Range image acquisition device and range image acquisition method

Abstract

The present invention provides a distance image acquisition device and a distance image acquisition method that can extend the measurement distance and ensure distance accuracy. The distance image acquisition device (1) includes a distance measurement sensor (10) that detects the measurement light by transferring the charge generated in the charge generation region (36) corresponding to the incidence of measurement light emitted from a light source (2) and reflected by an object (OJ) to the charge accumulation region (24, 25) using a transfer gate electrode (42, 43). The charge generation region (36) includes an avalanche multiplication region that generates avalanche multiplication. The control unit (4) divides the entire distance range (70) of the measurement object into a plurality of intervals (71A to 71E), controls the distance measuring sensor (10) in such a manner that the time difference (TD) between the emission timing of the measurement light of the light source (2) and the transmission timing of the charge of the transmission gate electrodes (42, 43) is different between the plurality of intervals (71A to 71E), and performs measurement on the plurality of intervals, and generates a distance image of the entire distance range (70) based on the measurement results for the plurality of intervals (71A to 71E).

Description

Technical Field

[0001] One aspect of the present invention relates to a range image acquisition device and a range image acquisition method. Background Art

[0002] As a distance measuring sensor for acquiring an image of the distance to an object using an indirect TOF (Time of Flight) method, a distance measuring sensor is known that includes a semiconductor layer having a photosensitive region, and a photogate electrode and a transfer gate electrode provided on the semiconductor layer for each pixel (see, for example, Patent Documents 1 and 2). This distance measuring sensor can transfer charges generated in the photosensitive region by incident light at high speed.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 2011-133464

[0006] Patent Document 2: Japanese Patent Application Laid-Open No. 2013-206903 Summary of the Invention

[0007] Problems to be solved by the invention

[0008] In distance measuring sensors like the one described above, the amount of light reflected by an object and returned to the sensor decreases as the distance to the object increases. Therefore, there is a limit to extending the measured distance. Furthermore, to extend the measured distance, the pulse width of the measuring light must be increased. However, increasing the pulse width degrades distance accuracy.

[0009] An object of one aspect of the present invention is to provide a range image acquisition device and a range image acquisition method that can extend a measurement distance and ensure distance accuracy.

[0010] Technical means to solve the problem

[0011] A distance image acquisition device according to one aspect of the present invention includes: a light source that emits measurement light; a distance measuring sensor having a charge generation region, a charge accumulation region, and a transfer gate electrode disposed in a region between the charge generation region and the charge accumulation region, the distance measuring sensor detecting the measurement light by transferring charge generated in the charge generation region in response to the measurement light emitted from the light source and reflected by an object to the charge accumulation region using the transfer gate electrode; and a control unit that controls the distance measuring sensor to generate a distance image of the object based on detection results of the distance measuring sensor, wherein the charge generation region includes an avalanche multiplication region that generates avalanche multiplication. The control unit divides the entire distance range of the measurement object into a plurality of intervals, controls the distance measuring sensor to generate a distance image for the entire distance range based on the measurement results of the plurality of intervals, and performs measurement in the plurality of intervals so that the time difference between the emission timing of the measurement light from the light source and the transfer timing of the charge by the transfer gate electrode differs between the plurality of intervals.

[0012] In this distance image acquisition device, the charge generation region includes an avalanche multiplication region that generates avalanche multiplication. This improves the sensitivity of the distance measuring sensor, resulting in an increase in the measured distance. On the other hand, as mentioned above, in order to extend the measured distance, it is generally necessary to increase the pulse width of the measuring light. When the pulse width is increased, distance accuracy deteriorates. Regarding this, in this distance image acquisition device, the entire distance range of the measured object is divided into multiple intervals. The time difference between the emission timing of the measuring light from the light source and the transmission timing of the charge from the transmission gate electrode is made different in each interval, and measurements are performed on each of the multiple intervals. Based on the results of the measurements for the multiple intervals, a distance image for the entire distance range is generated. This prevents the pulse width of the measuring light from widening even when the measured distance is long, ensuring distance accuracy. Furthermore, if the distance is simply divided into multiple intervals, there is a concern that the charge accumulation time (exposure time) will be reduced, resulting in insufficient charge accumulation. However, in this distance image acquisition device, the charge generation region includes the avalanche multiplication region, thus preventing insufficient charge accumulation. Therefore, it is less likely that the charge accumulation time will need to be extended to compensate for insufficient charge accumulation. Furthermore, by dividing the image into multiple sections, it is possible to suppress a decrease in measurement accuracy (multiple echoes) caused by the presence of transparent or semi-transparent objects between the distance measuring sensor and the object. As described above, this distance image acquisition device can extend the measured distance while ensuring distance accuracy.

[0013] Alternatively, the multiple intervals may include a first interval and a second interval farther from the light source than the first interval, and the control unit may control the ranging sensor so that, during measurement of the first interval, the charge accumulated in the charge storage region is read at a higher frequency than during measurement of the second interval. In this case, saturation of the charge generation region can be suppressed during measurement of the first interval, which is closer to the light source than the second interval. This suppression of saturation is particularly effective when the charge generation region includes an avalanche multiplication region.

[0014] Alternatively, the plurality of intervals may include a first interval and a second interval farther from the light source than the first interval, and the control unit may control the ranging sensor to transfer charge to the charge accumulation region at a lower transmission frequency during measurement of the first interval than during measurement of the second interval. In this case, saturation of the charge generation region can be prevented during measurement of the first interval, which is closer to the light source than the second interval.

[0015] Alternatively, the charge accumulation region may include a pair of charge accumulation regions, and the transfer gate electrode may include a pair of transfer gate electrodes disposed in regions between the charge generation region and the pair of charge accumulation regions. In this configuration, the entire distance range of the measurement target can be divided into multiple intervals, and the time difference between the timing of emission of measurement light from the light source and the timing of charge transfer by the transfer gate electrodes can be varied across the multiple intervals, allowing measurement to be performed across the multiple intervals.

[0016] Alternatively, the distance measuring sensor may have only one region serving as a charge accumulation region and only one electrode serving as a transfer gate electrode. With this configuration, the entire distance range of the measurement target can be divided into multiple intervals, and the time difference between the emission timing of the measurement light from the light source and the transfer timing of the charge from the transfer gate electrode can be varied across the multiple intervals, allowing measurement to be performed across the multiple intervals.

