Optical Detection Device and Driving Method of Optical Sensor

Abstract

The optical detection device of the present invention includes an optical sensor and a control unit. The optical sensor has a charge generation region, a charge storage region, a charge transfer region, a charge collection electrode disposed on the charge storage region, and a transfer gate electrode disposed on a region between the charge storage region and the charge transfer region. The control unit controls the potentials of the charge collection electrode and the transfer gate electrode such that in a first period, the potential of the region directly below the charge collection electrode becomes a first level, and the potential of the region directly below the transfer gate electrode is higher than the potential of the region directly below the charge collection electrode, and in a second period after the first period, the potential of the region directly below the charge collection electrode becomes a second level higher than the first level, and the potential of the region directly below the transfer gate electrode is lower than the potential of the region directly below the charge collection electrode.

Description

Technical Field

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

[0002] As a light sensor, a structure is known that includes a charge generation region that generates charges according to incident light, a charge storage region that stores the charges generated in the charge generation region, a charge transfer region that transfers the charges from the charge storage region, and a transfer gate electrode disposed on a region between the charge storage region and the charge transfer region. (For example, refer to Patent Document 1). In such a light sensor, charges can be transferred from the charge storage region to the charge transfer region at high speed.

[0003] Prior Art Documents

[0004] Patent Documents

[0005] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2015-5752 Summary of the Invention

[0006] Problems to be Solved by the Invention

[0007] In the light sensor as described above, it is required to not only increase the saturation charge amount of the charge storage region but also improve the efficiency of charge transfer from the charge storage region to the charge transfer region.

[0008] An object of one aspect of the present invention is to provide a light detection device and a method for driving a light sensor that can achieve both an increase in the saturation charge amount and an improvement in charge transfer efficiency.

[0009] Means for Solving the Problems

[0010] A photodetection device according to an aspect of the present invention, comprising: a photosensor; and a control unit for controlling the photosensor, the photosensor including: a charge generation region that generates charges according to incident light; a charge accumulation region that accumulates the charges generated in the charge generation region; a charge transfer region that transfers charges from the charge accumulation region; a charge collection electrode disposed on the charge accumulation region; and a transfer gate electrode disposed on a region between the charge accumulation region and the charge transfer region, the control unit controls the potentials of the charge collection electrode and the transfer gate electrode such that in a first period, the potential of the region directly below the charge collection electrode becomes a first level, and the potential of the region directly below the transfer gate electrode is higher than the potential of the region directly below the charge collection electrode, and in a second period after the first period, the potential of the region directly below the charge collection electrode becomes a second level higher than the first level, and the potential of the region directly below the transfer gate electrode is lower than the potential of the region directly below the charge collection electrode.

[0011] In this photodetection device, in the first period, the potential of the region directly below the transfer gate electrode is higher than the potential of the region directly below the charge collection electrode, and the charges generated in the charge generation region are accumulated in the charge accumulation region. In the second period, the potential of the region directly below the transfer gate electrode is lower than the potential of the region directly below the charge collection electrode, and the charges are transferred from the charge accumulation region to the charge transfer region. In this photodetection device, in the first period, the potential of the region directly below the charge collection electrode is the first level lower than the second level. Thereby, the potential well of the charge accumulation region can be deepened, and the saturation charge amount of the charge accumulation region can be increased. On the other hand, in the second period, the potential of the region directly below the charge collection electrode is the second level higher than the first level. Thereby, the potential difference between the charge accumulation region and the charge transfer region can be increased, and the charge transfer efficiency can be improved. Thus, according to this photodetection device, both an increase in the saturation charge amount and an improvement in the charge transfer efficiency can be achieved.

[0012] The charge generation region may also be a saturated avalanche multiplication region. In this case, avalanche multiplication can be caused in the charge generation region, and the detection sensitivity can be improved. On the other hand, in this case, the amount of charges generated in the charge generation region becomes extremely large, and since in this photodetection device, as described above, the saturation charge amount increases, even in such a case, the saturation of the capacitance can be suppressed.

[0013] The photosensor may further include: an overflow region; and an overflow gate electrode disposed on a region between the charge storage region and the overflow region. During the first period, the control unit controls the potentials of the charge collection electrode, the transfer gate electrode, and the overflow gate electrode such that the potential of the region directly below the overflow gate electrode is higher than the potential of the region directly below the charge collection electrode and lower than the potential of the region directly below the transfer gate electrode. In this case, the charges overflowing from the charge storage region during the first period can be moved to the overflow region.

