Photodiode and TOF distance measuring device

Abstract

The present invention discloses a photodiode and a TOF distance measuring device, wherein the photodiode comprises a substrate, a first electrode layer, a first electrode, a second electrode layer, a second electrode and an auxiliary electrode, wherein the first electrode layer is arranged on the substrate, the first electrode is arranged on the first electrode layer, the second electrode is arranged on the substrate, the second electrode is arranged on the second electrode layer, and the auxiliary electrode is connected to a potential or suspended to generate an electric field that opposes the direction of the electric field between the first electrode layer and the substrate, or to shield the electric field between the first electrode layer and the substrate. In the photodiode and the TOF distance measuring device of the present invention, since the auxiliary electrode generates an electric field that opposes the direction of the electric field between the first electrode layer and the substrate, or the auxiliary electrode shields the electric field between the first electrode layer and the substrate, the electric field at the edge of the first electrode layer can be reduced, thereby playing a role in reducing dark counts.

Description

Technical Field

[0001] The present invention relates to the technical field of image sensors, and in particular to a photodiode supporting TOF applications and a TOF distance measuring device. Background Art

[0002] Image sensors are devices that convert optical image information into electrical information. In image sensors, TOF (Time of Fly) is mainly used in systems that acquire 3D images. The system uses the time it takes for light to travel from a light source to an object and then reflect back to the image sensor to measure the distance from the imaging target to the image sensing device. Each pixel of the image sensor participates in the distance measurement to obtain a high-precision depth image.

[0003] With the widespread application of 3D images, such as AR (augmented reality), VR (virtual reality), drones, robots and digital cameras, TOF pixel circuits and sensor devices of pixel circuits will be further developed. Not only can they be used to obtain high-precision images, but they can also realize functions such as object recognition and obstacle detection. Moreover, the depth calculation of TOF is not affected by the grayscale and features of the surface of the target object, and can detect the target three-dimensional image very accurately.

[0004] A semiconductor-based photodetector is called an avalanche photodiode, or APD. This type of structure is usually composed of a large amount of solid semiconductor materials used for different purposes, such as absorption and multiplication. Avalanche photodiodes (APDs) are used to convert optical signals into electrical signals and serve as light receiving elements in optical communication systems. In optical transmission systems, optical transmitter modules and optical receiver modules are relatively core and expensive devices. Among optical receiver modules, optical receiver modules using APD detectors are the main and important products. However, in TOF image sensors, the dark count of pixels can seriously affect the frame rate and performance of the sensor. The so-called dark count refers to the fact that stray light (non-signal light) or electrical noise is also considered as a valid light signal by a single-photon detector. Summary of the invention

[0005] The object of the present invention is to provide a photodiode and a TOF distance measuring device capable of reducing dark counts.

[0006] The present invention provides a photodiode, comprising a substrate, a first electrode layer, a first electrode, a second electrode layer, a second electrode and an auxiliary electrode, wherein the first electrode layer is arranged on the substrate, the first electrode is arranged on the first electrode layer, the second electrode layer is arranged on the substrate, the second electrode is arranged on the second electrode layer, and the auxiliary electrode is connected to a potential or suspended to generate an electric field that is opposite to the direction of the electric field between the first electrode layer and the substrate, or to shield the electric field between the first electrode layer and the substrate.

[0007] Furthermore, the substrate is a P-type substrate, the first electrode layer is an N+ type doped layer, the first electrode and the second electrode are metal layers, the second electrode layer is a P+ type doped layer, the first electrode is connected to a potential, and the second electrode is grounded.

[0008] Furthermore, the auxiliary electrode comprises a metal layer or a polysilicon layer, and the metal layer or the polysilicon layer is connected to a potential or is suspended.

[0009] Furthermore, the photodiode further comprises a protection well, the first electrode layer is surrounded by the protection well, and the second electrode layer surrounds the outside of the protection well.

[0010] Furthermore, the protection well is an N-type doped region.

[0011] Furthermore, the first electrode layer, the second electrode layer and the protection well are all embedded in the top of the substrate, the protection well partially overlaps with the first electrode layer, and a gap filled by the substrate is provided between the second electrode layer and the protection well.

