PIN Photodiode Overflow Contact Layout for ROIC Over-Current Protection
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Solution Overview
Problem
Conventional photodiodes in imaging devices face challenges with high dark current and sensitivity, leading to potential damage and increased stress on read-out integrated circuits (ROICs) at high light levels, which affects image quality.
Innovation Solution
The system includes a pixel design with an overflow contact laterally spaced from the diffusion layer, using a metallic overflow contact, a cap layer of InP, and multiple SiNx layers with a transparent conductive oxide (TCO) that conforms around the SiNx layer to contact the diffusion layer, allowing electrical connection to a ROIC while isolating excess current through a common current sink.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If photodiodes are designed for high sensitivity to detect more photons, then image quality improves, but excess current increases which may damage the detector and increase stress on the ROIC
Solution Approach 1:
The patent introduces a P-type overflow contact layer as an intermediary component between the N-type absorption layer and the ROIC. This overflow contact layer provides a dedicated pathway for excess electrons to be diverted away from the ROIC, thereby protecting the detector while maintaining high sensitivity for normal operation
Solution Approach 2:
The patent segments the current collection function by creating separate contact structures: a first contact for normal signal collection and a second overflow contact for excess current management. This segmentation allows the system to handle different current levels through different pathways, protecting the ROIC from damage while maintaining high sensitivity
2Reliability
If photodiodes are designed for low dark current to improve image quality, then detection capability improves, but the detector remains vulnerable to damage from high current at high light levels
Solution Approach 1:
The patent implements beforehand cushioning by pre-configuring the overflow contact structure and depletion region to intercept and divert excess current before it can reach and damage the ROIC. The depletion region acts as a protective barrier that activates when excess current conditions occur
Solution Approach 2:
The overflow contact layer serves as a protective intermediary that absorbs and redirects harmful excess current away from vulnerable components, thereby strengthening the detector's resistance to damage while preserving low dark current characteristics
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 reduces excess current, increases sensitivity, and alleviates stress on ROICs, thereby enhancing image quality and simplifying ROIC design and signal processing.
Implementation Method 1
A transparent conductive oxide (TCO) can be deposited on the SiNx layer, wherein the TCO conforms around the SiNx layer to contact the diffusion layer
Implementation Method 2
A SiNx layer can be deposited over the cap layer
Data Source
Figure 1
Figure 2
AI summary
A system includes a pixel including a diffusion layer in contact with an absorption layer. A transparent conductive oxide (TCO) is electrically connected to the diffusion layer. An overflow contact is in electrical communication with the TCO. The overflow contact can be spaced apart laterally from the diffusion layer. The pixel can be one of a plurality of similar pixels arranged in a grid pattern, wherein each pixel has a respective overflow contact, forming an overflow contact grid offset from the grid pattern.