Microlens Material Segmentation for CMOS Image Sensor Distortion
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Solution Overview
Problem
CMOS image sensors face issues with microlens distortion or asymmetry due to overlap between adjacent microlenses, affecting the reliability and performance of the image sensor.
Innovation Solution
The image sensor design includes microlenses with distinct material compositions for their upper and lower portions, and a planarization layer with protruded and recessed portions to prevent overlap-induced distortion, where the boundary surface of the upper microlens portion is positioned higher than the lower side of the adjacent microlens, ensuring the lowest edge of the second microlens contacts the planarization layer rather than the upper microlens.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If microlenses are formed adjacent to each other on the color filter array, then light collection efficiency is improved, but distortion or asymmetry occurs due to overlap between adjacent microlenses
Solution Approach 1:
The microlens is divided into two distinct portions: a first portion formed of a first material and a second portion formed of a second material. This segmentation allows each portion to be independently controlled during formation, preventing overlap-induced distortion while maintaining adjacent positioning for optimal light collection.
Solution Approach 2:
Different materials are used for different portions of the microlens structure. The first material is used for the first portion and the second material for the second portion, allowing each region to have optimized properties that prevent distortion while maintaining overall light collection efficiency.
2Productivity
If microlenses are positioned closely together, then pixel density is increased, but overlap between microlenses causes asymmetry and reduces manufacturing precision
Solution Approach 1:
By segmenting the microlens into first and second portions made of different materials, the patent enables close positioning of adjacent microlenses without overlap. The distinct material boundaries prevent asymmetry even when microlenses are positioned closely together, thereby increasing pixel density while maintaining manufacturing precision.
Solution Approach 2:
The patent intentionally introduces asymmetry in material composition (first material vs. second material) to prevent the harmful symmetry-breaking that occurs during microlens formation. This controlled material asymmetry counteracts the geometric asymmetry that would otherwise result from overlap, allowing high pixel density with maintained shape symmetry.
Data Source
AI summary
The present invention discloses an image sensor including photodiodes formed in a semiconductor substrate, a color filter array formed over the photodiodes, and microlenses formed on the color filter array. A first microlens, which may be any one of two adjacent microlenses, includes an upper portion and a lower portion. The lower portion of the first microlens is formed of a material different than a material of the upper portion of the first microlens.