Patent Description:
Recently, a device called single photon avalanche diode (SPAD), which realizes optical communication, distance measurement, photon count, and the like by capturing a very weak optical signal, has been developed and studied. The SPAD performs avalanche amplification with respect to the charge that is generated by the incident photon. Accordingly, even though light is weak, the SPAD can detect the light. However, in the SPAD, when a dark current that is generated on a silicon substrate surface is amplified, dark current characteristics such as a dark count rate (DCR) deteriorate. Here, a SPAD in which a pinning region is formed on a silicon substrate surface to suppress a dark current is suggested (for example, refer to PTL <NUM>). The pinning region is a region in which an impurity concentration is adjusted so that a potential barrier is generated between the pinning region and an amplification region that performs avalanche amplification.

In the <CIT> a single photon avalanche diode is disclosed. A first semiconductor layer serves as a first implanted layer of a first conductivity type. A second semiconductor layer of a second conductivity type is provided under the first semiconductor layer. The second conductivity type is opposite to the first conductivity type. The second semiconductor layer is buried in an epitaxial layer grown above a substrate. The second semiconductor layer becomes fully depleted when an appropriate bias voltage is applied to the device.

In the related art, inflow of the dark current into the amplification region is prevented (or alternatively, reduced) due to the potential barrier between the pinning region and the amplification region, and thus it is possible to suppress deterioration of the dark current characteristics. However, the larger a potential difference between the pinning region and a cathode is, the smaller a depletion layer width between the pinning region and the cathode is. Accordingly, pixel capacity increases. Here, the pixel capacity represents electrostatic capacity of a pixel in which the SPAD is provided. When the pixel capacity increases, time necessary to take out charges collected in the pixel to perform recharge is lengthened, and thus it is difficult to improve a frame rate. When the pinning region is not provided, the pixel capacity decreases, but the dark current characteristics deteriorate. Accordingly, there is a problem that it is difficult to reduce the pixel capacity while suppressing the dark current.

The present technology has been made in consideration of the above-described Sony Semiconductor Solutions Corporations situation, and it is desirable that pixel capacity is reduced while suppressing a dark current in a photodiode that performs amplification of a charge.

According to a solution, the present invention provides an avalanche photodiode sensor in accordance with independent claim <NUM>. Further solutions and aspects are set forth in the dependent claims, the drawings and the following description.

The present technology has been made to solve the above-described problem. According to a first aspect, an avalanche photodiode sensor includes a photoelectric conversion region disposed in a substrate and that converts incident light into electric charge; a first region of a first conductivity type on the photoelectric conversion region; a cathode disposed in the substrate adjacent to the first region and coupled to the photoelectric conversion region; an anode disposed in the substrate adjacent to the cathode; and a contact of the first conductivity type disposed in the substrate. An impurity concentration of the first region is different than an impurity concentration of the contact. For example, the impurity concentration of the first region is lower than the impurity concentration of the contact. The avalanche photodiode sensor further includes a second region of the first conductivity type disposed in the substrate and positioned between the photoelectric conversion region and the first region. The impurity concentration of the first region is higher than an impurity concentration of the second region. The avalanche photodiode sensor further includes an insulating structure formed in the substrate between the photoelectric conversion region and an adjacent photoelectric conversion region. The cathode is positioned between the anode and the first region. The avalanche photodiode sensor further includes a film on a light receiving surface of the substrate. The film is on side surfaces of the insulating structure. In a plan view, the first region surrounds the contact, and the cathode surrounds the first region. In the plan view, the anode surrounds the cathode. In the plan view, the contact is located in a central area of the first region. The contact and the cathode are coupled to a first signal line that receives a first voltage, and the anode is coupled to a second signal line that receives a second voltage. The anode, the cathode, and the first region are one of rectangular shaped or circle shaped. In the plan view, the first region surrounds the cathode, the contact surrounds the first region, and the anode surrounds the contact. The avalanche photodiode sensor further includes a transistor including a source and drain formed in the first region; an oxide layer on the first region; and a gate on the oxide layer.

According to a second aspect of the present technology, an avalanche photodiode sensor includes a photoelectric conversion region disposed in a substrate and that converts incident light into electric charge; a first region of a first conductivity type disposed in the substrate; a cathode disposed in the substrate adjacent to the first region and coupled to the photoelectric conversion region; an anode disposed in the substrate adjacent to the cathode; and a contact of the first conductivity type disposed in the first region. An impurity concentration of the first region is lower than an impurity concentration of the contact.

The avalanche photodiode sensor further includes a second region of the first conductivity type disposed in the substrate and positioned between the photoelectric conversion region and the first region.

The impurity concentration of the first region is higher than an impurity concentration of the second region.

The avalanche photodiode sensor further includes an insulating structure formed in the substrate between the photoelectric conversion region and an adjacent photoelectric conversion region.

The avalanche photodiode sensor further includes a film on a light receiving surface of the substrate, and the film is on side surfaces of the insulating structure. In a plan view, the first region surrounds the contact, and the cathode surrounds the first region.