[0014] The photosensor may also have an intervening region having a conductivity type different from that of the charge storage region and disposed between the charge storage region and the charge collection electrode. In this case, generation of dark current near the charge collection electrode can be suppressed.

[0015] In a driving method of a photosensor according to an aspect of the present invention, the photosensor includes: a charge generation region that generates charges according to incident light; a charge storage region that stores the charges generated in the charge generation region; a charge transfer region that transfers charges from the charge storage region; a charge collection electrode disposed on the charge storage region; and a transfer gate electrode disposed on a region between the charge storage region and the charge transfer region. The driving method of the photosensor includes: a first step of controlling the potentials of the charge collection electrode and the transfer gate electrode such that the potential of the region directly below the charge collection electrode becomes a first level and the potential of the region directly below the transfer gate electrode is higher than the potential of the region directly below the charge collection electrode; and a second step, after the first step, of controlling the potentials of the charge collection electrode and the transfer gate electrode such that the potential of the region directly below the charge collection electrode becomes a second level higher than the first level and the potential of the region directly below the transfer gate electrode is lower than the potential of the region directly below the charge collection electrode.

[0016] In the first step of the driving method of the photosensor, the potential of the region directly below the transfer gate electrode is higher than the potential of the region directly below the charge collection electrode, and charges are stored in the charge storage region. In the second step, the potential of the region directly below the transfer gate electrode is lower than the potential of the region directly below the charge collection electrode, and charges are transferred from the charge storage region to the charge transfer region. In the first step, the potential of the region directly below the charge collection electrode is the first level lower than the second level. Thereby, the potential well of the charge storage region can be deepened, and the saturation charge amount of the charge storage region can be increased. On the other hand, in the second step, the potential of the region directly below the charge collection electrode is the second level higher than the first level. Thereby, the potential difference between the charge storage region and the charge transfer region can be increased, and the charge transfer efficiency can be improved. Thus, according to the driving method of the photosensor, both an increase in the saturation charge amount and an improvement in the charge transfer efficiency can be achieved.

[0017] Effect of the Invention

[0018] According to one aspect of the present invention, there can be provided an optical detection device and a driving method for an optical sensor that can achieve both an increase in the saturated charge amount and an improvement in the charge transfer efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is a structural diagram of the optical detection device according to the embodiment.

[0020] Figure 2 is along Figure 1 a cross-sectional view of the image sensor taken along line II-II shown in

[0021] Figure 3 is a diagram showing the connection method of the image sensor.

[0022] Figure 4 is a circuit diagram of the image sensor.

[0023] Figure 5 is a timing diagram showing an operation example of the image sensor.

[0024] Figure 6 (a) and (b) of

[0025] Figure 7 are potential distribution diagrams for explaining the operation example of the image sensor.

[0026] Figure 8 (a) and (b) of

[0027] Figure 9 is a potential distribution diagram for explaining the operation example of the image sensor.

[0028] Figure 10 (a) and (b) of

[0029] Figure 11 are potential distribution diagrams for explaining the first operation example of the image sensor according to the comparative example.

[0030] Figure 12 (a) and (b) of DETAILED DESCRIPTION OF THE INVENTION

[0031] Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings. In the following description, the same or corresponding elements are denoted by the same reference numerals, and repeated descriptions are omitted.

[0032] [Structure of the optical detection device]

[0033] As Figure 1 shown, the optical detection device 100 includes an image sensor (optical sensor) 1 and a control unit 60. The control unit 60 controls the image sensor 1. The control unit 60 is constituted by, for example, an on-chip integrated circuit mounted on a semiconductor substrate constituting the image sensor 1.

[0034] As Figure 1 and Figure 2 shown, the image sensor 1 includes a semiconductor layer 2 and an electrode layer 4. The semiconductor layer 2 has a first surface 2a and a second surface 2b. The second surface 2b is the surface of the semiconductor layer 2 on the side opposite to the first surface 2a. The semiconductor layer 2 includes a plurality of pixels 20 arranged along the first surface 2a. The plurality of pixels 20 are two-dimensionally arranged along the first surface 2a. Hereinafter, the thickness direction of the semiconductor layer 2 is referred to as the Z direction, one direction perpendicular to the Z direction is referred to as the X direction, and the 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 (the side opposite to the first side) is referred to as the second side. In Figure 1 , a part of the electrode layer 4 is omitted from the illustration.

