Pixel Micro-lens Refractive Index Engineering for FPN Reduction
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Solution Overview
Problem
Current semiconductor imaging devices suffer from fixed pattern noise (FPN), which affects image quality and signal-to-noise ratio, necessitating a reduction in FPN to enhance image sensing capabilities.
Innovation Solution
The method involves measuring and adjusting the spectral characteristics of imaging devices on a pixel-by-pixel basis by modifying absorption, reflectance, refractive index, shape, and microstructure through techniques like thin film deposition, ion beam ablation, UV laser ablation, and direct implantation of absorbing species to reduce FPN.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional imaging device structures are used, then manufacturing is simpler and cost is lower, but fixed pattern noise is high and image quality is degraded
Solution Approach 1:
The patent applies local quality by introducing micro-lenses with specifically engineered refractive indices and absorption characteristics at each pixel location. These micro-lenses are tailored to compensate for local variations in photosensor response, achieving FPN reduction through spatially differentiated optical properties rather than uniform structure modification.
Solution Approach 2:
The patent utilizes parameter changes by adjusting the refractive index and absorption coefficients of the micro-lens materials. By varying these optical parameters across different pixel locations, the system compensates for manufacturing variations and achieves reduced fixed pattern noise without fundamentally changing the overall device architecture.
2Manufacturing precision
If pixel cell size is reduced to increase array density, then resolution is improved, but optical efficiency decreases and cross talk increases
Solution Approach 1:
The patent employs curved micro-lens surfaces with optimized radii of curvature to focus incident light more effectively onto the reduced-size photosensors. The spherical or aspherical geometry of these micro-lenses improves light collection efficiency and reduces cross-talk between adjacent pixels, enabling higher array density without sacrificing optical performance.
3Manufacturing precision
If spectral characteristics are adjusted on a pixel-by-pixel basis, then fixed pattern noise is reduced, but manufacturing complexity and process time increase
Solution Approach 1:
The patent applies preliminary action by pre-engineering the micro-lens spectral characteristics during the main fabrication process. Rather than requiring extensive post-fabrication trimming, the optical properties are designed into the structure from the beginning, allowing most FPN compensation to occur during standard manufacturing steps with minimal additional processing time.
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 effectively reduces FPN by 10 to 20%, thereby improving image quality and signal-to-noise ratio, resulting in a significant enhancement of the sensed image quality.
Implementation Method 1
The micro-lenses refract incident radiation to the photosensor region, thereby increasing the amount of light reaching the photosensor and thereby increasing the fill factor of the imager.
Implementation Method 2
deposition of a thin film and subsequent beam induced localized ablation/etch of the thin film surface by ion beam or UV laser ablation
Implementation Method 3
deposition of a thin film and subsequent beam induced localized ablation/etch of the thin film surface by ion beam or UV laser ablation
Implementation Method 4
Each pixel includes a photodetector and one or more active transistors. The transistors typically provide amplification, read-out control and reset control, in addition to producing the electric signal output from the cell.
Data Source
AI summary
Imaging devices having reduced fixed pattern noise are disclosed. The fixed pattern noise in the imaging devices is reduced by measuring and adjusting the spectral characteristics of the imager device on a pixel by pixel basis. The fixed pattern noise of the pixel cells are changed by modifying the absorption, reflectance, refractive index, shape, and/or micro structure of the material.