the charges generated in the charge generation region 24 are not transferred to the first charge accumulation region P1.

[0083] Furthermore, in the accumulation period T2, the potential φ OV1 is the potential φ of the region (charge generating region 24) directly below the photogate electrode PG. PG A potential is applied to the photogate electrode PG and the first overflow gate electrode OV1 so that the potential of the first overflow gate electrode OV1 is lower than the potential of the first overflow gate electrode OV1. As a result, even if the first charge accumulation region P1 is saturated with charges, the charges overflowing from the first charge accumulation region P1 flow into the first overflow region Q1 and are accumulated in the first overflow region Q1.

[0084] In addition, in a period other than the period in which the first charge transfer process is performed, an unnecessary charge transfer process (unnecessary charge transfer step) is performed in which the charge generated in the charge generation region 24 is transferred to the unnecessary charge discharging region R. In the unnecessary charge transfer process, the potential φ RG is the potential φ in the region (charge generating region 24) directly below the photogate electrode PG.PG A potential is applied to the photogate electrode PG and the unnecessary charge transfer gate electrode RG so that the potential Vcc is lower than the unwanted charge transfer gate electrode RG. This causes the charges generated in the charge generation region 24 to be transferred to the unnecessary charge discharging region R.

[0085] After the charge transfer process is performed multiple times during the accumulation period T2, a first readout process (high sensitivity readout process) (first readout step) is performed (time T3) to read out the charge amount stored in the first charge storage region P1. After the first readout process, a voltage higher than the voltage applied during the accumulation period T2 is applied to the first overflow gate electrode OV1 to increase the potential φ OV1 In other words, in the second charge transfer process, the potential φ is reduced to transfer the charges stored in the first charge storage region P1 to the first overflow region Q1. OV1 By applying a potential to the first overflow gate electrode OV1 so that the potential Vcc decreases, the charges accumulated in the first charge accumulation region P1 are transferred to the first overflow region Q1. After the second charge transfer process, a second readout process (low-sensitivity readout process) (second readout step) is performed to read out the total amount of charges accumulated in the first charge accumulation region P1 and the first overflow region Q1 (time T4).

[0086] With reference to FIG. 17, a gating function that can be realized by the above operation will be described. As in the example (1) shown in FIG. 17, when detecting the pulsed light L reflected in the vicinity of the object OJ1 that is a distance d1 away from the image sensor 10D, a voltage signal with a phase shift by an amount corresponding to the distance d1 is applied to the first transfer gate electrode TX1. This makes it possible to execute a first charge transfer process for transferring the charge generated in the charge generation region 24 to the first charge accumulation region P1 during the period when the pulsed light L reflected in the vicinity of the object OJ1 (i.e., within a range a predetermined distance away from the image sensor 10D) is incident on the charge generation region 24. As a result, it becomes possible to detect only the pulsed light L reflected in the vicinity of the object OJ1. Similarly, as in the examples (2) to (4) shown in FIG. 17, when detecting the pulsed light L reflected in a range a predetermined distance away from the image sensor 10D, a voltage signal with a phase shift by an amount corresponding to the distance is applied to the first transfer gate electrode TX1. In this way, a gating function for detecting only light arriving at a predetermined timing can be realized by the photodetector 100. The gating function can be suitably used for measuring, for example, the fluorescence lifetime. [Actions and Effects of the Second Embodiment]

[0087] In the photodetector 100, the image sensor 10D has a first overflow region Q1 having a charge storage capacity larger than that of the first charge storage region P1, and a first overflow gate electrode OV1 disposed on a region between the first charge storage region P1 and the first overflow region Q1. This allows the charge overflowing from the first charge storage region P1 to be stored in the first overflow region Q1, and saturation of the storage capacity can be suppressed. Furthermore, during the execution of the first charge transfer process for transferring the charge generated in the charge generation region 24 to the first charge storage region P1, the potential φ of the region directly below the first overflow gate electrode OV1 is OV1 is the potential φ of the charge generating region 24 PGThis makes it possible to prevent the charges from remaining in the charge generation region 24 even when the charges are accumulated in the first charge accumulation region P1 to the extent that they overflow into the first overflow region Q1. Therefore, the photodetector 100 can improve the detection accuracy.

[0088] The control unit 4 executes the first readout process after executing the first charge transfer process multiple times, thereby making it possible to improve the S / N ratio.