[0035] Each pixel 20 has a semiconductor region 21, a semiconductor region 22, an avalanche multiplication region 23, a charge storage region 24, an intervening region 25, a charge transfer region 26, an overflow region 27, and a well region 31 in the semiconductor layer 2. Each of the regions 21 to 27, 31 is formed by performing various processes (such as etching, film formation, impurity implantation, etc.) on a semiconductor substrate (such as a silicon substrate).

[0036] The semiconductor region 21 is a p-type (first conductivity type) region, which is formed in a layer along the second surface 2b of the semiconductor layer 2. The carrier concentration of the semiconductor region 21 is higher than the carrier concentration of the semiconductor region 22. It is preferable that the thickness of the semiconductor region 21 is as thin as possible. As an example, the semiconductor region 21 is a p-type region having a carrier concentration of 1×10 16 cm -3 or more, and its thickness is about 1 μm. In addition, the semiconductor region 21 may also be formed by the accumulation of a transparent electrode formed on the second surface 2b with an insulating film interposed therebetween.

[0037] The semiconductor region 22 is a p-type region, which is formed in a layer in the semiconductor layer 2 and is located on the first side with respect to the semiconductor region 21. As an example, the semiconductor region 22 is a p-type region having a carrier concentration of 1×1015 cm -3 The p-type region with the following carrier concentration has a thickness of 2 μm or more, and is about 10 μm as an example.

[0038] The avalanche multiplication region 23 includes a first multiplication region 23a and a second multiplication region 23b. The first multiplication region 23a is a p-type region, which is formed in a layered manner in the semiconductor layer 2 and is located on the first side with respect to the semiconductor region 22. As an example, the first multiplication region 23a is a p-type region having a carrier concentration of 1×10 16 cm -3 or more, and has a thickness of about 1 μm. The second multiplication region 23b is an n-type (second conductivity type) region, which is formed in a layered manner in the semiconductor layer 2 and is located on the first side with respect to the first multiplication region 23a. As an example, the second multiplication region 23b is an n-type region having a carrier concentration of 1×10 16 cm -3 or more, and has a thickness of about 1 μm. A pn junction is formed between the first multiplication region 23a and the second multiplication region 23b. The semiconductor regions 21, 22, and the avalanche multiplication region 23 function as a charge generation region (light absorption region, photoelectric conversion region) 29 that generates charges according to incident light.

[0039] The charge storage region 24 is an n-type region, which is formed in a layered manner in the semiconductor layer 2 and is located on the first side with respect to the second multiplication region 23b. In this example, the charge storage region 24 extends along a plane perpendicular to the Z direction. As an example, the charge storage region 24 is an n-type region having a carrier concentration of 5×10 15 ~1×10 16 cm -3 or more, and has a thickness of about 1 μm.

[0040] The intervening region 25 is a p-type region, which is formed in a layered manner along the first surface 2a of the semiconductor layer 2. The intervening region 25 is disposed between the charge storage region 24 and a charge collection electrode 41 described later. The semiconductor region 21, the semiconductor region 22, the first multiplication region 23a, the second multiplication region 23b, the charge storage region 24, and the intervening region 25 are arranged in this order along the Z direction. As an example, the intervening region 25 is a p-type region having a carrier concentration of 1×10 15 cm -3 or more, and has a thickness of about 0.2 μm.

[0041] The charge transfer region 26 is an n-type region formed along the first surface 2a of the semiconductor layer 2. The charge transfer region 26 is disposed within the well region 31 and is located on the first side with respect to the second multiplication region 23b. The charge transfer region 26 is arranged in parallel with the charge storage region 24 in the X direction. As an example, the charge transfer region 26 is an n-type region having a carrier concentration of 1×10 18 cm -3 or more, and its thickness is about 0.2 μm.

[0042] The overflow region 27 is an n-type region formed along the first surface 2a of the semiconductor layer 2. The overflow region 27 is disposed within the well region 31 and is located on the first side with respect to the second multiplication region 23b. The overflow region 27 is located on the opposite side of the charge storage region 24 with respect to the charge transfer region 26 in the X direction. As an example, the overflow region 27 is an n-type region having a carrier concentration of 1×10 18 cm -3 or more, and its thickness is about 0.2 μm.

[0043] The well region 31 is a p-type region formed in a layer along the first surface 2a of the semiconductor layer 2. The well region 31 is located on the first side with respect to the second multiplication region 23b. As an example, the well region 31 is a p-type region having a carrier concentration of 1×10 16 to 5×10 17 cm -3 and its thickness is about 1 μm.

