JP7613865B2 - Light receiving element and light receiving device - Google Patents

Description

This disclosure relates to a light receiving element and a light receiving device.

A TOF (Time of Flight) sensor (light receiving device) is known as a method for measuring the distance to an object. For example, in the case of an indirect TOF sensor, the TOF sensor can measure the distance to the object by irradiating the object with light having a predetermined period and detecting the phase difference between the irradiated light and the reflected light. In this TOF sensor, the light is received multiple times at short intervals, increasing the signal amount and improving the S/N (Signal/Noise) ratio, enabling highly accurate distance measurement.

JP 2019-4149 A

The light receiving element of the TOF sensor (light receiving device) is required to have a wide dynamic range, i.e., to store a large amount of charge generated by receiving light, in order to ensure a sufficient S/N ratio for distance measurement. Furthermore, the light receiving element is required to reduce the effect of kTC noise in order to measure distance with high accuracy.

In light of this situation, this disclosure proposes a light receiving element and a light receiving device that can reduce the effects of kTC noise while ensuring a wide dynamic range.

According to the present disclosure, a light receiving element is provided that is provided in a semiconductor substrate and includes a photoelectric conversion unit that converts light into electric charges, a first charge storage unit to which the electric charges are transferred from the photoelectric conversion unit, and a second charge storage unit to which the electric charges are transferred from the photoelectric conversion unit, each of the first and second charge storage units being composed of a laminate of an electrode, a first insulating layer, and a semiconductor layer.

The present disclosure also provides a light-receiving element that includes a photoelectric conversion unit that is provided in a semiconductor substrate and converts light into electric charges, a first charge storage unit to which the electric charges are transferred from the photoelectric conversion unit, and a second charge storage unit to which the electric charges are transferred from the photoelectric conversion unit, and each of the first and second charge storage units has a semiconductor layer, an insulating layer embedded in a trench formed in the semiconductor layer, and a vertical electrode embedded in the insulating layer.

Furthermore, according to the present disclosure, there is provided a light receiving device including one or more light receiving elements, the light receiving elements being provided in a semiconductor substrate and including a photoelectric conversion unit that converts light into electric charge, a first charge storage unit to which the electric charge is transferred from the photoelectric conversion unit, and a second charge storage unit to which the electric charge is transferred from the photoelectric conversion unit, each of the first and second charge storage units being composed of a laminate of an electrode, a first insulating layer, and a semiconductor layer.

1 is a block diagram showing a configuration example of a distance measuring module 1 according to an embodiment of the present disclosure. FIG. 1 is an explanatory diagram (part 1) showing an example of a planar configuration of a light receiving unit 30 according to an embodiment of the present disclosure. FIG. 2 is an explanatory diagram (part 2) showing an example of a planar configuration of the light receiving unit 30 according to an embodiment of the present disclosure. FIG. 3 is an explanatory diagram (part 3) showing an example of a planar configuration of the light receiving unit 30 according to an embodiment of the present disclosure. 1 is an equivalent circuit diagram of a light receiving element 10 according to an embodiment of the present disclosure. 1 is an explanatory diagram for explaining the principle of a distance calculation method using a distance measurement module 1 according to an embodiment of the present disclosure. 10 is an equivalent circuit diagram of a portion of a light receiving element according to a comparative example. FIG. 2 is an equivalent circuit diagram of a portion of a light receiving element 10 according to an embodiment of the present disclosure. 1 is an explanatory diagram showing an example of a planar configuration of a light receiving element 10 according to a first embodiment of the present disclosure. 8 is a cross-sectional view of the light receiving element 10 taken along line AA' in FIG. 7. 2 is an explanatory diagram showing a cross-sectional configuration example of a charge storage unit MEM according to the first embodiment of the present disclosure; FIG. FIG. 10 is an energy band diagram of the charge storage unit MEM in FIG. 9 . 10 is an explanatory diagram showing another cross-sectional configuration example of the charge storage unit MEM according to the first embodiment of the present disclosure. FIG. 12 is an energy band diagram of the charge storage unit MEM in FIG. 11. 2 is an explanatory diagram showing an example of a cross-sectional configuration of a light receiving element 10 according to a first modified example of the embodiment. FIG. FIG. 14 is an enlarged view of region C in FIG. 13. 11 is an explanatory diagram showing an example of a cross-sectional configuration of a light receiving element 10 according to a second modified example of the embodiment. FIG. 13 is an explanatory diagram showing an example of a cross-sectional configuration of a light receiving element 10 according to a third modified example of the embodiment. FIG. 13 is an explanatory diagram showing an example of a cross-sectional configuration of a light receiving element 10 according to a fourth modified example of the embodiment. FIG. 13 is an explanatory diagram showing an example of a planar configuration of a light receiving element 10 according to a fifth modified example of the embodiment. FIG. 10 is an explanatory diagram showing an example of a planar configuration of a light receiving element 10 according to a second embodiment of the present disclosure. FIG. 20 is a cross-sectional view of the light receiving element 10 taken along line CC' in FIG. 19. 20 is a cross-sectional view of the light receiving element 10 taken along line DD' in FIG. 19. 13 is an explanatory diagram showing an example of a planar configuration of a light receiving element 10 according to a third embodiment of the present disclosure. FIG. 22 is a cross-sectional view of the light receiving element 10 taken along line EE' in FIG. 21. 22 is a cross-sectional view of the light receiving element 10 taken along the line FF' in FIG. 21. 1 is a block diagram showing an example configuration of a smartphone 900 as an electronic device to which a ranging module 1 according to an embodiment of the present disclosure is applied. FIG. 1 is a diagram illustrating an example of a schematic configuration of an endoscopic surgery system. FIG. 1 is a diagram illustrating an example of a configuration of an endoscope. 2 is a block diagram showing an example of the functional configuration of a camera head and a CCU. FIG. 1 is a block diagram showing an example of a schematic configuration of a vehicle control system; 4 is an explanatory diagram showing an example of the installation positions of an outside-vehicle information detection unit and an imaging unit; FIG.

Below, a preferred embodiment of the present disclosure will be described in detail with reference to the attached drawings. Note that in this specification and the drawings, components having substantially the same functional configuration are denoted by the same reference numerals, and duplicated explanations will be omitted.

In addition, in this specification and drawings, multiple components having substantially the same or similar functional configurations may be distinguished by adding different numbers after the same reference symbol. However, if there is no particular need to distinguish between multiple components having substantially the same or similar functional configurations, only the same reference symbol will be used. Also, similar components in different embodiments may be distinguished by adding different letters after the same reference symbol. However, if there is no particular need to distinguish between similar components, only the same reference symbol will be used.

The drawings referred to in the following description are intended to facilitate the explanation and understanding of the embodiments of the present disclosure, and for ease of understanding, the shapes, dimensions, ratios, etc. shown in the drawings may differ from the actual ones. Furthermore, the components included in the elements and devices shown in the drawings may be appropriately redesigned in consideration of the following description and known technologies.

In the following description, an embodiment of the present disclosure is described as being applied to a back-illuminated light receiving device, and therefore, in this light receiving device, light is incident from the back side of the substrate. Therefore, in the following description, the front surface of the substrate is the surface that faces the back side when the side where light is incident is defined as the back side.

The description of specific lengths and shapes in the following explanation does not mean only the same values as mathematically defined numerical values or geometrically defined shapes. In more detail, the description of specific lengths and shapes in the following explanation includes shapes that have an allowable degree of difference (error/distortion) in the element, its manufacturing process, and its use/operation, or shapes similar to those shapes. For example, when the description below refers to a "circular shape" or "nearly circular shape," it does not mean limited to a perfect circle, but also includes shapes similar to a perfect circle, such as an ellipse.

Furthermore, in the following explanation of circuits (electrical connections), unless otherwise specified, "electrically connected" means connecting multiple elements so that electricity (signals) is conducted between them. In addition, in the following explanation, "electrically connected" includes not only cases where multiple elements are directly and electrically connected, but also cases where elements are indirectly and electrically connected via other elements.

In the following description, unless otherwise specified, "shared" means that another element is provided so as to be shared by multiple one elements, or in other words, that another element is shared by each of a predetermined number of one elements.

The explanation will be given in the following order.
1. Configuration example of distance measuring module 1 according to an embodiment of the present disclosure 2. Configuration example of light receiving section 30 according to an embodiment of the present disclosure 3. Equivalent circuit of light receiving element 10 according to an embodiment of the present disclosure 4. Principle of distance calculation method using distance measuring module 1 according to an embodiment of the present disclosure 5. Background leading to creation of this embodiment 6. First embodiment 7. Second embodiment 8. Third embodiment 9. Summary 10. Configuration example of electronic device 11. Application example to endoscopic surgery system 12. Application example to moving body 13. Supplementary information

<<1. Configuration example of distance measurement module 1 according to an embodiment of the present disclosure>>
First, a schematic configuration of a distance measuring module 1 according to an embodiment of the present disclosure will be described with reference to Fig. 1. Fig. 1 is a block diagram showing a configuration example of a distance measuring module 1 according to an embodiment of the present disclosure. In detail, as shown in Fig. 1, the distance measuring module 1 can mainly include an irradiation unit 20, a light receiving unit 30, a control unit (irradiation control unit) 40, and a processing unit 60. Each functional block included in the distance measuring module 1 according to the present embodiment will be described below.

(Irradiation unit 20)
The irradiation unit 20 has an LED (Light Emitting Diode) light source (not shown) and an optical element (not shown). The wavelength of the irradiated light can be changed by appropriately selecting the LED light source. In this embodiment, the irradiation unit 20 is described as irradiating infrared light having a wavelength of, for example, 780 nm to 1000 nm, but this embodiment is not limited to irradiating such infrared light. In addition, the irradiation unit 20 can irradiate the target object 800 with irradiation light whose brightness periodically changes in synchronization with a periodic signal such as a rectangular signal supplied from the control unit 40 described later.

(Light receiving unit 30)
The light receiving unit 30 receives the reflected light reflected from the object 800. The light receiving unit 30 has a condenser lens (not shown) and a plurality of light receiving elements 10 described later. The condenser lens has a function of collecting the received light to each light receiving element 10. The light receiving element 10 generates electric charges (e.g., electrons) based on the intensity of the received light, and drives a built-in transistor (distribution transistor VG; see FIG. 3) in synchronization with a periodic signal such as a rectangular signal supplied from a control unit 40 described later, and transfers the generated electric charges to a charge storage unit MEM (see FIG. 3). Furthermore, the electric charges transferred to the charge storage unit MEM are converted into signals and finally transferred to a processing unit 60. Details of the light receiving element 10 will be described later.

(Control unit 40)
The control unit 40 supplies a periodic signal to the irradiating unit 20 and the light receiving unit 30 to control the timing of irradiating light and the driving timing of the transistors. The frequency of the signal can be, for example, 5 to 20 megahertz (MHz), but is not limited to such a frequency in this embodiment. The control unit 40 also controls the transistors (distribution transistors VG; see FIG. 3) to operate at different timings, for example differentially.

(Processing Unit 60)
The processing unit 60 acquires a signal from the light receiving unit 30, and based on the acquired signal, can acquire the distance to the object 800 by, for example, an indirect ToF (iToF) method. The method of calculating the distance will be described later.

2. Configuration example of the light receiving unit 30 according to the embodiment of the present disclosure
Next, with reference to Figures 2A to 2C, a planar configuration example of the light receiving unit 30 according to the embodiment of the present disclosure will be described. Figures 2A to 2C are explanatory diagrams showing a planar configuration example of the light receiving unit 30 according to the embodiment of the present disclosure. In detail, as shown in Figure 2A, the light receiving unit 30 according to this embodiment includes a pixel array unit 12, a vertical drive circuit unit 32, a column signal processing circuit unit 34, a horizontal drive circuit unit 36, an output circuit unit 38, and a control circuit unit 44, which are provided on a semiconductor substrate 200 made of, for example, silicon. Below, the details of each block of the light receiving unit 30 according to this embodiment will be described.

(Pixel array section 12)
The pixel array section 12 has a plurality of light receiving elements 10 arranged two-dimensionally in a matrix (row and column rows and columns) on the semiconductor substrate 200. Each light receiving element 10 has a photoelectric conversion section (photodiode PD) (not shown) that converts light into electric charge (e.g., electrons), and a plurality of pixel transistors (e.g., MOS (Metal-Oxide-Semiconductor) transistors) (not shown). In other words, the pixel array section 12 has a plurality of pixels that perform photoelectric conversion of incident light and output a signal corresponding to the resultant electric charge. The pixel transistors can include transistors having various functions, such as a transfer transistor, a selection transistor, a reset transistor, and an amplification transistor. Details of the equivalent circuit of the light receiving element 10 will be described later.