[0017] Alternatively, the control unit may fix the emission timing and shift the transmission timing from the emission timing, thereby varying the time difference between the emission timing and the transmission timing in a plurality of intervals. In this case, the time difference between the emission timing and the transmission timing can be varied in a plurality of intervals.

[0018] Alternatively, the control unit may fix the transmission timing and shift the emission timing from the transmission timing, thereby varying the time difference between the emission timing and the transmission timing in a plurality of intervals. In this case, the time difference between the emission timing and the transmission timing can be varied in a plurality of intervals.

[0019] The charge accumulation times in the measurement of the plurality of intervals may be equal to each other. In this case, for example, compared with extending the charge accumulation time in the measurement of the interval far from the light source where the charge accumulation amount is likely to be insufficient, the acquisition of the range image can be accelerated.

[0020] One aspect of the present invention relates to a distance image acquisition method for acquiring a distance image of an object. The method uses a light source that emits measurement light and a distance measuring sensor to divide the entire distance range of the object being measured into multiple intervals. The time difference between the timing of emission of the measurement light from the light source and the timing of charge transfer by a transfer gate electrode is varied between the multiple intervals, and measurement is performed for the multiple intervals. Based on the results of the measurement for the multiple intervals, a distance image for the entire distance range is generated. The distance measuring sensor includes a charge generation region, a charge accumulation region, and a transfer gate electrode disposed in an area between the charge generation region and the charge accumulation region. The method detects the measurement light by transferring charge generated in the charge generation region in response to the incidence of measurement light emitted from the light source and reflected by the object to the charge accumulation region using the transfer gate electrode. The charge generation region includes an avalanche multiplication region that generates avalanche multiplication.

[0021] In this distance image acquisition method, for the reasons described above, the measurement distance can be extended and distance accuracy can be ensured.

[0022] Effects of the Invention

[0023] According to one aspect of the present invention, a range image acquisition device and a range image acquisition method can be provided that can extend the measurement distance and ensure distance accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a structural diagram of a range image acquisition device according to an embodiment.

[0025] Figure 2 This is a top view of the pixel portion of the distance measuring sensor.

[0026] Figure 3 It is along Figure 2 Cross-sectional view along line III-III.

[0027] Figure 4 It is along Figure 2 Cross-sectional view along line IV-IV.

[0028] Figure 5 This is a timing chart for explaining the range image acquisition method according to the embodiment.

[0029] Figure 6 This is a timing chart for explaining the range image acquisition method according to the embodiment.

[0030] Figure 7 It is a plan view of a pixel portion of a distance measuring sensor according to a first modification.

[0031] Figure 8 It is along Figure 7Cross-sectional view along line VIII-VIII.

[0032] Figure 9 This is a timing chart for explaining the range image acquisition method according to the first modification.

[0033] Figure 10 This is a timing chart for explaining the range image acquisition method according to the second modification.

[0034] Figure 11 This is a timing chart for explaining the range image acquisition method according to the third modification. DETAILED DESCRIPTION

[0035] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals, and repeated descriptions are omitted.

[0036] [Distance image acquisition device]

[0037] like Figure 1 As shown, the distance image acquisition device 1 includes a light source 2, a distance measuring sensor 10, a signal processing unit 3, a control unit 4, and a display unit 5. The distance image acquisition device 1 is a device that acquires a distance image of an object OJ using an indirect TOF method. The distance image is an image containing information related to the distance d to the object OJ.

[0038] Light source 2 emits pulsed light (measurement light) L. Light source 2 includes, for example, an infrared LED. Pulsed light L is, for example, near-infrared light, and the frequency of pulsed light L is, for example, 10 kHz or higher. Distance sensor 10 detects pulsed light L emitted from light source 2 and reflected by object OJ. Distance sensor 10 is constructed by monolithically forming a pixel unit 11 and a CMOS readout circuit unit 12 on a semiconductor substrate (e.g., a silicon substrate). Distance sensor 10 is mounted on signal processing unit 3.

[0039] The signal processing unit 3 controls the pixel unit 11 and CMOS readout circuit unit 12 of the distance measuring sensor 10. The signal processing unit 3 performs predetermined processing on the signal output from the distance measuring sensor 10 to generate a detection signal. The control unit 4 controls the light source 2 and the signal processing unit 3. The control unit 4 generates a distance image of the object OJ based on the detection signal output from the signal processing unit 3. The display unit 5 displays the distance image of the object OJ generated by the control unit 4.

[0040] [Distance sensor]

[0041] like Figure 2 、 Figure 3 and Figure 4As shown, the distance measuring sensor 10 includes a semiconductor layer 20 and an electrode layer 40 in the pixel portion 11. The semiconductor layer 20 has a first surface 20a and a second surface 20b. The first surface 20a is a surface on one side of the semiconductor layer 20 in the thickness direction. The second surface 20b is a surface on the other side of the semiconductor layer 20 in the thickness direction. The electrode layer 40 is provided on the first surface 20a.

[0042] The semiconductor layer 20 and the electrode layer 40 constitute a plurality of pixels 11a arranged along the first surface 20a. The plurality of pixels 11a are arranged, for example, two-dimensionally along the first surface 20a. A distance image is formed by these pixels 11a. In the distance image, each pixel 11a contains information related to the distance d to the object OJ. Hereinafter, the thickness direction of the semiconductor layer 20 is referred to as the Z direction, the direction perpendicular to the Z direction is referred to as the X direction, and the direction perpendicular to both the Z direction and the X direction is referred to as the Y direction. One side in the Z direction is referred to as the first side, and the other side in the Z direction (the side opposite to the first side) is referred to as the second side. In Figure 2 In the figure, the wiring layer 60 described below is omitted.

[0043] Each pixel 11a includes a semiconductor region 21, an avalanche multiplication region 22, a charge sharing region 23, a pair of charge storage regions 24 and 25, a pair of charge discharge regions 26 and 27, multiple charge blocking regions 28, a well region 31, a LOCOS (Local Oxidation of Silicon) region 33, a barrier region 34, and a pair of recessed regions 35 in a semiconductor layer 20. Each region 21 to 28 and 31 to 35 is formed by subjecting a semiconductor substrate (e.g., a silicon substrate) to various processes (e.g., etching, film formation, impurity implantation, etc.).