[0044] In the well region 31, not only the charge transfer region 26 and the overflow region 27 are formed, but also the channel regions 32, 33, 34, the grounding regions 35, 36, and the LOCOS (Local Oxidation of Silicon) region 37 are formed. The channel regions 32 to 34 are n-type regions, and the grounding regions 35, 36 are p-type regions. The charge transfer region 26, the channel regions 32 to 34, and the grounding region 35 are arranged in this order in the X direction. The grounding region 36 is located on the opposite side of the overflow region 27 with respect to the charge storage region 24 in the X direction. The LOCOS region 37 is an insulating region provided so as to surround the grounding regions 35, 36.

[0045] The electrode layer 4 is provided on the first surface 2a of the semiconductor layer 2. Each pixel 20 has a charge collection electrode 41, a transfer gate electrode 42, and an overflow gate electrode 43 in the electrode layer 4. The charge collection electrode 41 and the gate electrodes 42, 43 are formed in the electrode layer 4 and are disposed on the first surface 2a of the semiconductor layer 2 with an insulating film 49 interposed therebetween. The insulating film 49 is, for example, a silicon nitride film, a silicon oxide film, or the like.

[0046] The charge collection electrode 41 and the gate electrodes 42 and 43 are formed of a material having conductivity and translucency (e.g., polysilicon). As an example, each of the charge collection electrode 41 and the gate electrodes 42 and 43 is rectangular when viewed from the Z direction and has two sides opposite to each other in the X direction and two sides opposite to each other in the Y direction.

[0047] The charge collection electrode 41 is disposed on the charge storage region 24. More specifically, the charge collection electrode 41 is disposed on the charge storage region 24 with the intervening region 25 and the insulating film 49 therebetween. The charge collection electrode 41 overlaps the charge storage region 24 in the Z direction. The transfer gate electrode 42 is disposed on the region between the charge storage region 24 and the charge transfer region 26 of the well region 31. The overflow gate electrode 43 is disposed on the region between the charge storage region 24 and the overflow region 27 of the well region 31.

[0048] On the well region 31, gate electrodes 44, 45, and 46 are further provided. The gate electrode 44 is disposed on the region between the charge transfer region 26 and the channel region 32 of the well region 31. The gate electrode 45 is disposed on the region between the channel regions 32 and 33 of the well region 31. The gate electrode 46 is disposed on the region between the channel regions 33 and 34 of the well region 31.

[0049] As Figure 3 and Figure 4 shown, control voltages S1 to S5 are applied to the charge collection electrode 41 and the gate electrodes 42 to 44 and 46. The gate electrode 45 is electrically connected to the charge transfer region 26. The overflow region 27 and the channel region 32 are electrically connected to the power supply voltage. The channel region 34 is electrically connected to the output terminal. The grounding regions 35 and 36 are grounded. The potential of the well region 31 is 0 V. The second multiplication region 23b is fixed at a potential higher than 0 V through the charge storage region 24, the region directly below the overflow gate electrode 43, and the overflow region 27. By fixing the second multiplication region 23b at a potential higher than 0 V, the first multiplication region 23a is electrically separated from the well region 31.

[0050] The gate electrode 44 discharges the charge accumulated in the charge transfer region 26 to the outside through the channel region 32 and constitutes a reset transistor R1 for resetting the charge transfer region 26. The gate electrode 45 constitutes a readout transistor (source follower) R2 for reading out the charge accumulated in the charge transfer region 26. The gate electrode 46 constitutes a selection transistor R3 for selecting the pixel 20 for which charge readout is to be performed.

[0051] [Driving method of image sensor]

[0052] Refer to Figures 5 to 9, an operation example of the image sensor 1 is described. The following operations are implemented by controlling the image sensor 1 by the control unit 60. More specifically, they are implemented by controlling the control voltages S1 to S5 by the control unit 60. In addition, in the following description, the "region directly below the electrode" refers to the region overlapping with the electrode in the Z direction.

[0053] First, a first reset process for resetting the charge storage region 24 is executed (at time T1, Figure 6 as shown in (a)). In the first reset process, the potential of the region directly below the charge collection electrode 41 (charge storage region 24) is made high level (second level), and the potential of the region directly below the overflow gate electrode 43 is made lower than the potential to control the potentials of the charge collection electrode 41 and the overflow gate electrode 43. Thereby, the charges remaining in the charge storage region 24 are discharged to the outside through the overflow region 27, and the charge storage region 24 is reset. In the first reset process, the potential of the region directly below the transfer gate electrode 42 and the potential of the region directly below the gate electrode 44 are made higher than the potential to control the potentials of the charge collection electrode 41, the transfer gate electrode 42, and the gate electrode 44.