Here, the row direction refers to the horizontal arrangement direction of the light receiving elements 10, and the column direction refers to the vertical arrangement direction of the light receiving elements 10. The row direction is the left-right direction in FIG. 2A, and the column direction is the up-down direction in FIG. 2A. In the pixel array section 12, pixel drive wiring 42 is wired along the row direction for each row of the matrix-like arrangement of light receiving elements 10, and vertical signal lines 48 are wired along the column direction for each column. For example, the pixel drive wiring 42 transmits a drive signal for driving the light receiving elements 10 when reading out a signal.

(Vertical drive circuit section 32)
The vertical drive circuit unit 32 is formed of, for example, a shift register, an address decoder, etc., selects a pixel drive wiring 42, supplies a pulse for driving the light receiving elements 10 to the selected pixel drive wiring 42, and drives all the light receiving elements 10 simultaneously or row by row. For example, the vertical drive circuit unit 32 selects and scans each light receiving element 10 of the pixel array unit 12 in the vertical direction (up and down direction in FIG. 2A ) in sequence row by row, and supplies a pixel signal based on a charge generated in accordance with the amount of light received by the photodiode PD of each light receiving element 10 to a column signal processing circuit unit 34 (described later) through a vertical signal line 48.

(Column signal processing circuit unit 34)
The column signal processing circuit unit 34 is arranged for each column of the light receiving elements 10, and performs signal processing such as noise removal for each column on signals output from one row of the light receiving elements 10. For example, the column signal processing circuit unit 34 performs signal processing such as CDS (Correlated Double Sampling) and AD (Analog-Digital) conversion in order to remove fixed pattern noise inherent to the light receiving elements 10.

(Horizontal drive circuit section 36)
The horizontal drive circuit unit 36 is formed, for example, by a shift register or an address decoder, and by sequentially outputting horizontal scanning pulses, it is possible to select each of the above-mentioned column signal processing circuit units 34 in turn, and output a signal from each of the column signal processing circuit units 34 to the horizontal signal line 46.

(Output circuit section 38)
The output circuit unit 38 can process and output signals sequentially supplied from each of the column signal processing circuits 34 through the horizontal signal line 46. The output circuit unit 38 may function as a functional unit that performs buffering, or may perform processing such as column variation correction and various digital signal processing. Note that buffering refers to temporarily storing signals to compensate for differences in processing speed and transfer speed when exchanging signals.

(Control circuit unit 44)
The control circuit unit 44 receives an input clock and data instructing an operation mode and the like, and can also output data such as internal information of the light receiving element 10. That is, the control circuit unit 44 generates clock signals and control signals that serve as a reference for the operation of the vertical drive circuit unit 32, the column signal processing circuit unit 34, the horizontal drive circuit unit 36, etc., based on the vertical synchronization signal, the horizontal synchronization signal, and the master clock. Then, the control circuit unit 44 outputs the generated clock signals and control signals to the vertical drive circuit unit 32, the column signal processing circuit unit 34, the horizontal drive circuit unit 36, etc.

(Distribution transistor driving unit 50, signal processing unit 52, data storage unit 54)
As shown in FIG. 2B and FIG. 2C, the light receiving element 10 may be provided with a distribution transistor driving unit 50, a signal processing unit 52, and a data storage unit 54. That is, the distribution transistor driving unit 50, the signal processing unit 52, and the data storage unit 54 may be provided on the semiconductor substrate 200. However, in this embodiment, this is not limited to this, and the distribution transistor driving unit 50, the signal processing unit 52, and the data storage unit 54 may be provided on another semiconductor substrate (not shown). First, the distribution transistor driving unit 50 controls the operation of a distribution transistor VG (see FIG. 3 ) described later. For example, the distribution transistor driving unit 50 may be provided adjacent to the pixel array unit 12 in the column direction as shown in FIG. 2B, or may be provided adjacent to the pixel array unit 12 in the row direction as shown in FIG. 2C, and is not particularly limited in this embodiment. In addition, the signal processing unit 52 has at least an arithmetic processing function, and performs various signal processing such as arithmetic processing based on the signal output from the output circuit unit 38. The data storage unit 54 temporarily stores data necessary for the signal processing performed by the signal processing unit 52 .

Note that the planar configuration example of the light receiving unit 30 according to this embodiment is not limited to the examples shown in Figures 2A to 2C, and may include other circuits, etc., and is not particularly limited.

<<3. Equivalent circuit of the light receiving element 10 according to the embodiment of the present disclosure>>
Next, an equivalent circuit of the light receiving element 10 according to the embodiment of the present disclosure will be described with reference to Fig. 3. Fig. 3 is an equivalent circuit diagram of the light receiving element 10 according to the embodiment of the present disclosure.

In detail, as shown in FIG. 3, the light receiving element 10 has a photodiode PD as a photoelectric conversion element (photoelectric conversion unit) that converts light into electric charge, and a charge discharge transistor OFG (note that the charge discharge transistor OFG is shown as one transistor in the equivalent circuit, but may be composed of multiple transistors electrically connected in parallel). In addition, the light receiving element 10 has two each of a distribution transistor VG, a charge storage unit (first charge storage unit, second charge storage unit) MEM, a transfer transistor TG, a floating diffusion region FD, a reset transistor RST, an amplification transistor AMP, and a selection transistor SEL.

As shown in FIG. 3, in the light receiving element 10, one of the source and drain of the charge draining transistor OFG is electrically connected to a photodiode PD that generates charge by receiving light. Furthermore, the other of the source and drain of the charge draining transistor OFG is electrically connected to a power supply circuit (power supply potential VDD). The charge draining transistor OFG becomes conductive in response to a voltage applied to its gate, and is able to drain the charge accumulated in the photodiode PD to the power supply circuit (power supply potential VDD).

As shown in FIG. 3, in the light receiving element 10, one of the source/drain of the distribution transistors VG1 and VG2 is electrically connected to the photodiode PD, and the other of the source/drain of the distribution transistors VG1 and VG2 is electrically connected to the charge storage units (first charge storage unit, second charge storage unit) MEM1 and MEM2, respectively. The distribution transistors VG1 and VG2 are turned on in response to the voltage applied to their gates (first distribution gate, second distribution gate), and can transfer the charge stored in the photodiode PD to the charge storage units MEM1 and MEM2, respectively. That is, in this embodiment, the voltages applied to the gates of the distribution transistors VG1 and VG2 are changed at different times, so that the charge stored in the photodiode PD can be distributed to one of the two charge storage units MEM1 and MEM2. In other words, it can be said that the two charge storage units MEM1 and MEM2 share one photodiode PD.

Also, as shown in FIG. 3, in the light receiving element 10, one of the source/drain of the transfer transistors TG1 and TG2 is electrically connected to the other of the source/drain of the distribution transistors VG1 and VG2 and the charge storage units MEM1 and MEM2. Furthermore, the other of the source/drain of the transfer transistors TG1 and TG2 is electrically connected to the floating diffusion regions FD1 and FD2. Then, the transfer transistors TG1 and TG2 become conductive in response to a voltage applied to their gates, and can transfer the charges stored in the charge storage units MEM1 and MEM2 to the floating diffusion regions FD1 and FD2. Note that in the embodiment of the present disclosure, since there are two charge storage units MEM1 and MEM2, the transfer transistors TG1 and TG2 can also share one floating diffusion region FD.

Floating diffusion regions FD1, FD2 are also electrically connected to the gates of amplification transistors AMP1, AMP2, which convert the charge into a voltage and output it as a signal. One of the source/drain of amplification transistors AMP1, AMP2 is also electrically connected to one of the source/drain of selection transistors SEL1, SEL2, which output the signal obtained by conversion to signal lines VSL1, VSL2 in accordance with a selection signal. Furthermore, the other of the source/drain of amplification transistors AMP1, AMP2 is electrically connected to a power supply circuit (power supply potential VDD).

The other of the source/drain of the selection transistors SEL1 and SEL2 is electrically connected to the signal lines VSL1 and VSL2 that transmit the converted voltage as a signal, and is further electrically connected to the column signal processing circuit unit 34 described above. Furthermore, the gates of the selection transistors SEL1 and SEL2 are electrically connected to a selection line (not shown) that selects the row to which the signal is output, and is further electrically connected to the vertical drive circuit unit 32 described above. That is, the charge accumulated in the floating diffusion regions FD1 and FD2 is converted into a voltage by the amplification transistors AMP1 and AMP2 under the control of the selection transistors SEL1 and SEL2, and is output to the signal lines VSL1 and VSL2.

As shown in FIG. 3, the floating diffusion regions FD1 and FD2 are electrically connected to one of the drains or sources of the reset transistors RST1 and RST2 for resetting the accumulated charge. The gates of the reset transistors RST1 and RST2 are electrically connected to a reset signal line (not shown) and are further electrically connected to the vertical drive circuit unit 32 described above. The other of the drains or sources of the reset transistors RST1 and RST2 are electrically connected to a power supply circuit (power supply potential VDD). The reset transistors RST1 and RST2 become conductive in response to a voltage applied to their gates, and can reset (discharge to the power supply circuit (power supply potential VDD)) the charge accumulated in the floating diffusion regions FD1 and FD2.

The equivalent circuit of the light receiving element 10 according to this embodiment is not limited to the example shown in FIG. 3, and may include other elements, for example, and is not particularly limited.

<<4. Principle of distance calculation method using distance measurement module 1 according to an embodiment of the present disclosure>>
Next, the principle of the distance calculation method (indirect type) using the distance measurement module 1 according to the embodiment of the present disclosure will be described with reference to Fig. 4. Fig. 4 is an explanatory diagram for explaining the principle of the distance calculation method using the distance measurement module 1 according to the embodiment of the present disclosure, and in detail, it shows a schematic diagram of the time variation of the intensity of the irradiated light and the reflected light in the distance measurement module 1.

As shown in FIG. 4, the distance measuring module 1 irradiates light modulated so that the light intensity varies periodically from the irradiation unit 20 toward the object 800. The irradiated light is reflected by the object 800 and detected as reflected light by the light receiving unit 30 of the distance measuring module 1. As shown in FIG. 4, the detected reflected light (second row from the top of FIG. 4) has a phase difference φ with respect to the irradiated light (first row from the top of FIG. 4), and the phase difference φ becomes larger if the distance from the distance measuring module 1 to the object 800 is long and becomes smaller if the distance from the distance measuring module 1 to the object 800 is short.

As described above, the light receiving element 10 according to this embodiment has, for example, the distribution transistors VG1 and VG2 which are differential with each other. Therefore, since the periods during which the distribution transistors VG1 and VG2 operate do not overlap, the charge stored in the photodiode PD is distributed to the charge storage units MEM1 and MEM2 during the periods of the regions 802a and 802b shown in gray in FIG. 4. In detail, the charge distributed to the charge storage units MEM1 and MEM2 is transferred to the floating diffusion regions FD1 and FD2, and is finally converted into a signal corresponding to the area which is the integral value during the periods of the regions 802a and 802b. Therefore, as is clear from FIG. 4, the difference between the integral value of the region 802a and the integral value of the region 802b changes according to the phase difference φ of the reflected light. Therefore, in this embodiment, the phase difference φ is calculated based on the difference between the integral value of the region 802a and the integral value of the region 802b, so that the distance to the object 800 can be calculated. In this embodiment, it is also possible to calculate the phase difference φ using the ratio of integral values instead of the difference between integral values, and to calculate the distance.

<<5. Background to the Creation of the Present Embodiment>>
The distance measuring module 1, the light receiving unit 30, the light receiving element 10, and the principle of the distance calculation method according to the embodiment of the present disclosure have been described above. Before describing the details of this embodiment, the background that led the inventors to create this embodiment will be described.

As explained above, the light receiving element 10 of the light receiving unit 30 of the distance measurement module 1 is required to have a wide dynamic range, i.e., to store a large amount of charge, in order to ensure a sufficient S/N ratio for distance measurement. Furthermore, in order to measure distances with high accuracy, the light receiving element 10 is required to reduce the influence of kTC noise, which is noise generated by thermal fluctuations of charge in the floating diffusion region FD, i.e., to reduce the influence of random noise.

