Patent ID: 12204049

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

JP 2016-17904 A describes a lidar device that measures distances to objects around a vehicle by applying light toward an area around the vehicle and receiving reflected light of the applied light returning from the objects.

The inventors have conducted detailed research, and as a result, found that the lidar device described in JP 2016-17904 A has measurement accuracy lower for the distance to an object near to the lidar device than for the distance to an object far from the lidar device.

The present disclosure improves measurement accuracy of a lidar device.

First Embodiment

A first embodiment of the present disclosure will now be described with reference to the drawings.

A lidar device1according to the present embodiment is installed in a vehicle and used to detect various objects around the vehicle. Lidar is also written as LIDAR. LIDAR is an abbreviation for light detection and ranging.

The lidar device1, as shown inFIG.1, includes a housing100and an optical window200.

The housing100is a rectangular resin box with an opening in one of its six surfaces and contains a photodetection module2described later.

The optical window200is a resin lid fixed to the housing100to cover the opening in the housing100. The photodetection module2installed in the housing100emits a laser beam, which passes through the optical window200.

Hereinafter, the direction along the length of the substantially rectangular opening is referred to as the X axis direction, the direction along the width of the opening is referred to as the Y axis direction, and the direction orthogonal to the X axis direction and the Y axis direction is referred to as the Z axis direction. Right and left in the X axis direction, and up and down in the Y axis direction are defined as viewed from the opening in the housing100. In the Z axis direction, forward is defined as a direction from the depth toward the opening in the housing100, and rearward is defined as a direction toward the depth.

The photodetection module2, as shown inFIGS.2,3, and4, includes a light emitting unit10, a scanning unit20, a light receiving unit30, and a frame40. The photodetection module2is installed in the housing100via the frame40.

The scanning unit20includes a mirror module21, a partition22, and a motor23.

The mirror module21, as shown inFIG.5, includes a pair of deflection mirrors211and212and a mirror frame213.

The pair of deflection mirrors211and212are flat members each having a reflective surface that reflects light. The mirror frame213includes a circular plate213aand a support213b. The circular plate213ais a disc-shaped portion and fixed to the rotational shaft of the motor23at the center of the circle. The support213bis a plate member with the deflection mirrors211and212fixed on both sides. The support213bprotrudes from the circular surface of the circular plate213ain a direction perpendicular to the circular surface of the circular plate213a.

The deflection mirrors211and212and the support213beach have an integrated shape of two rectangles with different lengths. More specifically, the deflection mirrors211and212and the support213bhave a shape of two integrated rectangles arranged along their central axes extending in the width direction, with the axes aligned with each other. Hereinafter, in the integrated portion of the deflection mirrors211and212and the support213bof the mirror module21, the rectangular part smaller in a longitudinal direction is referred to as a short portion, and the rectangular part larger in a longitudinal direction is referred to as a long portion.

The pair of deflection mirrors211and212integrated via the mirror frame213are placed with the long portion being under the short portion, with the central axis being aligned with the center of the circle of the circular plate213a, and to protrude from the circular surface of the circular plate213ain a direction perpendicular to the circular surface of the circular plate213a. This arrangement allows the deflection mirrors211and212to rotate about the rotational shaft of the motor23in accordance with the motor driving. The reflective surfaces of the deflection mirrors211and212are parallel with the rotational shaft of the motor23irrespective of the rotational position of the motor23.

The partition22is a disc-shaped member having a diameter equal to the length of the long portion of the mirror module21. The partition22is divided into two semicircular portions. The two semicircular portions hold the short portion of the mirror module21from both sides and fixed in contact with a step formed by the long portion and the short portion of the mirror module21.

Hereinafter, in the deflection mirrors211and212, the part above the partition22(i.e., the part of the short portion) is referred to as an emitted light deflection section20a, and the part below the partition22(i.e., the part of the long portion) is referred to as a received light deflection section20b.

The light emitting unit10, as shown inFIGS.2to4, includes a pair of light sources11and12, a pair of emitter lenses13and14, and an emitted light turning mirror15.

The light sources11and12have the same structure, and the structure of the light source11will be described herein. The light source11is, as shown inFIG.6, a so-called multi-stripe semiconductor laser including a plurality of light emitting areas A1and A2. The light emitting areas A1and A2are formed as rectangles arranged in their longitudinal directions. The light emitting areas A1and A2have an area length L in the arrangement direction equal to or greater than the area interspace S between the light emitting area A1and the light emitting area A2. The light emitting areas A1and A2emit light beams having optical axes parallel with each other.

Hereinafter, in the emitted light deflection section20a, the point on which light beams are incident from the light sources11and12is referred to as a reflection point. Furthermore, the plane orthogonal to the rotation axis and including the reflection point is referred to as a reference plane.

As shown inFIGS.2to4, the light source11is positioned to the left along the X axis away from the reflection point, with the light emitting surface facing the emitted light deflection section20a. The light source12is positioned to the rear along the Z axis away from the turning point at or near the middle of the path from the reflection point to the light source11, with the light emitting surface facing forward along the Z axis. Regarding the positions of the light sources11and12in the Y axis direction, the light source11is placed below the reference plane, and the light source12is placed above the reference plane. The light sources11and12are placed so that the light emitting areas A1and A2are arranged in the Y axis direction.

The emitter lens13is placed opposite the light emitting surface of the light source11. Similarly, the emitter lens14is placed opposite the light emitting surface of the light source12. The light sources11and12are placed near the focuses of the emitter lenses13and14, respectively.