In addition, according to a third aspect of the present technology, an avalanche photodiode sensor includes a photoelectric conversion region disposed in a substrate and that converts incident light into electric charge; a first region of a first conductivity type on the photoelectric conversion region; a first electrode disposed in the substrate adjacent to the first region and coupled to the photoelectric conversion region; a second electrode disposed in the substrate adjacent to the first electrode; and a third electrode of the first conductivity type disposed in the first region. An impurity concentration of the first region is lower than an impurity concentration of the third electrode.

According to the present technology, it is possible to attain an excellent effect capable of reducing pixel capacity while suppressing a dark current in a photodiode that performs amplification of a charge. Furthermore, the effect stated here is not limited, and may be any one effect described in the present technology.

Hereinafter, embodiments for carrying out the present technology (hereinafter, referred to as embodiments) will be described. Description will be made in the following order.

<FIG> is a block diagram illustrating a configuration example of a distance measurement module <NUM> according to a first embodiment of the present technology. The distance measurement module <NUM> measures a distance from an object by using a time of flight (ToF) method, and includes a light-emitting unit <NUM>, a control unit <NUM>, a light-receiving unit <NUM>, and a distance measurement computation unit <NUM>.

The light-emitting unit <NUM> emits pulse light as irradiation light in accordance with a control of the control unit <NUM>.

The light-receiving unit <NUM> receives reflected light with respect to intermittent light and generates measurement data indicating turnaround time of light on the basis of a clock signal transmitted from the control unit <NUM>, and the like. The light-receiving unit <NUM> supplies predetermined pieces of measurement data to the distance measurement computation unit <NUM> through a signal line <NUM>.

The control unit <NUM> controls the light-emitting unit <NUM> and the light-receiving unit <NUM>. The control unit <NUM> generates a timing signal indicating light-emission timing of irradiation light, and supplies the timing signal to the light-emitting unit <NUM> and the light-receiving unit <NUM> through signal lines <NUM> and <NUM>.

The distance measurement computation unit <NUM> computes a distance up to an object on the basis of the measurement data transmitted from the light-receiving unit <NUM>. The distance measurement computation unit <NUM> generates image data, in which a plurality of pieces of distance data indicating the distance that is computed are arranged in a two-dimensional lattice shape, in synchronization with a vertical synchronization signal, and outputs the image data. For example, the image data can be used in image processing in which gradation processing corresponding to a distance is performed, gesture recognition, and the like.

<FIG> is a block diagram illustrating a configuration example of the light-receiving unit <NUM> according to the first embodiment of the present technology. The light-receiving unit <NUM> includes a pixel array unit <NUM> and a read-out circuit <NUM>. A plurality of pixel circuits <NUM> are arranged in the pixel array unit <NUM> in a two-dimensional lattice shape.

Each of the pixel circuits <NUM> generates a pulse signal when receiving reflected light, and output the pulse signal to the read-out circuit <NUM>.

The read-out circuit <NUM> reads out the pulse signal transmitted from the pixel array unit <NUM>. The read-out circuit <NUM> measures a turnaround time from light-emission timing of irradiation light to light-reception timing indicated by the pulse signal by using a time to digital converter (TDC), and the like. Then, the read-out circuit <NUM> supplies measurement data indicating a measurement value to the distance measurement computation unit <NUM>. The distance measurement computation unit <NUM> divides a value, which is obtained by multiplying the turnaround time by the speed of light, by two to calculate a distance up to an object.

<FIG> is a circuit diagram illustrating a configuration example of a pixel circuit <NUM> according to the first embodiment of the present technology. The pixel circuit <NUM> includes a resistor <NUM> and a photodiode (or photoelectric conversion region) <NUM>. Furthermore, in the same drawing, circuits and elements other than the resistor <NUM> and the photodiode <NUM> are omitted.

The resistor <NUM> is inserted between a power supply and a cathode of a photodiode <NUM>. The photodiode <NUM> amplifies light through photoelectric conversion. For example, a SPAD can be used as the photodiode <NUM>.

A dark-state cathodic potential of the photodiode <NUM> is set as Vop. When the photodiode <NUM> receives reflected light and performs avalanche amplification, a large current flows to the resistor <NUM> and voltage drop occurs. When the cathodic potential decreases to a potential Vbd at which the avalanche amplification does not occur due to the voltage drop, the large current stops. This phenomenon is referred to as "quench.

Next, charges collected in the photodiode <NUM> are leaked due to recharge by the potential Vop, and the cathodic potential returns to the potential Vop from the potential Vbd immediately after the quench. Due to returning to the potential Vop, the photodiode <NUM> can response to a photon. Here, a charge amount Q stored in the photodiode <NUM> is expressed by the following expression.

Q = C x (Vop - Vbd). In the expression, C represents electrostatic capacity (pixel capacity) of the pixel circuit <NUM>. A unit of Q is, for example, a coulomb (C), and a unit of the pixel capacity C is, for example, a farad (F). In addition, a unit of the potential Vop and the potential Vbd is, for example, a volt (V).

