Image Sensor Barrier Doping Layout for Photodiode Crosstalk Control
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Solution Overview
Problem
Existing image sensors face challenges in reducing crosstalk between photodiodes, suppressing optical loss, and improving dark current characteristics.
Innovation Solution
The image sensor incorporates a substrate with pixel areas arranged along a specific direction, featuring photodiodes separated by device isolation layers and a potential barrier region doped with p-type impurities and carbon, which helps control charge movement and suppress diffusion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If photodiodes are placed closer together to increase pixel density, then productivity increases, but crosstalk between photodiodes increases
Solution Approach 1:
The patent introduces device isolation layers that divide and separate the photodiodes from each other. These isolation layers create physical boundaries between adjacent photodiodes, preventing charge carriers from leaking into neighboring pixels. This segmentation approach allows photodiodes to be placed closer together while maintaining electrical isolation, thus increasing pixel density without sacrificing signal integrity.
Solution Approach 2:
The device isolation layers act as intermediary structures between adjacent photodiodes. These layers, positioned in the semiconductor substrate between photodiodes, serve as mediators that block the direct interaction between neighboring photodiodes. By introducing this intermediate barrier, the patent enables higher photodiode density while preventing crosstalk through the isolating effect of the intermediary material.
2Object-generated harmful factors
If device isolation layers are added to reduce crosstalk, then crosstalk reduction improves, but device complexity increases
Solution Approach 1:
The patent combines multiple functions into the device isolation layers. These layers simultaneously serve as electrical isolation barriers to prevent crosstalk, as structural support elements, and as part of the overall device architecture. By merging these functions into a single integrated structure rather than adding separate components, the patent reduces the net increase in device complexity while achieving effective crosstalk suppression.
Solution Approach 2:
The device isolation layers are designed to perform multiple functions: electrical isolation between photodiodes, mechanical support for the pixel structure, and potential integration with other device components. This multi-functionality allows the same structural element to address crosstalk while contributing to overall device performance, thereby minimizing the penalty in device complexity.
3Object-generated harmful factors
If photodiodes are separated by larger distances to reduce crosstalk, then crosstalk reduction improves, but area per pixel increases
Solution Approach 1:
The device isolation layers create effective electrical segmentation between photodiodes without requiring large physical separations. By introducing these isolating structures, the patent achieves charge carrier confinement within each photodiode even when photodiodes are placed in close proximity. This allows minimal spacing between photodiodes while maintaining isolation, thus preventing crosstalk without increasing pixel area.
Solution Approach 2:
Instead of increasing horizontal separation distance between photodiodes, the patent introduces vertical isolation structures (device isolation layers extending through the substrate depth). This dimensional approach to isolation allows photodiodes to remain close in the horizontal plane while achieving effective electrical separation through the vertical dimension, thereby reducing crosstalk without increasing pixel footprint.
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 enhances crosstalk reduction, minimizes optical loss, and improves dark current characteristics, leading to improved performance in image sensing applications.
Implementation Method 1
the substrate further includes a potential barrier region between the photodiodes and between the pair of second device isolation layers, and the potential barrier region includes p-type impurities and carbon
Implementation Method 2
the first doped region adjacent to a sidewall of the second device isolation layers, and the first doped region includes p-type impurities and carbon
Implementation Method 3
in a first region of the first doped region where a distance from a surface adjacent to the second device isolation layers in a vertical direction is less than or equal to about 50 nm, a concentration of the p-type impurities is greater than a concentration of the carbon
Data Source
AI summary
An image sensor includes: a substrate having a first surface and a second surface opposite to the first surface in a first direction, the substrate including pixel areas arranged along a second direction parallel to the first surface; photodiodes in the substrate in each of the pixel areas and separated from each other in the second direction; a first device isolation layer between the pixel areas; and a pair of second device isolation layers extending between the photodiodes from the first device isolation layer along a third direction and being spaced apart from each other in the third direction, wherein the third direction is parallel to the first surface and different from the second direction, the substrate further includes a potential barrier region between the photodiodes and between the pair of second device isolation layers, and the potential barrier region includes p-type impurities and carbon.