[0089] The charge generation region 24 includes the avalanche multiplication region 22. This allows avalanche multiplication to occur in the charge generation region 24, thereby improving the detection sensitivity of the image sensor 10D. On the other hand, when the charge generation region 24 includes the avalanche multiplication region 22, the amount of generated charge becomes extremely large. However, even in this case, the photodetector 100 can sufficiently suppress saturation of the storage capacitance and sufficiently suppress the remaining charge in the charge generation region 24.

[0090] The control unit 4 executes a second charge transfer process for transferring the charge accumulated in the first charge accumulation region P1 to the first overflow region Q1, and a second readout process for reading out the total amount of charge accumulated in the first charge accumulation region P1 and the first overflow region Q1. This not only reads out the amount of charge accumulated in the first charge accumulation region P1 in the first readout process, but also reads out the total amount of charge accumulated in the first charge accumulation region P1 and the first overflow region Q1 in the second readout process, thereby improving the detection accuracy of the amount of charge.

[0091] The control unit 4 executes an unwanted charge transfer process in which the charge generated in the charge generation region 24 is transferred to the unwanted charge discharge region R by the unwanted charge transfer gate electrode RG during a period other than the period in which the first charge transfer process is executed. This makes it possible to transfer the charge generated in the charge generation region 24 during a period other than the period in which the first charge transfer process is executed to the unwanted charge discharge region R, thereby further suppressing the remaining charge in the charge generation region 24. The unwanted charge transfer process is particularly useful in an environment with a lot of disturbance light.

[0092] The control unit 4 executes the first charge transfer process during a period in which the pulsed light L reflected by the object OJ is incident on the charge generation region 24. This makes it possible to accurately detect the amount of charge generated in the charge generation region 24 during a period in which the pulsed light L reflected by the object OJ is incident on the charge generation region 24. [Modification of the second embodiment]

[0093] As a modified example, in the image sensor 10D, each pixel unit 11 may not be provided with the unnecessary charge discharging region R and the unnecessary charge transfer gate electrode RG. The image sensor of this modified example is driven, for example, as shown in FIG. 18. In this driving method, the unnecessary charge transfer process for transferring the charge generated in the charge generating region 24 to the unnecessary charge discharging region R is not performed. This modified example also suppresses the saturation of the storage capacitance and the remaining charge in the charge generating region 24, as in the second embodiment, and improves the detection accuracy. The image sensor of this modified example can be suitably used, for example, in a case where disturbance light is unlikely to be incident on the charge generating region 24 during a period other than the period during which the first charge transfer process is performed. One example of such a case is a case where light detection is performed in a dark room.

[0094] The present disclosure is not limited to the above-described embodiment and modified examples. For example, the materials and shapes of each component are not limited to those described above, and various materials and shapes can be adopted. In the distance measuring sensors 10A, 10C and the image sensor 10D, the charges transferred to the unnecessary charge discharge regions R, R1 to R4 may be accumulated and read out without being discharged to the outside. That is, the unnecessary charge discharge regions R, R1 to R4 may function as charge accumulation regions. In this case, light other than the signal light (light not including distance information) can be read out and used.

[0095] The avalanche multiplication region 22 may not be formed in the semiconductor layer 20. That is, the charge generation region 24 may not include the avalanche multiplication region 22. At least one of the well region 31 and the barrier region 32 may not be formed in the semiconductor layer 20. The signal processing unit 3 may be omitted, and the control unit 4 may be directly connected to the distance measuring sensors 10A to 10C. The second charge transfer process and the second readout process may not be executed. The first readout process may be executed after the first charge transfer process is executed once.

[0096] In the distance measurement sensors 10A to 10C and the image sensor 10D, light can be incident on the semiconductor layer 20 from either the first side or the second side. For example, when light is incident on the semiconductor layer 20 from the second side, the counter electrode 50 may be formed of a material having electrical conductivity and optical transparency (e.g., polysilicon). In any of the distance measurement sensors 10A to 10C and the image sensor 10D, the p-type and n-type conductivity types may be reversed to those described above. In any of the distance measurement sensors 10A to 10C and the image sensor 10D, the multiple pixels 11a may be arranged one-dimensionally along the first surface 20a of the semiconductor layer 20. Each of the distance measurement sensors 10A to 10C and the image sensor 10D may have only a single pixel 11a. The charge storage capacity of the first overflow region Q1 may be equal to or less than the charge storage capacity of the first charge storage region P1. The charge storage capacity of the second overflow region Q2 may be equal to or less than the charge storage capacity of the second charge storage region P2. [Explanation of symbols]