[0054] In addition, as Figure 5 shown, a high-level control voltage S2 and a low-level control voltage S2 are applied to the charge collection electrode 41. For example, the high-level control voltage S2 is a positive voltage, and the low-level control voltage S2 is a potential lower than the high-level control voltage S2. The low-level control voltage S2 can be either a positive potential or a negative potential. When the high-level control voltage S2 is applied to the charge collection electrode 41, the potential of the region directly below the charge collection electrode 41 becomes low level, and when the low-level control voltage S2 is applied to the charge collection electrode 41, the potential becomes high level. Thus, the magnitude relationship of the potentials is opposite to the magnitude relationship of the control voltages. The same applies to the transfer gate electrode 42, the overflow gate electrode 43, and the gate electrode 44. In addition, when adjusting the magnitude of the potential (depletion potential) of the region directly below the electrode, either the magnitude of the potential applied to the electrode can be adjusted, or the impurity concentration of the region directly below the electrode can be adjusted.

[0055] In the first period M1 after time T1, a charge storage process (first step) for storing the charges generated in the charge generation region 29 in the charge storage region 24 is executed (at time T2, Figure 6In (b) of this figure. During the first period M1, the potential of the region directly below the charge collection electrode 41 is made to be a low level (first level) lower than the above-mentioned high level (second level), and the potential of the region directly below the transfer gate electrode 42 is made higher than the potential . In this way, the potentials of the charge collection electrode 41 and the transfer gate electrode 42 are controlled.

[0056] During the first period M1, a voltage that is negative with respect to the potential of the well region 31 (for example, up to -60 V) is applied to the semiconductor region 21. That is, a reverse bias voltage is applied to the pn junction formed in the avalanche multiplication region 23. As a result, an electric field intensity of 3×10 5 ~4×10 5 V / cm is generated in the avalanche multiplication region 23. In this state, when light is incident on the semiconductor layer 2 from the second surface 2b, electrons are generated by the absorption of light in the semiconductor regions 21 and 22. The generated electrons are multiplied in the avalanche multiplication region 23 and move at high speed toward the charge storage region 24 having the highest potential.

[0057] As described above, during the first period M1, the potential of the region directly below the transfer gate electrode 42 is higher than the potential of the region directly below the transfer gate electrode 42 Therefore, the charges that have moved to the charge storage region 24 do not move to the charge transfer region 26 but are stored in the charge storage region 24.

[0058] In addition, during the first period M1, the potential of the region directly below the overflow gate electrode 43 is made higher than the potential of the region directly below the charge collection electrode 41 and lower than the potential of the region directly below the transfer gate electrode 42 . In this way, the potentials of the charge collection electrode 41, the transfer gate electrode 42, and the overflow gate electrode 43 are controlled. That is, the potential becomes the magnitude between the potential and the potential . As a result, as shown in (a) of Figure 7 , the charges that overflow from the charge storage region 24 can be made to move to the overflow region 27. The charges transferred to the overflow region 27 are discharged to the outside.

[0059] During the first period M1, pixel selection processing (at time T3) of the pixel 20 for selectively reading out charges is performed. In the pixel selection processing, the pixel 20 for reading out charges is selected using the selection transistor R3.

[0060] During the first period M1, following pixel selection processing, a second reset process for resetting the charge transfer region 26 is performed (at time T4, Figure 7 (b) of). The second reset process is performed using the reset transistor R1. In the second reset process, the potential of the region directly below the gate electrode 44 is controlled to decrease. The potential For example, it is decreased until it becomes the same level as the potential of the charge transfer region 26 . Thereby, the charge remaining in the charge transfer region 26 is discharged to the outside through the channel region 32, and the charge transfer region 26 is reset. After the second reset process is completed, the potential is restored.

[0061] During the first period M1, following the second reset process, a noise acquisition process is performed (at time T5). In the noise acquisition process, the kTC noise of the charge transfer region 26 is acquired. Thereby, the output can be calculated taking into account the kTC noise, and the detection accuracy can be improved.

[0062] In the second period M2 after the first period M1, a charge transfer process (second step) for transferring charge from the charge storage region 24 to the charge transfer region 26 is performed (at time T6, Figure 8 (a) of). In the second period M2, the potential of the region directly below the charge collection electrode 41 (charge storage region 24) is made high, and the potential of the region directly below the transfer gate electrode 42 is made lower than the potential and the potential of the region directly below the overflow gate electrode 43 is made higher than the potential to control the potentials of the charge collection electrode 41, the transfer gate electrode 42, and the overflow gate electrode 43. Thereby, the charge accumulated in the charge storage region 24 is transferred to the charge transfer region 26.