The emitted light turning mirror15, which is placed at the turning point described above, reflects and guides light emitted from the light source12to the reflection point described above. The emitted light turning mirror15is, as shown inFIG.8, placed above the path of light emitted from the light source11to the reflection point so as not to obstruct the path. The optical path from the light source11to the reflection point has the same length as the optical path from the light source12to the reflection point via the emitted light turning mirror15. The light source11has an optical axis inclined 1 to 2 degrees upward from the reference plane, and the light source12has an optical axis inclined 1 to 2 degrees downward from the reference plane. In other words, the optical axes of the light sources11and12are oriented symmetrically about the reference plane. The angles are not limited to 1 to 2 degrees, but may be determined as appropriate depending on the intended light beam emission angle in the sub-scanning direction.

The light receiving unit30, as shown inFIGS.2to4, includes a light receiving element31, a light receiving lens32, and a received light turning mirror33.

The light receiving element31, as shown inFIG.7, includes an avalanche photodiode array311(hereinafter, APD array311) and a lens array312. APD is an abbreviation for avalanche photodiode. The APD array311includes 12 avalanche photodiodes (hereinafter, APDs) arranged in a row. The lens array312includes 12 lenses facing the 12 APDs of the APD array311on a one-to-one basis, and narrows and guides light incident on the light receiving element31to each APD.

The light receiving element31is, as shown inFIGS.3and9, placed below the received light turning mirror33, with the light receiving surface facing upward along the Y axis and the APDs of the APD array311aligned with the X axis direction. InFIG.3, a part of the frame40is not shown to increase the visibility of each arranged component.

The received light turning mirror33is positioned to the left along the X axis from the received light deflection section20b. The received light turning mirror33bends the optical path substantially 90 degrees downward in the Y axis direction so that light incident from the received light deflection section20bvia the light receiving lens32reaches the light receiving element31.

The light receiving lens32is placed between the received light deflection section20band the received light turning mirror33. The light receiving lens32narrows the light beam incident on the light receiving element31so that its width in the Z axis direction becomes substantially equal to the APD element width.

The frame40is a member that integrates each component included in the light emitting unit10, the scanning unit20, and the light receiving unit30. That is, the components included in the light emitting unit10, the scanning unit20, and the light receiving unit30are installed in the housing100with the positional relationship between the components established.

The frame40, as shown inFIGS.2to4, includes a frame bottom41, a frame side42, a frame back43, and a partition44.

The frame bottom41is underlain by a light receiver substrate51to which the light receiving element31is fixed and a motor substrate52to which the scanning unit20is fixed. Thus, the frame bottom41has holes at a site through which light passes from the received light turning mirror33to the light receiving element31, and a site at which the motor23of the scanning unit20is placed.

The frame side42has a front surface, which is the surface facing the scanning unit20, and a cylindrical holder421is installed on the front surface. The holder421has the emitter lens13fitted in the opening in its front end (i.e., the right end in the X axis direction). The back surface of the frame side42is fitted with a light emitter substrate53on which the light source11is installed. When the light emitter substrate53is attached to the frame side42, the light source11is placed at the back end of the holder421(i.e., the left end in the X axis direction).

In the same manner as for the frame side42, a holder431is installed on the frame back43. The holder431has the emitter lens14fitted in its front end (i.e., the forward end in the Z axis direction). The back surface of the frame back43is fitted with a light emitter substrate54on which the light source12is installed. When the light emitter substrate54is attached to the frame back43, the light source12is placed at the back end of the holder431(i.e., the rearward end in the Z axis direction).

The partition44is positioned in a manner to define a space in which the components of the light emitting unit10are placed and a space in which components of the light receiving unit30are placed. The partition44is fitted with the emitted light turning mirror15, the received light turning mirror33, and the light receiving lens32.

The light receiver substrate51and the light emitter substrates53and54are each screwed to the frame40. The lidar device1allows three-dimensional fine adjustments to the installation position and the angle of each of the light receiving element31and the light sources11and12by modifying the installation positions and the angles of the light receiver substrate51and the light emitter substrates53and54. In the present embodiment, the holders421and431are integrated with the frame side42and the frame back43, respectively. However, the holders421and431may be integrated with the light emitter substrate53and the light emitter substrate54.

A controller (not shown) is fitted to, for example, the housing100. The controller controls the timing of light emission from the light sources11and12in synchronization with the rotation of the mirror module21of the scanning unit20. More specifically, the controller controls the light beam from the light source11to be incident on the deflection mirror211and the light beam from the light source12to be incident on the deflection mirror212.

As shown inFIG.8, the light emitted from the light source11is incident on the reflection point P on the emitted light deflection section20athrough the emitter lens13. The light emitted from the light source12passes through the emitter lens14. After that, its traveling direction is deflected substantially 90 degrees by the emitted light turning mirror15. The light is then incident on the reflection point P on the emitted light deflection section20a. It is noted that the light source11and the light source12use different surfaces of the emitted light deflection section20a. The light incident on the reflection point P is directed in accordance with the rotational position of the mirror module21.

As shown inFIG.9, the light reflected from a subject positioned in the predetermined direction in accordance with the rotational position of the mirror module21(i.e., the direction in which light is emitted from the emitted light deflection section20a) is reflected by the received light deflection section20band detected in the light receiving element31through the light receiving lens32and the received light turning mirror33. Note that subjects are various targets to be detected by the lidar device1.

More specifically, in the lidar device1, horizontal scanning in the X axis direction (hereinafter, main scanning) is mechanically achieved by the rotation of the mirror module21. Additionally, vertical scanning in the Y axis direction (hereinafter, sub-scanning) is electronically achieved by the light sources11and12for outputting four beams that are adjacent to each other in the vertical direction and the APD array311for receiving the four beams.

As shown inFIGS.8to10, the light sources11and12are placed so that their optical paths to the reflection point P on the emitted light deflection section20ahave an equal length, and their optical axes intersect at reflection point P. The light receiving element31is placed near the focus of the light receiving lens32.

