Avalanche Photodiode Breakdown Voltage Control via Diffusion Sink
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Solution Overview
Problem
Avalanche photodiodes (APDs) face significant challenges in controlling the breakdown voltage, which varies due to uncontrolled dopant diffusion and local process parameters, leading to inconsistent performance across APD arrays, particularly in applications like imaging sensors, where uniformity is critical.
Innovation Solution
The introduction of a diffusion mask with a second diffusion window acts as a diffusion sink to control the depth of the p-n junction, mitigating variations in breakdown voltage by limiting additional dopant availability, thus ensuring uniform breakdown voltages across APD arrays.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If dopant diffusion is performed to form the p-n junction, then the device region is created, but uncontrolled dopant diffusion causes variation in breakdown voltage across wafer
Solution Approach 1:
The diffusion mask is segmented into multiple regions: a first diffusion window for forming the device region and a second diffusion window for forming the diffusion sink. This segmentation allows independent control of dopant diffusion into the device region versus the sink region, enabling precise control of p-n junction depth and breakdown voltage uniformity.
Solution Approach 2:
The diffusion sink acts as an intermediary element that captures excess dopant atoms during diffusion. By positioning the second diffusion window to receive dopant that would otherwise diffuse uncontrollably, the diffusion sink mediates the dopant distribution process and prevents breakdown voltage variation.
2Manufacturing precision
If individual breakdown voltage measurement and compensation is performed, then breakdown voltage variation is corrected, but inspection cost and device complexity increase
Solution Approach 1:
The diffusion sink is formed during the manufacturing process itself, before final device assembly and testing. By pre-configuring the diffusion mask with the second window to create the diffusion sink, the system performs preliminary control of dopant distribution, eliminating the need for post-fabrication measurement and compensation of breakdown voltage.
Solution Approach 2:
The diffusion sink provides self-regulating dopant absorption during the diffusion process. The structure automatically adjusts dopant distribution based on local conditions, with the second diffusion window absorbing excess dopant as needed, thereby achieving breakdown voltage uniformity without external intervention or complex control circuitry.
3Manufacturing precision
If dopant diffusion depth is increased to control breakdown voltage, then breakdown voltage is adjusted, but dopant distribution uniformity across wafer deteriorates
Solution Approach 1:
The diffusion mask implements local quality by providing different diffusion characteristics in different regions. The first diffusion window allows controlled dopant entry for device formation, while the second diffusion window provides localized dopant absorption in areas where excess dopant would cause non-uniformity. This spatially-varying dopant management maintains uniform p-n junction depth and breakdown voltage across the entire wafer.
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 results in substantially uniform breakdown voltages across APD arrays, reducing the need for costly inspection methods and complex control circuitry, and enhancing the performance and reliability of APD arrays in applications such as imaging sensors.
Implementation Method 1
The introduction of a diffusion mask with a second diffusion window acts as a diffusion sink to control the depth of the p-n junction, mitigating variations in breakdown voltage by limiting additional dopant availability
Data Source
AI summary
Avalanche photodiodes and methods for forming them are disclosed. The breakdown voltage of an avalanche photodiode is controlled through the inclusion of a diffusion sink that is formed at the same time as the device region of the photodiode. The device region and diffusion sink are formed by diffusing a dopant into a semiconductor to form a p-n junction in the device region. The dopant is diffused through a first diffusion window to form the device region and a second diffusion window to form the diffusion sink. The depth of the p-n junction is based on an attribute of the second diffusion window.