[0044] The semiconductor region 21 is a p-type (first conductivity type) region, and is provided along the second surface 20b in the semiconductor layer 20. As an example, the semiconductor region 21 has a 1×10 15 cm －3 The p-type region with the following carrier concentration has a thickness of about 10 μm.

[0045] The avalanche multiplication region 22 includes a first multiplication region 22a and a second multiplication region 22b. The first multiplication region 22a is a p-type region formed on the first side of the semiconductor region 21 in the semiconductor layer 20. As an example, the first multiplication region 22a has a 1×10 16 cm －3The second multiplication region 22b is an n-type (second conductivity type) region formed on the first side of the first multiplication region 22a in the semiconductor layer 20. As an example, the second multiplication region 22b has a thickness of 1×10 16 cm －3 The thickness of the n-type region having a carrier concentration above 1 μm is about 1 μm. The first multiplication region 22 a and the second multiplication region 22 b form a pn junction.

[0046] The charge sharing region 23 is an n-type region formed on the first side of the second multiplication region 22b in the semiconductor layer 20. As an example, the charge sharing region 23 has a 5×10 15 ~1×10 16 cm －3 The carrier concentration of the n-type region is about 1μm in thickness.

[0047] Each charge storage region 24, 25 is an n-type region and is formed on the first side of the second multiplication region 22b in the semiconductor layer 20. Each charge storage region 24, 25 is connected to the charge sharing region 23. A pair of charge storage regions 24, 25 face each other in the X direction, sandwiching a portion of the first side of the charge sharing region 23. As an example, each charge storage region 24, 25 has a 1×10 18 cm －3 The thickness of the n-type region having a carrier concentration above 0.2 μm is about 0.2 μm. The second side portion of the charge sharing region 23 is located between the charge storage regions 24 and 25 and the second multiplication region 22 b.

[0048] Each of the charge discharge regions 26 and 27 is an n-type region and is formed on the first side of the second multiplication region 22b in the semiconductor layer 20. Each of the charge discharge regions 26 and 27 is connected to the charge sharing region 23. A pair of charge discharge regions 26 and 27 face each other in the Y direction, sandwiching a portion of the first side of the charge sharing region 23. As an example, each of the charge discharge regions 26 and 27 has a 1×10 18 cm －3 The thickness of the n-type region having the above carrier concentration is about 0.2 μm. The second side portion of the charge sharing region 23 is located between the charge discharge regions 26 and 27 and the second multiplication region 22 b.

[0049] Each charge blocking region 28 is a p-type region formed between each charge storage region 24, 25 and the charge sharing region 23 (the portion on the second side of the charge sharing region 23) in the semiconductor layer 20. As an example, each charge blocking region 28 has a 1×10 17 ~1×10 18 cm－3 The p-type region has a carrier concentration of about 0.2 μm.

[0050] The well region 31 is a p-type region formed on the first side of the second multiplication region 22b in the semiconductor layer 20. When viewed from the Z direction, the well region 31 surrounds the charge distribution region 23. The LOCOS region 33 is formed on the first side of the well region 31 in the semiconductor layer 20. The LOCOS region 33 is connected to the well region 31. The well region 31 and the LOCOS region 33 together constitute a plurality of readout circuits (e.g., source follower amplifiers, reset transistors, etc.). The plurality of readout circuits are electrically connected to the charge storage regions 24 and 25, respectively. As an example, the well region 31 has a 1×10 16 ~5×10 17 cm －3 As a structure for electrically isolating the pixel portion and the readout circuit portion, STI (Shallow Trench Isolation) may be used instead of the LOCOS region 33, or only the well region 31 may be used.

[0051] The barrier region 34 is an n-type region formed in the semiconductor layer 20 between the second multiplication region 22b and the well region 31. When viewed from the Z direction, the barrier region 34 includes the well region 31. That is, when viewed from the Z direction, the well region 31 is located within the barrier region 34. The barrier region 34 surrounds the charge sharing region 23. The concentration of n-type impurities in the barrier region 34 is higher than the concentration of n-type impurities in the second multiplication region 22b. As an example, the barrier region 34 is an n-type region having a carrier concentration ranging from approximately twice that of the second multiplication region 22b to approximately 1 μm thick.

[0052] Each recessed region 35 is an n-type region formed in the semiconductor layer 20 on the first side of the barrier region 34. The second end of each recessed region 35 is connected to the barrier region 34. The first end of each recessed region 35 is connected to each charge discharge region 26, 27. The concentration of n-type impurities in each charge discharge region 26, 27 is higher than the concentration of n-type impurities in each recessed region 35. The concentration of n-type impurities in each recessed region 35 is higher than the concentration of n-type impurities in the barrier region 34 and the concentration of p-type impurities in the well region 31. As an example, each recessed region 35 is an n-type region having a carrier concentration greater than that of the well region 31, and its thickness depends on the distance between each charge discharge region 26, 27 and the barrier region 34.

[0053] Each pixel 11a includes a photogate electrode 41, a pair of first transfer gate electrodes 42 and 43, and a pair of second transfer gate electrodes 44 and 45 in the electrode layer 40. Each gate electrode 41 to 45 is formed on the first surface 20a of the semiconductor layer 20 via an insulating film 46. The insulating film 46 is, for example, a silicon nitride film or a silicon oxide film.

[0054] The grating electrode 41 is formed on the first side of the charge sharing region 23 in the electrode layer 40. The grating electrode 41 is formed of a conductive and light-transmitting material (e.g., polysilicon). As an example, when viewed from the Z direction, the grating electrode 41 has a rectangular shape having two sides opposing each other in the X direction and two sides opposing each other in the Y direction.

[0055] Of the semiconductor region 21, the avalanche multiplication region 22, and the charge distribution region 23, the region directly below the grating electrode 41 (the region overlapping with the grating electrode 41 when viewed from the Z direction) functions as a charge generation region (light absorption region, photoelectric conversion region) 36 that generates charge in response to incident light. In other words, the grating electrode 41 is disposed on the charge generation region 36. In the charge generation region 36, the charge generated in the semiconductor region 21 is multiplied in the avalanche multiplication region 22 and distributed among the charge distribution region 23.