Time from a point of time at which lowering a cathodic potential initiates to a point of time at which the cathodic potential returns to the potential Vop is time for which the photodiode <NUM> is not able to react with a photon, and is referred to as "dead time. " In the dead time, time from occurrence of avalanche amplification to occurrence of quench is very short, and thus a length of the dead time is approximately limited by a recharge time of the photodiode <NUM>. The smaller the pixel capacity C is, the shorter the recharge time becomes. Accordingly, a reduction of the pixel capacity C is demanded to realize a high frame rate (that is, a frequency of a vertical synchronization signal).

Furthermore, the pixel circuit <NUM> is provided in the distance measurement module <NUM>, but the pixel circuit <NUM> may be provided in a circuit or a device other than the distance measurement module <NUM>. For example, the pixel circuit <NUM> can be used in a circuit and the like which perform optical communication, or a circuit and the like which perform photon count.

<FIG> is an example of a cross-sectional view of the photodiode <NUM> according to the first embodiment of the present technology. A direction perpendicular to a light-receiving surface of the photodiode <NUM> is set as a Z direction. In addition, a predetermined direction parallel to the light-receiving surface is set as an X direction. A direction perpendicular to the X direction and the Z direction is set as a Y direction.

When viewed form the Z direction, an insulating region (or insulating structure) <NUM> that isolates pixels is provided in the vicinity of an outer peripheral edge of the photodiode <NUM>.

In addition, a cover film <NUM> is formed on the light-receiving surface and a lateral surface of the insulating region <NUM>. The cover film <NUM> may include an oxide, such as zirconium oxide, hafnium oxide, and/or aluminum oxide, etc. A depletion layer <NUM> is formed on an upper side of the cover film <NUM> in a state in which the light-receiving surface is set as the lowest surface. For example, the depletion layer <NUM> includes an N-type semiconductor. An amplification region <NUM> including an N-layer <NUM> and a P-layer <NUM> is formed on an upper side of the depletion layer <NUM>. The N-layer <NUM> is formed on an upper side of the P-layer <NUM>.

In addition, in a state in which the light-receiving surface is set as a rear surface, a pinning region <NUM> is formed on a front surface opposite to the rear surface, and an anode electrode <NUM>, a cathode electrode <NUM>, and a contact <NUM> are buried in the pinning region <NUM>. A predetermined reference potential (ground potential and the like) is applied to the contact <NUM>. The anode electrode <NUM> and the contact <NUM> are formed through addition of, for example, an acceptor, and the cathode electrode <NUM> is formed through addition of, for example, a donor. The contact <NUM> may be located in a central area of the pinning region <NUM>. Furthermore, the contact <NUM> is an example of a reference electrode in the appended claims.

In addition, an impurity concentration of the pinning region <NUM> is adjusted so that a barrier region <NUM> having a potential barrier is formed between the pinning region <NUM> and the amplification region <NUM> in the Z direction. Details of the impurity concentration will be described later.

The depletion layer <NUM> generates a charge through photoelectric conversion, and the amplification region <NUM> performs avalanche amplification with respect to the charge. Then, the charge that is amplified is output from the cathode electrode <NUM>.

In addition, the impurity concentration of the pinning region <NUM> is set to a value different than (e.g., lower than) that of the contact <NUM>, for example, 1E17/cubic centimeters (/cm<NUM>). In addition, the impurity concentration of the pinning region <NUM> is set to a value higher than that of the barrier region <NUM>.

<FIG> is an example of a plan view of the photodiode <NUM> according to the first embodiment of the present technology. A shape of the photodiode <NUM> is, for example, a rectangular shape when viewed from the Z direction. The anode electrode <NUM> is disposed along an outer edge of the photodiode <NUM>. The cathode electrode <NUM> is disposed to be adjacent to an inner side of the anode electrode <NUM>. The pinning region <NUM> is provided to be adjacent to an inner side of the cathode electrode <NUM>. The contact <NUM> is disposed at the inside (the center and the like) of the pinning region <NUM>.

<FIG> is an example of a potential view of the photodiode <NUM> according to the first embodiment of the present technology. In the same drawing, the horizontal axis represents a distance from an outer edge of the photodiode <NUM> in the X direction, and the vertical axis represents a distance (depth) in the Z direction. In addition, in the same drawing, it is assumed that the darker a color of a region, the higher a potential of the region is. For example, a potential of the pinning region <NUM> is higher than that of the contact <NUM>. The reason for this is because the impurity concentration of the pinning region <NUM> is lower than that of the contact <NUM>.

<FIG> is an example of a potential view in a depth direction of the photodiode according to the first embodiment of the present technology. In the same drawing, the vertical axis represents a potential, and the horizontal axis represents a depth from a surface in a line segment Z1-Z2 in <FIG>.

As described above, since the impurity concentration of the pinning region <NUM> is set to be lower than that of the contact <NUM>, a potential of the pinning region <NUM> becomes higher than that of the contact <NUM>, and is close to a cathodic potential. For example, a potential of the contact <NUM> becomes <NUM> volts (V) in comparison to a cathodic potential of <NUM> volts (V).