[0063] Next, a readout process for reading out the charge accumulated in the charge transfer region 26 is performed (at time T7, Figure 8 (b) of). In the readout process, the charge accumulated in the charge transfer region 26 is read out using the readout transistor R2. In the readout process, the potential of the region directly below the charge collection electrode 41 is made high, and the potential of the region directly below the transfer gate electrode 42 is made higher than the potential and the potential of the region directly below the overflow gate electrode 43 is made lower than the potential to control the potentials of the charge collection electrode 41, the transfer gate electrode 42, and the overflow gate electrode 43.

[0064] Next, a third reset process for resetting the charge transfer region 26 is performed (at time T8, Figure 9 ). The third reset process is performed using the reset transistor R1. In the third reset process, the potential of the gate electrode 44 is controlled in such a way that the potential of the region directly below the gate electrode 44 decreases. The potential decreases, for example, until it becomes the same level as the potential of the charge transfer region 26 . As a result, the charges remaining in the charge transfer region 26 are discharged to the outside through the channel region 32, and the charge transfer region 26 is reset. After the third reset process is completed, the potential is restored.

[0065] Next, a deselection process for deselecting the selected pixel 20 is performed (at time T9). The deselection process is performed using the selection transistor R3. After the deselection process, until the start of the next charge accumulation process, the image sensor 1 is in the same state as during the first reset process (at time T10). That is, the potential of the region directly below the charge collection electrode 41 is set to a high level, and the potential of the region directly below the transfer gate electrode 42 is higher than the potential and the potential of the region directly below the overflow gate electrode 43 is lower than the potential . In this way, the charges flowing into the charge accumulation region 24 are discharged to the outside through the overflow region 27.

[0066] [Function and Effect]

[0067] In the light detection device 100, during the first period M1, the potential of the region directly below the transfer gate electrode 42 is higher than the potential of the region directly below the charge collection electrode 41 (charge accumulation region 24) . The charges generated in the charge generation region 29 are accumulated in the charge accumulation region 24. During the second period M2, the potential of the region directly below the transfer gate electrode 42 is lower than the potential of the region directly below the charge collection electrode 41 . The charges are transferred from the charge accumulation region 24 to the charge transfer region 26. In the light detection device 100, during the first period M1, the potential of the region directly below the charge collection electrode 41 is a low level (the first level) lower than the high level (the second level). Thus, the potential well of the charge storage region 24 can be deepened, and the saturation charge amount of the charge storage region 24 can be increased. On the other hand, during the second period M2, the potential of the region directly below the charge collection electrode 41 is a high level higher than the low level. Thus, the potential difference between the charge storage region 24 and the charge transfer region 26 can be increased, and the charge transfer efficiency can be improved. Thus, according to the optical detection device 100, both an increase in the saturation charge amount and an improvement in the charge transfer efficiency can be achieved.

[0068] That is, in the optical detection device 100, by providing the charge collection electrode 41 on the charge storage region 24, the potential of the region directly below the charge collection electrode 41 is made to change in magnitude between the first period M1 and the second period M2, thereby achieving both an increase in the saturation charge amount and an improvement in the charge transfer efficiency. Regarding this point, further explanation will be given with reference to Figures 10 to 12 . In Figure 10 and Figure 11 , as a comparative example, an operation example of an image sensor in the case where the potential is constant is shown. In Figure 10 (a) and Figure 10 (b), a first operation example in which the potential is constant at a low level in the comparative example is shown. In Figure 11 (a) and Figure 11 (b), a second operation example in which the potential is constant at a high level in the comparative example is shown. In Figure 12 (a) and Figure 12 (b), an operation example of the image sensor 1 of the optical detection device 100 is shown. In addition, in Figures 10 to 12 , the illustration of the overflow region and the overflow gate electrode is omitted.

[0069] In the first operation example in the comparative example where the potential is constant at a low level, as shown in Figure 10 (a), during charge storage, the potential well of the charge storage region 24 can be deepened. On the other hand, as shown in Figure 10 (b), during charge transfer, the potential difference between the charge storage region 24 and the charge transfer region 26 becomes small, and the charge transfer efficiency becomes low. The amount of charge that can be completely transferred from the charge storage region 24 to the charge transfer region 26 is on the order of the value obtained by multiplying the potential difference between the charge storage region 24 and the charge transfer region 26 by the capacitance of the charge transfer region 26. Therefore, when the potential difference is small, the amount that can be completely transferred decreases, and the detection sensitivity decreases. In addition, when the potential difference is small, obstacles are likely to occur in the transfer path, thereby also reducing the transfer efficiency.

