Avalanche Photodiode Depth Isolation to Reduce Dark Count Rate
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Solution Overview
Problem
The miniaturization of pixels in photodetection apparatuses leads to increased dark count rates (DCR) due to the proximity of semiconductor regions, causing electric field concentration and dark current issues.
Innovation Solution
The photoelectric conversion apparatus employs a semiconductor layer with a plurality of avalanche photodiodes, utilizing a specific arrangement of semiconductor regions of different conductivity types at varying depths and isolation portions to maintain pixel size while reducing electric field concentration and dark current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If pixel size is miniaturized, then photodetection density is improved, but dark count rate worsens due to electric field concentration between semiconductor regions
Solution Approach 1:
The patent introduces a depth dimension to the isolation structure by forming the third semiconductor region at a deeper position than the avalanche multiplication unit. This vertical stacking arrangement allows pixels to be placed closer together in the planar view without creating harmful electric field concentrations, as the isolation extends into the depth dimension rather than just laterally.
Solution Approach 2:
The third semiconductor region acts as an intermediary structure between adjacent pixels. It provides electrical isolation and prevents direct coupling between neighboring avalanche photodiodes, thereby reducing dark count rate while allowing miniaturization of the overall pixel footprint.
2Reliability
If third semiconductor region is arranged closer to avalanche multiplication unit, then isolation effectiveness is improved, but electric field concentration increases causing dark count rate worsening
Solution Approach 1:
Instead of arranging the third semiconductor region closer in the lateral plane (which would increase electric field concentration), the patent positions it at a deeper vertical level. This dimensional shift allows effective isolation while maintaining safe horizontal distances that prevent electric field concentration.
Solution Approach 2:
The patent creates different local quality characteristics at different depths. The avalanche multiplication unit resides at a shallower depth for optimal photon detection, while the third semiconductor region is positioned at a deeper depth for isolation purposes. This local differentiation allows each region to fulfill its specific function without compromising the other.
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
This configuration effectively minimizes pixel size while preventing avalanche crosstalk and dark count rate worsening, enhancing photodetection efficiency and reducing noise.
Implementation Method 1
an avalanche photodiode that can detect a weak signal of a single photon level by using avalanche (electronic avalanche) multiplication
Implementation Method 2
detect a weak signal of a single photon level by using avalanche (electronic avalanche) multiplication
Data Source
AI summary
A photoelectric conversion apparatus includes a plurality of avalanche photodiodes. Each of the plurality of avalanche photodiodes includes an avalanche multiplication unit formed by a first semiconductor region of a first conductivity type that is arranged at a first depth, and a second semiconductor region of a second conductivity type different from the first conductivity type and which is arranged at a second depth deeper than the first depth. A fourth semiconductor region at least one of a conductivity type and an impurity concentration of which is different from those of a third semiconductor region of the second conductivity type is arranged at a position shallower than the third semiconductor region, and a depth of a boundary portion between the third semiconductor region and the fourth semiconductor region is deeper than that of the avalanche multiplication unit.