Dual Grid Pixel Isolation for Low Cross-Talk Image Sensors
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Solution Overview
Problem
Image sensors face challenges with cross-talk between adjacent light detection regions, particularly as pixel sizes decrease below 1 micron, leading to degraded performance and reduced quantum efficiency due to metallic structures blocking photon penetration.
Innovation Solution
An optical structure incorporating a grid structure with a primary and secondary grid, where the secondary grid has a lower refractive index than the color filter, helps alleviate cross-talk by guiding light to the intended detection region while minimizing quantum efficiency loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If pixel size is decreased to increase resolution, then measurement precision is improved, but cross-talk between adjacent light detection regions increases
Solution Approach 1:
The patent divides the light blocking function into multiple segments: a first grid structure and a second grid structure. The first grid is formed in the substrate and the second grid is formed in the color filter layer, creating a segmented approach to block light paths between adjacent pixels. This segmentation allows effective cross-talk prevention at sub-micron pixel sizes by addressing light blocking at multiple spatial levels.
Solution Approach 2:
The patent extends the light blocking solution from a single plane to multiple dimensions by forming grids in both the substrate layer and the color filter layer. This multi-layer grid arrangement blocks light paths in three-dimensional space, effectively preventing cross-talk while maintaining small pixel dimensions for high resolution.
2Object-affected harmful factors
If metallic structures are used to block light paths, then cross-talk is reduced, but quantum efficiency decreases due to photon blocking
Solution Approach 1:
The patent extracts the light blocking function from metallic structures and implements it using dielectric grid structures instead. By removing the metallic component and using dielectric materials with appropriate refractive indices, the solution blocks cross-talk through refractive index mismatches rather than metallic absorption, thereby preserving quantum efficiency.
Solution Approach 2:
The patent changes the material parameter from metallic to dielectric and optimizes the refractive index of the dielectric material. The second grid structure uses a dielectric material with refractive index between 1.3 and 1.7, which is lower than the color filter material, creating effective light blocking through refractive index contrast without the photon absorption losses of metals.
3Device complexity
If a single grid structure is used, then device complexity is low, but cross-talk reduction effectiveness is insufficient at sub-micron pixel sizes
Solution Approach 1:
The patent segments the light blocking function into two distinct grid structures positioned at different layers: the first grid in the substrate and the second grid in the color filter layer. This segmentation provides comprehensive cross-talk prevention at sub-micron pixel sizes by blocking light paths at multiple spatial locations without excessive complexity.
Solution Approach 2:
The patent implements a nested structure where the second grid is formed within the color filter layer that itself is positioned over the substrate containing the first grid. This nested arrangement of grids at different hierarchical levels achieves effective cross-talk blocking while maintaining a compact and integrated device structure.
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 grid structure effectively reduces cross-talk between adjacent pixels without significantly compromising quantum efficiency, even at sub-micron pixel sizes, by reflecting light within the color filter and ensuring it reaches the intended detection region.
Implementation Method 1
The grid structure effectively reduces cross-talk between adjacent pixels without significantly compromising quantum efficiency, even at sub-micron pixel sizes, by reflecting light within the color filter and ensuring it reaches the intended detection region.
Implementation Method 2
the secondary grid has a lower refractive index than the color filter, helps alleviate cross-talk by guiding light to the intended detection region
Data Source
AI summary
The present disclosure provides an optical structure and a method for fabricating an optical structure, the method includes forming a light detection region in a substrate, forming an isolation structure at surrounding the light detection region, and forming a primary grid over the isolation structure, including forming a metal layer over the isolation structure, forming a first dielectric layer over the metal layer, and partially removing the metal layer and the first dielectric layer with a first mask by patterning, and forming a secondary grid at least partially surrounded by the primary grid laterally.