Therefore, the present inventors have come to create an embodiment of the present disclosure in consideration of the above-mentioned requirements. In detail, in a conventional light receiving element (comparative example to be described later), the charge generated in the photodiode PD is directly distributed to the floating diffusion region FD. In contrast, in the embodiment of the present disclosure created by the present inventors, the charge generated in the photodiode PD is not directly distributed to the floating diffusion region FD, but is once distributed to the charge storage unit MEM and then transferred to the floating diffusion region FD. In a conventional light receiving element, it is difficult to completely deplete the floating diffusion region FD after a reset operation (an operation of discharging the charge (noise) accumulated in the floating charge region FD before accumulating the charge generated by light reception). Therefore, when the charge (signal) generated in the photodiode PD is transferred to the floating charge region FD, it is difficult to avoid the kTC noise being superimposed on the signal. On the other hand, in this embodiment, as described below, it is possible to cancel the kTC noise generated in the floating charge region FD, thereby reducing the effect of the kTC noise on the charge (signal) generated in the photodiode PD.

Below, with reference to Figures 5 and 6, the operation of the light receiving element 10 according to the embodiment of the present disclosure will be described in comparison with the operation of the light receiving element according to the comparative example. Figure 5 is an equivalent circuit diagram of a portion of the light receiving element according to the comparative example, and Figure 6 is an equivalent circuit diagram of a portion of the light receiving element 10 according to the embodiment of the present disclosure. Note that the comparative example here refers to a light receiving element that the inventors had studied extensively before developing the embodiment of the present disclosure.

First, let us briefly explain kTC noise. As explained above, kTC noise is noise caused by thermal fluctuations of electric charge. Although such kTC noise (electric charge) occurs in the floating diffusion region FD, if the floating diffusion region FD can be ideally completely depleted in the reset operation of the global shutter operation (reading out from all light receiving elements at once), the kTC noise can be discharged in advance. However, since a high concentration of impurities is injected into the contact portion of the floating diffusion region FD to form an ohmic junction between the floating diffusion region FD and the wiring, the floating diffusion region FD cannot be completely depleted even when a reset operation is performed, and it is difficult to completely discharge the kTC noise from the floating diffusion region FD. Therefore, when the electric charge (signal) generated in the photodiode PD is transferred to the floating charge region FD, it is difficult to avoid the kTC noise being superimposed on the signal.

The equivalent circuit of the light receiving element according to the comparative example will be briefly described. As shown in FIG. 5, the light receiving element according to the comparative example has a photodiode PD and a charge discharge transistor OFG. Furthermore, the light receiving element has a transfer transistor TG, a floating diffusion region FD, and a reset transistor RST. More specifically, one of the source/drain of the charge discharge transistor OFG is electrically connected to the photodiode PD, and the other of the source/drain of the charge discharge transistor OFG is electrically connected to the power supply circuit (power supply potential VDD). The charge discharge transistor OFG becomes conductive in response to a voltage applied to its gate, and can discharge the charge accumulated in the photodiode PD. Also, as shown in FIG. 5, one of the source/drain of the transfer transistor TG is electrically connected to the photodiode PD, and the other of the source/drain of the transfer transistor TG is electrically connected to the floating diffusion region FD. The transfer transistor TG becomes conductive in response to a voltage applied to its gate, and can transfer the charge generated in the photodiode PD to the floating diffusion region FD. Furthermore, the floating diffusion region FD is electrically connected to one of the drain/source of a reset transistor RST for resetting the accumulated charge. The reset transistor RST becomes conductive in response to a voltage applied to its gate, and can discharge (reset) the charge accumulated in the floating diffusion region FD.

First, in the light receiving element according to the comparative example, before light reception begins, a discharge operation is performed to discharge the charge of the photodiode PD. That is, the charge drain transistor OFG is turned on, and the charge of the photodiode PD is discharged to the power supply circuit (power supply potential VDD). At this time, kTC noise (Nktc) is generated in the floating diffusion region FD.

Next, light reception begins, and an electric charge (Nsig) (signal) is generated in the photodiode PD. Then, the transfer transistor TG is turned on, and the electric charge in the photodiode PD is transferred to the floating diffusion region FD. Furthermore, the electric charge (Nsig, Nktc) accumulated in the floating diffusion region FD is read out as a signal.

Next, a discharge operation is performed to discharge the charge in the floating diffusion region FD. That is, the reset transistor RST is turned on, and the charge in the floating diffusion region FD is discharged to the power supply circuit (power supply potential VDD). Furthermore, the kTC noise (Nktc) newly generated in the floating diffusion region FD is read out.

In the comparative example, the charge amount (signal) generated by the photodiode PD by receiving light can be detected by subtracting the kTC noise (Nktc) newly generated in the floating diffusion region FD from the charge (Nsig and Nktc) accumulated in the floating diffusion region FD. However, since the kTC noise (Nktc) accumulated in the floating diffusion region FD and the kTC noise (Nktc) newly generated in the floating diffusion region FD are different charge amounts, it is difficult to strictly cancel the kTC noise by subtraction as described above. As a result, in the comparative example, it is difficult to ensure high distance measurement accuracy because it is not possible to obtain a signal from which the kTC noise has been completely removed.

Next, the operation of the light receiving element 10 according to this embodiment will be described. Note that FIG. 6 shows an equivalent circuit diagram of a portion of the light receiving element 10 according to the embodiment of this disclosure, but the details will not be described here to avoid duplication.

First, in the light receiving element 10 according to this embodiment, a discharge operation is performed to discharge the charge of the photodiode PD before starting light reception. That is, the charge drain transistor OFG is turned on, and the charge of the photodiode PD is discharged to the power supply circuit (power supply potential VDD). At this time, kTC noise (Nktc) is generated in the floating diffusion region FD.

Next, light reception begins, and an electric charge (Nsig) is generated in the photodiode PD. Then, the distribution transfer transistor VG turns on, and the electric charge (Nsig) in the photodiode PD is transferred to the storage unit MEM.

Next, a discharge operation is performed to discharge the kTC noise (Nktc) from the floating diffusion region FD. That is, the reset transistor RST is turned on, and the kTC noise (Nktc) from the floating diffusion region FD is discharged to the power supply circuit (power supply potential VDD).

Next, the kTC noise (Nktc) generated in the floating diffusion region FD is read out.

Then, the transfer transistor TG is turned on, and the charge (Nsig) (signal) stored in the storage unit MEM is transferred to the floating diffusion region FD. Then, the charge (Nsig, Nktc) stored in the floating diffusion region FD is read out as a signal.

In this embodiment, the amount of charge (signal) generated by the photodiode PD by receiving light can be detected by subtracting the kTC noise (Nktc) generated in the floating diffusion region FD from the charge (Nsig, Nktc) accumulated in the floating diffusion region FD. That is, in this embodiment, since it is possible to grasp the amount of charge of the kTC noise contained in the signal, it is possible to cancel the kTC noise. As a result, in this embodiment, a signal from which the kTC noise has been removed can be obtained, making it possible to ensure high distance measurement accuracy.

Furthermore, in the embodiment of the present disclosure created by the present inventors, the charge storage unit MEM is formed as a MOS (Metal-Oxide-Semiconductor) type capacitor. That is, in this embodiment, the charge storage unit MEM is formed as a MOS type capacitor consisting of a stack of an electrode made of a metal film or a polysilicon film, an insulating film made of an oxide film, and a semiconductor region. In this embodiment, it is possible to easily increase the capacitance of the storage unit MEM by increasing the interface area of the stack. Therefore, according to this embodiment, it is possible to increase the capacitance value and ensure a wide dynamic range. Details of the embodiment of the present disclosure created by the present inventors will be described below in order.

<<6. First embodiment>>
<6.1 Planar structure>
First, an example of the planar structure of the light receiving element 10 according to the first embodiment of the present disclosure will be described with reference to Fig. 7. Fig. 7 is an explanatory diagram showing an example of the planar configuration of the light receiving element 10 according to this embodiment, and is a diagram of the light receiving element 10 viewed from above the surface of the semiconductor substrate 200. Note that the left-right direction in Fig. 7 corresponds to the row direction (left-right direction) in Fig. 2A, and the up-down direction in Fig. 7 corresponds to the column direction (up-down direction) in Fig. 2A.

As shown in FIG. 7, an N-type semiconductor region 100 is formed in a P-type semiconductor substrate 200 in the center of the light receiving element 10, and the N-type semiconductor region 100 constitutes a part of a photodiode (photoelectric conversion unit) PD. Furthermore, the gate electrodes 150a, 150b of the distribution transistors VG1 and VG2 are arranged so as to be line-symmetric (approximately line-symmetric) with respect to a center line 600 that passes through the center point (center) O of the photodiode PD and extends in the vertical direction (column direction) of the light receiving element 10. The gate electrodes 150a, 150b of the distribution transistors VG1 and VG2 are arranged so as to overlap at least a part of the N-type semiconductor region 100.

In detail, the distribution transistor VG1 is composed of a gate electrode 150a, a gate insulating film (not shown) located between the gate electrode 150a and the semiconductor substrate 200, an N-type semiconductor region 100 as a source region, and an N-type semiconductor region 102a as a drain region. The N-type semiconductor region 100 as a source region is also used as a photodiode PD, and the N-type semiconductor region 102a as a drain region is also used as a charge storage unit MEM1. The distribution transistor VG2 is similar to the distribution transistor VG1.

Furthermore, as shown in FIG. 7, the gate electrodes 152a, 152b of the charge discharge transistors OFG1 and OFG2 are arranged so as to be line-symmetric (approximately line-symmetric) with respect to a center line 602 that passes through the center point O of the photodiode PD and extends in the left-right direction (row direction) of the light receiving element 10. The gate electrodes 152a, 152b of the charge discharge transistors OFG1 and OFG2 are arranged so as to overlap at least a portion of the N-type semiconductor region 100.

In detail, the charge discharge transistor OFG1 is composed of a gate electrode 152a, a gate insulating film (not shown) located between the gate electrode 152a and the semiconductor substrate 200, an N-type semiconductor region 100 as a source region, and an N-type semiconductor region 104a as a drain region. The N-type semiconductor region 100 as a source region is also used as a photodiode PD. The charge discharge transistor OFG2 is similar to the charge discharge transistor OFG1.

In addition, charge storage units MEM1 and MEM2 and transfer transistors TG1 and TG2 are provided so as to be mirror symmetrical with respect to the center line 600 and to sandwich the N-type semiconductor region 102 and the distribution transistors VG1 and VG2 from both sides. The charge storage unit MEM1 is arranged adjacent to the transfer transistor TG1 in the vertical direction (column direction) in FIG. 7, and the charge storage unit MEM2 is arranged adjacent to the transfer transistor TG2 in the vertical direction (column direction) in FIG. 7.

In detail, the charge storage unit MEM1 is composed of, for example, an electrode 154a, an insulating film (not shown) provided below the electrode 154a, and an N-type semiconductor region 102a provided below the insulating film, and its detailed structure will be described later. The transfer transistor TG1 is composed of a gate electrode 156a, a gate insulating film (not shown) located between the gate electrode 156a and the semiconductor substrate 200, an N-type semiconductor region 106a as a source region, and an N-type semiconductor region 108a as a drain region. The charge storage unit MEM2 and the transfer transistor TG2 are similar to the charge storage unit MEM1 and the transfer transistor TG1.

Furthermore, the reset transistors RST1, RST2, the amplification transistors AMP1, AMP2, and the selection transistors SEL1, SEL2 are arranged in mirror symmetry with respect to the center line 602, and sandwiching the N-type semiconductor region 102 and the charge discharge transistors OFG1, OFG2 from both sides. The reset transistor RST1, the amplification transistor AMP1, and the selection transistor SEL1 are arranged adjacent to each other in the left-right direction (row direction) in FIG. 7, and the reset transistor RST2, the amplification transistor AMP2, and the selection transistor SEL2 are also arranged adjacent to each other in the left-right direction (row direction) in FIG. 7.

In detail, the reset transistor RST1 is composed of a gate electrode 158a, a gate insulating film (not shown) located between the gate electrode 158a and the semiconductor substrate 200, an N-type semiconductor region 110a as a source region, and an N-type semiconductor region 112a as a drain region. The N-type semiconductor region 110a as a source region is also used as the floating diffusion region FD1, and the N-type semiconductor region 112a as a drain region is also used as the amplification transistor AMP1. The reset transistor RST2 is similar to the reset transistor RST1.

The amplification transistor AMP1 is composed of a gate electrode 160a, a gate insulating film (not shown) located between the gate electrode 160a and the semiconductor substrate 200, an N-type semiconductor region 112a as a drain region, and an N-type semiconductor region 114a as a source region. The N-type semiconductor region 112a as a drain region is also used as the drain region of the reset transistor RST1. The amplification transistor AMP2 is similar to the amplification transistor AMP1.

