Avalanche Photodiode Array Trench Shielding for Optical Crosstalk
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Solution Overview
Problem
Existing semiconductor photodetection devices face challenges in reducing optical crosstalk, which occurs when secondary light generated by avalanche multiplication is incident on adjacent cells, leading to reduced sensitivity and potential corrosion of light-shielding members with projecting portions.
Innovation Solution
A semiconductor photodetection device configuration featuring a light-shielding member with a projecting portion covered by an insulating film, which reflects incident light back to the pn junction, increasing photoelectron generation and preventing corrosion by isolating the light-shielding member from the atmospheric environment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a light-shielding member with a projecting portion is used to reduce optical crosstalk, then optical crosstalk reduction is improved, but the light-shielding member becomes exposed to the atmospheric environment and prone to corrosion
Solution Approach 1:
An insulating film is introduced as an intermediary layer between the light-shielding member and the atmospheric environment. This insulating film covers the projecting portion of the light-shielding member, preventing direct exposure to corrosive atmospheric elements while maintaining the light-shielding function. The insulating film acts as a protective mediator that resolves the contradiction between optical performance and environmental durability.
Solution Approach 2:
The structure combines the light-shielding member (typically metallic or highly reflective material) with an insulating film coating to create a composite structure. This composite approach allows the inner core material to provide optical shielding while the outer insulating layer provides corrosion protection, thus achieving both optical crosstalk reduction and improved reliability simultaneously.
2Object-affected harmful factors
If a light-shielding member is disposed inside the trench to reduce optical crosstalk, then optical crosstalk is reduced, but secondary light may still incident on adjacent cells
Solution Approach 1:
The light-shielding member is designed with a projecting portion that extends in the vertical dimension beyond the trench depth. This three-dimensional configuration allows the light-shielding member to block secondary light paths that would otherwise escape lateral containment, preventing incident on adjacent cells while maintaining detection accuracy through proper positioning.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The configuration effectively reduces optical crosstalk and enhances sensitivity by reflecting light towards the pn junction and protecting the light-shielding member from corrosion, thereby improving the device's performance and durability.
Implementation Method 1
The low refractive index substance reflects plasma emission generated during carrier multiplication in the avalanche photodiode
Implementation Method 2
When the secondary light is incident on an adjacent cell, the avalanche photodiode included in the adjacent cell may perform avalanche multiplication of a carrier generated by the incident secondary light
Implementation Method 3
an insulating layer covers the projecting portion. With this configuration, even if the light-shielding member includes the projecting portion, it is unlikely to be exposed to the atmospheric environment outside the semiconductor substrate
Data Source
AI summary
A semiconductor substrate has a first main surface and a second main surface that oppose each other and a plurality of cells that are arrayed two-dimensionally in a matrix. Each cell includes at least one avalanche photodiode arranged to operate in a Geiger mode. A trench penetrating through the semiconductor substrate is formed in the semiconductor substrate to surround each cell when viewed in a direction orthogonal to the first main surface. A light-shielding member optically separates mutually adjacent cells of the plurality of cells. The light-shielding member includes a first portion extending in a thickness direction of the semiconductor substrate between an opening end of the trench at the first main surface and an opening end of the trench at the second main surface and a second portion projecting out from the second main surface. The insulating film includes a portion that covers the second portion.