BSI Image Sensor Reflective Grid Reduces Pixel Cross-Talk
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Solution Overview
Problem
Back Side Illumination (BSI) image sensors face challenges with increasing cross-talk between neighboring pixel sensors as they shrink in size, reducing light collection efficiency and sensitivity, especially in low light environments.
Innovation Solution
A reflective grid is introduced surrounding and separating pixel sensors, comprising a low-n structure and isolation structures like deep trench isolation, which directs and reflects light to the pixel sensors, reducing cross-talk and enhancing light absorption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If pixel sensors are shrunk in size to increase integration density, then device integration is improved, but cross-talk between neighboring pixel sensors increases
Solution Approach 1:
The patent introduces isolation structures that divide and separate neighboring pixel sensors into distinct regions. These isolation structures create physical and optical boundaries between adjacent pixels, preventing light from one pixel from interfering with neighboring pixels. This segmentation approach allows pixel sensors to be closely packed for high integration density while maintaining optical isolation to reduce cross-talk.
Solution Approach 2:
The patent employs intermediate structures positioned between neighboring pixel sensors to mediate the optical interaction. These intermediary isolation structures act as barriers that block or redirect stray light, preventing direct optical coupling between adjacent pixels. The intermediary elements enable close pixel spacing without sacrificing optical isolation performance.
2Productivity
If pixel sensors are shrunk in size to increase integration density, then device integration is improved, but light collection efficiency decreases
Solution Approach 1:
The patent addresses the light collection problem by extending the isolation structures in multiple dimensions - both vertically (depth into the substrate) and laterally (width at the surface). This multi-dimensional approach creates effective optical barriers that block stray light paths without requiring excessive lateral spacing between pixels, thereby maintaining high integration density while improving light collection efficiency.
Solution Approach 2:
The patent utilizes curved or tapered isolation structures that extend deeper into the substrate with a curved profile. This curved geometry is more effective at blocking oblique light paths compared to straight vertical walls, as the curvature creates multiple internal reflections and blocks light from reaching adjacent pixels at various angles. This enables better optical isolation and light collection within the same footprint.
3Object-affected harmful factors
If isolation structures are introduced to reduce cross-talk, then cross-talk is reduced, but device complexity increases
Solution Approach 1:
The patent combines multiple functions into the isolation structures - they simultaneously serve as cross-talk barriers, light collection enhancers, and potential electrical isolation elements. By merging these functions into a single integrated structure rather than adding separate components for each function, the patent reduces overall device complexity while achieving multiple performance goals.
Solution Approach 2:
The isolation structures are designed to perform multiple functions: optical isolation to reduce cross-talk, light trapping to enhance pixel sensitivity, and potentially electrical isolation. This multi-functionality means that a single structural element addresses multiple problems, reducing the need for additional separate components and thereby limiting the increase in device complexity.
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
The solution effectively reduces cross-talk and improves the sensitivity and performance of BSI image sensors by trapping light within the pixel sensors, increasing their absorption efficiency.
Implementation Method 1
A reflective grid is introduced surrounding and separating pixel sensors, comprising a low-n structure and isolation structures like deep trench isolation, which directs and reflects light to the pixel sensors
Implementation Method 2
The solution effectively reduces cross-talk and improves the sensitivity and performance of BSI image sensors by trapping light within the pixel sensors, increasing their absorption efficiency
Data Source
AI summary
A BSI image sensor includes a substrate including a front side and a back side opposite to the front side, a pixel sensor disposed in the substrate, an isolation structure surrounding the pixel sensor and disposed in the substrate, a dielectric layer disposed over the pixel sensor on the front side of the substrate, and a plurality of conductive structures disposed in the dielectric layer and arranged to align with the isolation structure.