[0012] Furthermore, the auxiliary electrode is disposed above the substrate, and the bottom of the auxiliary electrode contacts the protection well and the substrate to cover the boundary between the protection well and the substrate at the top surface.

[0013] Furthermore, the auxiliary electrode is arranged above the protection well and the substrate, and is spaced a certain distance from the protection well and the substrate in the vertical direction. The projection of the auxiliary electrode toward the protection well and the substrate in the vertical direction overlaps with the protection well and the substrate respectively, so as to cover the junction of the protection well and the substrate on the top surface.

[0014] Furthermore, the bottom of the auxiliary electrode is in contact with the first electrode and the substrate respectively, so as to cover the junction between the first electrode and the substrate at the top surface.

[0015] Furthermore, the auxiliary electrode is arranged above the first electrode and the substrate, and is spaced a certain distance from the first electrode and the substrate in the vertical direction. The projection of the auxiliary electrode toward the first electrode and the substrate in the vertical direction overlaps with the first electrode and the substrate respectively, so as to cover the junction of the first electrode and the substrate on the top surface.

[0016] Furthermore, the auxiliary electrode further includes an oxide layer disposed between the polysilicon layer or the metal layer.

[0017] The present invention also provides a TOF distance measuring device, comprising the above-mentioned photodiode.

[0018] In the photodiode and TOF ranging device of the present invention, since the auxiliary electrode generates an electric field that is opposite to the direction of the electric field between the first electrode layer and the substrate, or the auxiliary electrode shields the electric field between the first electrode layer and the substrate, the electric field at the edge of the first electrode layer can be reduced, thereby reducing the dark count. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 FIG. 1 is a schematic structural diagram of a photodiode according to a first embodiment of the present invention.

[0020] Figure 2 for Figure 1 Top view of the photodiode shown.

[0021] Figure 3 FIG. 4 is a schematic structural diagram of a photodiode according to a second embodiment of the present invention.

[0022] Figure 4 FIG. 4 is a schematic structural diagram of a photodiode according to a third embodiment of the present invention.

[0023] Figure 5 FIG. 4 is a schematic structural diagram of a photodiode according to a fourth embodiment of the present invention. DETAILED DESCRIPTION

[0024] The specific implementation of the present invention is further described in detail below in conjunction with the accompanying drawings and examples. The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0025] First embodiment

[0026] Please refer to Figure 1 and Figure 2 , Figure 1 FIG. 1 shows a schematic diagram of the structure of a photodiode provided by a first embodiment of the present invention. Figure 2 Shows Figure 1 The photodiode of this embodiment includes a substrate 11, a first electrode layer 13, a first electrode 14, a second electrode layer 16, a second electrode 17, a protection well 19 and an auxiliary electrode 21. The first electrode layer 13 is provided on the substrate 11, and the first electrode 14 is provided on the first electrode layer 13. The first electrode layer 13 is surrounded by the protection well 19. The second electrode layer 16 is provided on the substrate 11 and surrounds the outside of the protection well 19. A gap filled by the substrate 11 is provided between the second electrode layer 16 and the protection well 19, and the second electrode 17 is provided on the second electrode layer 16. The auxiliary electrode 21 is provided above the substrate 11, and its bottom is in contact with the protection well 19 and the substrate 11, that is, the two ends of the auxiliary electrode 21 overlap the protection well 19 and the substrate 11 respectively. Specifically in this embodiment, the first electrode layer 13, the second electrode layer 16 and the protection well 19 are all embedded in the top of the substrate 11.

[0027] In this embodiment, the substrate 11 is a P-type substrate. It is understood that the substrate 11 may also be an N-type substrate.

[0028] In this embodiment, the first electrode layer 13 is an N+ type electrode layer. It is understood that the first electrode layer 13 may also be an N- type electrode layer, a P+ type electrode layer or a P- type electrode layer. Specifically in this embodiment, the first electrode layer 13 is a photoelectron generation region, and when irradiated with light, the first electrode layer 13 generates photoelectrons. Specifically, the first electrode layer 13 may be circular, and of course the first electrode layer 13 may also be other shapes such as square.

[0029] In this embodiment, the first electrode 14 is a metal layer, and the first electrode layer 13 is connected to a potential through the first electrode 14 , so that the first electrode layer 13 has a certain potential.

