Image Sensor Isolation Structure for Crosstalk Reduction
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Solution Overview
Problem
As the degree of integration of CMOS image sensors increases, the area of photodiodes decreases, leading to deteriorated sensitivity and dynamic range, and increased optical noise such as cross-talk.
Innovation Solution
An isolation structure is introduced with a deep well region and an isolation region of higher impurity concentration, connected to the deep well region, to electrically isolate charge accumulation regions, and an electrode forms an electric field in the isolation region to accumulate photo-charges, improving the area of photodiodes and reducing noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the degree of integration of CMOS image sensor is improved, then the area of photodiode is decreased, but the sensitivity and dynamic range are deteriorated
Solution Approach 1:
The patent introduces a deep well region extending vertically into the substrate beneath the photodiode, utilizing the third dimension (depth) to collect photocharges. This allows the photodiode surface area to be reduced for higher integration while maintaining charge collection capability through the vertical deep well structure, thereby resolving the contradiction between integration density and sensitivity.
2Productivity
If the degree of integration of CMOS image sensor is improved, then the area of photodiode is decreased, but the optical noise such as cross-talk is increased
Solution Approach 1:
The patent introduces an isolation region filled with material having different optical properties (such as silicon nitride or oxide) between adjacent photodiodes. This intermediary layer acts as an optical barrier that blocks stray light and prevents cross-talk between neighboring pixels, allowing higher integration density without compromising signal quality.
3Reliability
If isolation structure area is increased, then charge accumulation regions are electrically isolated, but the area of photodiode is decreased
Solution Approach 1:
The isolation structure is segmented into two functional parts: a shallow isolation region at the surface level and a deep well region extending vertically. This segmentation allows effective electrical isolation of charge accumulation regions while minimizing the lateral footprint, thereby preserving photodiode area for higher integration density.
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 solution significantly enhances the dynamic range and sensitivity of the image sensor by increasing the area of photodiodes and reducing dark current and cross-talk, while maintaining a relatively small area for the isolation structure.
Implementation Method 1
an isolation region disposed between charge accumulation regions for accumulating photo-charges in order to electrically isolate the charge accumulation regions from each other. Particularly, the charge accumulation regions may be disposed on the deep well region and have the second conductive type, and the isolation region may be connected with the deep well region and have the first conductive type.
Implementation Method 2
an insulating layer disposed on the isolation region and an electrode disposed on the insulating layer and forming an electric field in the isolation region so as to accumulate second photo-charges in the isolation region
Implementation Method 3
forming an electric field in the isolation region so as to accumulate second photo-charges in the isolation region
Implementation Method 4
the photodiode includes a p-type surface layer and an n-type charge accumulation region, and when incident light strikes the surface of the photodiode, electrons (photo-charges) are generated in the depletion region of the p-n junction of the photodiode
Data Source
AI summary
Disclosed is an image sensor having an isolation structure. The isolation structure includes a deep well region of a first conductive type disposed in a substrate of a second conductive type and an isolation region disposed between charge accumulation regions for accumulating photo-charges in order to electrically isolate the charge accumulation regions from each other. The charge accumulation regions are disposed on the deep well region and have the second conductive type. The isolation region is connected with the deep well region and has the first conductive type.