[0070] In the comparative example potential In the second operation example where the potential is constant at a high level, as Figure 11 shown in (b) of, during charge transfer, the potential difference between the charge storage region 24 and the charge transfer region 26 increases, and charge transfer efficiency can be ensured. On the other hand, as Figure 11 shown in (a) of, during charge storage, the potential well of the charge storage region 24 becomes shallower, and the saturated charge amount of the charge storage region 24 decreases. Thus, in the comparative example, since the potential is constant, it is impossible to achieve either an increase in the saturated charge amount or an improvement in charge transfer efficiency.

[0071] In contrast, in the driving method of the above-described image sensor 1, as Figure 12 shown in (a) of, during charge storage, since the potential is at a low level, the potential well of the charge storage region 24 can be deepened, and the saturated charge amount of the charge storage region 24 can be increased. In addition, the potential gradient range A formed at the edge of the charge storage region 24 can be expanded. As a result, the moving speed of the charges flowing into the charge storage region 24 can be increased. In addition, as Figure 12 shown in (b) of, during charge transfer, since the potential is at a high level, the potential difference between the charge storage region 24 and the charge transfer region 26 can be increased, and charge transfer efficiency can be improved. Thus, in the driving method of the above-described image sensor 1, the potential of the charge collection electrode 41 and the potential of the transfer gate electrode 42 are synchronously controlled. As a result, both an increase in the saturated charge amount and an improvement in charge transfer efficiency can be achieved.

[0072] The charge generation region 29 includes an avalanche multiplication region 23. Thus, avalanche multiplication can be caused in the charge generation region 29, and detection sensitivity can be improved. On the other hand, in this case, the amount of charge generated in the charge generation region 29 becomes extremely large. In the light detection device 100, as described above, the saturated charge amount increases. Therefore, even in such a case, saturation of the capacitance can be suppressed.

[0073] In the first period M1, the potential of the region directly below the overflow gate electrode 43 is made higher than the potential of the region directly below the charge collection electrode 41 and lower than the potential of the region directly below the transfer gate electrode 42 in such a manner that the potentials of the charge collection electrode 41, the transfer gate electrode 42, and the overflow gate electrode 43 are controlled. Thus, the charges overflowing from the charge storage region 24 during the first period M1 can be made to move to the overflow region 27.

[0074] The image sensor 1 has an intervening region 25, which has a conductivity type different from that of the charge storage region 24 and is disposed between the charge storage region 24 and the charge collection electrode 41. Thereby, generation of dark current near the charge collection electrode 41 can be suppressed.

[0075] In addition, in a state where a potential of a region directly below the charge collection electrode 41 is made to be a high level and a potential is applied to the charge collection electrode 41 (a state where a low-level control voltage S2 is applied to the charge collection electrode 41), generation of dark current near the charge collection electrode 41 can be effectively suppressed by the intervening region 25. The reason is as follows. The higher the hole concentration at the interface (the surface facing the charge collection electrode 41) of the intervening region 25 is, the lower the dark current is. In the case where the intervening region 25 is formed by ion implantation, the hole concentration of the intervening region 25 forms a peak at a position away from the interface. By applying a potential to the charge collection electrode 41 as described above, the hole concentration in the region directly below the interface of the intervening region 25 can be increased by an additive effect, and generation of dark current can be effectively suppressed.

[0076] In addition, as an image sensor that uses a transfer gate electrode to transfer charges, there is a distance measurement sensor. In the distance measurement sensor, a plurality of transfer gate electrodes are used, and charges are distributed between a plurality of charge transfer regions. In the distance measurement sensor, in order to attract charges, a grating electrode is disposed on the charge distribution region. The potential of the grating electrode remains constant. That is, the potential of the grating electrode of the distance measurement sensor does not change according to a period like the charge collection electrode 41 of the above-described image sensor 1. In the distance measurement sensor, since the charges flowing into the charge distribution region are immediately transferred to the charge transfer region, no charges are accumulated in the charge distribution region. Therefore, it is not required to increase the saturation charge amount of the charge distribution region.

