CN112038360A - Distance sensor pixel array structure, distance sensor and working method - Google Patents

Abstract

The invention discloses a distance sensor pixel array structure, a distance sensor and a working method. The pixel array structure of the distance sensor comprises a plurality of pixel units which are arranged in an array, each pixel unit comprises a single photon avalanche diode, and the adjacent pixel units work in a time-sharing mode, so that the single photon avalanche diodes at the corresponding positions can be sequentially started in a time-sharing mode when the distance sensor works, when a certain pixel unit works, the upper, lower, left and right adjacent pixel units are in a non-working state, crosstalk hardly reaches the other pixel unit in the working state, the crosstalk condition is improved, and false triggering cannot be generated; based on the method, the distance between adjacent pixels is reduced, so that the resolution can be greatly improved.

Description

Distance sensor pixel array structure, distance sensor and working method

technical field

The present invention relates to the technical field of sensors, in particular to a distance sensor pixel array structure, a distance sensor and a working method.

Background technique

The D TOF (Direct Time of Flight) distance sensor is avalanche triggering based on spad (single photon avalanche diode). When the resolution is high, the pixel pitch (the distance between adjacent pixels) needs to be very small, such as 1 μm, 2.5 μm, 3.5 μm, 5 μm, 10 μm, etc. Small pixel pitch is easily affected by crosstalk between adjacent pixels.

As the pixel pitch decreases, crosstalk increases rapidly. Compared with image sensor or ITOF, the crosstalk of DTOF will cause false triggering of adjacent spads, which directly causes the image to be blurred, instead of only bringing distance error or resolution reduction. Therefore, the pixel pitch of the current D TOF is very large, such as 20μm, 30μm, etc., resulting in low resolution.

Therefore, when D TOF realizes resolutions such as VGA and QVGA, it is necessary to reduce the pixel pitch to 5μm, and at this time, the problem of crosstalk must be solved.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a distance sensor pixel array structure, a distance sensor and a working method, which can reduce crosstalk between adjacent pixel units and avoid false triggering of single photon avalanche diodes.

In order to solve the above technical problems, according to the first aspect of the present invention, a distance sensor pixel array structure is provided, including:

A plurality of pixel units are arranged in an array, each pixel unit includes a single-photon avalanche diode, and adjacent pixel units work in time division.

Optionally, pixel units in adjacent i rows and j columns form a group of pixel units, and the distance sensor pixel array structure includes the multiple groups of pixel units.

Optionally, a complete metal isolation structure is provided between adjacent pixel units.

Optionally, a plurality of filters are further provided, each of the filters is correspondingly provided on each pixel unit, and at least some of the filters are filters of different wavelengths.

According to a second aspect of the present invention, a distance sensor is provided, including the distance sensor pixel array structure as described in the first aspect.

According to a third aspect of the present invention, a working method of a distance sensor is provided, comprising:

The single-photon avalanche diodes between adjacent pixel units work in time-sharing.

Optionally, the distance sensor includes an array of multiple groups of pixel units, each group of pixel units turns on different pixel units at different time periods, and at least one pixel unit is spaced between pixel units turned on in adjacent groups of pixel units.

Optionally, each pixel unit array works time-sharing according to the pixel arrangement position.

Optionally, in the form of progressive scanning, the pixel units of odd-numbered columns and even-numbered columns work in time division.

Optionally, in the form of column-by-column scanning, the pixel units of odd-numbered rows and even-numbered rows work in time division.

Compared with the prior art, in the technical solution of the present invention, the pixel array structure of the distance sensor includes a plurality of pixel units arranged in an array, each pixel unit includes a single-photon avalanche diode, and the adjacent pixel units work in a time-sharing manner. , so that when working, the single-photon avalanche diodes at the corresponding positions can be turned on in sequence in different periods of time. When a pixel unit is working, its adjacent pixel units are in non-working state, so it is difficult for crosstalk to reach another pixel unit. The pixel unit in the working state improves the crosstalk situation and does not generate false triggering; based on this, the present invention realizes that the distance between adjacent pixels is reduced, thereby greatly improving the resolution.