[0030] In this embodiment, the second electrode layer 16 is a P+ type electrode layer. It is understood that the second electrode layer 16 can also be a P- type electrode layer, an N+ type electrode layer or an N- type electrode layer. Specifically, the second electrode layer 16 can be a circular ring, and of course the second electrode layer 16 can also be other rings such as a circular shape.

[0031] In this embodiment, the second electrode 17 is a metal layer, and the second electrode layer 16 is grounded through the second electrode 17. By grounding the second electrode layer 16 and connecting the first electrode layer 13 to a potential, a potential difference can be generated between the first electrode layer 13 and the second electrode layer 16, so that the charge generated by the first electrode layer 13 moves to the second electrode layer 16.

[0032] In this embodiment, the protection well 19 is an N-type protection well (N-Well), which is used to isolate the current of the substrate 11. It can be understood that the protection well 19 can also be a P-type protection well (P-Well). Specifically, the protection well 19 can be a circular ring, and of course the protection well 19 can also be other rings such as a circular shape.

[0033] In this embodiment, the auxiliary electrode 21 includes a polysilicon layer 212 and an oxide layer 214, wherein the oxide layer 214 is located at the bottom of the polysilicon layer 212 and is in contact with the protection well 19 and the substrate 11. Specifically, the oxide layer 214 may be made of silicon dioxide. The auxiliary electrode 21 is connected to a potential, thereby generating an electric field that opposes the direction of the electric field between the first electrode layer 13 and the substrate 11. It is understood that the polysilicon layer 212 may also be replaced by a metal layer. In another embodiment, the auxiliary electrode 21 may also be not connected to a potential, but directly suspended, so that the auxiliary electrode 21 shields the electric field between the first electrode layer 13 and the substrate 11.

[0034] The photodiode of the present invention may be an avalanche photodiode.

[0035] In the photodiode of this embodiment, since the auxiliary electrode 21 generates an electric field that is opposite to the direction of the electric field between the first electrode layer 13 and the substrate 11, or the auxiliary electrode 21 shields the electric field between the first electrode layer 13 and the substrate 11, the electric field at the edge of the first electrode layer 13 can be reduced, thereby reducing the dark count.

[0036] Second embodiment

[0037] Please refer to Figure 3 , Figure 3 : shows a schematic diagram of the structure of the photodiode of the second embodiment of the present invention. The structure of the photodiode of this embodiment is basically the same as that of the photodiode of the first embodiment, except that, in this embodiment, the auxiliary electrode 21 is disposed above the protection well 19 and the substrate 11, and is spaced a certain distance from the protection well 19 and the substrate 11, that is, the projection of the auxiliary electrode 21 toward the protection well 19 and the substrate 11 overlaps with the protection well 19 and the substrate 11, respectively. In this embodiment, the auxiliary electrode 21 is made of a metal layer, and it does not include an oxide layer.

[0038] In the photodiode of this embodiment, the auxiliary electrode 21 can also generate an electric field that is opposite to the direction of the electric field between the first electrode layer 13 and the substrate 11, or the auxiliary electrode 21 shields the electric field between the first electrode layer 13 and the substrate 11, thereby reducing the electric field at the edge of the first electrode layer 13, thereby reducing the dark count.

[0039] Third embodiment

[0040] Please refer to Figure 4 , Figure 4 1 shows a schematic diagram of the structure of a photodiode according to a third embodiment of the present invention. The structure of the photodiode according to this embodiment is substantially the same as that of the photodiode according to the first embodiment, except that, in this embodiment, the photodiode omits the protection well 19. At this time, the bottom of the auxiliary electrode 21 is in contact with the first electrode 14 and the substrate 11, respectively, that is, the two ends of the auxiliary electrode 21 are overlapped with the first electrode 14 and the substrate 11, respectively.

[0041] In the photodiode of this embodiment, the auxiliary electrode 21 can also generate an electric field that is opposite to the direction of the electric field between the first electrode layer 13 and the substrate 11, or the auxiliary electrode 21 shields the electric field between the first electrode layer 13 and the substrate 11, thereby reducing the electric field at the edge of the first electrode layer 13, thereby reducing the dark count.

