Image Sensor Dielectric Layout for Small-Pixel Crosstalk Control
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Solution Overview
Problem
As image pixels become smaller, sensitivity to light decreases and electrical and optical crosstalk between adjacent pixels increases, affecting the performance of image sensors.
Innovation Solution
The use of multi-layer metal stacks for both active and black pixel regions, where the metal grid structure enhances light sensitivity and reduces crosstalk by directing light to active pixels while the light shield attenuates light to black pixels, using a common base number of metal layers to streamline fabrication.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If image pixels are made smaller to increase resolution, then the resolution is improved, but light sensitivity decreases and crosstalk between adjacent pixels increases
Solution Approach 1:
The patent divides the pixel array into distinct active pixel regions and black pixel regions, with black pixels serving as isolated reference elements. This segmentation allows active pixels to be optimized for light capture while black pixels provide stable dark current references, resolving the sensitivity issue in high-resolution arrays.
Solution Approach 2:
The patent introduces dummy pixels as intermediary elements positioned between active pixels and black pixels. These dummy pixels act as buffer zones that reduce optical and electrical crosstalk while maintaining the high resolution achieved through small pixel sizes.
2Measurement precision
If image pixels are made smaller to increase resolution, then the resolution is improved, but crosstalk between adjacent pixels increases
Solution Approach 1:
The patent segments the pixel array into active pixels, black pixels, and dummy pixels with clear spatial separation. This segmentation creates physical and functional boundaries that reduce both optical and electrical crosstalk between adjacent pixels, enabling high resolution without excessive interference.
Solution Approach 2:
The patent extracts and isolates black pixels from the active pixel array, positioning them at specific locations surrounded by dummy pixels. This extraction removes potential crosstalk sources from the main imaging area while preserving their utility for dark current measurement and calibration.
3Reliability
If different numbers of metal layers are used for active and black pixel regions to optimize performance, then light sensitivity and crosstalk reduction are improved, but fabrication complexity increases
Solution Approach 1:
The patent merges the metal layer structures of active and black pixel regions by using a common base number of metal layers for both. This unification simplifies fabrication processes while maintaining the ability to optimize light sensitivity and reduce crosstalk through the spatial arrangement and functional design of the pixel regions themselves.
Solution Approach 2:
The patent creates a universal metal layer structure that serves both active and black pixel regions. This multi-functional approach allows the same fabrication process to produce optimized structures for both pixel types, reducing manufacturing complexity while maintaining performance benefits.
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 approach improves light sensitivity and reduces crosstalk, maintaining performance metrics while minimizing fabrication complexity.
Implementation Method 1
the metal grid structure enhances light sensitivity and reduces crosstalk by directing light to active pixels
Implementation Method 2
the metal grid structure enhances light sensitivity and reduces crosstalk by directing light to active pixels
Implementation Method 3
the light shield attenuates light to black pixels
Implementation Method 4
photosensitive elements (e.g., photodiodes) that absorb a portion of the incident image light and generate image charge upon absorption of the image light
Data Source
AI summary
An image sensor includes an active pixel photodiode, a black pixel photodiode, a metal grid structure, a light shield, and a varying thickness dielectric layer. The varying thickness dielectric layer includes a first portion having a first dielectric layer thickness and a second portion having a second dielectric layer thickness different from the first dielectric layer thickness. The metal grid structure is disposed between the first portion of the varying thickness dielectric layer and a semiconductor material. The light shield is disposed between the second portion of the varying thickness dielectric layer and the black pixel photodiode.