Air-Gap Deep Trench Isolation for Pixel Crosstalk Reduction
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Solution Overview
Problem
Optical crosstalk between adjacent pixel regions in CMOS image sensors degrades spatial resolution, reduces sensitivity, causes color mixing, and leads to image noise after color correction.
Innovation Solution
The implementation of a deep trench isolation (DTI) structure with air gaps between pixel regions, which reduces optical crosstalk by lowering the critical angle for total internal reflection, ensuring incident light is absorbed by the intended pixel rather than adjacent ones.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If pixel regions are placed close together to increase pixel density, then productivity and sensor integration are improved, but optical crosstalk between adjacent pixels increases causing degraded spatial resolution and color mixing
Solution Approach 1:
The patent divides the sensor surface into isolated pixel regions by introducing deep trench isolation structures between adjacent pixels. These trenches physically segment the continuous silicon substrate into discrete pixel units, preventing optical crosstalk while maintaining high pixel density. The segmentation is achieved by etching trenches to a specific depth and filling them with reflective or absorptive materials.
Solution Approach 2:
The patent introduces intermediary materials within the deep trench isolation structures to mediate the optical interaction between adjacent pixel regions. These intermediaries (such as reflective layers or absorptive materials) act as optical barriers that prevent light from one pixel from interfering with adjacent pixels, thereby resolving the crosstalk issue while allowing close pixel spacing.
2Device complexity
If no isolation structure is used between pixel regions, then device complexity is reduced, but optical crosstalk causes color mixing and image noise
Solution Approach 1:
The patent applies local quality by making the isolation properties specific to the regions where they are needed. The deep trench isolation structures are selectively formed only between adjacent pixel regions where optical crosstalk occurs, rather than uniformly across the entire sensor. This localized approach provides effective isolation where required while minimizing overall device complexity.
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 enhances spatial resolution, increases overall sensitivity, decreases color mixing, and reduces image noise in captured images by effectively isolating pixel regions.
Implementation Method 1
reduces optical crosstalk by lowering the critical angle for total internal reflection
Data Source
AI summary
An isolation structure can be formed between adjacent and/or non-adjacent pixel regions (e.g., between diagonal or cross-road pixel regions), of an image sensor, to reduce and/or prevent optical crosstalk. The isolation structure may include a deep trench isolation (DTI) structure or another type of trench that is partially filled with a material such that an air gap is formed therein. The DTI structure having the air gap formed therein may reduce optical crosstalk between pixel regions. The reduced optical crosstalk may increase spatial resolution of the image sensor, may increase overall sensitivity of the image sensor, may decrease color mixing between pixel regions of the image sensor, and/or may decrease image noise after color correction of images captured using the image sensor.