Patent ID: 12205964

MODE FOR CARRYING OUT THE INVENTION

Hereinafter, a mode for carrying out the present technology (hereinafter, referred to as an embodiment) will be described. Note that the description will be given in the following order.1. Configuration Example of Distance Measurement System2. Configuration Example of Light Receiving Device3. Configuration Example of Pixel Circuit4. Plan View of Light Source and Pixel Array5. Pixel Cross-Sectional View6. Comparative Example7. Another Array Example of Pixels8. Usage Example of Distance Measurement System9. Application Example to Movable Body

1. Configuration Example of Distance Measurement System

FIG.1is a block diagram illustrating a configuration example of an embodiment of a distance measurement system to which the present technology is applied.

A distance measurement system11is a system that captures a distance image using a ToF method, for example. Here, the distance image is an image obtained by detecting a distance in a depth direction from the distance measurement system11to a subject for each pixel. A signal of each pixel includes a distance pixel signal that is based on the detected distance.

The distance measurement system11includes an illumination device21and an imaging device22.

The illumination device21includes an illumination control unit31and a light source32.

Under the control of a control unit42of the imaging device22, the illumination control unit31controls a pattern in which the light source32emits light. Specifically, in accordance with an emission code included in an emission signal supplied from the control unit42, the illumination control unit31controls a pattern in which the light source32emits light. For example, the emission code includes two values corresponding to 1 (High) and 0 (Low). When the value of the emission code is 1, the illumination control unit31turns on the light source32, and when the value of the emission code is 0, the illumination control unit31turns off the light source32.

Under the control of the illumination control unit31, the light source32emits light in a predetermined wavelength band. The light source32includes an infrared laser diode, for example. Note that the type of the light source32and the wavelength band of illumination light can be arbitrarily set in accordance with a use application or the like of the distance measurement system11.

The imaging device22is a device that receives reflected light of light (illumination light) that has been emitted from the illumination device21and reflected by a subject12, a subject13, and the like. The imaging device22includes an imaging unit41, the control unit42, a display unit43, and a storage unit44.

The imaging unit41includes a lens51and a light receiving device52.

The lens51forms an image of incident light on a light receiving surface of the light receiving device52. Note that a configuration of the lens51is an arbitrary, and the lens51may include a plurality of lens units, for example.

The light receiving device52includes a sensor that uses a single photon avalanche diode (SPAD) as each pixel, for example. Under the control of the control unit42, the light receiving device52receives reflected light from the subject12, the subject13, and the like, converts a resultant pixel signal into distance information, and outputs the distance information to the control unit42. The light receiving device52supplies, to the control unit42as a pixel value (distance pixel signal) of each pixel of a pixel array in which pixels are two-dimensionally arrayed in a matrix in a row direction and a column direction, a distance image storing a digital count value obtained by counting a time from when the illumination device21emits illumination light to when the light receiving device52receives the light. A light emission timing signal indicating a timing at which the light source32emits light is supplied also to the light receiving device52from the control unit42.

Note that, by the distance measurement system11repeating light emission of the light source32and reception of the reflected light a plurality of times (for example, several thousands to several tens of thousands of times), the imaging unit41generates a distance image from which influence of ambient light, multipath, or the like has been removed, and supplies the distance image to the control unit42.

The control unit42includes, for example, a control circuit or a processor such as a field programmable gate array (FPGA) or a digital signal processor (DSP), and the like. The control unit42performs control of the illumination control unit31and the light receiving device52. Specifically, the control unit42supplies an emission signal to the illumination control unit31, and supplies a light emission timing signal to the light receiving device52. The light source32emits illumination light in accordance with the emission signal. The light emission timing signal may be an emission signal supplied to the illumination control unit31. Furthermore, the control unit42supplies the distance image acquired from the imaging unit41, to the display unit43, and causes the display unit43to display the distance image. Moreover, the control unit42causes the storage unit44to store the distance image acquired from the imaging unit41. Furthermore, the control unit42outputs the distance image acquired from the imaging unit41, to the outside.

The display unit43includes a panel-shaped display device such as a liquid crystal display device or an organic Electro Luminescence (EL) display device, for example.

The storage unit44can include an arbitrary storage device or storage medium, or the like, and stores a distance image or the like.

2. Configuration Example of Light Receiving Device

FIG.2is a block diagram illustrating a configuration example of the light receiving device52.

The light receiving device52includes a pixel drive unit71, a pixel array72, a multiplexer (MUX)73, a time measurement unit74, a signal processing unit75, and an input-output unit76.

The pixel array72has a configuration in which pixels81are two-dimensionally arrayed in a matrix in the row direction and the column direction. Each of the pixels81detects the entry of a photon, and outputs a detection signal indicating a detection result, as a pixel signal. Here, the row direction refers to an array direction of the pixels81in a horizontal direction, and the column direction refers to an array direction of the pixels81in a vertical direction. Due to limitations of space, a pixel array configuration of the pixel array72that is illustrated inFIG.2includes ten rows and twelve columns, but the number of rows and the number of columns of the pixel array72are not limited to these, and can be arbitrary set.

For each pixel row, a pixel drive line82is wired in the horizontal direction to the matrix pixel array of the pixel array72. The pixel drive line82transmits a drive signal for driving the pixels81. The pixel drive unit71drives each of the pixels81by supplying a predetermined drive signal to each of the pixels81via the pixel drive lines82. Specifically, the pixel drive unit71performs control in such a manner as to set at least a part of the plurality of pixels81two-dimensionally arrayed in a matrix, as active pixels, and set the remaining pixels81as inactive pixels, at a predetermined timing synchronized with a light emission timing signal supplied from the outside via the input-output unit76. The active pixel is a pixel that detects the entry of a photon, and the inactive pixel is a pixel that does not detect the entry of a photon. As a matter of course, all of the pixels81of the pixel array72may be set as active pixels The detailed configuration of the pixels81will be described later.

Note thatFIG.2illustrates the pixel drive line82as one wire, but the pixel drive line82may include a plurality of wires. One end of the pixel drive line82is connected to an output end of the pixel drive unit71that corresponds to each pixel row.

