Microlens Array with Variable Focal Lengths for CMOS Image Sensors
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Solution Overview
Problem
In microlens arrays used in image sensors, the varying refractive indices of different wavelengths of light (blue, green, and red) cause inaccurate focusing, leading to decreased accuracy and reliability of the microlens-photo-sensor device.
Innovation Solution
A method is introduced where a microlens material is formed over a color filter array, with patterned photoresist elements used to control the exposure of the microlens material, allowing for different focal lengths to be achieved for each wavelength, ensuring accurate focusing on photo-sensors by compensating for the refractive differences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single microlens array is used for all wavelengths, then the device structure is simple, but the focusing accuracy for different wavelengths (blue, green, red) deteriorates due to varying refractive indices
Solution Approach 1:
The patent applies local quality by creating microlens elements with different focal lengths tailored to specific wavelength ranges. Each microlens element is optimized for a particular color (blue, green, or red) based on the refractive index characteristics of that wavelength, allowing accurate focusing for each wavelength band while maintaining a unified array structure.
Solution Approach 2:
The microlens array is segmented into multiple types of microlens elements, each designed with specific focal length characteristics for different wavelength ranges. This segmentation allows the system to handle the varying optical properties of different colors by assigning specialized lens elements to each wavelength band.
2Manufacturing precision
If the microlens array is optimized for one wavelength, then the focusing accuracy for that wavelength is improved, but the performance for other wavelengths deteriorates
Solution Approach 1:
The microlens array achieves multi-functionality by incorporating multiple types of microlens elements within a single array structure. Each element type is designed to handle a specific wavelength range, allowing the overall system to effectively process multiple wavelengths (blue, green, and red light) simultaneously, thus achieving universal performance across the visible spectrum.
Solution Approach 2:
Different regions of the microlens array contain elements with locally optimized properties for specific wavelengths. This local optimization ensures that each wavelength range achieves its best possible focusing accuracy while the entire array maintains versatility across all visible wavelengths.
3Ease of manufacture
If conventional photolithography exposure is used, then the manufacturing process is simple, but the ability to create different focal lengths for different wavelengths is insufficient
Solution Approach 1:
The patent employs parameter changes by varying the exposure dose during photolithography for different microlens elements. By controlling the amount of exposure energy received by each element type, the process creates different focal lengths in the microlens material, enabling wavelength-specific optimization while using a single conventional photolithography tool.
Solution Approach 2:
The manufacturing process uses periodic action by implementing multiple exposure steps with different exposure doses. The photolithography process is applied in stages, with each stage targeting specific microlens elements with appropriate exposure levels to achieve the desired focal length distribution across the array.
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 ensures that each wavelength of light is accurately focused onto its corresponding photo-sensor, enhancing the accuracy and reliability of the microlens-photo-sensor device by tailoring the focal lengths of the microlens array elements.
Implementation Method 1
The microlens material elements are then heated to form a microlens array
Implementation Method 2
blue light is more refractive than green light and red light, because the wavelength of blue light is about 430 nm
Implementation Method 3
Light that is incident on each microlens is focused towards a corresponding photo-sensor
Data Source
AI summary
A method of manufacturing a microlens device by depositing a microlens material layer over a substrate that includes photo-sensors. The microlens material layer is then exposed and developed to define microlens material elements, including first microlens material elements and second microlens material elements. Each second microlens material element is substantially greater in thickness relative to each first microlens material element. The microlens material elements are then heated to form a microlens array that includes first microlens array elements, each corresponding to a first microlens material element, and second microlens array elements, each corresponding to a second microlens material element. Each first microlens array element has a substantially greater focal length relative to each second microlens array element. For example, each second microlens array element is substantially greater in thickness relative to each first microlens array element.