[0042] Fourth embodiment

[0043] Please refer to Figure 5 , Figure 5: shows a schematic diagram of the structure of a photodiode according to a fourth embodiment of the present invention. The structure of the photodiode according to this embodiment is substantially the same as that of the photodiode according to the second embodiment, except that, in this embodiment, the photodiode omits the protection well 19. At this time, the auxiliary electrode 21 is disposed above the first electrode 14 and the substrate 11, and is spaced a certain distance from the first electrode 14 and the substrate 11, that is, the projection of the auxiliary electrode 21 toward the first electrode 14 and the substrate 11 overlaps with the first electrode 14 and the substrate 11, respectively.

[0044] In the photodiode of this embodiment, the auxiliary electrode 21 can also generate an electric field that is opposite to the direction of the electric field between the first electrode layer 13 and the substrate 11, or the auxiliary electrode 21 shields the electric field between the first electrode layer 13 and the substrate 11, thereby reducing the electric field at the edge of the first electrode layer 13, thereby reducing the dark count.

[0045] The invention also discloses a TOF distance measuring device, which comprises any one of the above-mentioned photodiodes.

[0046] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0047] The above are only specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art who is familiar with the technical field can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A photodiode, characterized in that: The invention comprises a substrate (11), a first electrode layer (13), a first electrode (14), a second electrode layer (16), a second electrode (17) and an auxiliary electrode (21), wherein the first electrode layer (13) is arranged on the substrate (11), the first electrode (14) is arranged on the first electrode layer (13), the second electrode layer (16) is arranged on the substrate (11), the second electrode (17) is arranged on the second electrode layer (16), and the auxiliary electrode (21) is connected to a potential or suspended to generate an electric field that is opposite to the direction of the electric field between the first electrode layer (13) and the substrate (11), or to shield the electric field between the first electrode layer (13) and the substrate (11); The auxiliary electrode (21) is disposed above the substrate (11), and the projections of the auxiliary electrode (21) toward the first electrode (14) and the substrate (11) in the vertical direction overlap with the first electrode (14) and the substrate (11) respectively, so as to cover the junction of the first electrode (14) and the substrate (11) on the top surface; or, the photodiode further comprises a protection well (19), the first electrode layer (13) is surrounded by the protection well (19), the second electrode layer (16) surrounds the outside of the protection well (19), the auxiliary electrode (21) is disposed above the substrate (11), and the projections of the auxiliary electrode (21) toward the protection well (19) and the substrate (11) in the vertical direction overlap with the protection well (19) and the substrate (11) respectively, so as to cover the junction of the protection well (19) and the substrate (11) on the top surface; The auxiliary electrode (21) comprises a metal layer or a polysilicon layer, and the metal layer or the polysilicon layer is connected to a potential or is suspended.

2. The photodiode according to claim 1, wherein: The substrate (11) is a P-type substrate, the first electrode layer (13) is an N+-type doped layer, the first electrode (14) and the second electrode (17) are metal layers, the second electrode layer (16) is a P+-type doped layer, the first electrode (14) is connected to a potential, and the second electrode (17) is grounded.

3. The photodiode according to claim 1, wherein: The protection well (19) is an N-type doped region.

4. The photodiode according to claim 1, wherein: The first electrode layer (13), the second electrode layer (16) and the protection well (19) are all embedded in the top of the substrate (11); the protection well (19) partially overlaps with the first electrode layer (13); and a gap filled by the substrate (11) is provided between the second electrode layer (16) and the protection well (19).

5. The photodiode according to claim 1, wherein: The bottom of the auxiliary electrode (21) is in contact with the protection well (19) and the substrate (11).

6. The photodiode according to claim 1, wherein: The auxiliary electrode (21) is spaced a certain distance from the protection well (19) and the substrate (11) in the vertical direction.

7. The photodiode according to claim 1, wherein: The bottom of the auxiliary electrode (21) is in contact with the first electrode (14) and the substrate (11) respectively.

8. The photodiode according to claim 1, wherein: The auxiliary electrode (21) is spaced a certain distance from the first electrode (14) and the substrate (11) in a vertical direction.

9. A TOF ranging device, characterized in that: Comprising a photodiode as described in any one of claims 1-8.

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