Composite Grid Structure for BSI Image Sensor Cross Talk Reduction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Back Side Illumination (BSI) image sensors face challenges with cross talk between neighboring pixel sensors and reduced light collection due to their decreasing size, which affects quantum efficiency, angular response, and signal-to-noise ratio (SNR) in low light environments.
Innovation Solution
A semiconductor structure with a composite grid comprising a metal grid and a low refractive index (low-n) grid is used to provide optical isolation and act as a light guide, increasing the effective size of color filters by directing incident light to their centers, while the color filters' upper surfaces are offset relative to the composite grid to reduce cross talk and improve light collection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If pixel sensors are reduced in size to increase integration density, then device integration is improved, but cross talk between neighboring pixel sensors increases and light collection area decreases
Solution Approach 1:
The patent introduces an intermediate structure (optical isolation layer or absorptive material) positioned between neighboring pixel sensors to block stray light paths. This mediator prevents cross-talk by absorbing or blocking photons that would otherwise leak between adjacent pixels, enabling higher integration density without sacrificing signal fidelity.
Solution Approach 2:
The patent applies different optical properties to different regions of the sensor structure. Specifically, the optical isolation structures are strategically placed only in regions where cross-talk is problematic (between pixels), while the pixel active areas maintain their light-sensitive properties. This localized application of optical isolation preserves quantum efficiency while reducing cross-talk.
2Productivity
If pixel sensors are reduced in size to increase integration density, then device integration is improved, but light collection area decreases affecting quantum efficiency
Solution Approach 1:
The patent addresses the light collection problem by extending the optical isolation structures into the vertical dimension (depth) rather than only lateral dimensions. By creating multi-layered or three-dimensional isolation structures, the patent effectively blocks cross-talk paths without reducing the lateral pixel size, thereby maintaining both high integration density and quantum efficiency.
3Object-affected harmful factors
If optical isolation structures are added to reduce cross talk, then cross talk is reduced, but device complexity increases
Solution Approach 1:
The patent combines multiple functions into the optical isolation structures. These structures simultaneously serve as cross-talk barriers, mechanical support elements, and in some embodiments, as part of the color filter array or microlens support structure. By merging functions, the patent reduces overall device complexity while maintaining effective cross-talk isolation.
Solution Approach 2:
The optical isolation structures are designed to perform multiple roles: blocking stray light between pixels, providing mechanical support for overlying structures, and in some embodiments, serving as part of the optical path management system. This multi-functionality reduces the need for separate dedicated components, 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 enhances quantum efficiency and angular response, reducing the minimum luminance required for a good SNR under oblique incident light, thereby improving the performance of BSI image sensors in low light conditions.
Implementation Method 1
a low refractive index (low-n) grid overlying the metal grid. The low-n grid has a refractive index less than the color filters, thereby isolating neighboring color filters and serving as a light guide to increase the effective size of the color filters
Implementation Method 2
The low-n grid has a refractive index less than the color filters, thereby isolating neighboring color filters
Data Source
AI summary
A semiconductor structure for back side illumination (BSI) pixel sensors is provided. Photodiodes are arranged within a semiconductor substrate. A composite grid includes a metal grid and a low refractive index (low-n) grid. The metal grid includes first openings overlying the semiconductor substrate and corresponding to ones of the photodiodes. The low-n grid includes second openings overlying the semiconductor substrate and corresponding to ones of the photodiodes. Color filters are arranged in the first and second openings of the corresponding photodiodes and have a refractive index greater than a refractive index of the low-n grid. Upper surfaces of the color filters are offset relative to an upper surface of the composite grid. A method for manufacturing the BSI pixel sensors is also provided.