CMOS Image Sensor Grid Isolation for Edge Pixel Uniformity
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Solution Overview
Problem
CMOS image sensors face challenges with reduced quantum efficiency and non-uniform pixel performance, particularly at edge regions, due to continually reduced pixel sizes in pursuit of higher resolution.
Innovation Solution
A composite grid isolation structure is introduced, comprising a first and second low refractive index dielectric grid and a metal grid, along with global and inner shifts of color filter matrixes, to enhance quantum efficiency and performance uniformity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If pixel sizes are reduced to increase resolution, then device density and resolution are improved, but quantum efficiency deteriorates due to inadequate light collection area
Solution Approach 1:
The patent introduces a three-dimensional isolation structure with vertical trenches and stacked dielectric layers (first, second, and third isolation structures at different depths) to manage light paths in the vertical dimension, compensating for the reduced horizontal light collection area of smaller pixels
Solution Approach 2:
The patent employs dielectric materials with specific refractive indices as intermediary layers between the color filter and photodiode to enhance total internal reflection and redirect incident light toward the photodiode active area, improving quantum efficiency without increasing pixel size
2Quantity of substance
If pixel sizes are reduced to increase resolution, then device density is improved, but performance uniformity deteriorates due to non-uniform light distribution across the sensor
Solution Approach 1:
The patent implements location-dependent global shifts where color filter matrixes in edge regions are shifted by different amounts compared to center region matrixes, with shift amounts gradually increasing from center to edge to compensate for non-uniform light incidence angles and improve performance uniformity across the entire sensor
Solution Approach 2:
The patent varies the global shift parameter for color filter matrixes based on their location within the sensor array, creating a gradient of shift values that compensates for position-dependent optical performance variations
3Reliability
If color filter matrixes are shifted to improve performance uniformity in edge regions, then quantum efficiency in edge regions is improved, but manufacturing complexity increases due to precise alignment requirements
Solution Approach 1:
The patent pre-calculates and pre-establishes the global shift values for all color filter matrixes based on their locations, with center region matrixes having zero shift and edge region matrixes having gradually increasing shifts, allowing manufacturing to follow a predetermined pattern rather than requiring complex real-time adjustments
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 improves quantum efficiency and performance uniformity by enhancing total internal reflection and enlarging the space for color filters, compensating for reduced incident light in edge regions.
Implementation Method 1
improves quantum efficiency and performance uniformity by enhancing total internal reflection
Data Source
AI summary
A CMOS image sensor includes a unit pixel array including a photodiode array, a color filter array, a micro-lens array, and a grid isolation structure laterally separating adjacent color filters. The grid isolation structure includes a first low-n grid, a second low-n grid underlying the first low-n grid, and a metal grid within the second low-n grid, the first low-n grid being narrower than the second low-n grid. The color filter array includes color filter matrixes, all color filter matrixes have the same arrangement pattern. Sizes of color filters in each color filter matrix vary depending on locations of the color filters in the color filter matrix. In an edge portion, a distance between a center of a color filter matrix and a center of a corresponding unit pixel matrix in plan view varies depending on a location of the unit pixel matrix in the CMOS image sensor.