Light beams from the light emitting areas A1and A2of the light source11are denoted by B11and B12, and light beams from the light emitting areas A1and A2of the light source12are denoted by B21and B22. As shown inFIG.11, the light beams emitted from the reflection point P on the emitted light deflection section20aare the light beam B11, the light beam B21, the light beam B12, and the light beam B22in this order from top to bottom along the Y axis. Additionally, the positions of the light sources11and12are finely adjusted so as not to form a gap between the light beams B11, B21, B12, and B22. As shown inFIG.12, the positions of the light sources11and12are also finely adjusted so that the APD array311of the light receiving element31receives reflected light (hereinafter, returning light beams) from the subject irradiated with the light beams B11, B21, B12, and B22, and the returning light beams are applied to the center in the Z axis direction of each APD with each beam hitting three different elements.

The reflective surface of the emitted light deflection section20ais parallel with the rotation axis of the mirror module21, and thus the inclination angle of the reflective surface in vertical plane including the path of light incident on the emitted light deflection section20ais unaffected by the rotational position of the mirror module21. The vertical planes refer to planes along the Y axis. More specifically, as indicated in the graph ofFIG.11, irrespective of the emission angle in the X axis direction (i.e., the horizontal angle), which is the main scanning direction of the light emitted from the emitted light deflection section20a, the emission angle in the Y axis direction (i.e., the vertical angle), which is the sub-scanning direction, is constant. Thus, the light beams are applied to a two-dimensionally defined scan range entirely.

The APD array311, as shown inFIG.13, is formed by arranging 12 APDs502in a row on the front surface of a substrate501of a p-type semiconductor (in the present embodiment, silicon). However, the substrate501may be formed of an i-type semiconductor.

The APD array311includes the 12 APDs502, one unnecessary-carrier discharge electrode503, and two bonding pads504on the front surface of the substrate501.

An APD502, as shown inFIG.14, includes an n+ region511, an n region512, an n region513, a p+ region514, an antireflection film515, and a signal extraction electrode516.

The n+ region511is an n-type region formed in the front surface of the substrate501. The n+ region511contains a higher concentration of n-type impurities than the n regions512and513.

The n region512is an n-type region formed in the front surface of the substrate501, and around and in contact with the n+ region511.

The n region513is an n-type region formed in the front surface of the substrate501and around, but not in contact with, the n region512.

The p+ region514is a p-type region formed in the back surface of the substrate501. The p+ region514contains a higher concentration of p-type impurities than the substrate501.

The antireflection film515is a film formed from, for example, silicon nitride and placed on the n+ region511. The antireflection film515reduces the surface reflection of light incident on the antireflection film515.

The signal extraction electrode516is an electrode formed from, for example, Al or Cu, placed on the n region512, and electrically connected to the n region512. The signal extraction electrode516receives a high voltage (e.g., 300 V).

In the substrate501, the n+ region511, the n region512, and the region under the n+ region511and the n region512are hereinafter referred to as a pixel region521. In the substrate501, the region other than the pixel region521is hereinafter referred to as a pixel neighboring region522.

The unnecessary-carrier discharge electrode503is an electrode formed from, for example, Al or Cu, placed on the n region513, and electrically connected to the n region513.

The APD array311also includes, on the back surface of the substrate501, a back-side electrode505formed from, for example, AlSiCu.

As shown inFIG.13, the antireflection film515is rectangular. The signal extraction electrode516includes a frame portion531and a linear portion532. The frame portion531is shaped as a rectangular frame surrounding the antireflection film515. The linear portion532is shaped as a straight line extending from the frame portion531in a direction perpendicular to the arrangement direction Da of the 12 APDs502.

The unnecessary-carrier discharge electrode503is formed around, but not in contact with, the 12 signal extraction electrodes516arranged in a row. The unnecessary-carrier discharge electrode503is also formed between every two adjacent frame portions531to surround each of the 12 signal extraction electrodes516.

The bonding pads504are formed from, for example, Al or Cu. The two bonding pads504are positioned on the rectangular substrate501at one end and the other end in the arrangement direction Da of the 12 APDs502. The two bonding pads504are electrically connected to the unnecessary-carrier discharge electrode503.

As shown inFIG.15, the pixel region521includes a depletion layer DL1immediately below the n+ region511and the n region512. In addition, the pixel neighboring region522includes a depletion layer DL2immediately below the region between the n region512and the n region513.

The depletion layer DL1has a length L1along a thickness direction D1of the substrate501, and the depletion layer DL2has a length L2along a direction D2from the n region512to the n region513, with the length L1being smaller than the length L2. The depletion layer DL1has an electric field intensity in the thickness direction D1greater than the electric field intensity of the depletion layer DL2in the direction D2.

For an APD502having the structure described above, as shown inFIG.14, when a returning light beam Br passes through the antireflection film515and enters the pixel region521, an electron-hole pair is generated in the pixel region521. Then, as indicated by an arrow AL1, the electron of the electron-hole pair generated in the pixel region521is absorbed by the n region512and then discharged through the signal extraction electrode516.

The lens array312is, as shown inFIGS.16and17, formed by arranging 12 convex lenses551in a row in the arrangement direction Da of the APDs502. The convex lenses551are formed from, for example, glass or silicone resin. As shown inFIG.17, the lens array312is fixed to the APD array311via an adhesive layer313to cover the APDs502. The adhesive layer313is formed from a material that cures when exposed to ultraviolet radiation. The adhesive layer313is also formed from a material having substantially the same transmittance as the transmittance of the convex lenses551and the antireflection film515. As shown inFIG.16, the 12 convex lenses551are placed opposite the antireflection films515of the 12 APDs502. Each of the 12 convex lenses551narrows light incident on the convex lens551and guides the light to the corresponding APD502.

The APD array311having the structure described above includes the 12 pixel regions521, the n regions512, the signal extraction electrodes516, the pixel neighboring regions522, the n regions513, and the unnecessary-carrier discharge electrode503.