Description of drawings

1 is a schematic diagram of a D TOF pixel unit array;

2 is a schematic cross-sectional view one of a D TOF pixel unit array;

3 is a schematic cross-sectional view II of a D TOF pixel unit array;

4 is a schematic diagram of a D TOF pixel unit crosstalk;

FIG. 5 is a schematic diagram of a pixel array structure of a distance sensor provided in an embodiment of the present invention;

6 is a schematic cross-sectional view 1 of a pixel array structure of a distance sensor provided in an embodiment of the present invention;

7 is a second schematic cross-sectional view of a pixel array structure of a distance sensor provided in an embodiment of the present invention;

FIG. 8 is a schematic diagram of a group of pixel units irradiated by incident light of different wavelengths according to an embodiment of the present invention.

Detailed ways

The pixel array structure of the distance sensor, the distance sensor and the working method of the present invention will be described in more detail below with reference to the schematic diagrams, wherein the preferred embodiments of the present invention are shown, and it should be understood that those skilled in the art can modify the present invention described herein, and The advantageous effects of the present invention are still achieved. Therefore, the following description should be construed as widely known to those skilled in the art and not as a limitation of the present invention.

The invention is described in more detail by way of example in the following paragraphs with reference to the accompanying drawings. The advantages and features of the present invention will become apparent from the following description and claims. It should be noted that, the accompanying drawings are all in a very simplified form and in inaccurate scales, and are only used to facilitate and clearly assist the purpose of explaining the embodiments of the present invention.

In the following description, it will be understood that when a layer (or film), region, pattern or structure is referred to as being "on" a substrate, layer (or film), region and/or pattern, it can be directly on another layer or on the substrate, and/or intervening layers may also be present. In addition, it will be understood that when a layer is referred to as being "under" another layer, it can be directly under the other layer, and/or one or more intervening layers may also be present. In addition, reference to "on" and "under" various layers may be made based on the drawings.

Referring to FIG. 1 , for an m*n resolution D TOF pixel unit array, each pixel unit (pixel) includes a single-photon avalanche diode (spad). The usual working mode is that m*n pixels work at the same time, or work row by row and column by column. However, when a single-photon avalanche diode avalanches, secondary photons will be generated, and when the secondary photons crosstalk to the pixel next door, it will cause the spad avalanche next door. If the next-door spad is also in working state, it will cause the next-door spad to trigger falsely, resulting in a false output signal. When the D TOF crosstalk exists, it will cause the entire distance picture to be blurred, and subsequent processing and correction cannot be performed. Therefore, the crosstalk must be solved.

Whether for a front-illuminated (FSI) sensor, as shown in Figure 2, or a back-illuminated (BSI) sensor, as shown in Figure 3, the main structure consists of adjacent and alternating spad areas (disposed in pixel unit 1), Light is irradiated into the semiconductor device from the front or back of the wafer. However, since the adjacent spads (that is, adjacent pixels) are not completely blocked, for example, there is still an unisolated part under the STI (Shallow Trench Isolation) structure 2 shown in FIG. 2, and the STI shown in FIG. 3 There is still an unisolated portion between structure 2 and DTI (deep trench isolation) structure 3, so crosstalk will occur.

As shown in Figure 4, the application of FSI is used for illustration. An isolation structure 2 is arranged between adjacent pixel units 1. When adjacent pixels work at the same time, after the spa avalanche of the jth pixel in the middle, the secondary The photons will crosstalk to the adjacent J-1 and J+1 pixels. Specifically, the avalanche of the J-th pixel generates a subphoton O, and there are multiple paths that cross-talk to the next-door pixel. Case A is that the subphoton O directly crosstalks to the pixel next door; Case B is that the subphoton O crosstalks to the pixel next door after being reflected by the upper surface (such as the metal layer 3); Case C is that the subphoton O crosstalks to the pixel next door after being reflected from the bottom. Since adjacent pixels work at the same time, the secondary photon O will cause false triggering of the spad next door, resulting in false output signals.

Therefore, the inventor breaks through the limitations of the prior art and makes time-sharing work between adjacent pixels, thereby avoiding the transmission of crosstalk and false triggering, and making it possible to reduce the pixel pitch.

Example 1

Embodiment 1 of the present invention provides a pixel array structure of a distance sensor. The implementation details of this embodiment will be specifically described below, and the following content is only provided for the convenience of understanding, and is not necessary for implementing this solution. The schematic diagram of this embodiment can refer to FIG. 5, including:

A plurality of pixel units 101 , 102 , 103 and 104 are arranged in an array, each pixel unit includes a single-photon avalanche diode (not shown), and adjacent pixel units work in a time-sharing manner.

