Conductive Pixel Separation Trenches for Low Cross-Talk Image Sensors
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Solution Overview
Problem
Highly integrated image sensors face challenges with increased cross-talk between pixels due to scaling down, leading to poor dark current properties.
Innovation Solution
The implementation of a substrate with adjacent pixel regions separated by a trench containing a conductive common bias line and an insulating device isolation layer, along with a channel stop region of opposite conductivity type, to reduce cross-talk and improve dark current properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If pixels are scaled down to increase integration density, then productivity and integration density are improved, but cross-talk between pixels increases and dark current properties deteriorate
Solution Approach 1:
The pixel array is divided into discrete pixel regions separated by deep trenches. Each pixel region is isolated from its neighbors by these trenches, preventing electrical cross-talk while maintaining high integration density. The segmentation is achieved through etching deep trenches between adjacent pixels and filling them with insulating material.
Solution Approach 2:
An insulating layer is introduced as an intermediary substance within the deep trenches to electrically isolate adjacent pixel regions. This intermediary prevents direct electrical interaction between pixels, reducing cross-talk and improving dark current properties while allowing pixels to remain closely spaced for high integration.
2Reliability
If deep trenches are introduced to reduce cross-talk, then dark current properties are improved, but device complexity and manufacturing difficulty increase
Solution Approach 1:
The pixel separation structure is merged with the existing device isolation architecture. The deep trenches serve dual purposes: they provide electrical isolation between pixels and integrate with the device isolation layers already present in the CMOS image sensor structure, reducing overall complexity.
Solution Approach 2:
The deep trench structure performs multiple functions simultaneously: it acts as an electrical isolation barrier between pixels, provides mechanical support, and integrates with the device isolation system. This multi-functionality reduces the need for additional separate structures, simplifying the overall device design.
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 the dark current properties of image sensors by reducing cross-talk and increasing integration density while maintaining high image quality.
Implementation Method 1
Each of the pixels may include a photodiode (PD), which converts incident light into electric signal
Implementation Method 2
The trench includes a conductive common bias line therein and an insulating device isolation layer between the common bias line and surfaces of the trench
Data Source
AI summary
An image sensor includes a substrate having adjacent pixel regions and respective photodiode regions therein, and a pixel separation portion including a trench extending into the substrate between the adjacent pixel regions. The trench includes a conductive common bias line therein and an insulating device isolation layer between the common bias line and surfaces of the trench. A conductive interconnection is coupled to the common bias line and is configured to provide a negative voltage thereto. Related fabrication methods are also discussed.