[0077] The present invention is not limited to the above-described embodiments. For example, in terms of materials and shapes of respective structures, they are not limited to the above-described materials and shapes, and various materials and shapes can be adopted. The charges transferred to the overflow region 27 are not necessarily discharged. For example, charges may be accumulated in the overflow region 27, and the accumulated charges are not read out. In this case, outside the overflow region 27, a charge discharge region for discharging the charges remaining in the charge storage region 24 to the outside may be provided. The intervening region 25 may not be provided. In this case, the charge storage region 24 may reach the first surface 2a of the semiconductor layer 2.

[0078] In the image sensor 1, light may be incident on the semiconductor layer 2 from either the first side or the second side. The conductivity types of p-type and n-type may also be opposite to the above. A plurality of pixels 20 may be arranged one-dimensionally along the first surface 2a of the semiconductor layer 2. Alternatively, only a single pixel 20 may be provided.

[0079] Description of Reference Numerals

[0080] 1……Image sensor (light sensor)

[0081] 23……Avalanche multiplication region

[0082] 24……Charge storage region

[0083] 25……Intervening region

[0084] 26……Charge transfer region

[0085] 27……Overflow region

[0086] 29……Charge generation region

[0087] 41……Charge collection electrode

[0088] 42……Transfer gate electrode

[0089] 43……Overflow gate electrode

[0090] 60……Control unit

[0091] 100……Light detection device

[0092] M1……First period

[0093] M2……Second period

[0094] ……Electric potential of the region directly below the charge collection electrode

[0095] ……Electric potential of the region directly below the gate electrode

[0096] ……Electric potential of the region directly below the overflow gate electrode.

Claims

1. An optical detection device, wherein: It includes: An optical sensor; and A control unit that controls the optical sensor, The optical sensor has: A charge generation region that generates charges according to incident light; A charge storage region that stores the charges generated in the charge generation region; A charge transfer region that transfers charges from the charge storage region; A charge collection electrode disposed on the charge storage region; And A transfer gate electrode that transfers on the region between the charge storage region and the charge transfer region, During a first period, the control unit controls the potentials of the charge collection electrode and the transfer gate electrode such that the potential of the region directly below the charge collection electrode becomes a first level, and the potential of the region directly below the transfer gate electrode is higher than the potential of the region directly below the charge collection electrode; During a second period after the first period, the control unit controls the potentials of the charge collection electrode and the transfer gate electrode such that the potential of the region directly below the charge collection electrode becomes a second level higher than the first level, and the potential of the region directly below the transfer gate electrode is lower than the potential of the region directly below the charge collection electrode.

2. The optical detection device according to claim 1, wherein: The charge generation region includes an avalanche multiplication region.

3. The optical detection device according to claim 1, wherein: The optical sensor further has: An overflow region; And An overflow gate electrode disposed on the region between the charge storage region and the overflow region, During the first period, the control unit controls the potentials of the charge collection electrode, the transfer gate electrode, and the overflow gate electrode such that the potential of the region directly below the overflow gate electrode is higher than the potential of the region directly below the charge collection electrode and lower than the potential of the region directly below the transfer gate electrode.

4. The optical detection device according to claim 2, wherein: The optical sensor further has: An overflow region; And An overflow gate electrode disposed on the region between the charge storage region and the overflow region, During the first period, the control unit controls the potentials of the charge collection electrode, the transfer gate electrode, and the overflow gate electrode such that the potential of the region directly below the overflow gate electrode is higher than the potential of the region directly below the charge collection electrode and lower than the potential of the region directly below the transfer gate electrode.

5. The optical detection device according to any one of claims 1 to 4, wherein: The optical sensor further has: An intervening region having a conductivity type different from that of the charge storage region, disposed between the charge storage region and the charge collection electrode.

6. A driving method for an optical sensor, wherein: The optical sensor includes: A charge generation region that generates charges according to incident light; A charge storage region that stores the charges generated in the charge generation region; A charge transfer region that transfers charges from the charge storage region; A charge collection electrode disposed on the charge storage region; And A transfer gate electrode configured to transfer over a region between the charge storage region and the charge transfer region The driving method of the optical sensor includes: A first step of controlling the potentials of the charge collection electrode and the transfer gate electrode such that the potential of the region directly below the charge collection electrode becomes a first level and the potential of the region directly below the transfer gate electrode is higher than the potential of the region directly below the charge collection electrode; and A second step of, after the first step, controlling the potentials of the charge collection electrode and the transfer gate electrode such that the potential of the region directly below the charge collection electrode becomes a second level higher than the first level and the potential of the region directly below the transfer gate electrode is lower than the potential of the region directly below the charge collection electrode.

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