The select transistor SEL1 is composed of a gate electrode 162a, a gate insulating film (not shown) located between the gate electrode 162a and the semiconductor substrate 200, an N-type semiconductor region 114a as a drain region, and an N-type semiconductor region 116a as a source region. The N-type semiconductor region 114a as a drain region is also used as the source region of the amplification transistor AMP1. The select transistor SEL2 is similar to the select transistor SEL1.

The planar structure of the light receiving element 10 according to this embodiment is not limited to the example shown in FIG. 7, and may include other elements, for example, and is not particularly limited.

<6.2 Cross-sectional structure>
Next, an example of the cross-sectional structure of the light-receiving element 10 according to the first embodiment of the present disclosure will be described with reference to Fig. 8. Fig. 8 is a cross-sectional view of the light-receiving element 10 cut along line A-A' in Fig. 7. In detail, the upper side in Fig. 8 corresponds to the back surface side of the semiconductor substrate 200, and the lower side in Fig. 8 corresponds to the front surface side of the semiconductor substrate 200.

First, as shown in FIG. 8, the light receiving element 10 has a semiconductor substrate 200 made of a silicon substrate or the like. In detail, N-type semiconductor regions 100a and 100b are formed in the P-type semiconductor substrate 200, thereby forming a photodiode PD in the semiconductor substrate 200.

Next, the upper side in FIG. 8, that is, the back surface side of the semiconductor substrate 200 will be described. An on-chip lens 208 made of styrene resin, acrylic resin, styrene-acrylic copolymer resin, siloxane resin, or the like is provided above the back surface of the semiconductor substrate 200, into which reflected light from the target object 800 is incident. A planarization film 204 made of, for example, silicon oxide (SiO ₂ ), silicon nitride (SiN), silicon oxynitride (SiON), or the like is provided below the on-chip lens 208. Furthermore, an anti-reflection film 202 made of an insulating film is provided below the planarization film 204. For example, the anti-reflection film 202 can be formed of hafnium oxide (HfO ₂ ), aluminum oxide (Al ₂ O ₃ ), titanium oxide (TiO ₂ ), silicon oxide, or the like, or a laminate of these materials.

Above the anti-reflection film 202, in the boundary region with the adjacent light receiving element 10, a light shielding film 206 is provided to prevent reflected light from the object 800 from entering the adjacent light receiving element 10. The light shielding film 206 is made of a material that blocks light, and can be formed using a metal material such as tungsten (W), aluminum (Al), or copper (Cu).

Furthermore, below the light-shielding film 206, a pixel separation section (first pixel separation section) 210 (FFTI) is provided to penetrate the semiconductor substrate 200 and prevent incident light from entering the adjacent light receiving element 10. The pixel separation section 210 is composed of, for example, a trench that penetrates from the back surface to the front surface of the semiconductor substrate 200, and an insulating film such as silicon oxide or a metal film such as aluminum that is embedded in the trench.

Next, the lower side in FIG. 8, i.e., the surface side of the semiconductor substrate 200, will be described. Two distribution transistors VG1 and VG2, which are vertical transistors, are formed on either side of the N-type semiconductor region 100b. In detail, the distribution transistors VG1 and VG2 each have a gate electrode 150a and 150b, which is made of, for example, a polysilicon film, provided on the surface of the semiconductor substrate 200.

Furthermore, charge storage units MEM1 and MEM2 are provided in the semiconductor substrate 200 so as to sandwich the distribution transistors VG1 and VG2 from the left and right direction. For example, the charge storage units MEM1 and MEM2 can be MOS (Metal-Oxide-Semiconductor) type capacitors consisting of a stack of electrodes 154a and 154b made of a metal film or a polysilicon film, an insulating film (not shown) made of an oxide film, and N-type semiconductor regions 102a and 102b (shown as MEM1 and MEM2 in FIG. 8). Details of the charge storage units MEM1 and MEM2 will be described later.

The gate electrodes 156a, 156b of the transfer transistors TG1, TG2 are provided on the surface of the semiconductor substrate 200 adjacent to the charge storage units MEM1, MEM2. Furthermore, N-type semiconductor regions 110a, 110b illustrated as floating diffusion regions FD1, FD2 are formed in the semiconductor substrate 200 adjacent to the gate electrodes 156a, 156b of the transfer transistors TG1, TG2.

Furthermore, a wiring layer 300 is provided on the surface of the semiconductor substrate 200. The wiring layer 300 includes an insulating film 302 and a metal film 304. Furthermore, an electrode 306 is provided on the surface of the wiring layer 300 opposite the semiconductor substrate 200.

In addition, a substrate 400 is provided on the surface of the wiring layer 300 opposite the semiconductor substrate 200. The substrate 400 also includes an insulating film 402 and a metal film 404, and an electrode 406 is provided on the surface on the wiring layer 300 side. For example, the electrode 306 of the wiring layer 300 and the electrode 406 of the substrate 400 are formed of copper (Cu) or the like, and can be joined to each other by being in contact with each other.

The cross-sectional structure of the light receiving element 10 according to this embodiment is not limited to the example shown in FIG. 8, and may include other elements, for example, and is not particularly limited.

Next, the charge storage unit MEM according to this embodiment will be described in detail with reference to Figures 9 and 10. Figure 9 is an explanatory diagram showing an example of the cross-sectional configuration of the charge storage unit MEM according to this embodiment, and corresponds to the cross-sectional view of Figure 8. Also, Figure 10 is an energy band diagram of the charge storage unit MEM in Figure 9. Note that in Figure 9, the upper side in Figure 9 is the front side of the semiconductor substrate 200, and the lower side in Figure 9 is the back side of the semiconductor substrate 200.

9, the charge storage unit MEM according to this embodiment is composed of an insulating layer 170 and an electrode 154 stacked on a semiconductor substrate (semiconductor layer) 200. The electrode 154 is composed of various metal films or polysilicon films, and the insulating layer 170 is composed of an oxide film such as a silicon oxide film. When a positive voltage (on voltage) is applied to the electrode, the charge storage unit MEM generates a depletion layer (inversion region) on the outermost surface of the semiconductor substrate (semiconductor layer) 200 located directly below the electrode (metal film or polysilicon film) 154 and the insulating layer 170, as shown in FIG. 10. Then, the charge is transferred to this generated depletion layer, and the charge is attracted to and stored in the electrode 154. In this embodiment, the capacity of the charge storage unit MEM can be easily increased by increasing the area of the electrode 154 (the area in contact with the semiconductor substrate).

Furthermore, in this embodiment, the capacitance of the charge storage unit MEM can be increased by reducing the thickness of the insulating layer 170 or by forming the insulating layer 170 using a material having a high dielectric constant (hafnium oxide (HfO ₂ )).

In addition, in the charge storage unit MEM as shown in FIG. 9, since the charge moves on the top surface of the semiconductor substrate 200, the charge may be captured by defects (e.g., dangling bonds) that occur on the surface and disappear, or the transfer of the charge to the floating diffusion region FD may be delayed. Therefore, in this embodiment, in order to avoid such charge capture, a structure of the charge storage unit MEM that can store the charge in a deep region of the semiconductor substrate 200 may be adopted. Details of such a charge storage unit MEM will be described below with reference to FIG. 11 and FIG. 12. FIG. 11 is an explanatory diagram showing another cross-sectional configuration example of the charge storage unit MEM according to this embodiment, and FIG. 12 is an energy band diagram of the charge storage unit MEM in FIG. 11. Note that in FIG. 11, the upper side in FIG. 11 is the surface side of the semiconductor substrate 200, and the lower side in FIG. 9 is the back side of the semiconductor substrate 200.

As shown in FIG. 11, the charge storage unit MEM according to this embodiment is composed of an insulating layer 170 and an electrode 154 stacked on a semiconductor substrate (semiconductor layer) 200. Furthermore, the charge storage unit MEM has a buried layer 172 buried in the semiconductor substrate 200 between the insulating layer 170 and the semiconductor substrate 200. For example, when the semiconductor substrate 200 is a P-type semiconductor substrate, the buried layer 172 is an N-type semiconductor region into which N-type impurities have been introduced.

When the charge storage unit MEM applies, for example, a negative voltage (off voltage) to the electrode, a depletion layer (channel region) is generated in the buried layer 172 embedded in the semiconductor substrate 200, as shown in FIG. 12. Then, charge is stored in the generated depletion layer. The depth at which the depletion layer is generated can be adjusted by appropriately selecting the impurity concentrations of the semiconductor substrate 200 and the buried layer 172, the thickness of the buried layer 172, the thickness of the insulating layer 170, etc. In this way, in this embodiment, it is possible to prevent charges from being captured by defects on the outermost surface, and the mobility of the charges can be increased.

As described above, according to this embodiment, it is possible to provide a light receiving element 10 that can reduce the effects of kTC noise while ensuring a wide dynamic range.

6.3 Modifications
The light receiving element 10 according to the embodiment of the present disclosure described above can also be modified as follows. Modifications 1 to 5 of the present embodiment will be described below. The light receiving element 10 according to Modifications 1 to 5 described below each have charge storage units MEM1 and MEM2 formed of MOS capacitors.

(Variation 1)
First, the first modification will be described with reference to Figs. 13 and 14. Fig. 13 is an explanatory diagram showing a cross-sectional configuration example of the light receiving element 10 according to the first modification of the present embodiment, and Fig. 14 is an enlarged view of the region C in Fig. 13. This modification has the charge storage units MEM1 and MEM2 made of MOS capacitors, but unlike the above-described present embodiment, has a vertical electrode 154 embedded in the semiconductor substrate 200 as shown in Fig. 13. In detail, as shown in Fig. 14, it has an insulating layer 170 embedded in a trench 174 formed in the semiconductor substrate 200, and a vertical buried electrode unit 178 embedded in the insulating layer 170. According to this modification, since the charge storage units MEM1 and MEM2 have the vertical electrode 154, the area of the insulating layer 170 sandwiched between the vertical electrode 154 and the semiconductor substrate (specifically, the N-type semiconductor regions 102a and 102b) 200 facing the electrode 154 can be increased. As a result, according to this modification, the area is increased, so that the capacitance of the charge storage units MEM1 and MEM2 can be further increased, and thus a wide dynamic range of the light receiving element 10 can be ensured.

(Variation 2)
Next, the second modification will be described with reference to FIG. 15. FIG. 15 is an explanatory diagram showing a cross-sectional configuration example of the light receiving element 10 according to the second modification of the present embodiment. In this modification, the light receiving element 10 also has charge storage units MEM1 and MEM2 made of MOS capacitors. Furthermore, in this modification, as shown in FIG. 15, the light receiving element 10 has a moth-eye structure 202a in which fine irregularities are formed, which is provided on the back surface (the surface opposite to the front surface) of the semiconductor substrate 200. In detail, as shown in FIG. 15, the moth-eye structure 202a is formed by arranging a plurality of substantially quadrangular pyramids having apexes on the semiconductor substrate 200 side in a matrix shape. In this modification, by providing the moth-eye structure 202a, it is possible to reduce abrupt changes in refractive index at the interface and prevent reflection.

(Variation 3)
Next, the third modification will be described with reference to FIG. 16. FIG. 16 is an explanatory diagram showing a cross-sectional configuration example of the light receiving element 10 according to the third modification of the present embodiment. In this modification, the light receiving element 10 also has charge storage units MEM1 and MEM2 made of MOS capacitors. Furthermore, in this modification, as shown in FIG. 16, the gate electrodes 150a and 150b of the distribution transistors VG1 and VG2 have buried gate units 170a and 170b buried in the semiconductor substrate 200. According to this modification, by doing so, the charge generated in the photodiode PD can be transferred to the charge storage units MEM1 and MEM2 more efficiently.

(Variation 4)
Next, the fourth modification will be described with reference to FIG. 17. FIG. 17 is an explanatory diagram showing a cross-sectional configuration example of the light receiving element 10 according to the fourth modification of the present embodiment. In this modification, the light receiving element 10 also has charge storage units MEM1 and MEM2 made of MOS capacitors. Furthermore, in this modification, as shown in FIG. 17, the light receiving element 10 has a pixel separation unit (second pixel separation unit) 210a (DTI (deep trench isolation)) that penetrates from the back surface (the surface opposite to the front surface) of the semiconductor substrate 200 to the middle of the semiconductor substrate 200 along the thickness direction of the semiconductor substrate 200. The pixel separation unit 210a can prevent incident light from entering the adjacent light receiving element 10.