[0056] The first transfer gate electrode 42 is located in the region between the charge generation region 36 and the charge accumulation region 24 in the charge sharing region 23. The first transfer gate electrode 43 is located in the region between the charge generation region 36 and the charge accumulation region 25 in the charge sharing region 23. Each of the first transfer gate electrodes 42 and 43 is formed of a conductive and light-transmitting material (e.g., polysilicon). As an example, when viewed from the Z direction, each of the first transfer gate electrodes 42 and 43 has a rectangular shape having two sides opposing each other in the X direction and two sides opposing each other in the Y direction.

[0057] The second transfer gate electrode 44 is located in the region between the charge generation region 36 and the charge discharge region 26 in the charge sharing region 23. The second transfer gate electrode 45 is located in the region between the charge generation region 36 and the charge discharge region 27 in the charge sharing region 23. Each of the second transfer gate electrodes 44 and 45 is formed of a conductive and light-transmitting material (e.g., polysilicon). As an example, when viewed from the Z direction, each of the second transfer gate electrodes 44 and 45 has a rectangular shape having two sides opposing each other in the X direction and two sides opposing each other in the Y direction.

[0058] The distance measuring sensor 10 further includes a relative electrode 50 and a wiring layer 60 in the pixel portion 11. The relative electrode 50 is provided on the second surface 20b of the semiconductor layer 20. When viewed from the Z direction, the relative electrode 50 includes a plurality of pixels 11a. The relative electrode 50 is opposite to the electrode layer 40 in the Z direction. The relative electrode 50 is formed of, for example, a metal material. The wiring layer 60 is provided on the first surface 20a of the semiconductor layer 20 in a manner covering the electrode layer 40. The wiring layer 60 is connected to each pixel 11a and the CMOS readout circuit portion 12 (see Figure 1 A light incident opening 60a is formed in a portion of the wiring layer 60 that faces the gate electrode 41 of each pixel 11a.

[0059] A trench 29 is formed in the semiconductor layer 20 to separate the pixels 11a from each other. The trench 29 is formed on the first surface 20a of the semiconductor layer 20. The bottom surface 29a of the trench 29 is located on the second side relative to the avalanche multiplying region 22. In other words, the trench 29 completely separates the avalanche multiplying region 22. An insulating material 47, such as silicon oxide, is disposed within the trench 29. Alternatively, a metal material, such as tungsten, or polysilicon may be disposed within the trench 29 in place of the insulating material 47.

[0060] In each pixel 11a, the avalanche multiplication region 22 reaches the trench 29. The avalanche multiplication region 22 is a region that causes avalanche multiplication. In each pixel 11a, when a reverse bias voltage of a predetermined value is applied, 3×10 5 ~4×10 5 The avalanche multiplication region 22 with an electric field strength of 100 V / cm extends over the entire region surrounded by the trench 29 .

[0061] [Range image acquisition method]

[0062] An operation example (distance image acquisition method) of the distance image acquisition device 1 will be described. The following operation is realized by the control unit 4 controlling the driving of each unit. First, a method for detecting the pulse light L by the distance measuring sensor 10 will be described.

[0063] In each pixel 11a of the distance measuring sensor 10, a negative voltage (e.g., -50V) is applied to the counter electrode 50 based on the potential of the grating electrode 41. In other words, a reverse bias is applied to the pn junction formed in the avalanche multiplication region 22. As a result, a 3×10 5 ~4×10 5 In this state, when the pulsed light L enters the semiconductor layer 20 through the light incident opening 60 a and the grating electrode 41 , the charges (electrons) generated by the absorption of the pulsed light L are multiplied in the avalanche multiplication region 22 and move at high speed to the charge sharing region 23 .

[0064] A pulse voltage signal (hereinafter referred to as voltage signal TX1 or TX2) is applied to the first transfer gate electrodes 42 and 43 of each pixel 11a. The pulse voltage signal applied to the first transfer gate electrodes 42 and 43 is, for example, a voltage signal that alternates between positive voltage (on) and negative voltage (off) based on the potential of the gate electrode 41. While a positive voltage is applied to the first transfer gate electrode 42, charge is transferred from the charge distribution region 23 to the charge accumulation region 24 at high speed. While a positive voltage is applied to the first transfer gate electrode 43, charge is transferred from the charge distribution region 23 to the charge accumulation region 25 at high speed.

[0065] As described below, the pulse voltage signals applied to the first transfer gate electrodes 42 and 43 are set so as to be turned on at different timings. As a result, the charges moved to the charge sharing region 23 are transferred to the charge storage regions 24 and 25 at the transfer timing corresponding to the pulse voltage signal and distributed. The charges accumulated in the charge storage regions 24 and 25 by the transfer during the predetermined period are transmitted as signals to the CMOS readout circuit section 12 (see FIG. 1 ) via the readout circuit formed by the well region 31 and the wiring layer 60. Figure 1 ) is transferred and read out. The amount of charge accumulated in the charge storage regions 24 and 25 corresponds to the amount (intensity) of the pulsed light L incident on the charge generation region 36 while a positive voltage is applied to the first transfer gate electrodes 42 and 43. In this manner, the distance measuring sensor 10 can detect the pulsed light L by transferring the charge generated in the charge generation region 36 in response to the incidence of the pulsed light L reflected by the object OJ to the charge storage regions 24 and 25 using the first transfer gate electrodes 42 and 43.

[0066] Next, refer to Figure 5 and Figure 6 An example of the operation of the distance image acquisition device 1 will be described. Figure 5 and Figure 6 As shown, in this distance image acquisition method, the entire distance range 70 of the measurement object is divided into multiple intervals (unit distance ranges). In this example, the multiple intervals include five intervals 71A to 71E. The lengths of intervals 71A to 71E are equal to each other. As an example, the entire distance range 70 is 22.5 meters, and the length of each interval 71A to 71E is 4.5 meters. Intervals 71A, 71B, 71C, 71D, and 71E approach the light source in this order. That is, interval 71A is a range of 0 to 4.5 meters from light source 2, interval 71B is a range of 4.5 to 9 meters from light source 2, interval 71C is a range of 9 to 13.5 meters from light source 2, interval 71D is a range of 13.5 to 18 meters from light source 2, and interval 71E is a range of 18 to 22.5 meters from light source 2.