The MUX73selects an output from the active pixels in accordance with switching between active pixels and inactive pixels in the pixel array72. Then, the MUX73outputs pixel signals input from the selected active pixels, to the time measurement unit74.

On the basis of pixel signals of active pixels that are supplied from the MUX73, and a light emission timing signal indicating a light emission timing of the light source32, the time measurement unit74generates a count value corresponding to a time from when the light source32emits light to when active pixels receive the light. The time measurement unit74is also referred to as a time to digital converter (TDC). The light emission timing signal is supplied from the outside (the control unit42of the imaging device22) via the input-output unit76.

On the basis of the light emission of the light source32and the reception of the reflected light that are repeatedly executed a predetermined times (for example, several thousands to several tens of thousands of times), the signal processing unit75creates a histogram indicating a time (count value) until reception of reflected light, for each pixel. Then, by detecting a peak of the histogram, the signal processing unit75determines a time until light emitted from the light source32returns by being reflected on the subject12or the subject13. The signal processing unit75generates a distance image storing a digital count value obtained by counting a time until the light receiving device52receives light, in each pixel, and supplies the distance image to the input-output unit76. Alternatively, furthermore, the signal processing unit75may perform calculation for obtaining a distance to an object on the basis of the determined time and a light speed, generate a distance image storing the calculation result in each pixel, and supply the distance image to the input-output unit76.

The input-output unit76outputs a signal (distance image signal) of the distance image that is supplied from the signal processing unit75, to the outside (the control unit42). Furthermore, the input-output unit76acquires a light emission timing signal supplied from the control unit42, and supplies the light emission timing signal to the pixel drive unit71and the time measurement unit74.

3. Configuration Example of Pixel Circuit

FIG.3illustrates a circuit configuration example of each of the plurality of pixels81arrayed in a matrix in the pixel array72.

The pixel81inFIG.3includes an SPAD101, a transistor102, a switch103, and an inverter104. Furthermore, the pixel81also includes a latch circuit105and an inverter106. The transistor102is formed by a P-type MOS transistor.

A cathode of the SPAD101is connected to a drain of the transistor102, and also connected to an input terminal of the inverter104and one end of the switch103. An anode of the SPAD101is connected to a source voltage VA (hereinafter, will also be referred to as an anode voltage VA.).

The SPAD101is a photodiode (single photon avalanche photodiode) that causes avalanche amplification of generated electrons and outputs a signal of a cathode voltage VS, when incident light enters. The source voltage VA supplied to the anode of the SPAD101is set to a negative bias (negative potential) of about −20 V, for example.

The transistor102is a constant current source operating in a saturation region, and performs passive quench by functioning as a quenching resistor. A source of the transistor102is connected to a source voltage VE, and a drain is connected to the cathode of the SPAD101, the input terminal of the inverter104, and one end of the switch103. Therefore, the source voltage VE is supplied also to the cathode of the SPAD101. A pull-up resistor can also be used in place of the transistor102connected in series with the SPAD101.

For detecting light (photon) with sufficient efficiency, a voltage (hereinafter, will be referred to as an excess bias.) larger than a breakdown voltage VBD of the SPAD101is applied to the SPAD101. For example, if the breakdown voltage VBD of the SPAD101is set to 20 V, and a voltage larger to be than the breakdown voltage VBD by 3 V is applied, the source voltage VE to be supplied to the source of the transistor102is set to 3 V.

Note that the breakdown voltage VBD of the SPAD101drastically changes in accordance with a temperature or the like. Therefore, an applied voltage to be applied to the SPAD101is controlled (adjusted) in accordance with a change of the breakdown voltage VBD. For example, if the source voltage VE is set to a fixed voltage, the anode voltage VA is controlled (adjusted).

One end of both ends of the switch103is connected to the cathode of the SPAD101, the input terminal of the inverter104, and the drain of the transistor102, and another end is connected to a ground connection line107connected to a ground (GND). The switch103can be formed by an N-type MOS transistor, for example, and turns on/off a gating control signal VG being an output of the latch circuit105, in accordance with a gating inverted signal VG_I inverted by the inverter106.

On the basis of a trigger signal SET and address data DEC that are supplied from the pixel drive unit71, the latch circuit105supplies the gating control signal VG for controlling the pixel81to become an active pixel or an inactive pixel, to the inverter106. The inverter106generates the gating inverted signal VG_I obtained by inverting the gating control signal VG, and supplies the gating inverted signal VG_I to the switch103.

The trigger signal SET is a timing signal indicating a switching timing of the gating control signal VG, and the address data DEC is data indicating an address of a pixel to be set as an active pixel among the plurality of pixels81arrayed in the matrix in the pixel array72. The trigger signal SET and the address data DEC are supplied from the pixel drive unit71via the pixel drive line82.

The latch circuit105reads the address data DEC at a predetermined timing indicated by the trigger signal SET. Then, in a case where pixel addresses indicated by the address data DEC include a pixel address of itself (corresponding pixel81), the latch circuit105outputs the gating control signal VG indicating Hi (1) for setting the corresponding pixel81as an active pixel. On the other hand, in a case where pixel addresses indicated by the address data DEC do not include a pixel address of itself (corresponding pixel81), the latch circuit105outputs the gating control signal VG indicating Lo (0) for setting the corresponding pixel81as an inactive pixel. Therefore, in a case where the pixel81is set as an active pixel, the gating inverted signal VG_I inverted by the inverter106and indicating Lo (0) is supplied to the switch103. On the other hand, in a case where the pixel81is set as an inactive pixel, the gating inverted signal VG_I indicating Hi (1) is supplied to the switch103. Accordingly, in a case where the pixel81is set as an active pixel, the switch103is turned off (unconnected), and in a case where the pixel81is set as an inactive pixel, the switch103is turned on (connected).

When the cathode voltage VS serving as an input signal indicates Lo, the inverter104outputs a detection signal PFout indicating Hi, and when the cathode voltage VS indicates Hi, the inverter104outputs the detection signal PFout indicating Lo. The inverter104is an output unit that outputs the entry of a photon to the SPAD101, as the detection signal PFout.