Therefore, in the embodiment of the present invention, by making the pixel units work in time-sharing with adjacent pixel units, the spacing is reduced, and the occurrence of crosstalk and false triggering when the spacing is small is avoided.

Example 2

Embodiment 2 of the present invention provides a pixel array structure of a distance sensor, which may be further optimized or improved on the basis of Embodiment 1. The implementation details of this embodiment will be specifically described below, and the following content is only provided for the convenience of understanding, and is not necessary for implementing this solution. This embodiment includes:

The spacing between adjacent pixel units is less than or equal to 5 μm, for example, the spacing between adjacent pixel units may be 1 μm, 2 μm, 3 μm, 4 μm, and so on. It can be seen that the pitch in the prior art is above 20 μm, so the present invention greatly reduces the pitch.

It can be understood that, for the case where the spacing between the adjacent pixel units is 5-20 μm, or even greater than 20 μm, the embodiments of the present invention can also be implemented. Those skilled in the art can flexibly adjust the spacing between adjacent pixel units according to actual needs.

Example 3

Embodiment 3 of the present invention provides a pixel array structure of a distance sensor, which may be further optimized or improved on the basis of Embodiment 1 or Embodiment 2. The implementation details of this embodiment will be specifically described below, and the following content is only provided for the convenience of understanding, and is not necessary for implementing this solution. The schematic diagram of this embodiment can refer to FIG. 5, including:

In this embodiment, pixel units in adjacent i rows and j columns form a group of pixel units 10 , and the pixel array structure of the distance sensor includes the plurality of groups of pixel units 10 .

For example, each group of pixel units 10 is a combination of 2×2 pixel units.

Typically, each group of pixel cells is the same array.

In addition, each group of pixel units 10 may also be in other array forms, such as 2×3, 3×3, and so on. In this embodiment, the array of each group of pixel units 10 does not need to be too complicated. Taking a simple 2×2 as an example, for example, each group of pixel units 10 is composed of pixel unit 101 , pixel unit 102 , pixel unit 103 and When the pixel units 104 are turned on in such a sequence, adjacent pixel units in the entire array can be prevented from being turned on at the same time, so that a simpler group of pixel units 10 can achieve higher efficiency while avoiding crosstalk.

Taking a pixel array of 2×2 groups as an example, the entire array with m×n resolution is actually composed of pixel arrays of m/2×n/2 groups.

Please refer to Figure 4. For example, when the secondary photon A/B/C occurs, for example, the J pixel unit is turned on at this time, and there are four around it (Figure 4 shows a J-1 pixel unit and J+1 pixel unit on the opposite side. unit) pixel unit is not in the open state, the secondary photon entering the surrounding pixel units will not have an impact, and will not cause the spad to be triggered by mistake. And it is precisely because the four surrounding pixel units are not in the open state, so when the secondary photon enters the adjacent pixel unit, it will also be blocked by this pixel unit, and will not enter the pixel unit in the open state. In this sense, Crosstalk is avoided.

Example 4

Embodiment 4 of the present invention provides a distance sensor pixel array structure, which may be further optimized or improved on the basis of Embodiment 1 or Embodiment 2 or Embodiment 3. The implementation details of this embodiment will be specifically described below, and the following content is only provided for the convenience of understanding, and is not necessary for implementing this solution. Refer to FIG. 6 for a schematic diagram of this embodiment, including:

A complete metal isolation structure 4 is disposed between adjacent pixel units 1 .

The complete metal isolation structure 4 enables complete isolation between the sidewalls of adjacent pixel units 1 . For example, the complete metal isolation structure 4 is barrel-shaped, and only the upper and lower surfaces of the pixel unit 1 are exposed.

Example 5

Embodiment 5 of the present invention provides a pixel array structure of a distance sensor, which can be further optimized or improved on the basis of any one of Embodiments 1 to 4. The implementation details of this embodiment will be specifically described below, and the following content is only provided for the convenience of understanding, and is not necessary for implementing this solution. The schematic diagrams of this embodiment can refer to FIG. 7 and FIG. 8 , including:

A plurality of filters 5 are also provided, each of the filters 5 is correspondingly arranged on each pixel unit 1 , and at least some of the filters are filters of different wavelengths.

Please refer to FIG. 8 , which illustrates the situation after light is irradiated to a group of pixel units, each pixel unit 1 is provided with a filter, and FIG. 8 shows that the four filters set on a group of pixel units are respectively 940nm Filters, 900nm filter, 920nm filter and 960nm filter, correspond to incident light of different wavelengths, namely 940nm incident light, 900nm incident light, 920nm incident light and 960nm incident light.

