Pixel Array With Isolated Photodiodes For Charge Blooming
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Solution Overview
Problem
As pixel arrays become smaller, charge blooming becomes a significant issue due to the lack of effective isolation between photodiodes, leading to reduced accuracy and occupancy density in image sensors.
Innovation Solution
The use of a sacrificial replacement layer method to form side walls that isolate individual photodiodes, allowing for better isolation and reducing the space taken up by standard photolithography methods, thereby improving photodiode isolation and occupancy density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If standard photolithography methods are used to isolate photodiodes, then photodiode isolation is achieved, but occupancy density is reduced due to space taken up by isolation structures
Solution Approach 1:
The pixel array is divided into individual isolated photodiode regions separated by removal of substrate material. This segmentation approach creates electrical isolation between adjacent photodiodes while minimizing the space required for isolation structures compared to traditional continuous isolation layers.
Solution Approach 2:
Substrate material is selectively removed (taken out) from regions between photodiodes to create isolation. This extraction of material rather than addition of isolation layers reduces the overall space required for isolation, thereby improving occupancy density while maintaining photodiode isolation.
2Measurement precision
If pixel arrays are made smaller to increase resolution, then image sensor resolution is improved, but charge blooming increases due to reduced isolation effectiveness
Solution Approach 1:
The pixel array is divided into individual isolated photodiode regions separated by removal of substrate material. This segmentation approach creates electrical isolation between adjacent photodiodes while minimizing the space required for isolation structures compared to traditional continuous isolation layers.
Solution Approach 2:
Isolation is applied locally at each photodiode region through selective substrate removal, rather than using continuous isolation layers. This local quality approach provides effective charge containment for each individual photodiode, preventing blooming even in compact high-resolution arrays.
3Object-generated harmful factors
If more space is allocated to isolation structures to prevent charge blooming, then charge spreading is reduced, but occupancy density decreases
Solution Approach 1:
Substrate material is selectively removed (taken out) from regions between photodiodes to create isolation. This extraction of material rather than addition of isolation layers reduces the overall space required for isolation, thereby improving occupancy density while maintaining photodiode isolation.
Solution Approach 2:
Isolation is applied locally at each photodiode region through selective substrate removal, rather than using continuous isolation layers. This local quality approach provides effective charge containment for each individual photodiode, preventing blooming even in compact high-resolution arrays.
Data Source
AI summary
A pixel array includes a semiconductor substrate, a plurality of isolation layer segments, and a plurality of photodiodes. Each of the plurality of isolation layer segments extends through the semiconductor substrate in a first direction. Each of the plurality of isolation layer segments encloses a portion of the semiconductor substrate in a plane perpendicular to the first direction. The plurality of isolation layer segments form a grid that defines a plurality of isolated sections of the semiconductor substrate. The plurality of isolated sections of the semiconductor substrate include the portions of the semiconductor substrate. Each of the photodiodes is formed in a respective one of the plurality of isolated sections of the semiconductor substrate.