Avalanche Photodiode Trench Isolation for Pixel Miniaturization
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Solution Overview
Problem
Miniaturization of pixels in photodetection apparatuses leads to increased dark count rate (DCR) due to local electric field concentration between semiconductor regions, worsening performance.
Innovation Solution
Implementing a trench structure with a third semiconductor region of a second conductivity type at a different depth to isolate pixels, reducing electric field concentration and preventing avalanche crosstalk, while maintaining efficient charge detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If pixel size is miniaturized, then device density is improved, but dark count rate worsens due to local electric field concentration
Solution Approach 1:
The isolation structure extends into the depth dimension rather than only in the planar direction. By forming a trench that reaches a predetermined depth and filling it with a third semiconductor region, the patent creates a three-dimensional isolation barrier that prevents electric field concentration at the interface between adjacent pixels, thereby reducing dark count rate while allowing pixel miniaturization.
Solution Approach 2:
The third semiconductor region acts as an intermediary element between adjacent pixels. This intermediate structure with different conductivity type creates a potential barrier that mediates the electric field distribution, preventing direct electric field coupling between neighboring pixels and thus reducing avalanche crosstalk and dark count rate.
2Reliability
If third semiconductor region is arranged at the same depth as avalanche multiplication unit, then pixel isolation is improved, but local electric field region forms causing dark count rate to worsen
Solution Approach 1:
Instead of arranging the third semiconductor region at the same depth as the avalanche multiplication unit (two-dimensional arrangement), the patent extends the isolation structure into the depth dimension by forming a trench and filling it with the third semiconductor region. This three-dimensional arrangement maintains effective pixel isolation while preventing the formation of local high electric field regions that would increase dark count rate.
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
Prevents DCR worsening and avalanche crosstalk, enabling miniaturization of pixels without compromising detection efficiency.
Implementation Method 1
an avalanche photodiode (APD) that can detect a weak signal of a single photon level by using avalanche (electronic avalanche) multiplication. The APD forms a high electric field region (avalanche multiplication unit) by a first semiconductor region of a first conductivity type having the same polarity as a signal charge, and a second semiconductor region of a second conductivity type having a polarity different from a signal charge.
Implementation Method 2
a photoelectric conversion apparatus... including a plurality of pixels, each pixel including an avalanche photodiode
Data Source
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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.