[0097] 1... distance measuring device (photodetection device), 100... photodetection device, 2... light source, 4... control unit, 10A, 10B, 10C... distance measuring sensor (image sensor, photo sensor), 10D... image sensor (photosensor), 22... avalanche multiplication region, 24... charge generation region, P1... first charge accumulation region, P2... second charge accumulation region, P3... third charge accumulation region, P4... fourth charge accumulation region, Q1... first overflow region, Q2... second overflow region, Q3... third overflow region, Q4...fourth overflow region, R, R1, R2, R3, R4...unnecessary charge discharge region, PG...photogate electrode, TX1...first transfer gate electrode, TX2...second transfer gate electrode, TX3...third transfer gate electrode, TX4...fourth transfer gate electrode, OV1...first overflow gate electrode, OV2...second overflow gate electrode, OV3...third overflow gate electrode, OV4...fourth overflow gate electrode, RG...unnecessary charge transfer gate electrode.

Claims

1. An optical sensor; A control unit that controls the optical sensor, The optical sensor includes: a charge generating region that generates charges in response to incident light; a charge storage region; An overflow area; a transfer gate electrode disposed on a region between the charge generation region and the charge storage region; an overflow gate electrode disposed on a region between the charge storage region and the overflow region; The control unit is a first charge transfer process for transferring charges generated in the charge generation region to the charge accumulation region by applying a potential to the transfer gate electrode so that a potential of a region immediately below the transfer gate electrode becomes lower than a potential of the charge generation region; After the first charge transfer process, a first readout process is performed to read out the amount of charge stored in the charge storage region; In the first charge transfer process, a potential is applied to the overflow gate electrode so that a potential of a region directly below the overflow gate electrode becomes lower than a potential of the charge generating region.

2. The photodetector according to claim 1 , wherein the control unit executes the first readout process after executing the first charge transfer process a plurality of times.

3. The photodetection device of claim 1 or 2, wherein the charge generation region includes an avalanche multiplication region.

4. The control unit is a second charge transfer process for transferring the charges stored in the charge storage region to the overflow region by applying a potential to the overflow gate electrode so as to reduce a potential of a region immediately below the overflow gate electrode after the first read process; 4. The photodetector according to claim 1, further comprising: a second readout process for reading out a total amount of charge accumulated in the charge accumulation region and the overflow region, after the second charge transfer process.

5. The optical sensor includes: An unnecessary charge discharging region; an unwanted charge transfer gate electrode disposed on a region between the charge generating region and the unwanted charge discharging region; The control unit performs an unwanted charge transfer process to transfer charges generated in the charge generation region to the unwanted charge discharge region by applying a potential to the unwanted charge transfer gate electrode so that the potential of the region directly below the unwanted charge transfer gate electrode is lower than the potential of the charge generation region during a period other than the period during which the first charge transfer process is performed.The photodetection device of any one of claims 1 to 4.

6. A light source that emits detection light is further provided, 6. The light detection device according to claim 1, wherein the control unit executes the first charge transfer process during a period in which reflected light of the detection light from an object is incident on the charge generation region.

7. a photogate electrode disposed on the charge generation region; The photodetection device of any one of claims 1 to 6, wherein the control unit applies potentials to the photogate electrode and the overflow gate electrode in the first charge transfer process so that the potential of the region directly below the transfer gate electrode is lower than the potential of the charge generation region, and the potential of the region directly below the overflow gate electrode is lower than the potential of the charge generation region.

8. 8. The photodetector according to claim 1, wherein the overflow region has a charge storage capacity larger than a charge storage capacity of the charge storage region.

9. A method for driving an optical sensor, comprising the steps of: The optical sensor includes: a charge generating region that generates charges in response to incident light; a charge storage region; An overflow area; a transfer gate electrode disposed on a region between the charge generation region and the charge storage region; an overflow gate electrode disposed on a region between the charge storage region and the overflow region; The method of driving the optical sensor includes: a charge transfer step of transferring charges generated in the charge generation region to the charge accumulation region by applying a potential to the transfer gate electrode so that a potential of a region immediately below the transfer gate electrode becomes lower than a potential of the charge generation region; a read step of reading out the amount of charge stored in the charge storage region after the charge transfer step; The method for driving a photosensor includes applying a potential to the overflow gate electrode in the charge transfer step so that a potential of a region directly below the overflow gate electrode becomes lower than a potential of the charge generating region.

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