Systems and methods

Abstract

To provide improved systems and methods for photodiodes used in an imaging device.SOLUTION: A system includes a pixel including a diffusion layer in contact with an absorption layer. The diffusion layer and absorption layer are in contact with one another along an interface that is inside of a mesa. A trench is defined in the absorption layer surrounding the mesa. An overflow contact is seated in the trench.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to diodes, and more particularly to photodiodes such as those used in pixels for imaging. [Background technology]

[0002] The lower the dark current of the photodiode in the imaging device, the better the image quality. Similarly, the more sensitive the photodiode in the imaging device, the better the image quality. At high light levels, excess photons can cause high currents, which can damage the detector and / or put more stress on the readout integrated circuit (ROIC). Photodetector arrays (PDAs) with mesa structures improve the modulation transfer function (MTF) of imaging devices. Summary of the Invention [Problem to be solved by the invention]

[0003] The prior art has been considered sufficient for their intended purposes. However, there continues to be a need for improved systems and methods for photodiodes used in imaging devices. The present disclosure provides a solution to this need. [Means for solving the problem]

[0004] The system includes a pixel including a diffusion layer in contact with an absorber layer. The diffusion layer and the absorber layer contact each other along an interface inside a mesa. A trench is defined in the cap layer and the absorber layer surrounding the mesa. An overflow contact is provided in the trench.

[0005] The overflow contact may surround the mesa. The pixel may be one of a plurality of similar pixels arranged in a grid pattern, with each pixel separated from adjacent pixels of the plurality of pixels by trenches. The overflow contact may be provided at a base of the trench forming an overflow contact grid, with the pixels in spaces of the overflow contact grid between intersecting lines of the overflow contact grid.

[0006] The trench can have a base between sidewalls of the trench, with an overflow contact provided on the base, with a lateral clearance on the base between the overflow contact and each of the sidewalls. The overflow contact is provided in contact with a transparent conductive oxide (TCO) that contacts the absorber layer. The TCO can include multiple layers of zinc oxide (ZnO), titanium oxide (TiO2), and / or indium tin oxide (ITO). The TCO can be formed in a gap in a silicon nitride (SiNx) layer. A contact metal can be electrically connected to the diffusion layer, configured to electrically connect the diffusion layer to a read out integrated circuit (ROIC).

[0007] The overflow contact can be metallic. A cap layer can be deposited on the absorbing layer opposite the substrate. The cap layer can include InP. A SiNx layer can be included on the cap layer. The SiNx layer can be in direct contact with the absorbing layer in the trench. An anti-reflective layer can be deposited on the substrate opposite the absorbing layer. The absorbing layer can include indium gallium arsenide (InGaAs) where the pixel is sensitive to infrared wavelengths of light. It is also contemplated that the absorbing layer can include silicon (Si) where the pixel is sensitive to visible wavelengths of light.

[0008] The method includes forming trenches in an absorber layer of a pixel array, the trenches being formed in a grid pattern surrounding respective pixels of the pixel array, each pixel being bounded by intersecting lines of the grid, and forming overflow contacts in the trenches according to the grid pattern.

[0009] The method may include depositing a SiNx layer on the absorber layer after forming the trench, and forming an overflow contact in the trench is performed after depositing the SiNx layer. Forming the overflow contact in the trench may include forming the overflow contact on a transparent oxide layer (TCO) formed in gaps of the SiNx layer.

[0010] These and other features of the subject disclosed systems and methods will become more readily apparent to those skilled in the art from the following detailed description of the preferred embodiments taken in conjunction with the drawings.