In addition, a potential of the barrier region <NUM> between the pinning region <NUM> and the amplification region <NUM> is higher than that of the pinning region <NUM>. The cathode electrode <NUM> is buried in the pinning region <NUM>, and thus there is a concern that even when light is not incident thereto, a dark current (in other words, leakage current) may occur. A hole in the leakage current migrates to a low-potential side. However, a potential barrier in the barrier region <NUM> occurs between the pinning region <NUM> and the amplification region <NUM>, and thus the hole does not reach the amplification region <NUM>. On the other hand, a potential barrier does not exist between the pinning region <NUM> and the contact <NUM> set to a ground potential, and the potential of the contact <NUM> is lower than that of the pinning region <NUM>, and thus a hole is absorbed to a ground.

In addition, an electron in the leakage current migrates to a high-potential side. As described above, the cathodic potential is higher in comparison to the pinning region <NUM>, and thus, the electron is output from the cathode electrode <NUM> and is not problematic. In addition, the potential of the amplification region <NUM> is lower than that of the pinning region <NUM>, and thus an electron does not jump into the amplification region <NUM>.

As a result, a hole that occurs as a dark current is not measured as the dark current, and it is possible to suppress deterioration of DCR.

In addition, when the impurity concentration of the pinning region <NUM> is set to be smaller than that of the contact <NUM>, a difference in the impurity concentration between the pinning region <NUM> and the cathode electrode <NUM> further decreases in comparison to an opposite case. According to this, a depletion layer width between the pinning region <NUM> and the cathode electrode <NUM> becomes wider. When the depletion layer width becomes wider, the charge amount capable of being stored in the junction portion between the pinning region <NUM> and the cathode electrode <NUM> deceases, and the pixel capacity C decreases.

Here, description will be given on the assumption of a comparative example in which the impurity concentration of the pinning region <NUM> is set to equal to or greater than the impurity concentration of the contact <NUM>. <FIG> is an example of a potential view in a depth direction of a photodiode in the comparative example.

When the impurity concentration of the pinning region <NUM> is set to be equal to or greater than the impurity concentration of the contact <NUM>, a potential barrier of the barrier region <NUM> is enlarged, and it is easy to suppress a leakage current. However, a difference in the impurity concentration between the pinning region <NUM> and the cathode electrode <NUM> increases, and the depletion layer width therebetween becomes narrower, and thus the pixel capacity C increases.

<FIG> is a timing chart illustrating an example of an operation of the pixel circuit <NUM> according to the first embodiment of the present technology. At a timing T0, when the photodiode <NUM> receives reflected light and performs avalanche amplification, a large current flows to a resistor <NUM>, and voltage drop occurs. Due to the voltage drop, when the cathodic potential is lowered to a ground potential GND (or <NUM> volt) at which avalanche amplification does not occur at a timing T1, the large current is stopped.

Next, charges collected in the photodiode <NUM> are leaked due to recharge by the potential Vop, and the cathodic potential at a timing T2 returns from the ground potential GND immediately after the quench to the potential Vop.

Time from the timing T0 at which lowering of the cathodic potential initiates to the timing T2 at which the cathodic potential returns to the potential Vop corresponds to the dead time. A length of the dead time is mostly limited by a recharge time from the timing T1 to the timing T2.

In the photodiode <NUM>, since the impurity concentration of the pinning region <NUM> is set to be smaller than that of the contact <NUM>, the pixel capacity C is reduced, and thus it is possible to shorten the recharge time. According to this, the dead time is shortened, and thus a high frame rate can be realized.

<FIG> is a timing chart illustrating an example of an operation of a pixel circuit according to a comparative example. In this comparative example, the impurity concentration of the pinning region <NUM> is set to be equal to or greater than the impurity concentration of the contact <NUM>, and thus the pixel capacity C increases, and the recharge time is lengthened. As a result, the dead time is lengthened, and it is difficult to realize the high frame rate.

<FIG> is an example of a cross-sectional view of the photodiode <NUM> before mounting a substrate according to the first embodiment of the present technology. Ion implantation is performed sequentially from a deeper side from the front surface. For example, through the ion implantation, the depletion layer <NUM> is formed, and the amplification region <NUM> is subsequently formed. In addition, the anode electrode <NUM>, the cathode electrode <NUM>, and the contact <NUM> are buried, and the pinning region <NUM> is formed. Due to formation of the pinning region <NUM>, a potential barrier (barrier region <NUM>) is formed between the pinning region <NUM> and the amplification region <NUM>.

<FIG> is an example of a cross-sectional view of the photodiode <NUM> after mounting the substrate according to the first embodiment of the present technology. The anode electrode <NUM>, the cathode electrode <NUM>, and the contact <NUM> are connected to substrates <NUM> and <NUM> through a signal line.

<FIG> is an example of a cross-sectional view of the photodiode before forming an insulating region according to the first embodiment of the present technology. After connecting the substrates <NUM> and <NUM>, the light-receiving surface is polished by a polishing device <NUM>.

<FIG> is an example of a cross-sectional view of the photodiode after forming the insulating region according to the first embodiment of the present technology. After the polishing, the insulating region <NUM> is formed in the vicinity of an outer edge of the photodiode <NUM> and pixels are isolated.

<FIG> is an example of a cross-sectional view of the photodiode after forming the cover film <NUM> according to the first embodiment of the present technology. After forming the insulating region <NUM>, the cover film <NUM> is formed on the light-receiving surface and the lateral surface of the insulating region <NUM>.