It can be understood that, the setting of the filter is not limited by the examples described in this embodiment.

Example 6

Embodiment 6 of the present invention provides a distance sensor. The distance sensor in this embodiment includes the distance sensor pixel array structure described in any one of Embodiments 1 to 5. The distance sensor is, for example, a D TOF distance sensor

Example 7

Embodiment 7 of the present invention provides a working method of a distance sensor. The implementation details of this embodiment will be specifically described below, and the following content is only provided for the convenience of understanding, and is not necessary for implementing this solution. This embodiment may be performed based on the structure of Embodiment 6, and may not be limited to the structure provided by the present invention. The method of the embodiment of the present invention includes:

In a working method of a distance sensor, the single-photon avalanche diodes between adjacent pixel units work in time-sharing.

Specifically, the distance sensor includes an array of multiple groups of pixel units, each group of pixel units turns on different pixel units at different time periods, and at least one pixel unit is spaced between pixel units turned on in adjacent groups of pixel units.

In this embodiment, each pixel unit array works in time division according to the pixel arrangement position. For example, as shown in FIG. 2, each group of pixel units includes pixel units 101-104, which are turned on at time periods t1, t2, t3, and t4, respectively, and there is no overlap between t1-t4.

It can be understood that, for a group of pixel units of other array types, they may also be turned on in different time periods in sequence.

Example 8

This embodiment may be further optimized or improved on the basis of Embodiment 7. Embodiment 8 mainly lies in that the pixel units of odd-numbered columns and even-numbered columns work in a time-sharing manner by adopting a progressive scanning format.

Example 9

This embodiment may be further optimized or improved on the basis of Embodiment 7. Embodiment 9 mainly lies in that a column-by-column scanning format is adopted, and the pixel units of odd-numbered rows and even-numbered rows work in time division.

In the technical solution of the present invention, the pixel array structure of the distance sensor includes a plurality of pixel units arranged in an array, each pixel unit includes a single-photon avalanche diode, and the adjacent pixel units work in a time-sharing manner, so that during operation, The single-photon avalanche diodes at the corresponding positions can be turned on in turn in different time periods. When a pixel unit is working, its adjacent pixel units are in the non-working state, so it is difficult for the crosstalk to reach another pixel unit that is working. The crosstalk situation is improved, and false triggering will not occur; based on this, the present invention realizes that the distance between adjacent pixels is reduced, thereby greatly improving the resolution.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit and scope of the invention. Thus, provided that these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims (10)

1. a distance sensor pixel array structure, is characterized in that, comprises: A plurality of pixel units are arranged in an array, each pixel unit includes a single-photon avalanche diode, and adjacent pixel units work in time division. 2 . The distance sensor pixel array structure according to claim 1 , wherein the pixel units of adjacent i rows and j columns form a group of pixel units, and the distance sensor pixel array structure includes the multiple groups of pixel units. 3 . 3 . The pixel array structure of the distance sensor according to claim 1 , wherein a complete metal isolation structure is arranged between adjacent pixel units. 4 . 4 . The pixel array structure of the distance sensor according to claim 1 , wherein a plurality of filters are further provided, and each of the filters is correspondingly arranged on each pixel unit, and at least part of the filters is provided. 5 . The filters are filters of different wavelengths. 5. A distance sensor, characterized by comprising the distance sensor pixel array structure according to any one of claims 1-4. 6. A working method of a distance sensor, comprising: The single-photon avalanche diodes between adjacent pixel units work in time-sharing. 7. The working method of a distance sensor according to claim 6, wherein the distance sensor comprises an array of multiple groups of pixel units, each group of pixel units turns on different pixel units at different time periods, and adjacent groups of pixels At least one pixel unit is spaced between the pixel units that are turned on. 8 . The working method of the distance sensor according to claim 7 , wherein each pixel unit array works in time division according to the pixel arrangement position. 9 . 9 . The working method of the distance sensor according to claim 6 , wherein the pixel units of the odd-numbered columns and the even-numbered columns work in a time-sharing manner by adopting the form of progressive scanning. 10 . 10 . The working method of the distance sensor according to claim 6 , wherein the pixel units of odd-numbered rows and even-numbered rows work in a time-sharing manner in a column-by-column scanning format. 11 .

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