(Variation 5)
Next, Modification 5 will be described with reference to Fig. 18. Fig. 18 is an explanatory diagram showing a cross-sectional configuration example of a light receiving element 10 according to Modification 5 of the present embodiment. In this modification, as shown in Fig. 18, the light receiving element 10 may have a plurality of, specifically, four, distribution transistors VG. In this modification as well, the light receiving element 10 has charge storage units (third charge storage units) MEM1, MEM2, MEM3, and MEM4 made of MOS capacitors.

<<7. Second embodiment>>
In the first embodiment and its modified examples described above, the insulating film (not shown) of the charge storage units MEM1 and MEM2 and the gate insulating film (not shown) of the amplifying transistors AMP1 and AMP2 may be thinned. In this way, the capacitance of the charge storage units MEM1 and MEM2 can be increased without increasing the size. Furthermore, random noise of the amplifying transistors AMP1 and AMP2 can be reduced because the number of crystal defects in the gate insulating film is reduced, the influence of crystal defects is reduced by increasing the mutual conductance gm of the transistor, and the interface state is reduced by shortening the heat treatment time and lowering the heat treatment temperature.

Here, with reference to FIG. 19, FIG. 20A, and FIG. 20B, the third embodiment of the present disclosure will be described with respect to the charge storage units MEM1 and MEM2 and the amplifying transistors AMP1 and AMP2 having a thinned insulating film. Note that FIG. 19 is an explanatory diagram showing a planar configuration example of the light receiving element 10 according to this embodiment, and is a diagram of the light receiving element 10 viewed from above the surface of the semiconductor substrate 200, which is similar to the light receiving element 10 of the first embodiment. Also, FIG. 20A is a cross-sectional view of the light receiving element 10 cut along line C-C' in FIG. 19, and FIG. 20B is a cross-sectional view of the light receiving element 10 cut along line D-D' in FIG. 19. In detail, in FIG. 20A and FIG. 20B, the upper side in the figure is the surface side of the semiconductor substrate 200, and the lower side in the figure is the back side of the semiconductor substrate 200.

In detail, in this embodiment, for example, as shown in FIG. 20A, the insulating film 720a located below the gate electrode 160 covered by the sidewall 730 of the amplification transistor AMP1 is made of, for example, an oxide film (third oxide film), and its film thickness is thinner than the insulating film 720 made of an oxide film (third oxide film) located below the gate electrode 158 of the reset transistor RST1 and the gate electrode 162 of the selection transistor SEL1.

In addition, in this embodiment, for example, as shown in FIG. 20B, the insulating film (insulating layer) 720a located below the electrode 154 covered by the sidewall 730 of the charge storage unit MEM1 is made of, for example, an oxide film (first oxide film), and its film thickness is thinner than the insulating film 720 made of an oxide film (second oxide film) located below the gate electrode 156 of the transfer transistor TG1.

In this embodiment, the insulating film 720a located below the gate electrode 160 of the amplification transistor AMP1 and the insulating film 720a located below the electrode 154 of the charge storage unit MEM1 may be oxide films made of the same material and may have approximately the same film thickness.

More specifically, in this embodiment, the insulating film 720a located below the gate electrode 160 of the amplification transistor AMP1 and the insulating film 720a located below the electrode 154 of the charge storage unit MEM1 are made of oxide films such as silicon oxide (SiO ₂ ) and silicon nitride (SiN). In addition, in this embodiment, the film thickness of the insulating film 720a located below the gate electrode 160 of the amplification transistor AMP1 and the insulating film 720a located below the electrode 154 of the charge storage unit MEM1 is preferably about half the film thickness of the insulating film 720 located below the gate electrodes 156, 158, and 162 of other elements (transfer transistor TG, reset transistor RST, and selection transistor SEL) in consideration of the effect of reducing random noise due to the thinner film and the increase in power consumption due to the increase in leakage current, and is more preferably, for example, 1.0 nm or more and 5.0 nm or less.

Furthermore, in this embodiment, the insulating film 720a located below the gate electrode 160 of the amplification transistor AMP1 and the insulating film 720a located below the electrode 154 of the charge storage unit MEM1 are preferably wider than the gate electrode 160 and the electrode 154 when viewed from above the semiconductor substrate 200 so as not to interfere with adjacent elements.

In this embodiment, it is not limited to thinning only the insulating film 720a of the charge storage units MEM1 and MEM2 or the gate insulating film 720a of the amplification transistors AMP1 and AMP2. In this embodiment, only the insulating film 720a of the charge storage units MEM1 and MEM2 may be thinned, and the insulating film 720 in contact with the gate electrodes 150, 152, 154, 156, 158, 160, 162 and electrode 154 of the elements (charge storage unit MEM, transfer transistor TG, distribution transistor VG, charge discharge transistor OFG, amplification transistor AMP, reset transistor RST, and selection transistor SEL) on the light receiving element 10 may be thinned.

As described above, according to this embodiment, the capacitance of the charge storage unit MEM can be increased and random noise of the transistor can be reduced without increasing the size by thinning the insulating film 720a of the charge storage unit MEM and the gate insulating film 720a of the amplifying transistor AMP. Therefore, according to this embodiment, by combining with the configuration of the first embodiment described above, it is possible to provide a light receiving element 10 and a distance measurement module 1 that can ensure a wider dynamic range while reducing the influence of kTC noise. This embodiment can be implemented in combination with the first embodiment described above and its modified examples.

<<8. Third embodiment>>
In the second embodiment, the insulating film 720a of the charge storage unit MEM and the gate insulating film 720a of the amplifier transistor AMP are thinned to increase the capacity of the charge storage unit MEM and reduce random noise of the amplifier transistor AMP. However, when the gate insulating film 720a is thinned, the effect as described above can be obtained, but the leakage current increases, so there is a limit to the thinning. Therefore, the present inventors came up with the idea of using a high-dielectric film having a high relative dielectric constant that can increase the capacity of the charge storage unit MEM compared to the above-mentioned oxide film even if it has the same film thickness, instead of the insulating film 720a. By using a high-dielectric film as the insulator film 720a, it is possible to increase the capacity of the charge storage unit MEM and reduce random noise of the amplifier transistor AMP while avoiding an increase in leakage current even if the film thickness is thinned.

21, 22A, and 22B, the fourth embodiment of the present disclosure will be described with respect to the charge storage units MEM1 and MEM2 and the amplifying transistors AMP1 and AMP2 having an insulating film made of a high dielectric film. FIG. 21 is an explanatory diagram showing a planar configuration example of the light receiving element 10 according to this embodiment, and is a diagram of the light receiving element 10 viewed from above the surface of the semiconductor substrate 200, which is similar to the light receiving element 10 of the first embodiment. FIG. 22A is a cross-sectional view of the light receiving element 10 cut along the line E-E' in FIG. 24, and FIG. 22B is a cross-sectional view of the light receiving element 10 cut along the line F-F' in FIG. 24. In detail, in FIG. 22A and FIG. 22B, the upper side in the figure is the surface side of the semiconductor substrate 200, and the lower side in the figure is the back side of the semiconductor substrate 200.

In detail, in this embodiment, for example, as shown in FIG. 22A, the insulating film (third insulating layer) 740 located below the gate electrode 160 covered with the sidewall 730 of the amplification transistor AMP1 is made of a high dielectric film. The relative dielectric constant of the insulating film 740 is higher than that of the insulating film (third insulating layer) 720 located below the gate electrode 158 of the reset transistor RST1 and the gate electrode 162 of the selection transistor SEL1.

In addition, in this embodiment, for example, as shown in FIG. 22B, the insulating film (first insulating layer) 740 located below the electrode 154 covered by the sidewall 730 of the charge storage unit MEM1 is made of a high dielectric film. The relative dielectric constant of the insulating film 740 is higher than that of the insulating film (second insulating layer) 720 located below the gate electrode 156 of the transfer transistor TG1.

In this embodiment, the insulating film 740 located below the gate electrode 160 of the amplification transistor AMP1 and the insulating film 740 located below the electrode 154 of the charge storage unit MEM1 may be formed from the same material.

More specifically, in this embodiment, the high dielectric film is a material having a higher dielectric constant than that of silicon oxide (SiO ₂ ) (3.9), and is preferably a material having a dielectric constant of 4 or more. In this embodiment, for example, the high dielectric film is a metal oxide film, and can be formed from a material such as Al ₂ O ₃ , HfSiON, Y ₂ O ₃ , Ta ₂ O ₅ , La ₂ O ₃ , TiO ₂ , HfO ₂ , ZrO ₂ , or HfZrO ₂ .

When the high dielectric film is used as the insulating film 740, metal materials such as TiN, TaN, and NiSi may be used as materials for forming the gate electrodes 150, 152, 154, 156, 158, 160, and 162 in order to adjust the Vth (threshold voltage).

Furthermore, in this embodiment, the insulating film 740 located below the gate electrode 160 of the amplification transistor AMP1 and the insulating film 740 located below the electrode 154 of the charge storage unit MEM1 are preferably wider than the gate electrode 160 and the electrode 154 when viewed from above the semiconductor substrate 200 so as not to interfere with adjacent elements.

In this embodiment, it is not limited to forming only the insulating film 740 of the charge storage units MEM1 and MEM2 and the gate insulating film 740 of the amplification transistors AMP1 and AMP2 from a high dielectric film. In this embodiment, only the insulating film 740 of the charge storage units MEM1 and MEM2 may be formed from a high dielectric film, and the insulating film 720 in contact with the gate electrodes 150, 152, 154, 156, 158, 160, 162 and electrode 154 of the elements (charge storage unit MEM, transfer transistor TG, distribution transistor VG, charge discharge transistor OFG, amplification transistor AMP, reset transistor RST, and selection transistor SEL) on the light receiving element 10 may be formed from a high dielectric film.

As described above, according to this embodiment, the insulating film 740 of the charge storage unit MEM and the gate insulating film 740 of the amplification transistor AMP are formed of a high dielectric film, so that it is possible to increase the capacity of the _charge storage unit MEM and reduce the random noise of the amplification transistor AMP without making the film thickness thinner than when SiO 2 is used. Therefore, according to this embodiment, by combining with the configuration according to the first embodiment described above, it is possible to provide a light receiving element 10 and a distance measuring module 1 that can ensure a wider dynamic range while reducing the influence of kTC noise. Note that this embodiment can be implemented in combination with the first embodiment described above and its modified examples.

<<9. Summary>>
As described above, according to the embodiments and modifications of the present disclosure, it is possible to provide a light receiving element 10 and a distance measurement module 1 that can reduce the influence of kTC noise while ensuring a wide dynamic range.

The present disclosure has been described above by giving embodiments and their modified examples, application examples, and applied examples, but the present disclosure is not limited to the above-mentioned embodiments, etc., and various modifications are possible. Note that the effects described in this specification are merely examples. The effects of the present disclosure are not limited to the effects described in this specification. The present disclosure may have effects other than those described in this specification.

In the above-described embodiments and modifications of the present disclosure, the conductivity type of each of the semiconductor regions may be reversed. For example, the present embodiments and modifications can be applied to elements that use holes as charges instead of electrons.

In the above-described embodiments and variations of the present disclosure, the semiconductor substrate does not necessarily have to be a silicon substrate, but may be another substrate (e.g., an SOI (Silicon on Insulator) substrate, a SiGe substrate, etc.). The semiconductor substrate may also be one in which a semiconductor structure or the like is formed on such various substrates.

In addition, in the above-described embodiments and variations of the present disclosure, the light receiving element 10 may be formed on a single chip together with the illumination unit and processing circuitry, or may be provided in a single package, and is not particularly limited.

In the embodiments and variants of the present disclosure, methods for forming the above-mentioned layers, films, elements, etc. may include, for example, physical vapor deposition (PVD) and chemical vapor deposition (CVD). Examples of the PVD method include vacuum deposition using resistance heating or high-frequency heating, EB (electron beam) deposition, various sputtering methods (magnetron sputtering, RF (radio frequency)-DC (direct current) combined bias sputtering, ECR (electron cyclotron resonance) sputtering, facing target sputtering, high-frequency sputtering, etc.), ion plating, laser ablation, molecular beam epitaxy (MBE), laser transfer, etc. Examples of the CVD method include plasma CVD, thermal CVD, MO (metal organic) CVD, photo CVD, etc. Further, other methods include electrolytic plating, electroless plating, spin coating, immersion, casting, microcontact printing, drop casting, various printing methods such as screen printing, inkjet printing, offset printing, gravure printing, and flexographic printing, stamping, spraying, and various coating methods such as air doctor coater, blade coater, rod coater, knife coater, squeeze coater, reverse roll coater, transfer roll coater, gravure coater, kiss coater, cast coater, spray coater, slit orifice coater, and calendar coater. In addition, examples of the patterning method for each layer include chemical etching such as shadow mask, laser transfer, and photolithography, and physical etching using ultraviolet light or laser. In addition, examples of the planarization technique include CMP (Chemical Mechanical Polishing), laser planarization, and reflow. In other words, the elements according to the embodiments and variations of the present disclosure can be manufactured easily and inexpensively using existing semiconductor device manufacturing processes.