Next, an operation to be performed in a case where the pixel81is set as an active pixel will be described with reference toFIG.4.

FIG.4is a graph indicating a change of the cathode voltage VS of the SPAD101and the detection signal PFout that change in accordance with the entry of a photon.

First of all, in a case where the pixel81is set as an active pixel, the switch103is turned off as described above.

Because the source voltage VE (for example, 3 V) is supplied to the cathode of the SPAD101, and the source voltage VA (for example, −20 V) is supplied to the anode, an inverse voltage larger than the breakdown voltage VBD (=20 V) is applied to the SPAD101. The SPAD101is thereby set to a Geiger mode. In this state, the cathode voltage VS of the SPAD101is the same as the source voltage VE like the cathode voltage VS at a time t0inFIG.4, for example.

If a photon enters the SPAD101set to the Geiger mode, avalanche amplification occurs, and current flows in the SPAD101.

If avalanche amplification occurs and current flows in the SPAD101at a time t1inFIG.4, after the time t1, by current flowing in the SPAD101, current flows also in the transistor102, and a voltage drop is caused by resistance components of the transistor102.

If the cathode voltage VS of the SPAD101becomes lower than 0 V at a time t2, because an anode to cathode voltage of the SPAD101enters a state of being lower than the breakdown voltage VBD, avalanche amplification stops. Here, an operation of causing a voltage drop by flowing current generated by avalanche amplification, in the transistor102, and stopping avalanche amplification by causing a state in which the cathode voltage VS is lower than the breakdown voltage VBD, in accordance with the caused voltage drop corresponds to a quench operation.

If avalanche amplification stops, current flowing in the resistor of the transistor102gradually decreases, and at a time t4, the cathode voltage VS returns to the original source voltage VE again, and a state in which a next new photon can be detected is caused (recharge operation).

The inverter104outputs the detection signal PFout indicating Lo, when the cathode voltage VS being an input voltage is equal to or larger than a predetermined threshold voltage Vth, and outputs the detection signal PFout indicating Hi, when the cathode voltage VS is smaller than the predetermined threshold voltage Vth. Accordingly, if a photon enters the SPAD101, avalanche amplification occurs, and the cathode voltage VS drops to fall below the threshold voltage Vth, the detection signal PFout is inverted from a low level to a high level. On the other hand, if avalanche amplification of the SPAD101converges, and the cathode voltage VS rises to reach the threshold voltage Vth or more, the detection signal PFout is inverted from the high level to the low level.

Note that, in a case where the pixel81is set as an inactive pixel, the gating inverted signal VG_I indicating Hi (1) is supplied to the switch103, and the switch103is turned on. If the switch103is turned on, the cathode voltage VS of the SPAD101is set to 0 V. Consequently, because the anode to cathode voltage of the SPAD101becomes equal to or smaller than the breakdown voltage VBD, a state in which the SPAD101does not react even if a photon enters the SPAD101is caused.

4. Plan View of Light Source and Pixel Array

InFIGS.5A and5B,FIG.5Aillustrates a plan view of the light source32.

The light source32includes a plurality of light emission units121arrayed in a matrix. The light emission unit121includes a vertical cavity surface emitting laser (VCSEL), for example. The illumination control unit31can individually turn on and off the light emission units121arrayed in a matrix, in accordance with an emission code included in an emission signal supplied from the control unit42.

InFIGS.5A and5B,FIG.5Billustrates a plan view of the pixel array72.

The pixel array72includes the pixels81two-dimensionally arrayed in a matrix as described above. Each of the pixels81is functionally classified into a pixel81M, a pixel81R, or a pixel81D.

The pixel81M is a pixel that receives reflected light of light that has been emitted from (the light emission units121of) the light source32and reflected by the subject12, the subject13, and the like, and is a measurement (distance measurement) pixel for measuring a distance to a subject.

The pixel81R is a reference pixel used for checking an adequate applied voltage to the SPAD101, and correcting distance data.

The pixel81D is a dummy pixel for separating the measurement pixel81M and the reference pixel81R. The dummy pixel81D can be a pixel having the same pixel structure as the measurement pixel81M, for example, and being different only in that the dummy pixel81D is merely not driven. Alternatively, furthermore, the dummy pixel81D may have the same pixel structure as the measurement pixel81M, and is driven for monitoring an internal voltage.

The numbers of pixels81M, pixels81R, and pixels81D are not specifically limited as long as a plurality of measurement pixels81M is arrayed in a matrix, and the dummy pixel81D is arrayed between the measurement pixels81M and the reference pixel81R. The measurement pixels81M can be arrayed in N1×N2 (N1 and N2 are integers equal to or larger than 1), the reference pixels81R can be arrayed in M1×M2 (M1 and M2 are integers equal to or larger than 1), and the dummy pixels81D can be arrayed in L1×L2 (L1 and L2 are integers equal to or larger than 1).

Furthermore, in the example inFIGS.5A and5B, a plurality of reference pixels81R is adjacently arrayed, but the reference pixels81R may be separately arrayed among the dummy pixels81D, and the dummy pixel81D may be arrayed between a pixel81R and another pixel81R.

5. Pixel Cross-Sectional View

InFIGS.6A and6B,FIG.6Aillustrates a cross-sectional view of the measurement pixel81M.

The pixel81M includes a first substrate201and a second substrate202that are bonded to each other. The first substrate201includes a semiconductor substrate211containing silicon or the like, and a wiring layer212. Hereinafter, for clearly distinguishing from a wiring layer312on the second substrate202side, which will be described later, the wiring layer212will be referred to as the sensor side wiring layer212. The wiring layer312on the second substrate202side will be referred to as the logic side wiring layer312. A surface of the semiconductor substrate211on which the sensor side wiring layer212is formed is a front surface, and the back surface on which the sensor side wiring layer212is not formed, and which is located on the upper side in the drawing corresponds to a light receiving surface that reflected light enters.