[0011] Preferred embodiments thereof are described in detail herein with reference to certain drawing figures so that those skilled in the art to which the subject disclosure pertains can readily understand, without undue experimentation, how to make and use the devices and methods of the subject disclosure. [Brief description of the drawings]

[0012] [Figure 1] 1 is a schematic cross-sectional elevation view of one embodiment of a system constructed in accordance with the present disclosure showing a mesa and a trench. [Diagram 2] FIG. 2 is a schematic plan view of the system of FIG. 1 showing a grid pattern of pixels. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Reference is now made to the drawings in which like reference numbers identify similar structural features or aspects of the subject disclosure. For purposes of explanation and illustration, and not limitation, a partial view of one embodiment of a system according to the present disclosure is shown in FIG. 1 and generally designated by reference numeral 100. As illustrative, another embodiment of a system according to the present disclosure, or aspects thereof, is provided in FIG. 2. The systems and methods described herein can be used to reduce excess current, increase sensitivity, and reduce stress in readout integrated circuits (ROICs) in imaging devices.

[0014] System 100 includes a pixel 102 that includes a diffusion layer 104 in contact with an absorption layer 106. The diffusion layer 104 and the absorption layer 106 contact each other along an interface 108 that is inside a mesa 109. A trench 110 is defined in the absorption layer 106 that surrounds the mesa 109. An overflow contact 112 is provided in the trench 110.

[0015] 2, pixel 102 is one of a plurality of similar pixels 102 arranged in a square tiled grid pattern 114, some of which are indicated by reference numeral 114 and associated phantom lines in FIG. 2. Trenches 110 separate each pixel 102 from adjacent ones of the plurality of pixels 102. An overflow contact 112 surrounds each mesa 109. The overflow contact 112 is provided at a base 116 of the trench 110 (as identified in FIG. 1), forming an overflow contact grid 118. A portion of the overflow contact grid 118 is indicated in FIG. 2 with reference numeral 118 and associated phantom lines. Pixel 102 lies in a space of the overflow contact grid 118 between intersecting lines 120 of the overflow contact grid 118.

[0016] Referring again to FIG. 1, a base 116 of the trench 110 is disposed between sidewalls 122 of the trench 110. An overflow contact 112 is provided at the base 116, with a lateral clearance 124 on the base 116 between the overflow contact 112 and each of the sidewalls 122. The overflow contact is provided in contact with a transparent conductive oxide (TCO) 126 that is in contact with the absorber layer 106 as well. The TCO 126 can include multiple layers of ZnO, TiO2, and / or indium tin oxide (ITO). The film resistivity of the TCO 126 can be designed based on the operating conditions of the detector, which can be done by adjusting the doping level of the TCO 126. The TCO 126 is formed in a gap 128 in the SiNx layer 130. For each pixel 102 (e.g., as shown in FIG. 2), a contact metal 132 electrically connects between the diffusion layer 104 and a readout integrated circuit (ROIC) 134. The TCO 126 normally acts as an insulator, but when the current reaches a certain maximum level, the resistive barrier of the TCO 126 can break and allow excess current to flow through the TCO to a common current sink 144 on the ROIC 134.

[0017] The overflow contact 112 may be metallic. A cap layer 136, for example of InP, may be deposited on the absorbing layer opposite a substrate 138, which may be of InP or any other suitable material. A SiNx layer 130 is included and disposed on the cap layer. The SiNx layer 130 directly contacts the absorbing layer 106 in the trench 110. An anti-reflective layer 140 may optionally be deposited on the substrate 138 opposite the absorbing layer 106. The absorbing layer 106 may include, for example, InGaAs, which renders the pixel 102 sensitive to infrared wavelengths of light. It is also contemplated that the absorbing layer 106 may include, for example, Si, which renders the pixel 102 sensitive to visible wavelengths of light. Those skilled in the art will readily appreciate that other suitable materials may be used to provide sensitivity to other suitable wavelengths.