<FIG> is a flowchart illustrating an example of a method of manufacturing the photodiode <NUM> according to the first embodiment of the present technology. The depletion layer <NUM> and the amplification region <NUM> are formed through ion implantation (step S901). Next, a signal line is wired (step S902), and the rear surface is polished (step S903). In addition, the insulating region <NUM> is formed (step S904), and the cover film is formed (step S905). After step S905, the remaining processes are executed, and a process of manufacturing the photodiode <NUM> is terminated.

As described above, in the first embodiment of the present technology, since the impurity concentration of the pinning region <NUM> is set to be lower than that of the contact <NUM>, a difference in the impurity concentration between the pinning region <NUM> and the cathode electrode <NUM> is made to be small, and thus it is possible to widen the depletion layer width therebetween. According to this, it is possible to reduce electrostatic capacity of the pixel circuit <NUM>.

In the above-described first embodiment, the impurity concentration of the pinning region <NUM> is set to be lower than that of the contact <NUM>. However, the potential barrier further decreases in comparison to a case where the impurity concentration is set to be equal to or greater than the impurity concentration of the contact <NUM>. Accordingly, when a dark current increases, there is a concern that a hole in the dark current jumps over the potential barrier, and jumps to the amplification region <NUM>. A photodiode <NUM> according to the second embodiment is different from the first embodiment in that the pixel capacity is reduced by a method other than adjustment of the impurity concentration of the pinning region <NUM>.

<FIG> is an example of a cross-sectional view of the photodiode <NUM> according to the second embodiment of the present technology. The photodiode <NUM> of the second embodiment is different from the first embodiment in that the contact <NUM> is connected to the cathode electrode <NUM> through a signal line. According to this, a cathodic potential is applied to the contact <NUM>, and a potential difference between the contact <NUM> and the cathode electrode <NUM> does not exist. Accordingly, the pixel capacity C of the photodiode <NUM> is further reduced in comparison to the first embodiment from the viewpoint of a circuit connected to the photodiode <NUM>.

In addition, when a potential difference exists between a wire between the contact <NUM> and the ground, and a wire connected to the cathode electrode <NUM>, wiring capacity occurs. However, in the second embodiment, the potential difference does not exist between the wires, and thus the wiring capacity does not occur. Accordingly, it is possible to further reduce the pixel capacity C to a certain extent corresponding to the non-occurrence of the wiring capacity.

In addition, the impurity concentration of the pinning region <NUM> of the second embodiment may be set to be smaller or equal to or greater than that of the contact <NUM>. Furthermore, a method of manufacturing the photodiode <NUM> of the second embodiment is the same as in the first embodiment except that the contact <NUM> and the cathode electrode <NUM> are connected to each other.

Furthermore, the cathode electrode <NUM> and the contact <NUM> are an example of a pair of electrodes described in the appended claims.

As described above, in the second embodiment of the present technology, the same potential is applied to the cathode electrode <NUM> and the contact <NUM>, and thus it is possible to further reduce the pixel capacity in comparison to a case where potentials different from each are applied thereto.

In the above-described first embodiment, the pinning region <NUM> is formed in the photodiode <NUM> through ion implantation. However, there is a concern that a defect damage may occur on a substrate the photodiode <NUM> is formed due to the ion implantation. A third embodiment is different from the first embodiment in that a semiconductor layer of a metal oxide semiconductor (MOS) transistor adjacent to the photodiode <NUM> is used as the pinning region.

<FIG> is an example of a cross-sectional view of a pixel circuit <NUM> according to the third embodiment of the present technology. The pixel circuit <NUM> of the third embodiment further includes a transistor <NUM>. In addition, the pinning region <NUM> is not formed in the photodiode <NUM>.

The transistor <NUM> is a MOS transistor including a metal layer <NUM>, an oxide film <NUM>, and a semiconductor layer <NUM>. The semiconductor layer <NUM> is provided on an upper side of the barrier region <NUM> of the photodiode <NUM>, and the oxide film <NUM> is formed on an upper side of the semiconductor layer <NUM>. In addition, the metal layer <NUM> is provided on an upper side of the oxide film <NUM>.

The metal layer <NUM> can be used as a gate of the transistor <NUM>, and a source and a drain are formed in the semiconductor layer <NUM>.

A negative bias lower than a reference potential (ground potential and the like) is applied to the gate of the transistor <NUM>. According to this, it is possible to suppress a dark current by inducing a hole in the dark current. That is, the semiconductor layer <NUM> functions as a pinning region.

On the other hand, impurities for pinning may not be added to a silicon surface of the photodiode <NUM>, and thus it is possible to remove a defect damage due to addition of the impurities. In addition, in a case where the oxide film <NUM> has a high quality, an interface level is lowered, and thus it is possible to lower the DCR. According to this, it is possible to raise a potential of the pinning region (semiconductor layer <NUM>) to a certain extent corresponding to lowering of the DCR due to lowering of the interface level. As a result, it is possible to further reduce the pixel capacity C in comparison to the first embodiment.

As described above, according to the third embodiment of the present technology, since the dark current is suppressed by applying a negative bias to the gate electrode of the transistor <NUM>, it is not necessary to form the pinning region in the photodiode <NUM>. According to this, it is possible to remove the defect damage of the photodiode <NUM> due to formation of the pinning region.

