Deep Trench Isolation for CMOS Global Shutter Pixel Electron Drift
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Solution Overview
Problem
Current CMOS image sensors face picture quality degradation due to electron drift from the photodiode to other structures, particularly in global shutter mode imaging, where effective shielding is challenging and requires high shielding efficiencies of up to 3,000,000 to 1.
Innovation Solution
The implementation of deep trench isolation structures and buried deep trench isolation structures around the photodiode to prevent electron drift to the floating diffusion region, while allowing charge transfer from the photodiode to the transfer gate, using dielectric and conductive materials to form a diffusion shield and transistor channel region.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If deep trench isolation structures are implemented to prevent electron drift, then image quality is improved, but device complexity increases
Solution Approach 1:
The isolation structure is divided into two distinct segments: a deep trench isolation structure extending from the surface and a buried deep trench isolation structure beneath the photosensitive region. This segmentation allows each structure to perform its isolation function independently, effectively preventing electron drift while maintaining manufacturability through modular fabrication processes.
Solution Approach 2:
The solution extends the isolation approach into the vertical dimension by creating trenches at different depths. The deep trench isolation structure addresses surface-level electron drift, while the buried deep trench isolation structure prevents drift from deeper regions, providing comprehensive shielding through multi-dimensional spatial arrangement.
2Object-affected harmful factors
If total electron shielding is implemented with shielding efficiency of 3,000,000 to 1, then carrier drift prevention is improved, but manufacturing precision requirements increase
Solution Approach 1:
The deep trench isolation structure is formed first, establishing the primary isolation barrier before photosensitive region formation. Subsequently, the buried deep trench isolation structure is created to provide additional shielding. This preliminary action sequence ensures that isolation structures are in place before critical photosensitive regions are formed, reducing the precision requirements for subsequent steps.
Solution Approach 2:
The isolation structures serve as intermediary elements between the photosensitive region and surrounding circuitry. These intermediary trenches filled with dielectric material create physical and electrical barriers that prevent direct interaction between drifting carriers and sensitive regions, achieving high shielding efficiency without requiring extreme manufacturing precision.
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 effectively shields electrons from drifting to the floating diffusion, enhancing image quality by preventing carrier drift and allowing controlled electron transfer, thus improving the overall performance of CMOS image sensors.
Implementation Method 1
Electron shielding, though, is a difficult challenge, since total shielding efficiencies may be needed on the order of 3,000,000 to one
Data Source
AI summary
Pixel sensor cells, e.g., CMOS optical imagers, methods of manufacturing and design structures are provided with isolation structures that prevent carrier drift to diffusion regions. The pixel sensor cell includes a photosensitive region and a gate adjacent to the photosensitive region. The pixel sensor cell further includes a diffusion region adjacent to the gate. The pixel sensor cell further includes an isolation region located below a channel region of the gate and about the photosensitive region, which prevents electrons collected in the photosensitive region to drift to the diffusion region.