The pixel regions521are formed in the substrate501and internally generate electrons and holes in accordance with the incident light. The n regions512are formed in the pixel regions521and absorb the electrons generated in the pixel regions521(hereinafter, first discharge carriers). The signal extraction electrodes516are formed on the substrate501and discharge, from the n regions512, the first discharge carriers absorbed in the n regions512.

The pixel neighboring regions522are formed so as to be adjacent to the pixel regions521in the substrate501and internally generate electrons and holes in accordance with the incident light. The n regions513are formed in the pixel neighboring regions522and absorb the electrons generated in the pixel neighboring regions522(hereinafter, second discharge carriers). The unnecessary-carrier discharge electrode503is formed on the substrate501and allows the second discharge carriers absorbed in the n regions513to be discharged from the n regions513.

In this manner, the APD array311allows the signal extraction electrodes516to discharge carriers generated in the pixel regions521by light entry into the pixel regions521(hereinafter, necessary carriers), and the unnecessary-carrier discharge electrode503to discharge carriers generated in the pixel neighboring regions522by light entry into the pixel neighboring regions522(hereinafter, unnecessary carriers). Thus, the APD array311reduces the discharge of unnecessary carriers through the signal extraction electrodes516. More specifically, the APD array311reduces the inclusion of unnecessary-carrier-caused signals in signals output through the signal extraction electrodes516.

If a pixel region521and a pixel neighboring region522receive light at the same time, the necessary carrier and the unnecessary carrier will reach the signal extraction electrode516at different times. Thus, the inclusion of unnecessary-carrier-caused signals in signals output through the signal extraction electrode516would reduce the accuracy in distance measurement. In the lidar device1, as shown inFIG.13, when light reflected from an object near to the lidar device1and received by the APD array311is called reflected light SP1, and light reflected from an object far from the lidar device1and received by the APD array311is called reflected light SP2, the reflected light SP1has a spot size greater than the spot size of the reflected light SP2. For this reason, in the APD array311, reflected light received from an object near to the APD array311would tend to enter a pixel neighboring region522, generating an unnecessary carrier.

However, even when receiving light reflected from an object near to the lidar device1, the APD array311reduces the inclusion of unnecessary-carrier-caused signals in signals output through the signal extraction electrodes516as described above. The APD array311thus improves the measurement accuracy of the lidar device1.

The substrate501is p-type. The n region512and the n region513in the front surface of the substrate501are n-type, which is a conductivity type different from the p-type. The length L1of the depletion layer DL1in the pixel region521along the thickness direction D1of the substrate501is smaller than the length L2of the depletion layer DL2between the n region512and the n region513along the direction D2from the n region512to the n region513. The dimensions can prevent electrons generated in the pixel region521from drifting toward the n region513. As a result, the APD array311further reduces the inclusion of unnecessary-carrier-caused signals in signals output through the signal extraction electrode516, thus further improving the measurement accuracy of the lidar device1.

The electric field intensity of the depletion layer DL1in the thickness direction D1is greater than the electric field intensity of the depletion layer DL2in the direction D2. This can prevent electrons generated in the pixel region521from drifting toward the n region513. As a result, the APD array311further reduces the inclusion of unnecessary-carrier-caused signals in signals output through the signal extraction electrode516, thus further improving the measurement accuracy of the lidar device1.

The APD array311includes the convex lenses551placed opposite the pixel regions521over the substrate501. This arrangement enables light incident on the convex lenses551to be narrowed and guided to the pixel regions521, so that the APD array311can have a higher effective aperture ratio to incident light and also reduce light incident on the pixel neighboring regions522.

The substrate501is shaped as a rectangular plate, and the APD array311includes the bonding pads504. The bonding pads504are positioned on the substrate501at both longitudinal ends of the substrate501and electrically connected to the unnecessary-carrier discharge electrode503. As a result, the APD array311does not easily cause the unnecessary-carrier discharge electrode503to have a potential difference along the longitudinal direction of the substrate501.

The lidar device1includes the light emitting unit10, the light receiving unit30, and the scanning unit20.

The light emitting unit10includes the light sources11and12that output light. The light receiving unit30includes the APD array311that receives light coming in a predetermined direction. The scanning unit20includes the reflective surface that reflects light incident from the light emitting unit10. By rotating the reflective surface about the predefined rotation axis, the scanning unit20changes the emission direction of the light incident from the light emitting unit10along the main scanning direction orthogonal to the rotation axis direction, and reflects and guides the light reflected from a subject within the scan range to the light receiving unit30.

The lidar device1, which includes the APD array311, achieves the same advantageous effects as the APD array311.

In the embodiment described above, the APD array311corresponds to a photodetection element, the substrate501corresponds to a semiconductor substrate, the n region512corresponds to a first absorption region, the signal extraction electrode516corresponds to a first discharge electrode, the n region513corresponds to a second absorption region, and the unnecessary-carrier discharge electrode503corresponds to a second discharge electrode. Although the APDs described above are produced by n-doping a p substrate, an n substrate may be p-doped. Although described based on the cross section of reach-through devices, which may have a thicker depletion layer, the above embodiment may be applied to reverse-type devices, which cannot have a thick depletion layer compared with reach-through devices. The above embodiment may be applied not only to APDs, but also to photodiodes with no multiplication effect or single-photon avalanche diodes with quite a high multiplication factor.

Second Embodiment

A second embodiment of the present disclosure will now be described with reference to the drawings. In the second embodiment, differences from the first embodiment will be described. Common components will be given the same reference numerals.

A lidar device1according to the second embodiment is different from the lidar device according to the first embodiment in that an APD array311includes a different number of bonding pads504.