[0018] The method includes forming trenches, e.g., trenches 110, in an absorber layer, e.g., absorber layer 106, of a pixel array (e.g., a layer of pixels 102 in a square tiled grid pattern 114 in FIG. 2). The trenches are formed in a grid pattern, e.g., grid pattern 114 in FIG. 2, surrounding each pixel of the pixel array, with each pixel being surrounded by intersecting lines of the grid (e.g., grid lines 142 in FIG. 2). The method includes forming overflow contacts, e.g., overflow contacts 112, in the trenches according to the grid pattern. The method may include depositing a SiNx layer (e.g., SiNx layer 130) on the absorber layer after forming the trenches, and forming the overflow contacts in the trenches is performed after depositing the SiNx layer. Forming the overflow contacts in the trenches may include forming the overflow contacts on a transparent oxide layer (TCO), e.g., TCO 126, formed in gaps, e.g., gaps 128, of the SiNx layer. The diffusion layer 104 is the P portion of the PIN diode, the absorption layer 106 is the I portion of the PIN diode, and the substrate 138 is the N portion of the PIN diode.

[0019] The methods and systems of the present disclosure, as described above and shown in the drawings, provide reduced excess current, increased sensitivity, and reduced stress in the readout integrated circuit (ROIC) of an imaging device, thereby improving image quality and reducing the design requirements and signal processing complexity of the ROIC as compared to conventional configurations. While the apparatus and methods of the subject disclosure have been shown and described with reference to preferred embodiments, those skilled in the art will readily appreciate that changes and / or modifications may be made thereto without departing from the scope of the subject disclosure.

Claims

1. 1. A system comprising: a pixel including a diffusion layer in contact with an absorption layer, the diffusion layer and the absorption layer contacting each other along an interface that is inside a mesa; a trench defined in the absorber layer surrounding the mesa; an overflow contact disposed in the trench; Equipped with the overflow contact is in contact with a transparent conductive oxide (TCO) that is in contact with the absorber layer; The system, wherein the transparent conductive oxide (TCO) is formed in gaps in a SiNx layer in the trench.

2. The system of claim 1 , wherein the overflow contact surrounds the mesa.

3. the pixel is one of a plurality of similar pixels arranged in a grid pattern; the trenches separate each pixel from adjacent pixels of the plurality of pixels; the overflow contacts are provided at bases of the trenches to form an overflow contact grid; The system of claim 1 , wherein the pixel is in a space of the overflow contact grid between intersecting lines of the overflow contact grid.

4. The system of claim 1 , wherein the overflow contact is metallic.

5. The system of claim 1 , further comprising a cap layer deposited on the absorbing layer opposite the substrate.

6. The system of claim 5 , wherein the cap layer comprises InP.

7. The system of claim 5 , further comprising a SiNx layer over the cap layer.

8. 8. The system of claim 7, wherein the SiNx layer is in direct contact with the absorber layer.

9. The system of claim 5 further comprising an anti-reflective layer deposited on the substrate opposite the absorbing layer.

10. the trench having a base between sidewalls of the trench; the overflow contact is disposed on the base; The system of claim 1 , wherein there is a lateral clearance in the base between the overflow contact and each of the side walls.

11. a contact metal electrically connected to the diffusion layer; The system of claim 1 , wherein the contact metal is configured to electrically connect the diffusion layer to a read out integrated circuit (ROIC).

12. The system of claim 11 , further comprising the read out integrated circuit (ROIC) in electrical communication with the contact metal.

13. The transparent conductive oxide (TCO) is ZnO, TiO ２ 10. The system of claim 1, further comprising: a first insulating layer; and / or multiple layers of indium tin oxide (ITO).

14. the absorption layer comprises InGaAs; The system of claim 1 , wherein the pixels are sensitive to infrared wavelengths of light.

15. the absorbing layer comprises Si; The system of claim 1 , wherein the pixels are sensitive to visible wavelengths of light.

16. forming trenches in an absorber layer of a pixel array, the trenches being formed in a grid pattern surrounding each pixel of the pixel array, with each pixel surrounding an intersecting line of the grid; forming overflow contacts in the trenches according to the grid pattern; Including, depositing a SiNx layer on the absorption layer after forming the trench, wherein forming the overflow contact in the trench is performed after depositing the SiNx layer; The method, wherein forming the overflow contact in the trench includes forming the overflow contact on a transparent oxide layer (TCO) formed in a gap of the SiNx layer.

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