A pixel region of the semiconductor substrate211includes an N well221, a P-type diffusion layer222, an N-type diffusion layer223, a hole storage layer224, and a high-concentration P-type diffusion layer225. Then, an avalanche amplification region257is formed by a depletion layer formed in a region in which the P-type diffusion layer222and the N-type diffusion layer223are connected.

The N well221is formed by impurity concentration of the semiconductor substrate211being controlled to an n-type, and forms an electric field for transferring electrons generated by photoelectric conversion in the pixel81M, to the avalanche amplification region257. At the central part of the N well221, an n-type region258having higher concentration than the N well221is formed in contact with the P-type diffusion layer222, and a potential gradient for causing carriers (electrons) generated in the N well221, to easily drift from the periphery to the center is formed. Note that, in place of the N well221, a P well may be formed by controlling impurity concentration of the semiconductor substrate211to a p-type.

The P-type diffusion layer222is a high-concentration P-type diffusion layer (P+) formed over the entire surface of the pixel region in a planar direction. The N-type diffusion layer223is a high-concentration N-type diffusion layer (N+) existing near the front surface of the semiconductor substrate211, and formed over the entire surface of the pixel region similarly to the P-type diffusion layer222. The N-type diffusion layer223is a contact layer connecting with a contact electrode281serving as a cathode electrode for supplying a negative voltage for forming the avalanche amplification region257, and has a protruding shape partially formed up to the contact electrode281on the front surface of the semiconductor substrate211.

The hole storage layer224is a P-type diffusion layer (P) formed in such a manner as to surround the side surfaces and the bottom surface of the N well221, and stores holes. Furthermore, the hole storage layer224is connected with the high-concentration P-type diffusion layer225electrically connected with a contact electrode282serving as an anode electrode of the SPAD101.

The high-concentration P-type diffusion layer225is a high-concentration P-type diffusion layer (P++) existing near the front surface of the semiconductor substrate211and formed in such a manner as to surround the outer periphery of the N well221, and forms a contact layer for electrically connecting the hole storage layer224with the contact electrode282of the SPAD101.

In a pixel boundary portion of the semiconductor substrate211that serves as a boundary with a neighboring pixel, a pixel separation unit259for separating pixels is formed. The pixel separation unit259may include only an insulation layer, for example, or may have a double structure in which an insulation layer containing SiO2 or the like covers the outer side (the N well221side) of a metal layer containing tungsten or the like.

In the sensor side wiring layer212, the contact electrodes281and282, metal wires283and284, contact electrodes285and286, and metal wires287and288are formed.

The contact electrode281connects the N-type diffusion layer223and the metal wire283, and the contact electrode282connects the high-concentration P-type diffusion layer225and the metal wire284.

The metal wire283is formed to be wider than the avalanche amplification region257in such a manner as to cover at least the avalanche amplification region257in a planar region. Furthermore, the metal wire283may have a structure for causing light having passed through the pixel region of the semiconductor substrate211, to be reflected toward the semiconductor substrate211side.

The metal wire284is formed in such a manner as to overlap with the high-concentration P-type diffusion layer225and surround the outer periphery of the metal wire283in the planar region.

The contact electrode285connects the metal wire283and the metal wire287, and the contact electrode286connects the metal wire284and the metal wire288.

On the other hand, the second substrate202includes a semiconductor substrate311containing silicon or the like, and the wiring layer312(the logic side wiring layer312).

On the front surface side of the semiconductor substrate311that corresponds to the upper side in the drawing, a plurality of MOS transistors Tr (Tr1, Tr2, etc.) is formed, and the logic side wiring layer312is formed.

The logic side wiring layer312includes metal wires331and332, metal wires333and334, and contact electrodes335and336.

The metal wire331is electrically and physically connected with the metal wire287of the sensor side wiring layer212by metal bonding of Cu—Cu or the like. The metal wire332is electrically and physically connected with the metal wire288of the sensor side wiring layer212by metal bonding of Cu—Cu or the like.

The contact electrode335connects the metal wire331and the metal wire333, and the contact electrode336connects the metal wire332and the metal wire334.

The logic side wiring layer312further includes a multilayer metal wire341between the layer of the metal wires333and334, and the semiconductor substrate311.

A logic circuit corresponding to the pixel drive unit71, the MUX73, the time measurement unit74, the signal processing unit75, and the like is formed in the second substrate202by the plurality of MOS transistors Tr formed on the semiconductor substrate311, and the multilayer metal wire341.

For example, via the logic circuit formed on the second substrate202, the source voltage VE to be applied the N-type diffusion layer223is supplied to the N-type diffusion layer223via the metal wires333, the contact electrode335, the metal wires331and287, the contact electrode285, the metal wire283, and the contact electrode281. Furthermore, the source voltage VA is supplied to the high-concentration P-type diffusion layer225via the metal wire334, the contact electrode336, the metal wires332and288, the contact electrode286, the metal wire284, and the contact electrode282. Note that, in a case where a P well obtained by controlling impurity concentration of the semiconductor substrate211to a p-type is formed in place of the N well221, a voltage to be applied to the N-type diffusion layer223becomes the source voltage VA, and a voltage to be applied to the high-concentration P-type diffusion layer225becomes the source voltage VE.

The cross-sectional structure of the measurement pixel81M has the above-described configuration, and the SPAD101serving as a light receiving element includes the N well221of the semiconductor substrate211, the P-type diffusion layer222, the N-type diffusion layer223, the hole storage layer224, and the high-concentration P-type diffusion layer225, and the hole storage layer224is connected with the contact electrode282serving as an anode electrode, and the N-type diffusion layer223is connected with the contact electrode281serving as a cathode electrode.

At least one layer of the metal wires283,284,287,288,331to334, or341serving as a light shielding member is disposed between the semiconductor substrate211of the first substrate201and the semiconductor substrate311of the second substrate202in all regions in the planar direction of the pixel81M. Therefore, even in a case where light is emitted by hot carries of the MOS transistor Tr of the semiconductor substrate311of the second substrate202, the light is configured not to reach the N well221and the n-type region258of the semiconductor substrate211serving as a photoelectric conversion region.

