Angled Pixel Grid Sidewalls for Light Collection and Crosstalk Isolation
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Solution Overview
Problem
CMOS image sensors face challenges in maximizing quantum efficiency due to optical crosstalk and light absorption by grid structures used to separate color filter regions, which reduces incident light collection and overall image sensor performance.
Innovation Solution
Implementing an angled or tapered grid structure in the pixel array, where the grid width approaches near-zero at the top surface to minimize spacing between color filter regions and increase light collection, while widening towards the bottom surface for optical crosstalk protection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a grid structure is used to separate color filter regions, then optical crosstalk between adjacent pixel sensors is reduced, but incident light is absorbed and reflected away from photodiodes, reducing quantum efficiency
Solution Approach 1:
The grid structure employs asymmetric geometry with a top surface at a first elevation and a bottom surface at a second elevation, creating non-uniform light interaction paths. This asymmetric design allows light to pass through the grid structure more effectively while still providing optical isolation between adjacent pixel sensors, thereby reducing both optical crosstalk and light absorption/reflection losses.
Solution Approach 2:
The grid structure extends in the vertical dimension with distinct top and bottom surfaces at different elevations, adding a third dimension to the optical isolation mechanism. This vertical dimensionality allows light to pass through the grid structure while maintaining separation between color filter regions, resolving the contradiction between optical crosstalk reduction and quantum efficiency maintenance.
2Loss of energy
If spacing between color filter regions is reduced, then quantum efficiency increases due to greater light collection surface area, but optical crosstalk protection decreases
Solution Approach 1:
The asymmetric grid structure with different top and bottom elevations allows color filter regions to be positioned closer together while maintaining optical isolation. The vertical asymmetry creates effective optical barriers even at reduced horizontal spacing, enabling both high quantum efficiency and optical crosstalk protection.
Solution Approach 2:
The grid structure is formed from a dielectric material that provides both mechanical support and optical isolation properties. This composite approach combines structural integrity with optical functionality, allowing reduced spacing between color filter regions while maintaining effective optical crosstalk protection through the dielectric material's properties.
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 design enhances quantum efficiency by increasing the surface area for light collection and reducing light absorption, while providing effective optical crosstalk protection, thereby improving the overall performance of the CMOS image sensor.
Implementation Method 1
A pixel sensor of the CMOS image sensor may include a photodiode region configured to convert photons of incident light into a photocurrent of electrons
Data Source
AI summary
A grid structure in a pixel array may be at least partially angled or tapered toward a top surface of the grid structure such that the width of the grid structure approaches a near-zero width near the top surface of the grid structure. This permits the spacing between color filter regions in between the grid structure to approach a near-zero spacing near the top surfaces of the color filter regions. The tight spacing of color filter regions provided by the angled or tapered grid structure provides a greater surface area and volume for incident light collection in the color filter regions. Moreover, the width of the grid structure may increase at least partially toward a bottom surface of the grid structure such that the wider dimension of the grid structure near the bottom surface of the grid structure provides optical crosstalk protection for the pixel sensors in the pixel array.