CMOS Image Sensor Pixel Layout for Dark Current Balance
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Solution Overview
Problem
The existing solid-state imaging devices face challenges in achieving higher image quality due to increased dark current differences between effective and optical black (OPB) pixel regions, leading to inadequate black level adjustment and image degradation.
Innovation Solution
The solid-state imaging device is configured with a substrate having a pixel region divided into effective and OPB pixel regions, where the OPB pixel region has a smaller area occupied by the dug structure compared to the effective pixel region, and a p-type semiconductor region is formed adjacent to the dug structure in the substrate to absorb electrons generated by substrate damage, reducing dark current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If a trench part is formed in the substrate between adjacent pixels to reduce dark current, then dark current is reduced in effective pixel regions, but the difference in dark current between effective and OPB pixel regions increases, degrading image quality
Solution Approach 1:
The patent applies different trench part configurations to different regions: effective pixel regions have trench parts formed between adjacent pixels, while OPB pixel regions have no trench parts or smaller area trench parts. This local differentiation allows dark current reduction in effective regions without creating excessive dark current differences that would degrade black level adjustment accuracy.
Solution Approach 2:
The pixel region is segmented into effective pixel regions and OPB pixel regions with different trench part configurations. This segmentation allows independent optimization of each region's dark current characteristics, resolving the contradiction between dark current reduction and black level adjustment accuracy.
2Ease of manufacture
If trench parts are formed in both effective and OPB pixel regions with equal area percentages, then manufacturing is simplified, but dark current differences between regions increase and image quality degrades
Solution Approach 1:
Different area percentages of trench parts are used in different regions: effective pixel regions use larger area percentages for dark current reduction, while OPB pixel regions use smaller or zero area percentages to maintain appropriate dark current levels. This local quality differentiation resolves the contradiction between manufacturing simplicity and dark current control precision.
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 configuration reduces dark current in both effective and OPB pixel regions, minimizing their difference and enhancing image quality by effectively absorbing electrons generated due to substrate damage during trench formation.
Implementation Method 1
electrons generated due to damage (defect) of the substrate caused by formation of the trench part are absorbed by holes of the p-type semiconductor region and a dark current is reduced accordingly
Data Source
AI summary
Provided is a solid-state imaging device capable of obtaining an image with a higher image quality. The solid-state imaging device includes a substrate, a pixel region formed on the substrate and configured such that a plurality of pixels is arrayed therein, a dug structure formed in the pixel region, and a p-type semiconductor region formed in a region adjacent to the dug structure in the substrate. Further, the pixel region is divided into an effective pixel region where effective pixels including photoelectric conversion units not shielded from light are arrayed and an OPB pixel region formed adjacent to the effective pixel region and configured such that light shielding pixels including photoelectric conversion units shielded from light are arrayed therein. In addition, in plan view, the percentage of an area occupied by the dug structure in the OPB pixel region is smaller than the percentage of an area occupied by the dug structure in the effective pixel region.