In the pixel81M, the SPAD101serving as a light receiving element has a light receiving surface including planes of the N well221and the hole storage layer224, and the MOS transistor Tr serving as a light emission source that performs hot carrier light emission is provided on the opposite side of the light receiving surface of the SPAD101. Then, the metal wire283and the metal wire341serving as a light shielding member are provided between the SPAD101serving as a light receiving element, and the MOS transistor Tr serving as a light emission source, and hot carrier light emission is configured not to reach the N well221and the n-type region258of the semiconductor substrate211serving as a photoelectric conversion region.

A pixel structure of the dummy pixel81D is formed by the same structure as the measurement pixel81M.

InFIGS.6A and6B,FIG.6Billustrates a cross-sectional view of the reference pixel81R.

Note that, inFIG.6B, parts corresponding toFIG.6Aare assigned the same reference numerals, and the description thereof will be appropriately omitted.

The cross-sectional structure of the reference pixel81R illustrated inFIG.6Bis different from that of the measurement pixel81M illustrated inFIG.6Ain that a light guiding unit361that propagates light (photon) generated by hot carrier light emission is provided between the SPAD101serving as a light receiving element and the MOS transistor Tr serving as a light emission source that performs hot carrier light emission.c

More specifically, in a part of regions of all regions in the planar direction between the semiconductor substrate211of the first substrate201and the semiconductor substrate311of the second substrate202of the pixel81R, a region in which none of the metal wires283,284,287,288,331to334, and341that shield light is formed is provided, and the light guiding unit361that propagates light is formed in a stack direction of metal wires.

Therefore, as for a position in the planar direction, if hot carrier light emission occurs in the MOS transistor Tr1formed at a position overlapping the light guiding unit361at least partially, the SPAD101of the pixel81R can receive light generated by hot carrier light emission and having passed through the light guiding unit361, and output a detection signal (pixel signal). Note that all the metal wires283,341, and the like need not be completely opened as described above, and the light guiding unit361is only required to be opened to such an extent that light passes through.

Furthermore, on the top surface of the hole storage layer224being the light receiving surface side of the pixel81R, a light shielding member (light shielding layer)362is formed in such a manner as to surround the light receiving surface of the hole storage layer224. The light shielding member362shields ambient light or the like that enters from the light receiving surface side. Note that, because the influence of ambient light or the like can be removed by generation processing of a histogram as described above, the light shielding member362is not essential and can be omitted.

The MOS transistor Tr1that emits light propagating through the light guiding unit361and reaching the photoelectric conversion region of the pixel81R may be a MOS transistor provided as a light emission source as a circuit element not provided in the measurement pixel81M, or may be a MOS transistor formed also in the measurement pixel81M.

Accordingly, in a case where the MOS transistor Tr1is provided as a light emission source peculiarly in the reference pixel81R, a circuit in the pixel region formed in the second substrate202is different between the reference pixel81and the measurement pixel81M. In this case, the MOS transistor Tr1peculiarly provided as a light emission source corresponds to a circuit that controls the light emission source, for example.

A light emission timing at which the MOS transistor Tr1peculiarly provided as a light emission source is caused to emit light can be set to the same timing as a timing at which the light emission units121of the light source32emit light, for example. In this case, for example, by setting a timing at which the reference pixel81R receives light from the light emission source (MOS transistor Tr1), as a reference of a distance zero, it is possible to correct a distance to be calculated from a timing at which the measurement pixel81M receives light. In other words, the reference pixel81R can be used for correcting distance data.

Furthermore, for example, the reference pixel81R can be used for checking adequateness of an applied voltage to the SPAD101. In this case, in the pixel81R, the MOS transistor Tr1peculiarly provided as a light emission source is caused to emit light, and the cathode voltage VS of the SPAD101at the time of a quench operation, that is to say, the cathode voltage VS at the time t2inFIG.4can be checked and used for adjusting the anode voltage VA.

On the other hand, in a case where the MOS transistor Tr1serving as a light emission source is a MOS transistor formed also in the measurement pixel81M, a circuit in the pixel region formed in the second substrate202can be made the same between the reference pixel81and the measurement pixel81M.

Note that the light emission source of the reference pixel81R is not limited to a MOS transistor, and may be another circuit element such as a diode or a resistor element.

Furthermore, the light receiving device52has a stack structure in which the first substrate201and the second substrate202are bonded to each other as described above, but may include a single substrate (semiconductor substrate), or may have a stack structure of three or more substrates. Moreover, a back side light receiving sensor structure in which the back surface side of the first substrate201that is opposite to the front surface on which the sensor side wiring layer212is formed is regarded as a light receiving surface is employed, but a front side light receiving sensor structure may be employed.

6. Comparative Example

FIG.7illustrates a configuration example of a light source and a pixel array in another distance measurement system according to a comparative example to be compared with the structures of the light source32and the pixel array72of the distance measurement system11.

A light source401inFIG.7includes a plurality of light emission units411M arrayed in a matrix, and a plurality of light emission units411R. The light emission units411M and the light emission units411R each include a vertical cavity surface emitting laser (VCSEL), for example, similarly to the light emission units121of the light source32.

As compared with the configuration of the light source32of the distance measurement system11illustrated inFIGS.5A and5B, the light emission units411M correspond to the light emission units121, and the light source401further includes the light emission units411R in addition to the light emission units121. The light emission units411R are reference light emission units411provided for emitting light onto reference pixels412R of a pixel array402.

In the pixel array402inFIG.7, measurement pixels412M, reference pixels412R, and dummy pixels412D are arrayed in an alignment similar to that of the pixel array72inFIGS.5A and5B. Nevertheless, all of the pixel structures of the pixels412M, the pixels412R, and the pixels412D have the same structure as the structure of the measurement pixel81M illustrated inFIG.6A.

