SPAD Isolated Junction Structure for Crosstalk-Free Bias Optimization
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Solution Overview
Problem
Conventional back-to-back avalanche diodes face challenges in optimizing p-n junction depth and suffer from disturbances between junctions, limiting their ability to independently optimize excess bias and photon detection efficiency.
Innovation Solution
A single-photon avalanche diode (SPAD) with isolated junctions is developed using a semiconductor-on-insulator (SOI) technology, featuring a buried insulator layer and shallow trench isolation structures to isolate individual p-n junctions, allowing for independent optimization of junction depths and reduced disturbances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional back-to-back avalanche diode schemes are used, then the device can detect single photons, but disturbs occur between the two junctions and independent optimization of junction depths is difficult
Solution Approach 1:
The patent divides the single avalanche diode into two separate avalanche diodes (first and second) with independent p-n junctions. Each junction can be independently optimized for its specific wavelength detection requirements, eliminating the disturbs that occur in conventional back-to-back configurations where the junctions share a common deep N-well and interfere with each other.
Solution Approach 2:
The patent introduces a buried insulator layer as an intermediary between the first and second avalanche diodes. This insulator layer electrically isolates the two junctions, preventing harmful disturbances and crosstalk between them while allowing each junction to operate independently at optimized bias conditions for its specific detection wavelength.
2Device complexity
If conventional back-to-back avalanche diode schemes are used, then the device structure is simplified, but independent optimization of excess bias for each junction is not possible
Solution Approach 1:
The patent segments the avalanche detection function into two independent diodes, each with its own p-n junction that can be independently biased. This segmentation enables separate optimization of excess bias for each junction according to its specific detection wavelength requirements, while maintaining a relatively simple overall device structure through the use of standard semiconductor fabrication processes.
Solution Approach 2:
The patent applies local quality by allowing each avalanche diode to have independently optimized parameters including junction depth and excess bias. The first avalanche diode can be optimized for shorter wavelengths while the second is optimized for longer wavelengths, with each junction having tailored doping profiles and bias conditions suited to its specific function.
3Ease of manufacture
If dual junctions share a deep N-well, then manufacturing is simplified, but independent optimization of junction depths is prevented
Solution Approach 1:
The patent segments the common deep N-well structure into separate isolation regions using a buried insulator layer. This allows each avalanche diode to have its own independently controlled junction depth while maintaining manufacturing simplicity through the use of standard isolation techniques. The first and second p-n junctions can be formed with different depths optimized for their respective wavelengths without interfering with each other.
Solution Approach 2:
The buried insulator layer serves as an intermediary that replaces the need for a shared deep N-well. This insulator layer provides electrical isolation between the two avalanche diodes, enabling independent junction depth optimization while maintaining ease of manufacture through standard semiconductor processing techniques.
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 design enhances photon detection efficiency and flexibility for multiple wavelength detections by eliminating crosstalk and enabling optimized excess bias for each SPAD, resulting in improved performance.
Implementation Method 1
isolated from the first p-n junction by a buried insulator layer
Implementation Method 2
the reverse bias is very high such that a phenomenon called impact ionization occurs. This phenomenon is able to cause an avalanche current to develop
Implementation Method 3
a SPAD is based around a semiconductor p-n junction that can be illuminated with ionizing radiation along a wide portion of the electromagnetic spectrum
Data Source
AI summary
The present disclosure relates to semiconductor structures and, more particularly, to a single-photon avalanche diode with isolated junctions and methods of manufacture. The structure includes a first p-n junction in a semiconductor material; and a second p-n junction in a second semiconductor material isolated from the first p-n junction by a buried insulator layer.