[0067] In this distance image acquisition method, measurements are performed for each of intervals 71A to 71E. In this example, the frame rate is 30 fps, and the length of one data DT is 33.3 ms. Data DT includes five subframes F1 to F5 corresponding to intervals 71A to 71E. In other words, in this distance image acquisition method, the frame (data DT) corresponding to the entire distance range 70 is time-divided into multiple subframes F1 to F5. The length of subframes F1 to F5 is equal to each other, and in this example, is 6.6 ms.

[0068] Each subframe F1-F5 includes a first period P1 and a second period P2 continuous with the first period P1. During the first period P1, pulsed light L is emitted from the light source 2, and the pulsed light L reflected by the object OJ is detected by the ranging sensor 10. During the second period P2, no pulsed light L is emitted from the light source 2, and the ranging sensor 10 detects only the background light. That is, the measuring light and background light are detected during the first period P1, while only the background light is detected during the second period P2. When generating the distance image of the object OJ, the difference between the signal obtained during the first period P1 and the signal obtained during the second period P2 is used as the signal light. The length of the first period P1 and the second period P2 are equal, which is 3.3 ms in this example.

[0069] In each subframe F1 to F5, the time difference TD between the emission timing of the pulse light L of the light source 2 and the transfer timing of the charge of the first transfer gate electrodes 42 and 43 is made different between the intervals 71A to 71E and the measurement is performed in the intervals 71A to 71E. The details of the operation in each subframe F1 to F5 are described below. Figure 5 and Figure 6 2 shows an intensity signal SL of the pulse light L emitted from the light source 2 , a voltage signal TX1 applied to the first transfer gate electrode 42 , and a voltage signal TX2 applied to the first transfer gate electrode 43 .

[0070] like Figure 5 and Figure 6As shown, in subframe F1, the voltage signal TX1 applied to the first transfer gate electrode 42 has the same period, pulse width, and phase as the intensity signal SL of the pulsed light L emitted from the light source 2. That is, in subframe F1, there is no time difference TD between the emission timing and the transmission timing (it is zero). The voltage signal TX2 applied to the first transfer gate electrode 43 rises and turns on immediately after the voltage signal TX1 of the first transfer gate electrode 42 is turned off. The voltage signal TX2 has the same period and pulse width as the intensity signal SL and the voltage signal TX1. The pulse width of the pulsed light L, voltage signals TX1, and TX2 is, for example, 30 ns. During the period when both voltage signals TX1 and TX2 are turned off, a positive voltage is applied to the second transfer gate electrodes 44 and 45, and charge is transferred from the charge distribution region 23 to the charge discharge regions 26 and 27 at high speed. The charge transferred to the charge discharge regions 26 and 27 is discharged to the outside.

[0071] exist Figure 5 In FIG, the timing of reading out the charges accumulated in the charge accumulation regions 24 and 25 is represented by symbol R. Figure 5 As shown, in the subframe F1, in each of the first period P1 and the second period P2, in addition to the start and end points of the period, charges are read out once between the start and end points. That is, the number of readouts N is three.

[0072] like Figure 1 As shown, when pulse light L is emitted from light source 2 and reflected by object OJ and detected by distance measuring sensor 10, the phase of the intensity signal of pulse light L detected by distance measuring sensor 10 is shifted relative to the phase of intensity signal SL of pulse light L emitted from light source 2, corresponding to the distance d to object OJ. Therefore, by acquiring the amount of charge accumulated in charge accumulation regions 24 and 25 in subframe F1 for each pixel 11a, data for generating a distance image for section 71A can be obtained.

[0073] In subframe F2, the voltage signal TX1 applied to the first transmission gate electrode 42 is phase-shifted by a time TS from the intensity signal SL of the pulsed light L emitted by the light source 2. That is, in subframe F2, the time difference TD is the time TS. The time TS corresponds to interval 71B and is, for example, 30 ns. In this example, the time TS is equal to the pulse width of the pulsed light L. In other respects, the voltage signals TX1 and TX2 are identical to those in subframe F1. Figure 5 As shown, in subframe F2, charge is read out twice, at the start and end of each of the first period P1 and the second period P2, and the number of readouts N is 2. By acquiring the amount of charge accumulated in the charge accumulation regions 24 and 25 in subframe F2 for each pixel 11a, data for generating a distance image for section 71B can be obtained.

[0074] In subframe F3, the voltage signal TX1 applied to the first transfer gate electrode 42 is phase-shifted by twice the time TS from the intensity signal SL of the pulsed light L emitted by the light source 2. That is, in subframe F3, the time difference TD is 2TS. This time 2TS corresponds to interval 71C and is, for example, 60 ns. In all other respects, the voltage signals TX1 and TX2 are identical to those in subframe F1. The number of readouts N in subframe F3 is the same as in subframe F2, being two. By acquiring the charge accumulated in the charge storage regions 24 and 25 for each pixel 11a in subframe F3, data for generating a distance image for interval 71C can be obtained.

[0075] In subframe F4, the phase of the voltage signal TX1 applied to the first transfer gate electrode 42 is shifted by three times the time TS from the intensity signal SL of the pulsed light L emitted by the light source 2. That is, in subframe F4, the time difference TD is 3TS. This time 3TS corresponds to interval 71D and is, for example, 90 ns. In other respects, the voltage signals TX1 and TX2 are identical to those in subframe F1. The number of readouts N in subframe F4 is the same as in subframe F2, being two. By acquiring the charge accumulated in the charge storage regions 24 and 25 for each pixel 11a in subframe F4, data for generating a distance image for interval 71D can be obtained.

[0076] In subframe F5, the phase of the voltage signal TX1 applied to the first transfer gate electrode 42 is shifted by four times the time TS from the intensity signal SL of the pulsed light L emitted by the light source 2. That is, in subframe F5, the time difference TD is 4TS. This time 4TS corresponds to interval 71E and is, for example, 120 ns. In other respects, the voltage signals TX1 and TX2 are identical to those in subframe F1. The number of readouts N in subframe F4 is the same as in subframe F2, being two. By acquiring the amount of charge accumulated in the charge storage regions 24 and 25 for each pixel 11a in subframe F5, data for generating a distance image for interval 71E can be obtained.

