Pixel Separation Layout for Image Sensors With Reduced Charge Crosstalk
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Solution Overview
Problem
Image sensors face challenges in reducing electric field concentration and obtaining pattern margins for forming transfer gates, which affect their performance and efficiency.
Innovation Solution
The image sensor design includes a substrate with a pixel separation pattern and a device separation layer, featuring a recessed region between transfer gates to reduce electric field concentration and provide patterning margins, thereby preventing charge drift and crosstalk between pixels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional pixel separation structure is used, then manufacturing is simpler, but electric field concentration occurs between adjacent transfer gates causing charge drift and crosstalk
Solution Approach 1:
The pixel separation pattern is divided into multiple segments: a first pixel separation part extending in a first direction and a second pixel separation part extending in a second direction intersecting the first direction. This segmented structure effectively reduces electric field concentration between adjacent transfer gates by distributing the separation function across multiple oriented parts, preventing charge drift and crosstalk between pixels while maintaining manufacturability
Solution Approach 2:
The pixel separation pattern is positioned specifically in the region between adjacent transfer gates where electric field concentration occurs. By concentrating the separation structure locally at the critical interface between pixels rather than uniformly across the entire pixel area, the design achieves effective charge isolation while minimizing overall structural complexity and maintaining manufacturing efficiency
2Productivity
If transfer gates are formed closer together to increase pixel density, then productivity increases, but electric field concentration causes charge leakage between pixels
Solution Approach 1:
The pixel separation pattern incorporates parts extending in different directions (first direction and second direction intersecting the first direction), creating a two-dimensional separation network. This multi-directional approach provides effective charge isolation even when transfer gates are positioned closely together, enabling high pixel density while maintaining reliable charge isolation through enhanced spatial separation in multiple dimensions
3Reliability
If a complex pixel separation pattern is used to prevent charge drift, then pixel separation effectiveness improves, but manufacturing precision requirements increase
Solution Approach 1:
The pixel separation pattern merges multiple separation functions into a single integrated structure that includes both first pixel separation parts and second pixel separation parts. This unified design achieves comprehensive charge isolation and electric field reduction while maintaining manufacturability, as the combined structure can be formed in a single fabrication process step rather than requiring multiple precise alignment steps
Data Source
AI summary
An image sensor includes a substrate, and a pixel separation pattern disposed in the substrate and interposed between a plurality of unit pixels. The plurality of unit pixels include a first unit pixel region and a second unit pixel region adjacent to the first unit pixel region in a first direction. The first unit pixel region and the second unit pixel region respectively include a first transfer gate and a second transfer gate. The pixel separation pattern includes a first pixel separation part interposed between the first unit pixel region and the second unit pixel region, and a second pixel separation part spaced apart from the first pixel separation part in the first direction. A top surface of the first pixel separation part is lower than a top surface of the second pixel separation part.