The APD array311according to the second embodiment, as shown inFIG.18, includes three bonding pads504. The three bonding pads504are positioned on a rectangular substrate501: one at one end in the arrangement direction Da, another at the other end, and the other at the center.

The APD array311has higher performance of discharging unnecessary carriers owing to the additional bonding pad504.

Third Embodiment

A third embodiment of the present disclosure will now be described with reference to the drawings. In the third embodiment, differences from the first embodiment will be described. Common components will be given the same reference numerals.

A lidar device1according to the third embodiment is different from the lidar device according to the first embodiment in that an APD array311includes no lens array312and a different number of bonding pads504.

The APD array311according to the third embodiment, as shown inFIG.19, includes four bonding pads504. The four bonding pads504are respectively positioned at the four corners of a rectangular substrate501.

The APD array311has higher performance of discharging unnecessary carriers owing to the additional bonding pads504.

Fourth Embodiment

A fourth embodiment of the present disclosure will now be described with reference to the drawings. In the fourth embodiment, differences from the first embodiment will be described. Common components will be given the same reference numerals.

A lidar device1according to the fourth embodiment is, as shown inFIG.20, different from the lidar device according to the first embodiment in that an APD array311includes an unnecessary-carrier discharge electrode503of a different shape.

The unnecessary-carrier discharge electrode503of the APD array311according to the fourth embodiment is, as shown inFIG.20, formed around, but not in contact with, 12 signal extraction electrodes516arranged in a row. However, the unnecessary-carrier discharge electrode503is not formed between any two adjacent frame portions531.

In the APD array311, the unnecessary-carrier discharge electrode503is not placed between any two adjacent pixel regions521. This arrangement allows the space between every two adjacent pixel regions521to be narrowed, and the APD array311may have a smaller size.

Fifth Embodiment

A fifth embodiment of the present disclosure will now be described with reference to the drawings. In the fifth embodiment, differences from the first embodiment will be described. Common components will be given the same reference numerals.

An APD array311according to the fifth embodiment is, as shown inFIG.21, formed by arranging 12 APDs502in a row on the front surface of a substrate501of a p-type semiconductor (in the present embodiment, silicon). However, the substrate501may be formed of an i-type semiconductor.

The APD array311includes the 12 APDs502and one light shielding electrode503on the front surface of the substrate501.

An APD502, as shown inFIG.22, includes an n+ region511, an n region512, a p+ region514, an antireflection film515, and a signal extraction electrode516.

The n+ region511is an n-type region formed in the front surface of the substrate501. The n+ region511contains a higher concentration of n-type impurities than the n region512.

The n region512is an n-type region formed in the front surface of the substrate501, and around and in contact with the n+ region511.

The p+ region514is a p-type region formed in the back surface of the substrate501. The p+ region514contains a higher concentration of p-type impurities than the substrate501.

The antireflection film515is a film formed from, for example, silicon nitride and placed on the n+ region511. The antireflection film515reduces the surface reflection of light incident on the antireflection film515.

The signal extraction electrode516is an electrode formed from, for example, Al or Cu, placed on the n region512, and electrically connected to the n region512. The signal extraction electrode516receives a high voltage (e.g., 300 V).

In the substrate501, the n+ region511, the n region512, and the region under the n+ region511and the n region512are hereinafter referred to as a pixel region521. In the substrate501, the region other than the pixel region521is hereinafter referred to as a pixel neighboring region522.

The light shielding electrode503is an electrode formed from, for example, Al or Cu and placed opposite the pixel neighboring regions522with a dielectric film (not shown) between them.

The APD array311also includes, on the back surface of the substrate501, a back-side electrode505formed from, for example, AlSiCu.

As shown inFIG.21, the antireflection film515is rectangular. The signal extraction electrode516includes a frame portion531and a linear portion532. The frame portion531is shaped as a rectangular frame surrounding the antireflection film515. The linear portion532is shaped as a straight line extending from the frame portion531in a direction perpendicular to the arrangement direction Da of the 12 APDs502.

The light shielding electrode503is formed around, but not in contact with, the 12 signal extraction electrodes516arranged in a row. The light shielding electrode503is also formed between every two adjacent frame portions531to surround each of the 12 signal extraction electrodes516.

The linear portion532of the signal extraction electrode516is connected with a bonding wire315used to apply a high voltage to the signal extraction electrode516from outside the APD array311.

For an APD502having the structure described above, as shown inFIG.22, when a returning light beam Br passes through the antireflection film515and enters the pixel region521, an electron-hole pair is generated in the pixel region521. Then, as indicated by an arrow AL1, the electron of the electron-hole pair generated in the pixel region521is absorbed by the n region512and discharged through the signal extraction electrode516.

The APD array311, as shown inFIG.23, also includes light shielding films507and508. The light shielding films507and508are formed by applying a member (e.g., made of black potting resin) capable of attenuating, absorbing, or reflecting light within the sensitive wavelength range of the APDs502(e.g., a wavelength of 1.2 μm or less).

The light shielding film507is placed on the front surface and the side surfaces of the substrate501to cover the four sides of the rectangular substrate501. The light shielding film508is placed on the front surface of the substrate501to cover the areas of the 12 linear portions532arranged in a row, from one end to the other end in the arrangement direction Da.

The light shielding films507and508are formed by application with the bonding wires315connected to the linear portions532of the signal extraction electrodes516. The light shielding films507and508thus cover substantially the entire part of each bonding wire315on the front surface of the substrate501.

The APD array311having the structure described above includes the 12 pixel regions521, the n regions512, the signal extraction electrodes516, the pixel neighboring regions522, the light shielding electrode503, and the light shielding films507and508.

The pixel regions521are formed in the substrate501and internally generate electrons and holes in accordance with the incident light. The n regions512are formed in the pixel regions521and absorb the electrons generated in the pixel regions521(hereinafter, discharge carriers). The signal extraction electrodes516are formed on the substrate501and allow the discharge carriers absorbed in the n regions512to be discharged from the n regions512.