[0077] In this manner, the time difference TD between the emission timing of the pulsed light L from the light source 2 and the transfer timing of the charge from the first transfer gate electrodes 42 and 43 is varied between intervals 71A to 71E, and measurement is performed for each of these intervals. More specifically, the emission timing is fixed, and the transfer timing is offset from the emission timing, so that the time difference TD is varied between intervals 71A to 71E. Furthermore, during measurement of interval 71A (subframe F1), the charge accumulated in the charge storage regions 24 and 25 is read at a higher readout frequency (a higher number of readouts N) than during measurement of intervals 71B to 71E (subframes F2 to F5), which are farther from the light source 2 than interval 71A. Furthermore, the length of the first period P1 in subframes F1 to F5 is 3.3 ms and is identical across all of them, and the charge storage time (exposure time) during measurement of intervals 71A to 71E is identical across all of them.

[0078] In the range image acquisition method of the embodiment, a range image for the entire range 70 is generated based on the measurement results for intervals 71A to 71E. Specifically, the data used to generate the range image for intervals 71A to 71E is obtained by measuring the aforementioned intervals 71A to 71E (subframes F1 to F5). By synthesizing this data, a range image for the entire range 70 can be generated.

[0079] [Function and Effect]

[0080] As described above, in the distance image acquisition device 1, the charge generation region 36 includes the avalanche multiplication region 22 that generates avalanche multiplication. This improves the sensitivity of the distance measuring sensor 10, resulting in a longer measured distance. On the other hand, as mentioned above, increasing the pulse width of the pulsed light L is generally necessary to extend the measured distance. However, increasing the pulse width degrades distance accuracy. Regarding this issue, in the distance image acquisition device 1, the entire distance range 70 of the measurement target is divided into a plurality of sections 71A to 71E. The time difference TD between the emission timing of the pulsed light L from the light source 2 and the transmission timing of the first transfer gate electrodes 42 and 43 is varied between the sections 71A to 71E. Measurements are performed in each of the sections 71A to 71E, and a distance image for the entire distance range 70 is generated based on the measurement results for the sections 71A to 71E. This prevents the pulse width of the pulsed light L from increasing, ensuring distance accuracy, even when the measured distance is long.

[0081] For example, unlike the range image acquisition device 1 , when the entire distance range 70 is measured without dividing the range into sections 71A to 71E, the pulse width becomes approximately 150 ns as described below. That is, in the indirect TOF method, the following equation (1) holds.

[0082] ΔD=cW / 2…(1)

[0083] ΔD is the distance accuracy, c is the speed of light, and W is the pulse width of the pulse light L. In formula (1), the distance accuracy ΔD is set to 22.5 m, and the speed of light c is set to 3×10 8 m / s, the pulse width W becomes 150 ns. In contrast, in the range image acquisition device 1, as described above, the pulse width W of the pulsed light L is 30 ns, and the distance accuracy ΔD is 4.5 m. That is, compared to the case where the range is not divided into sections 71A to 71E, the distance accuracy ΔD is improved to 1 / 5 (30 ns / 150 ns). Thus, in the range image acquisition device 1, by time-segmenting the ranging range and acquiring distance data, it is possible to extend the distance and improve distance accuracy. Furthermore, in practice, the right side of the above equation (1) can be further multiplied by the N / S ratio.

[0084] Furthermore, simply dividing the range into sections 71A to 71E might reduce the charge accumulation time (exposure time) and lead to insufficient charge accumulation. However, in the range image acquisition device 1, since the charge generation region 36 includes the avalanche multiplication region 22, insufficient charge accumulation can be suppressed. Therefore, the need to extend the charge accumulation time to compensate for insufficient charge accumulation is less likely to occur. Furthermore, dividing the range into sections 71A to 71E can also suppress a decrease in measurement accuracy (multiple echoes) caused by the presence of transparent or semi-transparent objects between the distance measuring sensor 10 and the object. For example, unlike the range image acquisition device 1, if the entire distance range 70 is measured without dividing the range into sections 71A to 71E, the output would be a distance that averages the distance to an object in section 71A and the distance to an object in section 71E, potentially reducing measurement accuracy. In contrast, in the range image acquisition device 1, dividing the range into sections 71A to 71E can suppress this decrease in measurement accuracy. As described above, according to the distance image acquisition device 1 , the measurement distance can be extended while ensuring distance accuracy.

[0085] During measurement of interval 71A (first interval), the charge accumulated in charge storage regions 24 and 25 is read at a higher readout frequency (a higher number of readouts N) than during measurement of intervals 71B to 71E (second interval), which are farther from light source 2 than interval 71A. This suppresses signal saturation, which would otherwise occur in charge generation region 36 during measurement of interval 71A. This suppression of saturation is particularly effective when charge generation region 36 includes avalanche multiplication region 22. Signal saturation is more likely to occur during measurement of interval 71A because the intensity of pulse light L reflected by object OJ and returned to distance measuring sensor 10 increases as the interval approaches light source 2.

[0086] The distance measuring sensor 10 includes a pair of charge storage regions 24 and 25, and a pair of first transfer gate electrodes 42 and 43 disposed in the region between the charge generation region 36 and the pair of charge storage regions 24 and 25. Even with this configuration, the entire distance range 70 to be measured can be divided into a plurality of intervals 71A to 71E, and the time difference TD between the emission timing and the transfer timing can be varied between intervals 71A to 71E, allowing measurement to be performed in each of these intervals.

[0087] By fixing the emission timing of the pulsed light L and shifting the transfer timing of the charge of the first transfer gate electrodes 42 and 43 from the emission timing of the pulsed light L, the time difference TD between the emission timing and the transfer timing is made different in the intervals 71A to 71E. Thus, the time difference TD between the emission timing and the transfer timing can be made different in the intervals 71A to 71E.

[0088] The charge accumulation time (exposure time) during measurement of intervals 71A to 71E is equal to each other. This allows for faster acquisition of distance images, compared to, for example, extending the charge accumulation time during measurement of intervals farther from the light source 2 and where charge accumulation is likely to be insufficient (e.g., interval 71E).