More specifically, similarly to the measurement pixel412M, the reference pixel412R has a configuration in which the reference pixel412R includes a light shielding member that shields light emitted by hot carrier, in such a manner as not to reach a photoelectric conversion region, between the SPAD101and the MOS transistor Tr serving as a light emission source, and light emitted from the reference light emission units411R is received from the light receiving surface side.

In such a configuration, as compared with the distance measurement system11illustrated inFIGS.5A and5B, because the light emission units411R for the reference pixels412R are additionally required, a mounting area of the light emission units411R is required, and power for driving the light emission units411R increases. Power consumption accordingly increases as well. Furthermore, an optical axis needs to be adjusted in such a manner that light emitted from the light emission units411R is received by the reference pixels412R, and such a configuration is susceptible to an optical axis deviation.

In contrast to this, according to the structures of the light source32and the pixel array72of the distance measurement system11, because the light emission units411R for the reference pixels412R become unnecessary, not only power saving can be achieved but also adjustment of an optical axis deviation becomes unnecessary. Then, because a light emission source is provided in the pixel region of the reference pixel81R, specifically, provided on the opposite side of the light receiving surface of the SPAD101, and the light guiding unit361that propagates light is provided, light can be surely received.

7. Another Array Example of Pixels

FIG.8is a cross-sectional view illustrating another array example of pixels in the pixel array72.

In the cross-sectional view ofFIG.8, parts corresponding toFIGS.6A and6Bare assigned the same reference numerals. The structure illustrated inFIGS.6A and6Bare further simplified, and a part of the reference numerals is omitted.

In the array example of the pixel array72illustrated inFIGS.5A and5B, the reference pixels81R are arranged on a pixel row or a pixel column separated from the measurement pixels81M over the dummy pixels81D, but the reference pixels81R and the measurement pixels81M may be arranged on the same pixel row or pixel column.

The cross-sectional view ofFIG.8illustrates a cross-sectional view of the pixels81arranged on one pixel row or pixel column.

As illustrated inFIG.8, the reference pixels81R and the measurement pixels81M can be arranged on the same pixel row or pixel column. Also in this case, it is desirable that the dummy pixel81D is arranged between the reference pixel81R and the measurement pixel81M. Therefore, even in a case where light from the MOS transistor Tr serving as a light emission source of the reference pixel81R leaks to a neighboring pixel81, the influence on the measurement pixel81M can be suppressed. Note that the dummy pixel81D between the reference pixel81R and the measurement pixel81M may be omitted.

8. Usage Example of Distance Measurement System

The application of the present technology is not limited to application to a distance measurement system. More specifically, the present technology can be applied to general electronic devices such as a smartphone, a tablet terminal, a mobile phone, a personal computer, a game machine, a television receiver, a wearable terminal, a digital still camera, or a digital video camera, for example. The above-described imaging unit41may have a module configuration in which the lens51and the light receiving device52are collectively packaged, or may have a configuration in which the lens51and the light receiving device52are separately formed, and only the light receiving device52is formed as one chip.

FIG.9is a diagram illustrating a usage example of the above-described distance measurement system11or the light receiving device52.

The above-described distance measurement system11can be used in various cases of sensing light such as visible light, infrared light, ultraviolet, or an X-ray, for example, as described below.A device that captures an image to be used for viewing, such as a digital camera or a portable device equipped with a camera functionA device to be used for traffic, such as an in-vehicle sensor that captures images of a front side, a rear side, and a periphery of an automobile, the inside of the vehicle, and the like for safe driving such as an automatic stop, recognition of a state of a driver, and the like, a monitoring camera that monitors a running vehicle and a road, or a distance measurement sensor that measures a distance such as an inter-vehicular distanceA device used in home electronics such as a TV, a refrigerator, or an air conditioner, for capturing an image of a gesture of a user, and performing a device operation suitable for the gestureA device used for medical and healthcare, such as an endoscope or a device that captures an image of blood vessels by receiving infrared lightA device used for security, such as a monitoring camera intended for crime prevention, or a camera intended for human authenticationA device used for beauty, such as a skin measuring device that captures an image of a skin, or a microscope that captures an image of a skin of scalpA device used for sport, such as an action camera or a wearable camera intended for sport or the likeA device used for agriculture, such as a camera for monitoring a state of a field or a crop

9. Application Example to Movable Body

The technology according to the present disclosure (present technology) can be applied to various products. For example, the technology according to the present disclosure can be implemented as a device mounted on a movable body of any type of an automobile, an electric car, a hybrid electric car, a motorbike, a bicycle, a personal mobility, a plane, a drone, a ship, a robot, and the like.

FIG.10is a block diagram illustrating a schematic configuration example of a vehicle control system being an example of a movable body control system to which the technology according to the present disclosure can be applied.

A vehicle control system12000includes a plurality of electronic control units connected via a communication network12001. In the example illustrated inFIG.10, the vehicle control system12000includes a drive system control unit12010, a body system control unit12020, a vehicle exterior information detection unit12030, a vehicle interior information detection unit12040, and an integrated control unit12050. Furthermore, as functional configurations of the integrated control unit12050, a microcomputer12051, a voice/image output unit12052, and an in-vehicle network interface (I/F)12053are illustrated.

The drive system control unit12010controls operations of a device related to a drive system of a vehicle in accordance with various programs. For example, the drive system control unit12010functions as a control device of a drive force generation device for generating drive force of a vehicle, such as an internal-combustion engine or a driving motor, a drive force transmission mechanism for transmitting drive force to wheels, a steering mechanism for adjusting a steering angle of the vehicle, a braking device for generating braking force of the vehicle, and the like.

The body system control unit12020controls operations of various devices provided in a vehicle body, in accordance with various programs. For example, the body system control unit12020functions as a control device of a keyless entry system, a smart key system, a powered window device, or various lamps such as a headlamp, a back lamp, a brake lamp, a blinker, or a fog lamp. In this case, radio waves transmitted from a mobile device substituting for a key, or signals of various switches can be input to the body system control unit12020. The body system control unit12020receives input of these radio waves or signals, and controls a door lock device of the vehicle, the powered window device, lamps, and the like.