<<10. Configuration Examples of Electronic Devices>>
In addition, the light receiving element 10 can be applied to the distance measuring module 1 as described above, and can also be applied to various electronic devices such as a camera with a distance measuring function and a smartphone with a distance measuring function. Therefore, with reference to Fig. 23, a configuration example of a smartphone 900 as an electronic device to which the present technology is applied will be described. Fig. 23 is a block diagram showing a configuration example of a smartphone 900 as an electronic device to which the distance measuring module 1 according to the embodiment of the present disclosure is applied.

23, the smartphone 900 includes a CPU (Central Processing Unit) 901, a ROM (Read Only Memory) 902, and a RAM (Random Access Memory) 903. The smartphone 900 also includes a storage device 904, a communication module 905, and a sensor module 907. The smartphone 900 further includes a ranging module 908 to which the above-mentioned ranging module 1 can be applied, and also includes an imaging device 909, a display device 910, a speaker 911, a microphone 912, an input device 913, and a bus 914. The smartphone 900 may also have a processing circuit such as a DSP (Digital Signal Processor) instead of or in addition to the CPU 901.

The CPU 901 functions as an arithmetic processing device and a control device, and controls all or part of the operations in the smartphone 900 according to various programs recorded in the ROM 902, the RAM 903, the storage device 904, or the like. The ROM 902 stores programs and arithmetic parameters used by the CPU 901. The RAM 903 temporarily stores programs used in the execution of the CPU 901 and parameters that change appropriately during the execution. The CPU 901, the ROM 902, and the RAM 903 are connected to each other by a bus 914. The storage device 904 is a data storage device configured as an example of the storage unit of the smartphone 900. The storage device 904 is configured, for example, by a magnetic storage device such as a hard disk drive (HDD), a semiconductor storage device, an optical storage device, or the like. This storage device 904 stores the programs and various data executed by the CPU 901, as well as various data acquired from the outside.

The communication module 905 is, for example, a communication interface configured with a communication device for connecting to the communication network 906. The communication module 905 may be, for example, a wired or wireless LAN (Local Area Network), Bluetooth (registered trademark), or a communication card for WUSB (Wireless USB). The communication module 905 may also be a router for optical communication, a router for ADSL (Asymmetric Digital Subscriber Line), or a modem for various communications. The communication module 905 transmits and receives signals, for example, between the Internet and other communication devices using a predetermined protocol such as TCP/IP. The communication network 906 connected to the communication module 905 is a network connected by wire or wirelessly, for example, the Internet, a home LAN, infrared communication, or satellite communication.

The sensor module 907 includes various sensors, such as a motion sensor (e.g., an acceleration sensor, a gyro sensor, a geomagnetic sensor, etc.), a biometric sensor (e.g., a pulse sensor, a blood pressure sensor, a fingerprint sensor, etc.), or a position sensor (e.g., a GNSS (Global Navigation Satellite System) receiver, etc.).

The distance measurement module 908 is provided on the surface of the smartphone 900, and can obtain, for example, the uneven shape and movement of the user's fingertips, palm, face, etc., facing the surface as distance measurement results. Such distance measurement results can be used for user authentication and recognition of the user's gestures. The distance measurement module 908 can also obtain, for example, the distance from the smartphone 900 to the target object 800, and obtain three-dimensional shape data of the surface of the target object 800.

The imaging device 909 is provided on the surface of the smartphone 900 and can capture an image of an object 800 or the like located around the smartphone 900. In detail, the imaging device 909 can be configured to include an imaging element (not shown) such as a CMOS (Complementary MOS) image sensor, and a signal processing circuit (not shown) that performs imaging signal processing on a signal photoelectrically converted by the imaging element. Furthermore, the imaging device 909 can further include an optical system mechanism (not shown) composed of an imaging lens, an aperture mechanism, a zoom lens, a focus lens, etc., and a drive system mechanism (not shown) that controls the operation of the optical system mechanism. The imaging element collects incident light from the object 800 as an optical image, and the signal processing circuit photoelectrically converts the formed optical image on a pixel-by-pixel basis, reads out the signal of each pixel as an imaging signal, and performs image processing to obtain an image.

The display device 910 is provided on the surface of the smartphone 900 and can be, for example, a display device such as an LCD (Liquid Crystal Display) or an organic EL (Electro Luminescence) display. The display device 910 can display an operation screen, an image captured by the imaging device 909 described above, and the like.

The speaker 911 can output, for example, telephone call audio and audio associated with the nesting content displayed by the display device 910 described above to the user.

The microphone 912 can pick up, for example, the user's voice during a call, voice including commands to activate functions of the smartphone 900, and voice from the surrounding environment of the smartphone 900.

The input device 913 is a device operated by a user, such as a button, a keyboard, a touch panel, or a mouse. The input device 913 includes an input control circuit that generates an input signal based on information input by the user and outputs the signal to the CPU 901. By operating the input device 913, the user can input various data to the smartphone 900 and instruct processing operations.

The above shows an example of the configuration of the smartphone 900. Each of the above components may be configured using general-purpose parts, or may be configured using hardware specialized for the function of each component. Such a configuration may be changed as appropriate depending on the technical level at the time of implementation.

<<11. Application example to endoscopic surgery system>>
The technology according to the present disclosure (the present technology) can be applied to various products. For example, the technology according to the present disclosure may be applied to an endoscopic surgery system.

Figure 24 is a diagram showing an example of the general configuration of an endoscopic surgery system to which the technology disclosed herein (the present technology) can be applied.

Figure 24 shows an operator (doctor) 11131 performing surgery on a patient 11132 on a patient bed 11133 using an endoscopic surgery system 11000. As shown in the figure, the endoscopic surgery system 11000 is composed of an endoscope 11100, other surgical tools 11110 such as an insufflation tube 11111 and an energy treatment tool 11112, a support arm device 11120 that supports the endoscope 11100, and a cart 11200 on which various devices for endoscopic surgery are mounted.

The endoscope 11100 is composed of a lens barrel 11101, the tip of which is inserted into the body cavity of the patient 11132 at a predetermined length, and a camera head 11102 connected to the base end of the lens barrel 11101. In the illustrated example, the endoscope 11100 is configured as a so-called rigid scope having a rigid lens barrel 11101, but the endoscope 11100 may also be configured as a so-called flexible scope having a flexible lens barrel.

The tip of the lens barrel 11101 is provided with an opening in which an objective lens is fitted. A light source device 11203 is connected to the endoscope 11100, and light generated by the light source device 11203 is guided to the tip of the lens barrel 11101 by a light guide extending inside the lens barrel 11101, and is irradiated toward an observation target in the body cavity of the patient 11132 through the objective lens. The endoscope 11100 may be a direct-viewing endoscope, an oblique-viewing endoscope, or a side-viewing endoscope. Furthermore, the tip of the lens barrel 11101 may be equipped with an irradiation unit 20 and a light receiving unit 30 of the distance measuring module 1 according to the embodiment of the present disclosure. By mounting a part of the distance measuring module 1, the accuracy of the surgery can be improved not only by the doctor's visual observation, but also by referring to the distance information from the distance measuring module 1.

For example, as shown in the configuration of FIG. 25 showing an example of the configuration of the endoscope 11100, an iToF sensor 15004, which is the irradiation unit 20 and the light receiving unit 30 of the distance measurement module 1 according to the embodiment of the present disclosure, is provided in the camera head 11102. In detail, reflected light (observation light) from the observation object passes through the lens barrel 11101, is collected by the lens 15001 in the camera head 11102, is reflected by the half mirror 15002, and is received by the iToF sensor 15004. Furthermore, the observation light is photoelectrically converted by the iToF sensor 15004 to generate an electrical signal corresponding to the observation light, is stored in the memory 15005, and is then transmitted to the distance measurement signal processing device 11209 described later.

Furthermore, as shown in FIG. 25, an image sensor 15003 is provided inside the camera head 11102, and reflected light (observation light) from the object of observation passes through the lens barrel 11101, is collected by the lens 15001, is reflected by the half mirror 15002, and is received by the image sensor 15003. The observation light is photoelectrically converted by the image sensor 15003 to generate an electrical signal corresponding to the observation light, that is, an image signal corresponding to the observed image. The image signal is temporarily stored in the memory 15005, and then transmitted to the camera control unit (CCU: Camera Control Unit) 11201 as RAW data.

The CCU 11201 is composed of a CPU (Central Processing Unit), a GPU (Graphics Processing Unit), etc., and controls the overall operation of the endoscope 11100 and the display device 11202. Furthermore, the CCU 11201 receives an image signal from the camera head 11102, and performs various image processing on the image signal, such as development processing (demosaic processing), in order to display an image based on the image signal.

Under the control of the CCU 11201, the display device 11202 displays an image based on an image signal that has been subjected to image processing by the CCU 11201.

The light source device 11203 is composed of a light source such as an LED (Light Emitting Diode) and supplies irradiation light to the endoscope 11100 when photographing the surgical site, etc.

The input device 11204 is an input interface for the endoscopic surgery system 11000. A user can input various information and instructions to the endoscopic surgery system 11000 via the input device 11204. For example, the user inputs an instruction to change the imaging conditions (type of irradiation light, magnification, focal length, etc.) of the endoscope 11100.

The treatment tool control device 11205 controls the operation of the energy treatment tool 11112 for cauterizing tissue, incising, sealing blood vessels, etc. The insufflation device 11206 sends gas into the body cavity of the patient 11132 via the insufflation tube 11111 to inflate the body cavity for the purpose of ensuring the field of view of the endoscope 11100 and ensuring the working space of the surgeon. The recorder 11207 is a device capable of recording various information related to the surgery. The printer 11208 is a device capable of printing various information related to the surgery in various formats such as text, image, or graph. The distance measurement signal processing device 11209 is a device provided with the control unit 40 and processing unit 60 of the distance measurement module 1 according to an embodiment of the present disclosure, and is capable of acquiring distance information.

The light source device 11203 that supplies irradiation light to the endoscope 11100 when photographing the surgical site can be composed of a white light source composed of, for example, an LED, a laser light source, or a combination of these. When the white light source is composed of a combination of RGB laser light sources, the output intensity and output timing of each color (each wavelength) can be controlled with high precision, so that the white balance of the captured image can be adjusted in the light source device 11203. In this case, it is also possible to capture images corresponding to each of the RGB colors in a time-division manner by irradiating the observation object with laser light from each of the RGB laser light sources in a time-division manner and controlling the drive of the image sensor of the camera head 11102 in synchronization with the irradiation timing. According to this method, a color image can be obtained without providing a color filter to the image sensor.

The light source device 11203 may be controlled to change the intensity of the light it outputs at predetermined time intervals. The image sensor of the camera head 11102 may be controlled to acquire images in a time-division manner in synchronization with the timing of the change in the light intensity, and the images may be synthesized to generate an image with a high dynamic range that is free of so-called blackout and whiteout.

The light source device 11203 may be configured to supply light of a predetermined wavelength band corresponding to the special light observation. In the special light observation, for example, by utilizing the wavelength dependency of light absorption in body tissue, a narrow band light is irradiated compared to the irradiation light (i.e., white light) during normal observation, and a predetermined tissue such as blood vessels on the mucosal surface is photographed with high contrast, so-called narrow band imaging is performed. Alternatively, in the special light observation, a fluorescent observation may be performed in which an image is obtained by fluorescence generated by irradiating excitation light. In the fluorescent observation, excitation light is irradiated to the body tissue and the fluorescence from the body tissue is observed (autofluorescence observation), or a reagent such as indocyanine green (ICG) is locally injected into the body tissue and excitation light corresponding to the fluorescent wavelength of the reagent is irradiated to the body tissue to obtain a fluorescent image. The light source device 11203 may be configured to supply narrow band light and/or excitation light corresponding to such special light observation.

Figure 26 is a block diagram showing an example of the functional configuration of the camera head 11102 and CCU 11201 shown in Figure 24.

