Multi-layered Microlens Refractive Index Segmentation
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Solution Overview
Problem
Current image sensor microlens systems face challenges in achieving high quantum efficiency and optimal light focusing due to limitations in refractive index combinations and manufacturing processes, such as the checkerboard effect and reduced fill factor in reflowed pin cushion microlenses.
Innovation Solution
A multi-layered microlens system is developed, comprising a first layer with a higher refractive index, a second layer with a lower refractive index, and a third antireflective coating layer, where the second layer is a fluoropolymer, and the thicknesses are optimized to enhance light focusing and reduce crosstalk, using a method involving semiconductor substrates and etching processes to form hemispherical elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a single-layer microlens structure is used, then the manufacturing process is simple, but the quantum efficiency is insufficient and light focusing is suboptimal
Solution Approach 1:
The microlens system is divided into three distinct layers with different refractive indices. The first layer (n1=1.56) contains hemispherical elements, the second layer (n2=1.38) is a fluoropolymer intermediate layer, and the third layer (n3=1.4) is an antireflective coating. This segmentation allows each layer to contribute differently to light focusing and reduction of optical losses, achieving superior quantum efficiency compared to single-layer structures.
Solution Approach 2:
The patent employs a composite microlens structure combining materials with different refractive indices. The first layer uses a material with n1=1.56, the second layer uses fluoropolymer with n2=1.38, and the third layer uses antireflective coating material with n3=1.4. This composite approach optimizes light focusing and minimizes reflections at interfaces, thereby enhancing quantum efficiency while maintaining manufacturability.
2Ease of manufacture
If reflowed pin cushion microlenses are used, then manufacturing is simplified, but the checkerboard effect and reduced fill factor occur
Solution Approach 1:
The microlens structure is segmented into three layers with the hemispherical elements formed in the first layer before applying subsequent layers. This segmentation prevents the checkerboard effect that occurs in reflowed pin cushion microlenses by maintaining uniform fill factor across the sensor array, as each layer is applied independently without the variability introduced by reflow processes.
3Device complexity
If traditional microlens designs are used, then the structure is simple, but crosstalk between pixels increases
Solution Approach 1:
The three-layer composite structure with optimized refractive indices (n1=1.56, n2=1.38, n3=1.4) creates improved light confinement within each pixel region. The intermediate fluoropolymer layer with lower refractive index acts as an optical isolation layer, reducing light leakage and crosstalk between adjacent pixels while maintaining overall structural simplicity.
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 multi-layered microlens system significantly improves quantum efficiency by up to 11% and reduces crosstalk, achieving better light focusing and modulation transfer function compared to traditional pin cushion reflowed microlenses, while eliminating the checkerboard effect and simplifying the manufacturing process.
Implementation Method 1
a first layer including a first refractive index, the first layer including one or more substantially hemispherical elements formed therein; a second layer including a second refractive index coupled over the one or more substantially hemispherical elements of the first layer; and a third layer including a third refractive index coupled over the second layer
Data Source
AI summary
Implementations of a microlens system may include a first layer including a first refractive index, the first layer including one or more substantially hemispherical elements formed therein; a second layer including a second refractive index coupled over the substantially hemispherical elements of the first layer; and a third layer including a third refractive index coupled over the second layer. A value of the first refractive index may be larger than a value of the third refractive index and a value of the second refractive index and the value of the second refractive index may be less than a value of the third refractive index.