The vehicle exterior information detection unit12030detects information regarding the outside of the vehicle on which the vehicle control system12000is mounted. For example, an imaging unit12031is connected to the vehicle exterior information detection unit12030. The vehicle exterior information detection unit12030causes the imaging unit12031to capture an image of the outside of the vehicle, and receives the captured image. On the basis of the received image, the vehicle exterior information detection unit12030may perform object detection processing or distance detection processing of a human, a car, an obstacle, a road sign, characters on a road, and the like.

The imaging unit12031is an optical sensor that receives light and outputs an electrical signal corresponding to a light reception amount of the light. The imaging unit12031can output an electrical signal as an image, and output an electrical signal as information regarding distance measurement. Furthermore, light to be received by the imaging unit12031may be visible light, or may be invisible light such as infrared light.

The vehicle interior information detection unit12040detects information regarding the vehicle interior. For example, a driver state detection unit12041that detects a state of a driver is connected to the vehicle interior information detection unit12040. The driver state detection unit12041includes a camera for capturing an image of a driver, for example. On the basis of detection information input from the driver state detection unit12041, the vehicle interior information detection unit12040may calculate a fatigue degree or a concentration degree of the driver, or may determine whether or not the driver dozes off.

On the basis of information regarding the vehicle interior or vehicle exterior that is acquired by the vehicle exterior information detection unit12030or the vehicle interior information detection unit12040, the microcomputer12051can calculate control target values of the drive force generation device, the steering mechanism, or the braking device, and output a control command to the drive system control unit12010. For example, the microcomputer12051can perform cooperative control intended to implement functions of an advanced driver assistance system (ADAS) including collision avoidance or shock mitigation of the vehicle, follow-up driving that is based on an inter-vehicular distance, maintained vehicle speed driving, collision warning of the vehicle, lane deviation warning of the vehicle, or the like.

Furthermore, the microcomputer12051can perform cooperative control intended for automated driving of autonomously driving without depending on the operation of a driver, or the like, by controlling the drive force generation device, the steering mechanism, the braking device, or the like on the basis of information regarding the periphery of the vehicle that is acquired by the vehicle exterior information detection unit12030or the vehicle interior information detection unit12040.

Furthermore, the microcomputer12051can output a control command to the body system control unit12020on the basis of information regarding the vehicle exterior that is acquired by the vehicle exterior information detection unit12030. For example, the microcomputer12051can perform cooperative control intended to achieve antidazzle by controlling a headlamp in accordance with a position of a leading vehicle or an oncoming vehicle that has been detected by the vehicle exterior information detection unit12030, and switching high beam to low beam, or the like.

The voice/image output unit12052transmits an output signal of at least one of voice or an image to an output device that can visually or aurally notify an occupant of the vehicle or the vehicle exterior of information. In the example inFIG.10, an audio speaker12061, a display unit12062, and an instrument panel12063are exemplified as output devices. The display unit12062may include at least one of an onboard display or a headup display, for example.

FIG.11is a diagram illustrating an example of an installation position of the imaging unit12031.

InFIG.11, a vehicle12100includes imaging units12101,12102,12103,12104, and12105as the imaging unit12031.

The imaging units12101,12102,12103,12104, and12105are provided at positions such as a front nose of the vehicle12100, side mirrors, a rear bumper, a backdoor, and an upper part of a front window inside a vehicle room, for example. The imaging unit12101provided at the front nose and the imaging unit12105provided at the upper part of the front window inside the vehicle room mainly acquire images of a front side of the vehicle12100. The imaging units12102and12103provided at the side mirrors mainly acquire images of the sides of the vehicle12100. The imaging unit12104provided at the rear bumper or the backdoor mainly acquires images of the back side of the vehicle12100. The images of the front side that are acquired by the imaging units and12101and12105are mainly used for the detection of a leading vehicle, a pedestrian, an obstacle, a traffic light, a traffic sign, a traffic lane, or the like.

Note thatFIG.11illustrates an example of image capturing ranges of the imaging units12101to12104. An image capturing range12111indicates an image capturing range of the imaging unit12101provided at the front nose, image capturing ranges12112and12113respectively indicate image capturing ranges of the imaging units12102and12103provided at the side mirrors, and an image capturing range12114indicates an image capturing range of the imaging unit12104provided at the rear bumper or the backdoor. For example, a birds-eye image of the vehicle12100viewed from above is obtained by overlapping image data captured by the imaging units12101to12104.

At least one of the imaging units12101to12104may have a function of acquiring distance information. For example, at least one of the imaging units12101to12104may be a stereo camera including a plurality of image sensors, or may be an image sensor including pixels for phase difference detection.

For example, by obtaining a distance to each three-dimensional object in the image capturing ranges12111to12114, and a temporal variation (relative speed with respect to the vehicle12100) of the distance, on the basis of distance information acquired from the imaging units12101to12104, the microcomputer12051can especially extract, as a leading vehicle, a three-dimensional object that is the closest three-dimensional object existing on a travelling path of the vehicle12100, and is running at a predetermined speed (for example, equal to or larger than 0 km/h) in substantially the same direction as the vehicle12100. Moreover, the microcomputer12051can preliminarily set an inter-vehicular distance to be ensured in front of a leading vehicle, and perform automatic brake control (including follow-up stop control), automatic acceleration control (including follow-up departure control), and the like. In this manner, cooperative control intended for automated driving of autonomously driving without depending on the operation of a driver, or the like can be performed.

For example, on the basis of distance information acquired from the imaging units12101to12104, the microcomputer12051can extract three-dimensional object data regarding a three-dimensional object, while classifying three-dimensional objects into other three-dimensional objects such as a two-wheeled vehicle, a standard-sized vehicle, a large-sized vehicle, a pedestrian, and a telephone pole, and use the extracted three-dimensional object data for automatic avoidance of an obstacle. For example, the microcomputer12051identifies obstacles near the vehicle12100, as an obstacle visible by a driver of the vehicle12100, and an obstacle less-visible by the driver. Then, the microcomputer12051determines collision risk indicating a degree of risk of collision with each obstacle, and when the collision risk is equal to or larger than a setting value and there is a possibility of collision, the microcomputer12051can perform drive assist for collision avoidance by outputting a warning to the driver via the audio speaker12061or the display unit12062, and performing forced deceleration or avoidance steering via the drive system control unit12010.