The pixel neighboring regions522are formed so as to be adjacent to the pixel regions521in the substrate501and internally generate electrons and holes in accordance with the incident light. The light shielding electrode503and the light shielding films507and508are formed from a member capable of blocking light with a wavelength that allows the generation of electrons and holes in the pixel neighboring regions522, and placed so as to cover the pixel neighboring regions522.

In this manner, the APD array311allows the signal extraction electrodes516to discharge carriers generated in the pixel regions521by light entry into the pixel regions521(hereinafter, necessary carriers). In the APD array311, the light shielding electrode503and the light shielding films507and508placed so as to cover the pixel neighboring regions522reduce carrier generation in the pixel neighboring regions522caused by light entry into the pixel neighboring regions522. Thus, the APD array311reduces the discharge of carriers generated in the pixel neighboring regions522(hereinafter, unnecessary carriers) through the signal extraction electrodes516. More specifically, the APD array311reduces the inclusion of unnecessary-carrier-caused signals in signals output through the signal extraction electrodes516.

If a pixel region521and a pixel neighboring region522receive light at the same time, the necessary carrier and the unnecessary carrier will reach the signal extraction electrode516at different times. Thus, the inclusion of unnecessary-carrier-caused signals in signals output through the signal extraction electrode516would reduce the accuracy in distance measurement. In the lidar device1, as shown inFIG.21, when light reflected from an object near to the lidar device1and received by the APD array311is called reflected light SP1, and light reflected from an object far from the lidar device1and received by the APD array311is called reflected light SP2, the reflected light SP1has a spot size greater than the spot size of the reflected light SP2. For this reason, in the APD array311, reflected light received from an object near to the APD array311would tend to enter a pixel neighboring region522, generating an unnecessary carrier.

However, even when receiving light reflected from an object near to the lidar device1, the APD array311reduces the inclusion of unnecessary-carrier-caused signals in signals output through the signal extraction electrodes516as described above. The APD array311thus improves the measurement accuracy of the lidar device1.

The light shielding film507is an insulator member. The light shielding film507covers at least a portion of each pixel neighboring region522in the substrate501, the portion formed in an edge of the substrate501.

Applying high voltage to the APDs502generates high voltage in the edges of the substrate501. Thus, with the edges of the substrate501exposed, the package for the APD array311would be larger in order to satisfy the creepage distance requirement defined in IEC 60950 (i.e., to ensure a predefined creepage distance). IEC 60950 is an international standard for the safety of information technology equipment.

For the APD array311, however, the light shielding film507that is an insulator member covers the edges of the substrate501. Thus, the above creepage distance requirement may be relaxed for the APD array311, allowing the package for the APD array311to be smaller.

The signal extraction electrodes516are each connected with the bonding wires315. The light shielding film507covers a portion of each bonding wire315in addition to the pixel neighboring regions522. This covering in the APD array311reduces the exposure of the high-voltage bonding wires315on an edge of the substrate501. Thus, the above creepage distance requirement may be relaxed for the APD array311, allowing the package for the APD array311to be smaller.

The lidar device1includes the light emitting unit10, the light receiving unit30, and the scanning unit20.

The light emitting unit10includes the light sources11and12that output light. The light receiving unit30includes the APD array311that receives light coming in a predetermined direction. The scanning unit20includes the reflective surface that reflects light incident from the light emitting unit10. By rotating the reflective surface about the predefined rotation axis, the scanning unit20changes the emission direction of the light incident from the light emitting unit10along the main scanning direction orthogonal to the rotation axis direction, and reflects and guides the light reflected from a subject within a scan range to the light receiving unit30.

The lidar device1, which includes the APD array311, achieves the same advantageous effects as the APD array311.

In the embodiment described above, the APD array311corresponds to a photodetection element, the substrate501corresponds to a semiconductor substrate, the n region512corresponds to an absorption region, the signal extraction electrode516corresponds to a discharge electrode, and the light shielding electrode503and the light shielding films507and508correspond to light shields. Although the APDs described above are produced by n-doping a p substrate, an n substrate may be p-doped. Although described based on the cross section of reach-through devices, which may have a thicker depletion layer, the above embodiment may be applied to reverse-type devices, which cannot have a thick depletion layer compared with reach-through devices. The above embodiment may be applied not only to APDs, but also to photodiodes with no multiplication effect or single-photon avalanche diodes with quite a high multiplication factor.

Sixth Embodiment

A sixth embodiment of the present disclosure will now be described with reference to the drawings. In the sixth embodiment, differences from the fifth embodiment will be described. Common components will be given the same reference numerals.

A lidar device1according to the sixth embodiment, as shown inFIGS.24and25, is different from the lidar device according to the fifth embodiment in that an APD array311additionally includes a light shielding electrode509.

The light shielding electrode509is an electrode formed from, for example, A1or Cu and, as shown inFIG.24, and is placed on the front surface of the substrate501to cover the areas of 12 frame portions531arranged in a row, from one end to the other end in the arrangement direction Da. However, the light shielding electrode509has openings opposite the 12 antireflection films515arranged in a row. The light shielding electrode509is, as shown inFIG.25, placed opposite the light shielding electrode503and the signal extraction electrode516with a dielectric film (not shown) between them.

The APD array311having the structure described above includes the light shielding electrode509. The light shielding electrode509is formed of metal capable of blocking light with a wavelength that allows the generation of electrons and holes in the pixel neighboring regions522. The light shielding electrode509is electrically isolated from the signal extraction electrodes516of every two adjacent pixel regions521and is placed so as to cover the gap between the signal extraction electrodes516of every two adjacent pixel regions521.

