CMOS Image Sensor Conductive Grid for Pixel Cross-Talk Isolation
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Solution Overview
Problem
CMOS image sensors face challenges in enhancing quantum efficiency and suppressing cross-talk between pixels, which affects their performance in capturing images effectively.
Innovation Solution
Incorporating an isolation structure with a conductive grid overlying the semiconductor substrate and surrounding photodiodes, which is electrically connected to interconnects on both sides of the substrate, and further integrating color filters and micro lenses to enhance light reflection and isolation between pixels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional CMOS image sensor structure is used, then the device complexity is low and manufacturing is easier, but the quantum efficiency is insufficient and cross-talk between pixels occurs
Solution Approach 1:
The isolation structure is segmented into multiple conductive layers (first conductive layer, second conductive layer, third conductive layer) that are distributed throughout the substrate. Each layer serves specific isolation and reflection functions, dividing the complex isolation task into manageable segments that improve quantum efficiency while maintaining manufacturability through standardized layering processes
Solution Approach 2:
The conductive layers are nested within the substrate structure, with the first conductive layer positioned at a first depth, the second conductive layer at a second depth, and the third conductive layer at a third depth. This nested arrangement allows multiple isolation and reflection functions to be integrated within the existing substrate volume, improving quantum efficiency without significantly increasing device footprint or manufacturing complexity
2Object-affected harmful factors
If no isolation structure is used, then the device complexity is minimal, but cross-talk between adjacent pixels occurs
Solution Approach 1:
The conductive layers are positioned at specific local depths within the substrate (first depth, second depth, third depth respectively) to provide localized isolation and light reflection. This local quality approach targets cross-talk suppression at the pixel boundaries where it occurs most, while maintaining manufacturing simplicity through standardized layer deposition processes
Solution Approach 2:
The conductive layers act as intermediary structures between adjacent photodiodes, providing both electrical isolation and optical reflection. These intermediary layers block stray light from reaching adjacent pixels and provide electrical isolation, effectively suppressing cross-talk while maintaining a relatively simple overall device structure
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 conductive grid improves quantum efficiency by reflecting light back to the pixels and reduces cross-talk, leading to enhanced image sensor performance by ensuring incident light is focused on individual pixels without interference, thereby improving image acquisition.
Implementation Method 1
The conductive grid improves quantum efficiency by reflecting light back to the pixels
Data Source
AI summary
An image sensor includes a pixel and an isolation structure. The pixel includes a photosensitive region and a circuitry region next to the photosensitive region. The isolation structure is located over the pixel, where the isolation structure includes a conductive grid and a dielectric structure covering a sidewall of the conductive grid, and the isolation structure includes an opening or recess overlapping the photosensitive region. The isolation structure surrounds a peripheral region of the photosensitive region.