Image Sensor Conductive Trench Isolation for Dark Current Suppression
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Solution Overview
Problem
Current CMOS image sensors face challenges in minimizing dark current, which affects their performance, especially in low-light conditions and high-temperature environments, due to the diffusion of photo-generated charges across pixel boundaries.
Innovation Solution
The design incorporates a semiconductor substrate with a grid-like device isolation structure and conductive patterns in trenches, where a negative voltage is applied to specific conductive patterns to suppress charge diffusion and enhance dark current characteristics by eliminating positive charges, thereby improving image sensor performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If conventional device isolation structures are used, then manufacturing is simpler, but dark current increases due to charge diffusion across pixel boundaries
Solution Approach 1:
The device isolation structure is segmented into multiple conductive patterns (first conductive pattern in first trench, second conductive pattern in second trench) with different depths and configurations. This segmentation allows each conductive pattern to perform specific functions in suppressing charge diffusion at different locations, thereby reducing dark current while maintaining manageable structural complexity
Solution Approach 2:
Different conductive patterns are positioned at different locations and depths within the pixel region. The first conductive pattern is in a first trench extending from the first surface, while the second conductive pattern is in a shallower second trench. This local differentiation optimizes charge suppression at specific critical areas where charge diffusion occurs, effectively reducing dark current without requiring uniform complex structures throughout
2Object-affected harmful factors
If deeper trenches are used for device isolation, then charge diffusion is better suppressed, but manufacturing precision requirements increase
Solution Approach 1:
Instead of using uniformly deep trenches throughout, the patent employs partial depth variation where the first trench extends deeper than the second trench. The first conductive pattern is positioned in the deeper first trench to provide strong charge suppression where needed, while the second conductive pattern in the shallower second trench provides additional suppression at different locations. This partial depth differentiation effectively suppresses charge diffusion while avoiding the manufacturing precision challenges of uniformly deep trenches
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 approach effectively reduces dark current, enhancing the image sensor's ability to capture high-quality images in various lighting conditions and improving overall performance by minimizing noise and improving sensitivity.
Implementation Method 1
a negative voltage is applied to specific conductive patterns to suppress charge diffusion and enhance dark current characteristics by eliminating positive charges
Implementation Method 2
Image sensor convert photonic images into electrical signals
Data Source
AI summary
An image sensor including a semiconductor substrate having a first surface and a second surface, and a pixel region having a photoelectric conversion region; a first conductive pattern in a first trench defining the pixel region and extending from the first surface toward the second surface; a second conductive pattern in a second trench shallower than the first trench and defined between a plurality of active patterns on the first surface of the pixel region; a transfer transistor and a plurality of logic transistors on the active patterns; and a conductive line on the second surface and electrically connected to the first conductive pattern.