This arrangement enables the APD array311to reduce light incident on the pixel neighboring region522formed between every two adjacent pixel regions521. As a result, the APD array311further reduces the inclusion of unnecessary-carrier-caused signals in signals output through the signal extraction electrode516, thus further improving the measurement accuracy of the lidar device1.

In the embodiment described above, the light shielding electrode509corresponds to light shielding metal.

Seventh Embodiment

A seventh embodiment of the present disclosure will now be described with reference to the drawings. In the seventh embodiment, differences from the fifth embodiment will be described. Common components will be given the same reference numerals.

A lidar device1according to the seventh embodiment is, as shown inFIG.26, different from the fifth embodiment in that the light shielding films507and508are removed, and a lens array312, a light shield317, and a light shielding film560are added.

A light receiving element31according to the seventh embodiment further includes the lens array312and the light shield317. The lens array312includes 12 lenses facing 12 APDs502for the APD array311on a one-to-one basis, and narrows light incident on the light receiving element31and guides the light to each APD502. The lens array312is, as shown inFIGS.26and27, formed by arranging 12 convex lenses551in a row in the arrangement direction Da of the APDs502. The convex lenses551are formed from, for example, glass or silicone resin. As shown inFIG.27, the lens array312is fixed to the APD array311via an adhesive layer313to cover the APDs502. The adhesive layer313is formed from a material that cures when exposed to ultraviolet radiation. The adhesive layer313is also formed from a material having substantially the same transmittance as the transmittance of the convex lenses551and antireflection films515. As shown inFIG.26, the 12 convex lenses551are placed opposite the antireflection films515of the 12 APDs502. Each of the 12 convex lenses551narrows light incident on the convex lens551and guides the light to the corresponding APD502.

The light shield317is, for example, formed from silicone resin, epoxy resin, or acrylic resin mixed or painted with a member capable of absorbing light within the sensitive wavelength range of the APDs502. The light shield317is, as shown inFIGS.26and27, placed on the side surfaces of the substrate501to cover the four sides of the rectangular substrate501. As a result, the light shield317is placed on side surfaces of the lens array312and covers three of the four sides of the rectangular lens array312that are also included in the rectangle of the substrate501.

The APD array311according to the seventh embodiment, as shown inFIG.26, further includes the light shielding film560. The light shielding film560is formed, in the same manner as the light shielding films507and508, by applying a member capable of attenuating, absorbing, or reflecting light within the sensitive wavelength range of the APDs502. The light shielding film560is placed on the front surface of the substrate501to cover an area other than the lens array312.

The APD array311having the structure described above includes the convex lenses551placed opposite the pixel regions521over the substrate501. This arrangement enables light incident on the convex lenses551to be narrowed and guided to the pixel regions521, so that the APD array311can have a higher effective aperture ratio to incident light and also reduce light incident on the pixel neighboring regions522.

The light incident surface of the convex lenses551for receiving light includes a light incident surface incapable of guiding incident light to the pixel regions521(in the present embodiment, the side surfaces of the lens array312), and at least a portion of the surface incapable of guiding incident light is covered with the light shielding film560capable of blocking light with a wavelength that allows the generation of electrons and holes in the pixel neighboring regions522.

This arrangement enables the APD array311to reduce light incident on the pixel neighboring regions522. As a result, the APD array311further reduces the inclusion of unnecessary-carrier-caused signals in signals output through the signal extraction electrode516, thus further improving the measurement accuracy of the lidar device1.

In the embodiment described above, the light shielding film560corresponds to a lens light shield.

The embodiments of the present disclosure have been described. However, the present disclosure is not limited to the above embodiments, but may be implemented in various modified embodiments.

[First Modification]

Although the substrate501is p-type, and the n region512and the n region513are n-type in the above embodiments, for example, the substrate501may be n-type or i-type, and the n region512and the n region513may be p-type. In this case, carriers discharged through the signal extraction electrode516are holes.

[Second Modification]

Although the substrate501in the above embodiments is formed from silicon, the material for the substrate501is not limited to silicon as long as it is a semiconductor. The substrate501may be formed from, for example, InGaAs.

[Third Modification]

Although the substrate501is p-type, and the n region512is n-type in the above embodiments, for example, the substrate501may be n-type or i-type, and the n region512may be p-type. In this case, carriers discharged through the signal extraction electrode516are holes.

[Fourth Modification]

Although the substrate501in the above embodiments is formed from silicon, the material for the substrate501is not limited to silicon as long as it is a semiconductor. The substrate501may be formed from, for example, InGaAs. In this case, the APDs have a sensitive wavelength range of 3 μm or less (i.e., wavelengths from visible light to mid-infrared light).

In some cases, a plurality of components may share the functions of one component in the above embodiments. In other cases, one component may implement functions of a plurality of components. Some of the components in the above embodiments may be omitted. At least some components in one of the above embodiments may be added to or substituted for components in another of the above embodiments.

An aspect of the present disclosure is a photodetection element (311) including at least one pixel region (521), a first absorption region (512), a first discharge electrode (516), a pixel neighboring region (522), a second absorption region (513), and a second discharge electrode (503).

The pixel region is formed in a semiconductor substrate (501) and internally generates an electron and a hole in accordance with the incident light.

The first absorption region is formed in the pixel region and absorbs a first discharge carrier that is either of the electron and the hole generated in the pixel region.

The first discharge electrode is formed on the semiconductor substrate and discharges, from the first absorption region, the first discharge carrier absorbed in the first absorption region.

The pixel neighboring region is formed so as to be adjacent to the pixel region in the semiconductor substrate and internally generates an electron and a hole in accordance with the incident light.

The second absorption region is formed in the pixel neighboring region and absorbs a second discharge carrier that is the same carrier of either of the electron and the hole generated in the pixel neighboring region, as the first discharge carrier.

