Image Sensor Metal Grid Reduces Optical Crosstalk
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Solution Overview
Problem
Image sensors with split pixel structures face issues with optical crosstalk due to high angle light from adjacent large photodiodes, leading to saturation and reduced sensing ability, especially in high intensity light conditions.
Innovation Solution
A metal grid is introduced between small and large photodiodes to absorb or reflect high angle light, reducing optical crosstalk and enhancing light sensitivity by positioning metal elements within a buffer layer and on top of pixel isolators, thereby isolating small photodiodes from neighboring large photodiodes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a metal grid is introduced to reduce optical crosstalk, then light sensitivity is improved, but device complexity increases
Solution Approach 1:
A metal grid is introduced as an intermediary element positioned between the small photodiodes and large photodiodes. The grid acts as a mediator that selectively blocks high-angle light paths from large photodiodes to small photodiodes while allowing normal operation of the photodiodes themselves, thus reducing optical crosstalk without requiring fundamental changes to the photodiode structure
Solution Approach 2:
The metal grid is positioned in a buffer layer above the pixel isolators, adding a new spatial dimension (vertical layering) to the isolation strategy. This third-dimensional approach complements the traditional lateral isolation by pixel isolators, creating a multi-layered isolation architecture that effectively blocks oblique light paths without increasing lateral footprint
2Object-affected harmful factors
If pixel isolators are used to separate photodiodes, then optical crosstalk is reduced, but manufacturing complexity increases
Solution Approach 1:
The isolation architecture is segmented into two distinct components: pixel isolators for lateral separation and a metal grid for vertical/oblique light blocking. This segmentation allows each component to perform its specific isolation function optimally, with pixel isolators handling lateral light paths and the metal grid handling high-angle oblique light paths, thereby reducing overall optical crosstalk through divided functional responsibility
3Reliability
If photodiodes of different sizes are used for HDR sensing, then imaging performance is improved, but optical crosstalk increases
Solution Approach 1:
The metal grid is selectively positioned around small photodiodes rather than uniformly across the entire sensor array. This localized approach applies the anti-crosstalk measure specifically where needed - at the boundaries between small and large photodiodes - rather than uniformly across all photodiodes, thereby reducing optical crosstalk for HDR imaging while minimizing the overall impact on device complexity and light sensitivity
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 configuration effectively minimizes optical crosstalk, improves high intensity light sensing, and enhances the overall performance of image sensors, particularly in High Dynamic Range (HDR) imaging applications.
Implementation Method 1
A metal grid is introduced between small and large photodiodes to absorb or reflect high angle light, reducing optical crosstalk
Implementation Method 2
A metal grid is introduced between small and large photodiodes to absorb or reflect high angle light, reducing optical crosstalk
Data Source
AI summary
Image sensors include a substrate material having a plurality of small photodiodes (SPDs) and a plurality of large photodiodes (LPDs) disposed therein. A plurality of pixel isolators is formed in the substrate material, each pixel isolator being disposed between one of the SPDs and one of the LPDs. A passivation layer is disposed on the substrate material and a buffer layer is disposed on the passivation layer. A plurality of first metal elements is disposed in the buffer layer, each first metal element being disposed over one of the pixel isolators, and a plurality of second metal elements is disposed over the plurality of first metal elements.