Buried-Junction Photodiode Mesa Layout for Crosstalk Reduction
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Solution Overview
Problem
Photodiode devices experience significant electrical and optical crosstalk, particularly as pixel pitch decreases, leading to increased noise and fabrication inefficiencies due to the need for electrical passivation of materials with high electric fields.
Innovation Solution
A hybrid design combining a mesa structure with a buried p-n junction, where absorber material is selectively removed using geometric configurations like trenches and pits to reduce crosstalk while minimizing the need for passivation of materials with high electric fields, optimizing the distance of etching to balance crosstalk reduction and passivation requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If absorber material is removed to reduce crosstalk, then optical and electrical crosstalk is reduced, but the need for electrical passivation increases due to exposed materials with high electric fields
Solution Approach 1:
The patent extracts and removes absorber material from regions where it would cause crosstalk between adjacent photodiode pixels. By selectively removing the absorber layer in specific geometric patterns (such as circular or rectangular regions) around each pixel, the patent eliminates the source of optical and electrical crosstalk while preserving the functional absorber material within each pixel area.
Solution Approach 2:
The patent applies different structural configurations to different regions of the photodiode array. Each pixel region has its own optimized geometry (circular, rectangular, or other shapes) with absorber material removed only where necessary to prevent crosstalk. This local optimization allows each pixel to have the minimal passivation requirements needed while maintaining overall array performance.
2Area of stationary object
If pixel pitch is decreased to increase pixel density, then more pixels fit in the same area, but crosstalk between pixels increases
Solution Approach 1:
The patent segments the absorber material distribution across the photodiode array by introducing periodic geometric patterns that create isolated regions of removed absorber material between pixels. This segmentation effectively divides the continuous absorber layer into discrete functional units, preventing the propagation of optical and electrical signals between adjacent pixels even when they are closely spaced.
3Reliability
If electrical passivation is applied to materials with high electric fields, then electrical stability is improved, but fabrication efficiency decreases and noise may increase
Solution Approach 1:
The patent performs the absorber material removal action before final device assembly and passivation steps. By pre-configuring the geometric patterns of removed absorber material, the patent eliminates the need for extensive subsequent passivation work, as the exposed regions have reduced electric field requirements. This preliminary structural optimization simplifies the overall fabrication process.
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 approach significantly reduces dark current and dark count rates, achieving a thirty-time reduction in dark count rate compared to unoptimized devices, while maintaining high-quality passivation and supporting Geiger-mode operations.
Implementation Method 1
etching away at least a portion of the absorber material to form a mesa structure
Implementation Method 2
Photodiodes are semiconductor devices that may convert light into electrical current
Implementation Method 3
significantly reduces dark current and dark count rates, achieving a thirty-time reduction in dark count rate compared to unoptimized devices
Data Source
Figure 1A~1B
Figure 1C
Figure 2
AI summary
Devices, systems, and methods are provided for reducing electrical and optical crosstalk in photodiodes. A photodiode may include a first layer with passive material, the passive material having no electric field. The photodiode may include a second layer with an absorbing material, the second layer above the first layer. The photodiode may include a diffused region with a buried p-n junction. The photodiode may include an active region with the buried p-n junction and having an electric field greater than zero. The photodiode may include a plateau structure based on etching through the second layer to the first layer, the etching performed at a distance of fifteen microns or less from the buried p-n junction.