Shared Ground Contact in CMOS Pixel Arrays
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Solution Overview
Problem
Conventional image sensor devices with CMOS pixel arrays experience increased ground resistance due to the lack of a sufficient ground connection, leading to uneven output responses across the pixel array, resulting in dark or bright spots in the image.
Innovation Solution
Incorporating a shared ground contact between pixels in the pixel array to reduce ground resistance, while maintaining electrical and optical isolation, by forming a p-type region on a substrate with an n-type layer or region between the substrate and the p-type region, and using shallow trench isolations to isolate adjacent pixels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an n-type substrate or n-epi layer is used to reduce dark current and cross-talk between pixels, then electrical and optical isolation between adjacent pixels is improved, but ground resistance across the pixel array increases
Solution Approach 1:
The pixel array is divided into multiple pixel cells, each with its own ground contact. This segmentation allows each pixel to have a dedicated ground path, reducing the overall ground resistance while maintaining the isolation benefits of the n-type substrate structure.
Solution Approach 2:
An intermediate ground contact structure is introduced between the n-type substrate and the p-type pixel region. This intermediary ground contact provides a low-resistance path for ground current while maintaining the electrical isolation properties of the n-type substrate through the barrier region.
2Device complexity
If a surface p-type region with ground strap is used as the only ground conductor, then device complexity is reduced, but output response uniformity across the pixel array deteriorates
Solution Approach 1:
Instead of a single ground strap, multiple ground contacts are distributed across the pixel array. This segmentation of the ground conductor system reduces the resistance drop across the array, ensuring more uniform output response while adding manageable complexity to the ground conductor structure.
3Manufacturing precision
If ground resistance is reduced by adding more ground contacts, then output response uniformity is improved, but device complexity increases
Solution Approach 1:
Adjacent pixels share common ground contacts, merging the ground conductor resources. This approach reduces the total number of ground contacts needed compared to having a dedicated ground contact for each pixel, thereby reducing device complexity while still improving output response uniformity across the array.
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
The shared ground contact reduces ground resistance across the pixel array, improving image quality by ensuring consistent output responses and enhancing the fill factor of the pixel array.
Implementation Method 1
an n-type layer or region may reside between the substrate and the p-type region
Implementation Method 2
a ground contact shared by at least two pixels of the array and configured to reduce the ground resistance across the pixel array
Implementation Method 3
Each image pixel of the array is configured for sensing light incident on the image pixel and comprises a photosensitive area within a p-type region for accumulating photo-generated charges within the area
Data Source
AI summary
Methods, devices, and systems for an image sensor device are disclosed. An image sensor device comprises an array of image pixels wherein each pixel is configured for sensing light incident on the pixel. An image sensor device may further comprise a ground contact shared between at least two image pixels of the plurality. The ground contacts may be provided in an even pattern, a random pattern, or a repeating random pattern across the array. The image sensor device may further include an array of shared pixel structures comprising a plurality of pixels, wherein a ground contact may be evenly or randomly placed within each pixel structure across the array of pixel structures.