Avalanche Photodiode Array With Separation Regions
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Solution Overview
Problem
In photodetectors, particularly in solid-state image sensors with avalanche photodiodes (APDs), electric field concentration at the end portions of the pixel array can lead to high voltage breakdown and increased leakage current, affecting the stability and efficiency of photodetection.
Innovation Solution
The photodetector design includes at least two avalanche photodiodes (APDs) on a semiconductor substrate, with a first region outside the APDs and separated from them by a separation region. Different semiconductor layers with specific conductive types and impurity concentrations are used, allowing for distinct voltage applications to the APDs and the first region to manage electric field distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If APDs are arranged in an array and connected through the same N-type semiconductor layer, then photodetection sensitivity is enhanced and image generation from faint incident light is achieved, but electric field concentration occurs at the end portion of the APD pixel array causing high voltage breakdown and increased leakage current
Solution Approach 1:
The patent divides the pixel array into multiple independent pixel units, each with its own P-type semiconductor layer and N-type semiconductor layer. This segmentation isolates the electric fields of adjacent pixels through separation regions, preventing electric field concentration at the array boundaries while maintaining high photodetection sensitivity through avalanche multiplication in each pixel.
Solution Approach 2:
The patent introduces separation regions between adjacent pixels that act as intermediary structures. These separation regions, consisting of depleted P-type and N-type semiconductor layers, serve as electric field barriers that prevent the spread of electric fields from one pixel to another, thereby resolving the electric field concentration problem at array endpoints while preserving the sensitivity enhancement benefits.
2Measurement precision
If APDs are arranged in an array and connected through the same N-type semiconductor layer, then photodetection sensitivity is enhanced and image generation from faint incident light is achieved, but leakage current increases at the end portion of the pixel array
Solution Approach 1:
The patent segments the pixel array into independent pixel units with individual P-type and N-type semiconductor layers. This segmentation creates electrical isolation between pixels through separation regions, which suppresses leakage current generation at array boundaries while preserving the avalanche multiplication effect for enhancing photodetection sensitivity in each pixel.
Solution Approach 2:
The separation regions act as intermediary structures between adjacent pixels, consisting of depleted P-type and N-type semiconductor layers. These intermediaries block the flow of leakage current between pixels by creating potential barriers, thereby reducing overall leakage current while maintaining the sensitivity enhancement provided by avalanche photodetection in each pixel.
3Device complexity
If the same voltage is applied to all APDs in the array, then simplified voltage control is achieved, but electric field distribution becomes uneven causing unstable operation at array endpoints
Solution Approach 1:
The patent applies different voltages to different regions of the pixel array based on their specific characteristics. Endpoint pixels are assigned different voltage levels compared to internal pixels, creating local voltage optimization that compensates for edge effects. This local quality adjustment ensures uniform electric field distribution across all pixels, preventing unstable operation at array endpoints while maintaining manageable voltage control through systematic voltage assignment.
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 relaxes electric field concentration at the end portions of the pixel array, enhancing the withstand voltage and reducing leakage current, thereby ensuring stable and efficient photodetection operations.
Implementation Method 1
a signal charge generated by photoelectric conversion is multiplied using avalanche breakdown
Implementation Method 2
a signal charge generated by photoelectric conversion is multiplied using avalanche breakdown
Data Source
AI summary
A solid-state image sensor includes at least two or more APDs formed on a substrate. First regions are arranged outside the APDs as viewed in plane. Adjacent ones of the APDs and the first regions are separated from each other through a separation region. A first voltage V21 is applied to a fourth semiconductor layer of the APD, and a second voltage V22 is applied to a fifth semiconductor layer of the first region. The first voltage V21 is higher than the second voltage V22.