In the above-described first embodiment, the cathode electrode <NUM> is formed at the periphery of the pinning region <NUM>. However, the further a pixel size increases, the longer a junction portion between the cathode electrode <NUM> and the pinning region <NUM> becomes. Accordingly, the pixel capacity increases. Here, the length of the junction portion represents a length in a direction parallel to a boundary line between the cathode electrode <NUM> and the pinning region <NUM>. The photodiode <NUM> of the fourth embodiment is different from the first embodiment in that the pixel capacity is reduced by disposing the cathode electrode <NUM> on an inner side of the pinning region <NUM>.

<FIG> is an example of a plan view of the photodiode <NUM> according to the fourth embodiment of the present technology. In the photodiode <NUM> of the fourth embodiment, the cathode electrode <NUM> is disposed on an inner side (the center and the like) of the pinning region <NUM> when viewed from the Z direction. In addition, the contact <NUM> is disposed at the periphery of the pinning region <NUM>. When the cathode electrode <NUM> is disposed on an inner side of the pinning region <NUM>, a junction portion between the cathode electrode <NUM> and the pinning region <NUM> becomes shorter in comparison to the first embodiment, and thus the pixel capacity is reduced.

As described above, in the fourth embodiment of the present technology, since the cathode electrode <NUM> is disposed on an inner side of the pinning region <NUM>, it is possible to further shorten the junction portion in comparison to a case where the cathode electrode <NUM> is disposed at the periphery of the pinning region <NUM>. According to this, it is possible to reduce the electrostatic capacity of the pixel circuit <NUM>.

In the above-described first embodiment, the shape of the photodiode <NUM> is set to a rectangular shape. However, in a case of the rectangular shape, an intense electric field is likely to occur at an end of the photodiode <NUM>, and thus avalanche amplification occurs at the outside of the amplification region <NUM>, and thus there is a concern that an operation of the pixel circuit <NUM> is blocked. This phenomenon is referred to as an edge breakdown phenomenon. The fifth embodiment is different from the first embodiment in that the shape of the photodiode <NUM> is set to a circular shape.

<FIG> is an example of a plan view of the photodiode <NUM> according to the fifth embodiment of the present technology. The photodiode <NUM> of the fifth embodiment is different from the first embodiment in that a shape on a plane parallel to the light-receiving surface is set to a circular shape. Shapes of the cathode electrode <NUM>, the pinning region <NUM>, and the contact <NUM> in the photodiode <NUM> are also set to a circular shape.

When the shape of the photodiode <NUM> is set to a circular shape, an effective area of the amplification region <NUM> decreases, and thus there is a possibility that an occurrence probability (photon detection efficiency (PDE)) of avalanche amplification with respect to one photon decreases. However, an intense electric field is less likely to occur at an end of the photodiode <NUM>, and thus it is possible to suppress the edge breakdown phenomenon. In addition, it is possible to enhance long-term reliability.

Furthermore, the shape of the photodiode <NUM> is set to the circular shape, but a polygonal shape such as a pentagon and a hexagon close to a circle may be employed.

As described above, in the fifth embodiment of the present technology, the shape of the photodiode <NUM> is set to a circular shape, and thus an edge disappears. As a result, it is possible to suppress the edge breakdown phenomenon.

The technology (the present technology) according to the present disclosure is applicable to various products. For example, the technology according to the present disclosure can be realized as a device that is mounted on a moving body any one kind among an automobile, an electric vehicle, a hybrid electric vehicle, a motorcycle, a bicycle, a personal mobility, an airplane, a drone, a ship, a robot, and the like.

<FIG> is a block diagram illustrating a schematic configuration example of a vehicle control system that is an example of a moving body control system to which the technology according to the present disclosure is applicable.

A vehicle control system <NUM> includes a plurality of electronic control units which are connected to each other through a communication network <NUM>. In the example illustrated in <FIG>, the vehicle control system <NUM> includes a drive system control unit <NUM>, a body system control unit <NUM>, a vehicle exterior information detection unit <NUM>, a vehicle interior information detection unit <NUM>, and an integrated control unit <NUM>. In addition, as a functional configuration of the integrated control unit <NUM>, a microcomputer <NUM>, a voice and image output unit <NUM>, and an in-vehicle network interface (I/F) <NUM> are illustrated in the drawing.

The drive system control unit <NUM> controls an operation of a device relating to the drive system of the vehicle in accordance with various programs. For example, the drive system control unit <NUM> functions as a control device of a drive force generation device such as an internal combustion engine and a drive motor which generate a drive force of the vehicle, a drive force transmission mechanism that transmits the drive force to wheels, a steering mechanism that adjusts a steering angle of the vehicle, and a braking device that generates a braking force of the vehicle, and the like.

The body system control unit <NUM> controls an operation of various devices which are mounted to a vehicle body in accordance with various programs. For example, the body system control unit <NUM> functions as a control device of a keyless entry system, a smart key system, a power window device, and various lamps such as a head lamp, a back lamp, a brake lamp, a winker, and a fog lamp. In this case, an electric wave that is transmitted from a portable device that substitutes for a key, or signals of various switches can be input to the body system control unit <NUM>. The body system control unit <NUM> receives input of the electric wave or the signals, and controls a door lock device, a power window device, a lamp, and the like of the vehicle.