The camera head 11102 has a lens unit 11401, an imaging unit 11402, a drive unit 11403, a communication unit 11404, and a camera head control unit 11405. The CCU 11201 has a communication unit 11411, an image processing unit 11412, and a control unit 11413. The camera head 11102 and the CCU 11201 are connected to each other via a transmission cable 11400 so that they can communicate with each other.

The lens unit 11401 is an optical system provided at the connection with the lens barrel 11101. Observation light taken in from the tip of the lens barrel 11101 is guided to the camera head 11102 and enters the lens unit 11401. The lens unit 11401 is composed of a combination of multiple lenses including a zoom lens and a focus lens.

The imaging unit 11402 may have one imaging element (so-called single-plate type) or multiple imaging elements (so-called multi-plate type). When the imaging unit 11402 is configured as a multi-plate type, for example, each imaging element may generate an image signal corresponding to each of RGB, and a color image may be obtained by combining these. Alternatively, the imaging unit 11402 may be configured to have a pair of imaging elements for acquiring image signals for the right eye and the left eye corresponding to 3D (dimensional) display. By performing 3D display, the surgeon 11131 can more accurately grasp the depth of the biological tissue in the surgical site. Note that when the imaging unit 11402 is configured as a multi-plate type, multiple lens units 11401 may be provided corresponding to each imaging element.

Furthermore, the imaging unit 11402 does not necessarily have to be provided in the camera head 11102. For example, the imaging unit 11402 may be provided inside the lens barrel 11101, immediately after the objective lens.

The driving unit 11403 is composed of an actuator, and moves the zoom lens and focus lens of the lens unit 11401 a predetermined distance along the optical axis under the control of the camera head control unit 11405. This allows the magnification and focus of the image captured by the imaging unit 11402 to be appropriately adjusted.

The communication unit 11404 is configured with a communication device for transmitting and receiving various information to and from the CCU 11201. The communication unit 11404 transmits the image signal obtained from the imaging unit 11402 as RAW data to the CCU 11201 via the transmission cable 11400.

The communication unit 11404 also receives control signals for controlling the operation of the camera head 11102 from the CCU 11201 and supplies them to the camera head control unit 11405. The control signals include information on the imaging conditions, such as information specifying the frame rate of the captured image, information specifying the exposure value during imaging, and/or information specifying the magnification and focus of the captured image.

The above-mentioned frame rate, exposure value, magnification, focus, and other imaging conditions may be appropriately specified by the user, or may be automatically set by the control unit 11413 of the CCU 11201 based on the acquired image signal. In the latter case, the endoscope 11100 is equipped with the so-called AE (Auto Exposure) function, AF (Auto Focus) function, and AWB (Auto White Balance) function.

The camera head control unit 11405 controls the operation of the camera head 11102 based on a control signal from the CCU 11201 received via the communication unit 11404.

The communication unit 11411 is configured with a communication device for transmitting and receiving various information to and from the camera head 11102. The communication unit 11411 receives an image signal transmitted from the camera head 11102 via the transmission cable 11400.

The communication unit 11411 also transmits a control signal to the camera head 11102 for controlling the driving of the camera head 11102. The image signal and the control signal can be transmitted by electrical communication, optical communication, etc.

The image processing unit 11412 performs various image processing operations on the image signal, which is the RAW data transmitted from the camera head 11102.

The control unit 11413 performs various controls related to the imaging of the surgical site, etc. by the endoscope 11100, and the display of the captured image obtained by imaging the surgical site, etc. For example, the control unit 11413 generates a control signal for controlling the driving of the camera head 11102.

The control unit 11413 also displays the captured image showing the surgical site on the display device 11202 based on the image signal that has been image-processed by the image processing unit 11412. At this time, the control unit 11413 may recognize various objects in the captured image using various image recognition techniques. For example, the control unit 11413 can recognize surgical tools such as forceps, specific body parts, bleeding, mist generated when using the energy treatment tool 11112, and the like, by detecting the shape and color of the edges of objects included in the captured image. When the control unit 11413 displays the captured image on the display device 11202, it may use the recognition result to superimpose various types of surgical support information on the image of the surgical site. By superimposing the surgical support information and presenting it to the surgeon 11131, the burden on the surgeon 11131 can be reduced and the surgeon 11131 can proceed with the surgery reliably.

The transmission cable 11400 connecting the camera head 11102 and the CCU 11201 is an electrical signal cable for electrical signal communication, an optical fiber for optical communication, or a composite cable of these.

In the illustrated example, communication is performed wired using a transmission cable 11400, but communication between the camera head 11102 and the CCU 11201 may also be performed wirelessly.

The above describes an example of an endoscopic surgery system to which the technology disclosed herein can be applied. The technology disclosed herein can be applied to the imaging unit 11402 of the configuration described above. Specifically, the light receiving element 10 can be applied as part of the configuration of the imaging unit 11402. By applying the technology disclosed herein as part of the configuration of the imaging unit 11402, the distance to the surgical site can be measured with high accuracy, and a clearer image of the surgical site can be obtained.

Note that, although an endoscopic surgery system has been described here as an example, the technology disclosed herein may also be applied to other systems, such as a microsurgical system.

<<12. Examples of applications to moving objects>>
The technology according to the present disclosure (the present technology) can be applied to various products. For example, the technology according to the present disclosure may be realized as a device mounted on any type of moving body such as an automobile, an electric vehicle, a hybrid electric vehicle, a motorcycle, a bicycle, a personal mobility device, an airplane, a drone, a ship, or a robot.

Figure 27 is a block diagram showing a schematic configuration example of a vehicle control system, which is an example of a mobile object control system to which the technology disclosed herein can be applied.

The vehicle control system 12000 includes a plurality of electronic control units connected via a communication network 12001. In the example shown in FIG. 27, the vehicle control system 12000 includes a drive system control unit 12010, a body system control unit 12020, an outside vehicle information detection unit 12030, an inside vehicle information detection unit 12040, and an integrated control unit 12050. In addition, the functional configuration of the integrated control unit 12050 includes a microcomputer 12051, an audio/video output unit 12052, and an in-vehicle network I/F (Interface) 12053.

The drive system control unit 12010 controls the operation of devices related to the drive system of the vehicle according to various programs. For example, the drive system control unit 12010 functions as a control device for a drive force generating device for generating a drive force for the vehicle, such as an internal combustion engine or a drive motor, a drive force transmission mechanism for transmitting the drive force to the wheels, a steering mechanism for adjusting the steering angle of the vehicle, and a braking device for generating a braking force for the vehicle.

The body system control unit 12020 controls the operation of various devices installed in the vehicle body according to various programs. For example, the body system control unit 12020 functions as a control device for a keyless entry system, a smart key system, a power window device, or various lamps such as headlamps, tail lamps, brake lamps, turn signals, and fog lamps. In this case, radio waves or signals from various switches transmitted from a portable device that replaces a key can be input to the body system control unit 12020. The body system control unit 12020 accepts the input of these radio waves or signals and controls the vehicle's door lock device, power window device, lamps, etc.

The outside-vehicle information detection unit 12030 detects information outside the vehicle equipped with the vehicle control system 12000. For example, an imaging unit 12031 is connected to the outside-vehicle information detection unit 12030. The outside-vehicle information detection unit 12030 causes the imaging unit 12031 to capture an image outside the vehicle and receives the captured image. The outside-vehicle information detection unit 12030 may perform object detection processing or distance detection processing for people, cars, obstacles, signs, or characters on the road surface based on the received image. In addition, an iToF sensor 12032 is connected to the outside-vehicle information detection unit 12030. The iToF sensor 12032 can function as a distance measurement module 1 according to an embodiment of the present disclosure.

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

The in-vehicle information detection unit 12040 detects information inside the vehicle. For example, a driver state detection unit 12041 that detects the state of the driver is connected to the in-vehicle information detection unit 12040. The driver state detection unit 12041 includes, for example, a camera that captures an image of the driver, and the in-vehicle information detection unit 12040 may calculate the driver's degree of fatigue or concentration based on the detection information input from the driver state detection unit 12041, or may determine whether the driver is dozing off.

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

The microcomputer 12051 can also perform cooperative control for the purpose of autonomous driving, which allows the vehicle to travel autonomously without relying on the driver's operation, by controlling the driving force generating device, steering mechanism, braking device, etc. based on information about the surroundings of the vehicle acquired by the outside vehicle information detection unit 12030 or the inside vehicle information detection unit 12040.

The microcomputer 12051 can also output control commands to the body system control unit 12030 based on information outside the vehicle acquired by the outside-vehicle information detection unit 12030. For example, the microcomputer 12051 can control the headlamps according to the position of a preceding vehicle or an oncoming vehicle detected by the outside-vehicle information detection unit 12030, and perform cooperative control aimed at preventing glare, such as switching high beams to low beams.

The audio/image output unit 12052 transmits at least one output signal of audio and image to an output device capable of visually or audibly notifying information to vehicle occupants or the outside of the vehicle. In the example of FIG. 27, an audio speaker 12061, a display unit 12062, and an instrument panel 12063 are exemplified as output devices. The display unit 12062 may include, for example, at least one of an on-board display and a head-up display.

Figure 28 shows an example of the installation position of the imaging unit 12031.

In FIG. 28, the imaging unit 12031 includes imaging units 12101, 12102, 12103, 12104, and 12105.

The imaging units 12101, 12102, 12103, 12104, and 12105 are provided, for example, at the front nose, side mirrors, rear bumper, back door, and upper part of the windshield inside the vehicle cabin of the vehicle 12100. The imaging unit 12101 provided at the front nose and the imaging unit 12105 provided at the upper part of the windshield inside the vehicle cabin mainly acquire images of the front of the vehicle 12100. The imaging units 12102 and 12103 provided at the side mirrors mainly acquire images of the sides of the vehicle 12100. The imaging unit 12104 provided at the rear bumper or back door mainly acquires images of the rear of the vehicle 12100. The imaging unit 12105 provided at the upper part of the windshield inside the vehicle cabin is mainly used to detect a leading vehicle, pedestrians, obstacles, traffic lights, traffic signs, lanes, etc. In addition, the iToF sensor module 12201, which incorporates the irradiation unit 20 and the light receiving unit 30 of the distance measurement module 1 according to the embodiment of the present disclosure, is provided, for example, on the front nose of the vehicle 12100.

In addition, FIG. 24 shows an example of the imaging ranges of the imaging units 12101 to 12104. Imaging range 12111 indicates the imaging range of the imaging unit 12101 provided on the front nose, imaging ranges 12112 and 12113 indicate the imaging ranges of the imaging units 12102 and 12103 provided on the side mirrors, respectively, and imaging range 12114 indicates the imaging range of the imaging unit 12104 provided on the rear bumper or back door. For example, an overhead image of the vehicle 12100 viewed from above is obtained by superimposing the image data captured by the imaging units 12101 to 12104.

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

For example, the microcomputer 12051 can extract, as a preceding vehicle, the closest three-dimensional object on the path of the vehicle 12100 that is traveling in approximately the same direction as the vehicle 12100 at a predetermined speed (e.g., 0 km/h or faster) by calculating the distance to each three-dimensional object within the imaging range 12111 to 12114 and the change in this distance over time (relative speed with respect to the vehicle 12100) based on the distance information obtained from the imaging units 12101 to 12104. Furthermore, the microcomputer 12051 can set the distance to be secured in advance in front of the preceding vehicle, and perform automatic brake control (including follow-up stop control) and automatic acceleration control (including follow-up start control). In this way, cooperative control can be performed for the purpose of autonomous driving, which runs autonomously without relying on the driver's operation.

For example, the microcomputer 12051 classifies and extracts three-dimensional object data on three-dimensional objects, such as two-wheeled vehicles, ordinary vehicles, large vehicles, pedestrians, utility poles, and other three-dimensional objects, based on the distance information obtained from the imaging units 12101 to 12104, and can use the data to automatically avoid obstacles. For example, the microcomputer 12051 distinguishes obstacles around the vehicle 12100 into obstacles that are visible to the driver of the vehicle 12100 and obstacles that are difficult to see. Then, the microcomputer 12051 determines the collision risk, which indicates the risk of collision with each obstacle, and when the collision risk is equal to or exceeds a set value and there is a possibility of a collision, the microcomputer 12051 can provide driving assistance for collision avoidance by outputting an alarm to the driver via the audio speaker 12061 or the display unit 12062, or by performing forced deceleration or avoidance steering via the drive system control unit 12010.