The second discharge electrode is formed on the semiconductor substrate and discharges, from the second absorption region, the second discharge carrier absorbed in the second absorption region.

The photodetection element according to the present disclosure having the above configuration allows the first discharge electrode to discharge carriers generated in the pixel region by light entry into the pixel region (hereinafter, necessary carriers), and the second discharge electrode to discharge carriers generated in the pixel neighboring region by light entry into the pixel neighboring region (hereinafter, unnecessary carriers). Thus, the photodetection element according to the present disclosure reduces the discharge of unnecessary carriers through the first discharge electrode. More specifically, the photodetection element according to the present disclosure reduces the inclusion of unnecessary-carrier-caused signals in signals output from through the first discharge electrode.

If the pixel region and the pixel neighboring region receive light at the same time, the necessary carrier and the unnecessary carrier will reach the first discharge electrode at different times. Thus, the inclusion of unnecessary-carrier-caused signals in signals output from the first discharge electrode would reduce the accuracy in distance measurement. In the lidar device, light reflected from an object near to the lidar device and received by the photodetection element according to the present disclosure has a spot size greater than the spot size of light reflected from an object far from the lidar device and received by the photodetection element according to the present disclosure. For this reason, in the photodetection element according to the present disclosure, reflected light received from an object near to the lidar device would tend to enter the pixel neighboring region, generating an unnecessary carrier.

However, even when receiving light reflected from an object near to the lidar device, the photodetection element according to the present disclosure reduces the inclusion of unnecessary-carrier-caused signals in signals output through the first discharge electrode as described above. The photodetection element according to the present disclosure thus improves the measurement accuracy of the lidar device.

Another aspect of the present disclosure is a lidar device (1) including a light emitting unit (10), a light receiving unit (30), and a scanning unit (20). The light emitting unit includes a light source that outputs light. The light receiving unit includes a photodetection element that receives light arriving from a predetermined direction. The scanning unit includes a reflective surface for reflecting light incident from the light emitting unit. By rotating the reflective surface about a predefined rotation axis, the scanning unit changes the emission direction of light incident from the light emitting unit along the main scanning direction orthogonal to the rotation axis direction, and reflects and guides light reflected from a subject within a scan range to the light receiving unit.

The photodetection element includes at least one pixel region, a first absorption region, a first discharge electrode, a pixel neighboring region, a second absorption region, and a second discharge electrode.

The lidar device according to the present disclosure having the above configuration, which includes the photodetection element according to the aspect of the present disclosure, achieves the same advantageous effects as the photodetection element according to the present disclosure.

Still another aspect of the present disclosure is a photodetection element including at least one pixel region (521), an absorption region (512), a discharge electrode (516), a pixel neighboring region (522), and a light shield (503,507,508).

The pixel region is formed in a semiconductor substrate (501) and internally generates an electron and a hole in accordance with the incident light.

The absorption region is formed in the pixel region and absorbs a discharge carrier that is either of the electron and the hole generated in the pixel region.

The discharge electrode is formed on the semiconductor substrate and discharges, from the absorption region, the discharge carrier absorbed in the absorption region.

The pixel neighboring region is formed so as to be adjacent to the pixel region in the semiconductor substrate and internally generates an electron and a hole in accordance with the incident light.

The light shield is formed from a member capable of blocking light with a wavelength allowing the generation of the electron and the hole in the pixel neighboring region, and is placed so as to cover the pixel neighboring region.

The photodetection element according to the present disclosure having the above configuration allows the discharge electrode to discharge carriers generated in the pixel region by light entry into the pixel region (hereinafter, necessary carriers). In the photodetection element of the present disclosure, the light shield placed so as to cover the pixel neighboring region reduces carrier generation in the pixel neighboring region caused by light entry into the pixel neighboring region. Thus, the photodetection element according to the present disclosure reduces the discharge of carriers generated in the pixel neighboring region (hereinafter, unnecessary carriers) through the discharge electrode. More specifically, the photodetection element according to the present disclosure reduces the inclusion of unnecessary-carrier-caused signals in signals output through the discharge electrode.

If the pixel region and the pixel neighboring region were to receive light at the same time, the necessary carrier and the unnecessary carrier would reach the discharge electrode at different times. Thus, the inclusion of unnecessary-carrier-caused signals in signals output from the discharge electrode would reduce the accuracy in distance measurement. In the lidar device, light reflected from an object near to the lidar device and received by the photodetection element according to the present disclosure has a spot size greater than the spot size of light reflected from an object far from the lidar device and received by the photodetection element according to the present disclosure. For this reason, in the photodetection element according to the present disclosure, reflected light received from an object near to the lidar device would tend to enter the pixel neighboring region, generating an unnecessary carrier.

However, even when receiving light reflected from an object near to the lidar device, the photodetection element according to the present disclosure reduces the inclusion of unnecessary-carrier-caused signals in signals output through the discharge electrode as described above. The photodetection element according to the present disclosure thus improves the measurement accuracy of the lidar device.

Still another aspect of the present disclosure is a lidar device (1) including a light emitting unit (10), a light receiving unit (30), and a scanning unit (20). The light emitting unit includes a light source that outputs light. The light receiving unit includes a photodetection element that receives light coming in a predetermined direction. The scanning unit includes a reflective surface for reflecting light incident from the light emitting unit. By rotating the reflective surface about a predefined rotation axis, the scanning unit changes the emission direction of light incident from the light emitting unit along the main scanning direction orthogonal to the rotation axis direction, and reflects and guides light reflected from a subject within a scan range to the light receiving unit.

The photodetection element includes at least one pixel region, an absorption region, a discharge electrode, a pixel neighboring region, and a light shield.

The lidar device according to the present disclosure having the above configuration, which includes the photodetection element according to the above aspect of the present disclosure, achieves the same advantageous effects as the photodetection element according to the present disclosure.