The vehicle exterior information detection unit <NUM> detects information on an outer side of the vehicle on which the vehicle control system <NUM> is mounted. For example, an imaging unit <NUM> is connected to the vehicle exterior information detection unit <NUM>. The vehicle exterior information detection unit <NUM> allows the imaging unit <NUM> to capture a vehicle exterior image, and receives the captured image. The vehicle exterior information detection unit <NUM> may perform object detection processing of a person, a vehicle, an obstacle, a sign, a character on a road, or the like, or distance detection processing on the basis of the image that is received.

The imaging unit <NUM> is an optical sensor that receives light and outputs an electric signal corresponding to the amount of light received. The imaging unit <NUM> can output the electric signal as an image or as distance measurement information. In addition, light received by the imaging unit <NUM> may be visible light, or invisible light such as infrared rays.

The vehicle interior information detection unit <NUM> detects vehicle interior information. For example, a driver state detection unit <NUM> that detects a driver state is connected to the vehicle interior information detection unit <NUM>. For example, the driver state detection unit <NUM> includes a camera that images a driver, and the vehicle interior information detection unit <NUM> may calculate the degree of fatigue or the degree of concentration of a driver, or may determine whether or not the driver drowses on the basis of detection information that is input from the driver state detection unit <NUM>.

The microcomputer <NUM> calculates a control target value of the drive force generation device, the steering mechanism, or the braking device on the basis of vehicle interior or exterior information that is acquired by the vehicle exterior information detection unit <NUM> or the vehicle interior information detection unit <NUM>, and can output a control command to the drive system control unit <NUM>. For example, the microcomputer <NUM> can perform a cooperative control to realize a function of an advanced driver assistance system (ADAS) which includes collision avoidance or impact mitigation of the vehicle, following travel based on an inter-vehicle distance, vehicle speed maintenance travel, vehicle collision alarm, vehicle lane deviation alarm, and the like.

In addition, the microcomputer <NUM> can perform a cooperative control for automatic driving and the like in which the vehicle autonomously travels without depending on an operation of a driver by controlling the drive force generation device, the steering mechanism, the braking device, and the like on the basis of information in the vicinity of the vehicle which is acquired by the vehicle exterior information detection unit <NUM> or the vehicle interior information detection unit <NUM>.

In addition, the microcomputer <NUM> can output a control command to the body system control unit <NUM> on the basis of the vehicle exterior information acquired by the vehicle exterior information detection unit <NUM>. For example, the microcomputer <NUM> can perform a cooperative control to realize glare protection such as switching of a high beam into a low beam by controlling the head lamp in correspondence with a position of a preceding vehicle or an oncoming vehicle which is detected by the vehicle exterior information detection unit <NUM>.

The voice and image output unit <NUM> transmits at least one output signal between a voice and an image to an output device capable of visually or aurally notifying a passenger in a vehicle or an outer side of the vehicle of information. In the example in <FIG>, as the output device, an audio speaker <NUM>, a display unit <NUM>, and an instrument panel <NUM> are exemplified. For example, the display unit <NUM> may include at least one of an on-board display and a head-up display.

<FIG> is a view illustrating an example of an installation position of the imaging unit <NUM>.

In <FIG>, as the imaging unit <NUM>, imaging units <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> are provided.

For example, the imaging units <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> are installed at positions such as a front nose, a side-view mirror, a rear bumper, a back door, an upper side of a vehicle front glass in a vehicle room, of the vehicle <NUM>. The imaging unit <NUM> provided at the front nose, and the imaging unit <NUM> that is provided on an upper side of the vehicle front glass in a vehicle room mainly acquire images on a forward side of the vehicle <NUM>. The imaging units <NUM> and <NUM> which are provided in the side-view mirror mainly acquire images on a lateral side of the vehicle <NUM>. The imaging unit <NUM> that is provided in the rear bumper or the back door mainly acquires images on a backward side of the vehicle <NUM>. The imaging unit <NUM> that is provided on an upper side of the vehicle front glass in the vehicle room can be mainly used to detect a preceding vehicle, a pedestrian, an obstacle, a traffic signal, a traffic sign, a vehicle lane, and the like.

Furthermore, <FIG> illustrates an example of a photographing range of the imaging units <NUM> to <NUM>. An image capturing range <NUM> represents an image capturing range of the imaging unit <NUM> that is provided in the front nose, image capturing ranges <NUM> and <NUM> respectively represent image capturing ranges of the imaging units <NUM> and <NUM> which are provided in the side-view mirrors, an image capturing range <NUM> represents an image capturing range of the imaging unit <NUM> that is provided in the rear bumper or the back door. For example, when a plurality of pieces of image data captured by the imaging unit <NUM> to <NUM> are superimposed on each other, it is possible to obtain an overlooking image when the vehicle <NUM> is viewed from an upper side.