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

The above describes an example of a vehicle control system to which the technology disclosed herein can be applied. The technology disclosed herein can be applied to the vehicle outside information detection unit 12030 and the imaging unit 12031 of the above-described configurations. Specifically, the light receiving element 10 or the distance measurement module 1 can be applied to the distance detection processing block of the vehicle outside information detection unit 12030 and the imaging unit 12031. By applying the technology disclosed herein to the vehicle outside information detection unit 12030 and the imaging unit 12031, the distance to an object such as a person, a car, an obstacle, a sign, or letters on the road surface can be measured with high accuracy, and the obtained distance information can be used to reduce driver fatigue and increase the safety of the driver and the vehicle.

<<13. Supplementary Information>>
Although the preferred embodiment of the present disclosure has been described in detail above with reference to the attached drawings, the technical scope of the present disclosure is not limited to such examples. It is clear that a person having ordinary knowledge in the technical field of the present disclosure can conceive of various modified or amended examples within the scope of the technical ideas described in the claims, and it is understood that these also naturally belong to the technical scope of the present disclosure.

Furthermore, the effects described in this specification are merely descriptive or exemplary and are not limiting. In other words, the technology disclosed herein may achieve other effects that are apparent to a person skilled in the art from the description in this specification, in addition to or in place of the above effects.

The present technology can also be configured as follows.
(1)
a photoelectric conversion unit provided in the semiconductor substrate and converting light into electric charges;
a first charge accumulation unit to which the charges are transferred from the photoelectric conversion unit;
a second charge accumulation unit to which the charges are transferred from the photoelectric conversion unit;
Equipped with
Each of the first and second charge storage units is formed of a stack of an electrode, a first insulating layer, and a semiconductor layer.
Photodetector.
(2)
Each of the first and second charge accumulation units accumulates the charge in an inversion region generated in the outermost surface of the semiconductor layer located immediately below the first insulating layer by applying a first voltage to the electrode.
The light receiving element according to (1) above.
(3)
The stack further includes a buried layer buried in the semiconductor layer between the first insulating layer and the semiconductor layer.
The light receiving element according to (1) above.
(4)
the semiconductor layer is a semiconductor layer of a first conductivity type,
The buried layer is a semiconductor layer of a second conductivity type that is opposite to the first conductivity type.
The light receiving element according to (3) above.
(5)
Each of the first and second charge accumulation units accumulates the charge in a channel region generated in the semiconductor layer by applying a second voltage to the electrode.
The light receiving element according to (3) or (4) above.
(6)
a photoelectric conversion unit provided in the semiconductor substrate and converting light into electric charges;
a first charge accumulation unit to which the charges are transferred from the photoelectric conversion unit;
a second charge accumulation unit to which the charges are transferred from the photoelectric conversion unit;
Equipped with
Each of the first and second charge storage units includes
A semiconductor layer;
an insulating layer embedded in a trench formed in the semiconductor layer;
a vertical electrode embedded in the insulating layer;
having
Photodetector.
(7)
The electrode is made of a metal film,
The first insulating layer is made of an oxide film.
The light receiving element according to any one of (1) to (5) above.
(8)
The thickness of the oxide film is 5.0 nm or less.
The light receiving element according to (7) above.
(9)
The first insulating layer has a relative dielectric constant of 4 or more.
The light receiving element according to any one of (1) to (5) above.
(10)
a first distribution transistor that distributes the charge from the photoelectric conversion unit to the first charge accumulation unit;
a second distribution transistor that distributes the charge from the photoelectric conversion unit to the second charge accumulation unit;
Further comprising:
The light receiving element according to any one of (1) to (5) above.
(11)
The light receiving element according to (10) above, wherein a predetermined voltage is applied to the gates of the first and second distribution transistors at different timings.
(12)
The semiconductor substrate further includes a moth-eye structure having fine projections and recesses formed on a surface opposite to the surface of the semiconductor substrate.
The light receiving element according to any one of (1) to (11) above.
(13)
Further comprising a first pixel isolation portion penetrating the semiconductor substrate.
The light receiving element according to any one of (1) to (11) above.
(14)
a second pixel separating portion extending from a surface of the semiconductor substrate opposite to the front surface to a middle portion of the semiconductor substrate along a thickness direction of the semiconductor substrate;
The light receiving element according to any one of (1) to (11) above.
(15)
one or more floating diffusion regions;
a first transfer transistor that transfers the charges transferred to the first charge storage unit to the one or more floating diffusion regions;
a second transfer transistor that transfers the charges transferred to the second charge storage unit to the one or more floating diffusion regions;
Further comprising:
The light receiving element according to (10) above.
(16)
one or more amplifying transistors that amplify the charges transferred to the floating diffusion region and output the amplified charges as a pixel signal;
one or more selection transistors that output the pixel signal according to a selection signal;
one or more reset transistors for resetting the charge stored in the floating diffusion region;
Further comprising:
The light receiving element according to (15) above.
(17)
the first insulating layer is made of a first oxide film;
each of the first and second transfer transistors has a second oxide film provided on the semiconductor substrate;
The first oxide film has a smaller thickness than the second oxide film.
The light receiving element according to (16) above.
(18)
each of the amplification transistor, the selection transistor, and the reset transistor has a third oxide film provided on the semiconductor substrate;
a thickness of the third oxide film of the amplification transistor is thinner than a thickness of the third oxide film of the selection transistor and the reset transistor;
The light receiving element according to (17) above.
(19)
each of the first and second transfer transistors has a second insulating layer provided on the semiconductor substrate;
The first insulating layer has a higher dielectric constant than the second insulating layer.
The light receiving element according to (16) above.
(20)
each of the amplification transistor, the selection transistor, and the reset transistor has a third insulating layer provided on the semiconductor substrate;
the third insulating layer of the amplification transistor has a higher relative dielectric constant than the third insulating layers of the selection transistor and the reset transistor;
The light receiving element according to (19) above.
(21)
a plurality of third charge accumulation units to which the charges are transferred from the photoelectric conversion unit;
Each of the third charge accumulation units is formed of a stack of an electrode, a fourth insulating layer, and a semiconductor layer.
The light receiving element according to (1) above.
(22)
A light receiving device including one or more light receiving elements,
The light receiving element is
a photoelectric conversion unit provided in the semiconductor substrate and converting light into electric charges;
a first charge accumulation unit to which the charges are transferred from the photoelectric conversion unit;
a second charge accumulation unit to which the charges are transferred from the photoelectric conversion unit;
having
Each of the first and second charge storage units is formed of a stack of an electrode, a first insulating layer, and a semiconductor layer.
Light receiving device.
(23)
an illumination unit that illuminates an object with light by periodically varying the brightness;
An irradiation control unit that controls the irradiation unit;
Further equipped with
The photoelectric conversion unit receives reflected light from the object.
The light receiving device described in (22) above.

REFERENCE SIGNS LIST 1 Range-finding module 10 Light-receiving element 12 Pixel array section 20 Irradiation section 30 Light-receiving section 32 Vertical drive circuit section 34 Column signal processing circuit section 36 Horizontal drive circuit section 38 Output circuit section 40 Control section 42 Pixel drive wiring 44 Control circuit section 46 Horizontal signal line 48 Vertical signal line 50 Distribution transistor drive section 52 Signal processing section 54 Data storage section 60 Processing section 100, 102, 102a, 102b, 104a, 104b, 106a, 106b, 108a, 108b, 110a, 110b, 112a, 112b, 114a, 114b, 116a, 116b N-type semiconductor region 150a, 150b, 152a, 152b, 156a, 156b, 158a, 158b, 160a, 160b, 162a, 162b Gate electrode 154a, 154b, 306, 406 Electrode 170, 720, 720a Insulating layer 172 Buried layer 174 Trench 178 Buried electrode portion 200 Semiconductor substrate 202 Anti-reflection film 202a Moth-eye structure 204 Planarization film 206 Light-shielding film 208 On-chip lens 210, 210a Pixel separation portion 300 Wiring layer 302, 402 Insulating film 304, 404 Metal film 400 Substrate 600, 602 Center line 710 Via 730 Sidewall 740 High dielectric constant film 800 Object 802a, 802b Area 900 Smartphone 901 CPU
902 ROM
903 RAM
904 Storage device 905 Communication module 907 Sensor module 908 Distance measurement module 909 Imaging device 910 Display device 911 Speaker 912 Microphone 913 Input device AMP, AMP1, AMP2 Amplification transistor FD, FD1, FD2 Floating diffusion region MEM, MEM1, MEM2 Charge storage section O Center point OFG, OFG1, OFG2 Charge discharge transistor PD Photodiode RST, RST1, RST2 Reset transistor SEL, SEL1, SEL2 Selection transistor TG, TG1, TG2 Transfer transistor VDD Power supply potential VG, VG1, VG2 Distribution transistor VSL, VSL1, VSL2 Signal line

Claims (7)

a photoelectric conversion unit provided in the semiconductor substrate and converting light into electric charges;
a first charge accumulation unit to which the charges are transferred from the photoelectric conversion unit;
a second charge accumulation unit to which the charges are transferred from the photoelectric conversion unit;
a first distribution transistor that distributes the charge from the photoelectric conversion unit to the first charge accumulation unit;
a second distribution transistor that distributes the charge from the photoelectric conversion unit to the second charge accumulation unit;
one or more floating diffusion regions;
a first transfer transistor that transfers the charges transferred to the first charge storage unit to the one or more floating diffusion regions;
a second transfer transistor that transfers the charges transferred to the second charge storage unit to the one or more floating diffusion regions;
one or more amplifying transistors that amplify the charges transferred to the floating diffusion region and output the amplified charges as a pixel signal;
one or more selection transistors that output the pixel signal according to a selection signal;
one or more reset transistors for resetting the charge stored in the floating diffusion region;
Equipped with
each of the first and second charge storage units includes a stack of an electrode, a first insulating layer, and a semiconductor layer ;
the first insulating layer is made of a first oxide film;
each of the first and second transfer transistors has a second oxide film provided on the semiconductor substrate;
The first oxide film is thinner than the second oxide film,
each of the amplification transistor, the selection transistor, and the reset transistor has a third oxide film provided on the semiconductor substrate;
a thickness of the third oxide film of the amplification transistor is smaller than a thickness of the third oxide film of the selection transistor and the reset transistor;
Photodetector. Each of the first and second charge accumulation units accumulates the charge in an inversion region generated in the outermost surface of the semiconductor layer located immediately below the first insulating layer by applying a first voltage to the electrode.
The light receiving element according to claim 1 . The stack further includes a buried layer buried in the semiconductor layer between the first insulating layer and the semiconductor layer.
The light receiving element according to claim 1 . the semiconductor layer is a semiconductor layer of a first conductivity type,
The buried layer is a semiconductor layer of a second conductivity type that is opposite to the first conductivity type.
The light receiving element according to claim 3 . Each of the first and second charge accumulation units accumulates the charge in a channel region generated in the semiconductor layer by applying a second voltage to the electrode.
The light receiving element according to claim 3 . A light receiving device including one or more light receiving elements,
The light receiving element is
a photoelectric conversion unit provided in the semiconductor substrate and converting light into electric charges;
a first charge accumulation unit to which the charges are transferred from the photoelectric conversion unit;
a second charge accumulation unit to which the charges are transferred from the photoelectric conversion unit;
a first distribution transistor that distributes the charge from the photoelectric conversion unit to the first charge accumulation unit;
a second distribution transistor that distributes the charge from the photoelectric conversion unit to the second charge accumulation unit;
one or more floating diffusion regions;
a first transfer transistor that transfers the charges transferred to the first charge storage unit to the one or more floating diffusion regions;
a second transfer transistor that transfers the charges transferred to the second charge storage unit to the one or more floating diffusion regions;
one or more amplifying transistors that amplify the charges transferred to the floating diffusion region and output the amplified charges as a pixel signal;
one or more selection transistors that output the pixel signal according to a selection signal;
one or more reset transistors for resetting the charge stored in the floating diffusion region;
having
each of the first and second charge storage units includes a stack of an electrode, a first insulating layer, and a semiconductor layer ;
the first insulating layer is made of a first oxide film;
each of the first and second transfer transistors has a second oxide film provided on the semiconductor substrate;
The first oxide film is thinner than the second oxide film,
each of the amplification transistor, the selection transistor, and the reset transistor has a third oxide film provided on the semiconductor substrate;
a thickness of the third oxide film of the amplification transistor is smaller than a thickness of the third oxide film of the selection transistor and the reset transistor;
Light receiving device. an illumination unit that illuminates an object with light by periodically varying the brightness;
An irradiation control unit that controls the irradiation unit;
Further equipped with
The photoelectric conversion unit receives reflected light from the object.
The light receiving device according to claim 6 .

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