[0089] [Modification]

[0090] You can also Figure 7 and Figure 8 The distance measuring sensor 10 is configured as in the first modified example shown. The distance measuring sensor 10 of the first modified example includes the charge storage region 24, the charge discharge region 26, the first transfer gate electrode 42, and the second transfer gate electrode 44. In other words, the distance measuring sensor 10 does not include the charge storage region 25, the charge discharge region 27, the first transfer gate electrode 43, and the second transfer gate electrode 45.

[0091] In each pixel 11a of the distance measuring sensor 10 of the first modified example, the charge storage region 24 is arranged in the center of the charge distribution region 23 when viewed from the Z direction. The charge discharge region 26, for example, has a rectangular ring shape and is arranged along the outer edge of the charge distribution region 23 when viewed from the Z direction. The gate electrode 41, for example, has a rectangular ring shape and is arranged outside the charge storage region 24 and inside the charge discharge region 26 when viewed from the Z direction. The first transfer gate electrode 42, for example, has a rectangular ring shape and is arranged outside the charge storage region 24 and inside the gate electrode 41 when viewed from the Z direction. The second transfer gate electrode 44, for example, has a rectangular ring shape and is arranged outside the gate electrode 41 and inside the charge discharge region 26 when viewed from the Z direction. Furthermore, the charge storage region 24, the charge discharge region 26, the gate electrode 41, the first transfer gate electrode 42, and the second transfer gate electrode 44 may be formed in any other shape, such as an octagon.

[0092] like Figure 9 As shown, when using the distance measuring sensor 10 of the first variant, as in the above-mentioned embodiment, the time difference TD between the emission timing of the pulse light L of the light source 2 and the transmission timing of the charge of the first transmission gate electrode 42 can be made different between the intervals 71A to 71E and the intervals 71A to 71E can be measured.

[0093] exist Figure 9 In the example, one data frame is divided into six subframes G1 to G6. In subframe G1, the voltage signal TX1 applied to the first transfer gate electrode 42 has the same period, pulse width, and phase as the intensity signal SL of the pulsed light L emitted from the light source 2. That is, in subframe G1, there is no time difference TD between the emission timing and the transmission timing (it is zero). While the voltage signal TX1 is off, a positive voltage is applied to the second transfer gate electrode 44, and charge is transferred from the charge distribution region 23 to the charge discharge region 26 at high speed. The charge transferred to the charge discharge region 26 is discharged to the outside.

[0094] In subframes G2 to G6, time difference TD is time TS, 2TS, 3TS, 4TS, and 5TS, respectively. Regarding other points, voltage signal TX1 is the same as that in subframe G1.

[0095] like Figure 9 As shown, data corresponding to subframe F1 in the above-described embodiment can be obtained from the data acquired in adjacent subframes G1 and G2. Similarly, data corresponding to subframe F3 in the above-described embodiment can be obtained from the data acquired in subframes G2 and G3. Similarly, data corresponding to subframes F3 to F5 in the above-described embodiment can be obtained from the data acquired in subframes G3 to G6. Therefore, a range image for the entire distance range 70 can be generated based on the measurement results for subframes G1 to G6. This first modified example, as in the above-described embodiment, can extend the measured distance while maintaining distance accuracy.

[0096] You can also Figure 10 A distance image is obtained as in the second modified example shown. In the second modified example, unlike the above-described embodiment, the timing of charge transfer of the first transfer gate electrodes 42 and 43 is fixed, and the emission timing of the pulse light L is offset from the transmission timing, so that the time difference TD between the emission timing and the transmission timing varies between the intervals 71A to 71E.

[0097] Specifically, in Figure 10In the example shown in FIG2 , in subframes F2 to F5, the emission timing of pulsed light L from light source 2 is offset by times TS, 2TS, 3TS, and 4TS, respectively, relative to the transfer timing of charge from first transfer gate electrodes 42 and 43. Even in this case, by synthesizing the measurement data for intervals 71A to 71E, a distance image covering the entire distance range 70 can be generated. Therefore, similar to the above-described embodiment, this second variation can extend the measurement distance while maintaining distance accuracy.

[0098] like Figure 11 As shown in the third modification example, in the first modification example, as in the second modification example, by fixing the transmission timing of the charge of the first transmission gate electrode 42 and deviating the emission timing of the pulse light L from the transmission timing, the time difference TD between the emission timing and the transmission timing can also be made different between the intervals 71A to 71E.

[0099] exist Figure 11 In the example shown in FIG2 , in subframes G2 to G6, the emission timing of pulsed light L from light source 2 is offset by times TS, 2TS, 3TS, 4TS, and 5TS, respectively, relative to the charge transfer timing of first transfer gate electrode 42. Even in this case, data corresponding to subframes F1 to F5 in the above-described embodiment can be obtained from the data acquired in subframes G1 to G6, allowing a distance image to be generated for the entire distance range 70. Therefore, similar to the above-described embodiment, this third variation can extend the measured distance while maintaining distance accuracy.

[0100] The present invention is not limited to the above-mentioned embodiments and variations. For example, the materials and shapes of each component are not limited to the above-mentioned materials and shapes, and a variety of materials and shapes can be used. In the distance sensor 10, the bottom surface 29a of the groove 29 may be located on the first side relative to the avalanche multiplication region 22, and the avalanche multiplication region 22 may be connected to multiple pixels 11a. Alternatively, the groove 29 may not be formed in the semiconductor layer 20, and the avalanche multiplication region 22 may be connected to multiple pixels 11a. The charge discharge regions 26, 27 and the second transfer gate electrodes 44, 45 may also be omitted. The conductivity types of p-type and n-type may also be opposite to the above-mentioned examples. Multiple pixels 11a may also be arranged one-dimensionally along the first surface 20a of the semiconductor layer 20. The distance sensor 10 may also have only a single pixel 11a.

[0101] The entire distance range 70 may be divided into any number of intervals, two or more. The lengths of the multiple intervals may also differ. The lengths of the first period P1 in subframes F1 to F5 may also differ. That is, the charge accumulation times during the measurement of intervals 71A to 71E may also differ. The number of readouts N in subframe F1 may be two, at the start and end of the period, or four or more. The number of readouts N in subframes F2 to F5 may also be three or more.