At least one of the imaging units12101to12104may be an infrared camera that detects infrared light. For example, the microcomputer12051can recognize a pedestrian by determining whether or not a pedestrian exists in captured images of the imaging units12101to12104. The recognition of a pedestrian is performed by a procedure of extracting feature points in captured images of the imaging units12101to12104serving as infrared cameras, and a procedure of determining whether or not a detected object is a pedestrian, by performing pattern matching processing on a series of feature points indicating an outline of the object, for example. If the microcomputer12051determines that a pedestrian exists in captured images of the imaging units12101to12104, and recognizes the pedestrian, the voice/image output unit12052controls the display unit12062to display a rectangular profile line for enhancement, with being superimposed on the recognized pedestrian. Furthermore, the voice/image output unit12052may control the display unit12062to display an icon indicating the pedestrian, or the like at a desired position.

Heretofore, an example of the vehicle control system to which the technology according to the present disclosure can be applied has been described. The technology according to the present disclosure can be applied to the imaging unit12031or the like among the configurations described above. Specifically, for example, the distance measurement system11inFIG.1can be applied to the imaging unit12031. The imaging unit12031is a LIDAR, for example, and is used for detecting an object near the vehicle12100and a distance to the object. By applying the technology according to the present disclosure to the imaging unit12031, detection accuracy of an object near the vehicle12100and a distance to the object enhances. Consequently, for example, it becomes possible to perform collision warning of a vehicle at an appropriate timing, and prevent a traffic accident.

Note that, in this specification, a system means a set of a plurality of constituent elements (apparatuses, modules (parts), and the like), and it does not matter whether or not all the constituent elements are provided in the same casing. Thus, a plurality of apparatuses stored in separate casings and connected via a network, and a single apparatus in which a plurality of modules is stored in a single casing are both regarded as systems.

Furthermore, an embodiment of the present technology is not limited to the above-described embodiment, and various changes can be made without departing from the scope of the present technology.

Note that effects described in this specification are mere exemplifications, and are not limited, and effects other than those described in this specification may be caused.

Note that the present technology can employ the following configurations.

(1) A light receiving device including:a plurality of pixels each includinga light receiving element having a light receiving surface, anda light emission source provided on an opposite side of the light receiving surface with respect to the light receiving element,in which the plurality of pixels includesa first pixel including a light shielding member provided between the light receiving element and the light emission source, anda second pixel including a light guiding unit that is configured to propagate a photon and is provided between the light receiving element and the light emission source.

(2) The light receiving device according to (1) described above,in which the second pixel further includes a light shielding member configured to cover the light receiving surface of the light receiving element.

(3) The light receiving device according to (1) or (2) described above,in which the light emission source of the second pixel is caused to emit light at a same timing as an emission timing at which reflected light to be received by the light receiving element of the first pixel is emitted.

(4) The light receiving device according to any one of (1) to (3) described above,in which two or more substrates including a first substrate and a second substrate are bonded to each other,the light receiving element is formed on the first substrate, andthe light emission source is formed on the second substrate.

(5) The light receiving device according to (4) described above,in which a circuit in a pixel region of the second substrate is different between the first pixel and the second pixel.

(6) The light receiving device according to (5) described above,in which the circuit different between the first pixel and the second pixel is a circuit configured to control the light emission source formed in the second pixel.

(7) The light receiving device according to (4) described above,in which a circuit in a pixel region of the second substrate is same between the first pixel and the second pixel.

(8) The light receiving device according to any one of (1) to (7) described above,in which the light receiving element is an SPAD.

(9) The light receiving device according to (8) described above,in which a signal of the pixel is used for any of distance measurement, correction of distance data, or adequateness check of an applied voltage of the SPAD.

(10) The light receiving device according to (9) described above,in which, in the adequateness check of an applied voltage of the SPAD, an applied voltage to the SPAD of the second pixel is measured.

(11) The light receiving device according to (10) described above,in which an anode voltage of the SPAD is controlled on a basis of the measured applied voltage of the SPAD.

(12) The light receiving device according to any one of (1) to (11) described above,in which a third pixel not used for distance measurement is further included between the first pixel and the second pixel in a planar direction.

(13) The light receiving device according to (12) described above,in which the third pixel is a non-driven pixel.

(14) The light receiving device according to (12) described above,in which the third pixel is a pixel driven for monitoring an internal voltage.

(15) The light receiving device according to any one of (1) to (14) described above,in which the first pixels are arrayed in N1×N2 (N1 and N2 are integers equal to or larger than 1).

(16) The light receiving device according to any one of (1) to (15) described above,in which the second pixels are arrayed in M1×M2 (M1 and M2 are integers equal to or larger than 1).

(17) The light receiving device according to any one of (1) to (16) described above,in which the light emission source is formed by any of a transistor, a diode, or a resistor element.

(18) A distance measurement system including:an illumination device configured to emit illumination light; anda light receiving device configured to receive reflected light of the illumination light,in which the light receiving device includea plurality of pixels each includinga light receiving element having a light receiving surface, anda light emission source provided on an opposite side of the light receiving surface with respect to the light receiving element, andthe plurality of pixels includesa first pixel including a light shielding member provided between the light receiving element and the light emission source, anda second pixel including a light guiding unit that is configured to propagate a photon and is provided between the light receiving element and the light emission source.

REFERENCE SIGNS LIST

11Distance measurement system21Illumination device22Imaging device31Illumination control unit32Light source41Imaging unit42Control unit52Light receiving device71Pixel drive unit72Pixel array73MUX74Time measurement unit75Signal processing unit76Input-output unit81(81R,81M,81D) Pixel101SPAD102Transistor103Switch104Inverter201First substrate202Second substrate211Semiconductor substrateTr MOS transistor361Light guiding unit362Light shielding member