Transparent Refraction Structure for BSI Image Sensor Cross-Talk
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Solution Overview
Problem
Backside illuminated (BSI) CMOS image sensors face issues with cross-talk and blooming due to insufficient isolation between neighboring pixels, particularly in pixel array architectures with full phase detection auto-focusing (PDAF) functions, leading to degradation in image resolution.
Innovation Solution
The implementation of transparent refraction structures in conjunction with an optical lens to align incident photons vertically, increasing the angle of incidence at interfaces between photodiode layers and deep trench isolation structures, thereby enhancing the probability of total reflection and reducing photon escape to neighboring pixels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If deep trench isolation structures are used to isolate neighboring pixels, then cross-talk between pixels is reduced, but manufacturing complexity increases due to the need for precise trench formation and filling
Solution Approach 1:
The patent changes the refractive index parameter by introducing transparent refraction structures with higher refractive index than the surrounding medium. This optical parameter change enhances photon reflection at the photodiode-isolation interface, reducing cross-talk without requiring complex trench formation processes. The refraction structures achieve isolation improvement through optical physics rather than complex geometric confinement.
2Productivity
If transparent refraction structures are added to enhance photon reflection, then light capture efficiency improves, but device complexity increases due to additional structural components
Solution Approach 1:
The transparent refraction structures serve multiple functions simultaneously: they act as optical elements to refract and reflect photons toward the photodiode, while also serving as part of the isolation architecture between neighboring pixels. This multi-functionality improves light capture efficiency without proportionally increasing device complexity, as the same structures provide both optical enhancement and pixel isolation.
Solution Approach 2:
The transparent refraction structures act as intermediary elements between the incident photons and the photodiode active region. By introducing this intermediate optical element, photons are guided more effectively into the photodiode, enhancing light capture efficiency. The intermediary structure simplifies the overall optical path management compared to direct illumination approaches.
3Object-affected harmful factors
If the angle of incidence is increased to enhance total reflection, then photon confinement within subpixel improves, but manufacturing precision requirements increase for aligning incident photons vertically
Solution Approach 1:
The transparent refraction structures are positioned and configured in advance during manufacturing to pre-determine the optical path of incident photons. By preliminarily establishing the refraction geometry and material properties, the structures automatically guide photons at optimal angles for total reflection at the photodiode-isolation interface, reducing the need for precise post-manufacturing alignment and simplifying manufacturing tolerances.
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 configuration enhances image resolution by increasing the probability of photons being reflected within the subpixel, thereby improving light capture efficiency and reducing image degradation from cross-talk.
Implementation Method 1
transparent refraction structures in conjunction with an optical lens to align incident photons vertically, increasing the angle of incidence at interfaces between photodiode layers and deep trench isolation structures
Implementation Method 2
increasing the angle of incidence at interfaces between photodiode layers and deep trench isolation structures, thereby enhancing the probability of total reflection
Data Source
AI summary
A plurality of photovoltaic junctions for a subpixel may be formed in a semiconductor substrate. After thinning the backside of the semiconductor substrate, at least one transparent refraction structure may be formed on the backside surface of the thinned semiconductor substrate. Each transparent refraction structure has a variable thickness that decreases with a lateral distance from a vertical axis passing through a geometrical center of the second-conductivity-type pillar structures for the subpixel. A subpixel optics assembly including an optical lens may be formed over the at least one transparent refraction structure. Each transparent refraction structure may reduce the tilt angle of light that propagate downward into the photodetectors, and increases total internal reflection of light and increase the efficiency of the photodetectors.