[0102] In the above embodiment, during measurement of interval 71A (first interval), the charge accumulated in charge storage regions 24 and 25 is read out at a higher readout frequency than during measurement of intervals 71B to 71E (second interval), which are farther from light source 2 than interval 71A. This suppresses signal saturation in charge generation region 36 during measurement of interval 71A. Alternatively or additionally, during measurement of interval 71A, the charge accumulated in charge storage regions 24 and 25 may be transferred at a lower transfer frequency than during measurement of intervals 71B to 71E. For example, while in interval 71A of the above embodiment, charge transfer is performed once for each emission of pulse light L, charge transfer may be performed once for each emission of two or four pulse light L. In this case, signal saturation can also be suppressed. In this case, the readout frequencies in intervals 71A to 71E may be the same.

[0103] Explanation of symbols

[0104] 1 ...distance image acquisition device, 2 ...light source, 4 ...control unit, 10 ...distance measuring sensor, 22 ...avalanche multiplication region, 24, 25 ...charge accumulation regions, 36 ...charge generation region, 42, 43 ...first transfer gate electrodes, 70 ...entire distance range, 71A ...segment (first segment),

[0105] 71B...section (second section), 71C to 71E...section, L...pulse light (measurement light),

[0106] OJ…object, TD…time difference.

Claims

1. A distance image acquisition device, wherein: have: a light source that emits measurement light; a distance measuring sensor comprising a charge generation region, a charge accumulation region, and a transfer gate electrode disposed in a region between the charge generation region and the charge accumulation region, wherein the transfer gate electrode is used to transfer charge generated in the charge generation region in response to the incidence of the measurement light emitted from the light source and reflected by the object to the charge accumulation region, thereby detecting the measurement light; as well as a control unit configured to control the distance measuring sensor to generate a distance image of the object based on a detection result of the distance measuring sensor; The charge generation region includes an avalanche multiplication region for generating avalanche multiplication, The control unit, Divide the entire distance range of the measurement object into multiple intervals. The distance measuring sensor is controlled so that a time difference between an emission timing of the measurement light by the light source and a transfer timing of the charge by the transfer gate electrode is different among the plurality of intervals and measurement is performed in the plurality of intervals. The distance image of the entire distance range is generated based on the measurement results of the plurality of intervals.

2. The distance image acquisition device according to claim 1, wherein: The plurality of intervals include a first interval and a second interval farther from the light source than the first interval. The control unit controls the distance measuring sensor so that the charge accumulated in the charge accumulation region is read out at a higher reading frequency during measurement of the first section than during measurement of the second section.

3. The distance image acquisition device according to claim 1, wherein: The plurality of intervals include a first interval and a second interval farther from the light source than the first interval. The control unit controls the distance measuring sensor so that the charge is transferred to the charge storage area at a lower transfer frequency during measurement of the first section than during measurement of the second section.

4. The distance image acquisition device according to claim 2, wherein: The plurality of intervals include a first interval and a second interval farther from the light source than the first interval. The control unit controls the distance measuring sensor so that the charge is transferred to the charge storage area at a lower transfer frequency during measurement of the first section than during measurement of the second section.

5. The distance image acquisition device according to claim 1, wherein: The charge storage region includes a pair of charge storage regions, The transfer gate electrode includes a pair of transfer gate electrodes respectively arranged on regions between the charge generation region and the pair of charge storage regions.

6. The distance image acquisition device according to claim 2, wherein: The charge storage region includes a pair of charge storage regions, The transfer gate electrode includes a pair of transfer gate electrodes respectively arranged on regions between the charge generation region and the pair of charge storage regions.

7. The distance image acquisition device according to claim 3, wherein: The charge storage region includes a pair of charge storage regions, The transfer gate electrode includes a pair of transfer gate electrodes respectively arranged on regions between the charge generation region and the pair of charge storage regions.

8. The distance image acquisition device according to claim 4, wherein: The charge storage region includes a pair of charge storage regions, The transfer gate electrode includes a pair of transfer gate electrodes respectively arranged on regions between the charge generation region and the pair of charge storage regions.

9. The distance image acquisition device according to claim 1, wherein: The distance measuring sensor has only one region as the charge accumulation region and has only one electrode as the transfer gate electrode.

10. The distance image acquisition device according to claim 2, wherein: The distance measuring sensor has only one region as the charge accumulation region and has only one electrode as the transfer gate electrode.

11. The distance image acquisition device according to claim 3, wherein: The distance measuring sensor has only one region as the charge accumulation region and has only one electrode as the transfer gate electrode.

12. The distance image acquisition device according to claim 4, wherein: The distance measuring sensor has only one region as the charge accumulation region and has only one electrode as the transfer gate electrode.

13. The distance image acquisition device according to any one of claims 1 to 12, wherein: The control unit fixes the emission timing and shifts the transmission timing from the emission timing, thereby making the time difference between the emission timing and the transmission timing different among the plurality of sections.

14. The distance image acquisition device according to any one of claims 1 to 12, wherein: The control unit fixes the transmission timing and shifts the emission timing from the transmission timing, thereby making the time difference between the emission timing and the transmission timing different among the plurality of sections.

15. The distance image acquisition device according to any one of claims 1 to 12, wherein: The charge accumulation times in the measurement of the plurality of intervals are equal to each other.

16. The distance image acquisition device according to claim 13, wherein: The charge accumulation times in the measurement of the plurality of intervals are equal to each other.

17. The distance image acquisition device according to claim 14, wherein: The charge accumulation times in the measurement of the plurality of intervals are equal to each other.

18. A method for obtaining a range image, wherein: A distance image acquisition method for acquiring a distance image of an object. Using a light source that emits measuring light and a distance measuring sensor, Divide the entire distance range of the measurement object into multiple intervals. The time difference between the emission timing of the measurement light from the light source and the transfer timing of the charge of the transfer gate electrode is made different among the plurality of intervals and the measurement is performed in the plurality of intervals. generating the distance image of the entire distance range based on the measurement results of the plurality of intervals, The distance measuring sensor includes a charge generation region, a charge accumulation region, and the transfer gate electrode arranged in a region between the charge generation region and the charge accumulation region, and detects the measurement light by transmitting the charge generated in the charge generation region corresponding to the incidence of the measurement light emitted from the light source and reflected by the object to the charge accumulation region using the transfer gate electrode, wherein the charge generation region includes an avalanche multiplication region that generates avalanche multiplication.

Images