At least one of the imaging units <NUM> to <NUM> may have a function of acquiring distance information. For example, at least one of the imaging units <NUM> to <NUM> may be a stereo camera including a plurality of imaging elements, or may be an imaging element that includes pixels for phase difference detection.

For example, the microcomputer <NUM> can extract a three-dimensional object, which is a closest three-dimensional object, particularly, on a proceeding path of the vehicle <NUM> and travels in approximately the same direction as that of the vehicle <NUM> that travels at a predetermined velocity (for example, <NUM>/h or greater), as a preceding vehicle by obtaining distances to respective three-dimensional objects in the image capturing ranges <NUM> to <NUM> and a variation of the distances with the passage of time (relative velocity to the vehicle <NUM>) on the basis of the distance information obtained from the imaging units <NUM> to <NUM>. In addition, the microcomputer <NUM> can set a distance between vehicles to be secured in advance in front of the preceding vehicle to perform automatic brake control (also including a following stop control), an automatic acceleration control (also including a following acceleration control), and the like. As described above, it is possible to perform a cooperative control for automatic driving in which a vehicle autonomously travels without depending on an operation by a driver, and the like.

For example, the microcomputer <NUM> can extract three-dimensional object data relating to a three-dimensional object by classifying a plurality of pieces of the three-dimensional object data into data of a two-wheel vehicle, data of typical vehicle, data of a large-sized vehicle, data of pedestrian, and data of other three-dimensional objects such as an electric pole on the basis of the distance information obtained from the imaging units <NUM> to <NUM>, and can use the three-dimensional object data for automatic obstacle avoidance. For example, the microcomputer <NUM> discriminates obstacles at the periphery of the vehicle <NUM> into an obstacle that is visually recognized by a driver of the vehicle <NUM> and an obstacle that is difficult to be visually recognized by the driver. In addition, the microcomputer <NUM> determines collision risk indicating the degree of danger of collision with each of the obstacles. In a situation in which the collision risk is equal to or greater than a set value, and collision may occur, the microcomputer <NUM> can assist driving for collision avoidance by outputting an alarm to the driver through the audio speaker <NUM> or the display unit <NUM>, or by performing compulsory deceleration or avoidance steering through the drive system control unit <NUM>.

At least one of the imaging units <NUM> to <NUM> may be an infrared camera that detects infrared rays. For example, the microcomputer <NUM> can recognize a pedestrian by determining whether or not the pedestrian exists in image captured by the imaging units <NUM> to <NUM>. For example, the pedestrian recognition is performed by a procedure of extracting a specific point in images captured by the imaging units <NUM> to <NUM> as an infrared camera, and a procedure of performing pattern matching processing for a series of specific points indicating a contour line of an object to determine whether or not the object is a pedestrian. When the microcomputer <NUM> determines that a pedestrian exists on the images captured by the imaging units <NUM> to <NUM>, and recognizes the pedestrian, the voice and image output unit <NUM> controls the display unit <NUM> to overlap and display a quadrangular contour line for emphasis on the pedestrian who is recognized. In addition, the voice and image output unit <NUM> may control the display unit <NUM> to display an icon and the like indicating the pedestrian at a desired position.

Hereinbefore, description has been given of an example of the vehicle control system to which the present technology relating to the present disclosure is applicable. The technology relating to the present disclosure is applicable to, for example, the vehicle exterior information detection unit <NUM> among the above-described configurations. Specifically, the distance measurement module <NUM> in <FIG> is applicable to the vehicle exterior information detection unit <NUM> in <FIG>. When the technology relating to the present disclosure is applied to the vehicle exterior information detection unit <NUM>, a dark current is suppressed, and thus accurate distance data can be obtained. Accordingly, it is possible to improve reliability of a vehicle control system.

Furthermore, the above-described embodiments illustrate an example for embodiment of the present technology, and matters in the embodiments and invention-specific matters in the appended claims have a corresponding relationship. Similarly, the invention-specific matters in the appended claims and matters in the embodiment of the present technology to which the same term is given have a corresponding relationship. However, the present technology is not limited to the embodiments and can be embodied by making various modifications in the embodiments.

Furthermore, the effects described in this specification are illustrative only and are not limited thereto, and other effects may exist.

It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and alterations may occur depending on design requirements and other factors insofar as they are within the scope of the appended claims.

Claim 1:
An avalanche photodiode sensor (<NUM>), comprising:
a photoelectric conversion region (<NUM>) disposed in a substrate and that is configured to convert incident light into electric charge;
a first region (<NUM>) of a first conductivity type on the photoelectric conversion region (<NUM>);
a second region (<NUM>) of the first conductivity type disposed in the substrate and positioned between the photoelectric conversion region (<NUM>) and the first region (<NUM>), wherein the impurity concentration of the first region (<NUM>) is higher than an impurity concentration of the second region (<NUM>);
a cathode (<NUM>) disposed in the substrate adjacent to the first region (<NUM>) and coupled to the photoelectric conversion region (<NUM>);
an anode (<NUM> disposed in the substrate adjacent to the cathode (<NUM>); and
a contact (<NUM>) of the first conductivity type disposed in the first region (<NUM>), an impurity concentration of the first region (<NUM>) being lower than an impurity concentration of the contact (<NUM>).