CMOS Image Sensor Crosstalk Reduction via Deep Dopant Regions
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Solution Overview
Problem
CMOS image sensors face significant challenges with crosstalk, particularly electrical crosstalk, which leads to reduced sensitivity and image quality issues due to charge carrier diffusion between pixels, especially in high luminous environments and with smaller pixel sizes.
Innovation Solution
The implementation of a CMOS image sensor design featuring a N type epitaxial layer and deep dopant regions to attract and trap photo-generated charge carriers, combined with buried wells and barrier layers to prevent lateral migration and enhance red sensitivity, while using shallow trench isolations and graded doping to reduce crosstalk between adjacent pixels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If pixel size is reduced to increase resolution, then higher resolution is achieved, but electrical crosstalk increases due to charge carrier diffusion between adjacent pixels
Solution Approach 1:
The patent divides the semiconductor structure into distinct segmented regions including deep dopant regions, buried wells, and isolation structures that physically separate adjacent pixels. These segments create electrical boundaries that prevent charge carrier diffusion between pixels while maintaining small pixel dimensions for high resolution imaging.
Solution Approach 2:
The patent applies different doping concentrations and types in specific local regions beneath each pixel. Deep dopant regions with high doping concentrations are placed at certain depths, while buried wells with different doping characteristics are positioned at other depths, creating localized electrical properties that trap charge carriers within each pixel's collection region and prevent lateral diffusion to neighboring pixels.
2Object-affected harmful factors
If deep dopant regions and buried wells are added to reduce crosstalk, then electrical crosstalk is minimized, but device complexity increases
Solution Approach 1:
The patent combines multiple anti-crosstalk mechanisms into a unified vertical structure beneath each pixel. The deep dopant regions, buried wells, and isolation structures are integrated in a stacked configuration that addresses electrical crosstalk through their collective action, rather than requiring separate independent structures for each function.
Solution Approach 2:
The patent transitions from two-dimensional planar isolation methods to three-dimensional vertical structuring. By adding depth dimensions with dopant regions at different depths (deep dopant regions at greater depth, buried wells at intermediate depth), the patent achieves crosstalk reduction through vertical electrical field management rather than relying solely on lateral isolation structures.
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 design effectively minimizes crosstalk and enhances red sensitivity by trapping charge carriers and reducing lateral diffusion, resulting in improved image quality and reduced blurring or streaking in images.
Implementation Method 1
Photons impinging on the PD regions 105 are absorbed in the silicon, creating photo-generated electron-hole pairs
Implementation Method 2
N type epitaxial layer and deep dopant regions to attract and trap photo-generated charge carriers
Implementation Method 3
lateral diffusion of charge carriers when a PD region becomes full or saturated with charge carriers
Implementation Method 4
buried wells and barrier layers to prevent lateral migration
Data Source
AI summary
A color pixel array includes first, second, and third pluralities of color pixels each including a photosensitive region disposed within a first semiconductor layer. In one embodiment, a second semiconductor layer including deep dopant regions is disposed below the first semiconductor layer. The deep dopant regions each reside below a corresponding one of the first plurality of color pixels but substantially not below the second and third pluralities of color pixels. In one embodiment, buried wells are disposed beneath the second and third pluralities of color pixels but substantially not below the first plurality of color pixels.