Backside Illuminated Pixel With Negative Charge Trench Isolation
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Solution Overview
Problem
Increasing the resolution of CMOS image sensors leads to smaller pixels, which increases the likelihood of interference such as crosstalk between pixels, affecting image quality.
Innovation Solution
A backside illuminated image sensor pixel design featuring a photoelectric conversion region between two surfaces of a semiconductor substrate, with a negative charge material-based back deep trench isolation and a vertical transfer gate to minimize crosstalk and dark current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the number of pixels in a pixel array is increased to increase resolution, then image resolution is improved, but the pixel size becomes smaller which increases crosstalk between pixels
Solution Approach 1:
The patent introduces deep trench isolation structures that physically segment adjacent pixels from each other. These trenches extend deep into the substrate and are filled with isolation material, creating effective barriers that divide the pixel array into isolated units, thereby preventing crosstalk while maintaining high pixel density for high resolution imaging.
Solution Approach 2:
The patent employs an intermediate layer containing negative charge material positioned between adjacent pixels. This intermediate structure acts as a mediator that generates an electric field to repel charge carriers, preventing them from moving between pixels. The negative charge material serves as an active barrier that dynamically prevents crosstalk without requiring physical separation of the pixels.
2Measurement precision
If pixel size is reduced to increase the number of pixels, then resolution is improved, but dark current increases affecting image quality
Solution Approach 1:
The deep trench isolation structures segment the semiconductor substrate into isolated pixel regions. By creating deep physical barriers between pixels, the trenches prevent the generation and movement of dark current carriers that would otherwise diffuse between adjacent pixels, thereby reducing overall dark current in the image sensor.
Solution Approach 2:
The negative charge material layer serves as an intermediary that actively suppresses dark current generation. The negative charges create a potential barrier that repels minority carriers (holes in n-type substrate), preventing them from reaching the photoelectric conversion region where they would generate dark current signals.
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 design effectively reduces crosstalk and dark current, enhancing image quality by ensuring efficient charge transfer and minimizing interference between pixels.
Implementation Method 1
a negative charge material-based back deep trench isolation
Implementation Method 2
a photoelectric conversion region interposed between a first surface and a second surface of a semiconductor substrate to generate charges in response to light received through the second surface
Data Source
AI summary
A pixel for a backside illuminated (BSI) image sensor includes a semiconductor substrate having a first surface and a second surface, a photoelectric conversion region between the first surface and the second surface to generate charges in response to light received through the second surface, first trench-type isolation region surrounding the photoelectric conversion region and extending vertically from the second surface, a floating diffusion region in the semiconductor substrate below the photoelectric conversion region, and a transfer gate extending vertically from the first surface towards the photoelectric conversion region to transfer the charges from the photoelectric conversion region to the floating diffusion region. The first trench-type isolation region is formed of a negative charge material.