Microlens Radius Variation for Image Sensor Sensitivity
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Solution Overview
Problem
Conventional image sensors with microlenses of the same radius of curvature suffer from reduced sensitivity due to vertical shifts in focus caused by varying incident light angles, particularly in larger digital imaging devices, leading to unsatisfactory spot sizes at peripheral areas.
Innovation Solution
Designing image sensors with microlenses of different radii of curvature, where smaller radii are used at central areas and larger radii at peripheral areas, or for different color pixels, and incorporating asymmetrical microlens structures to better focus light, achieved through a method involving photoresist material patterning and reflowing to form distinct contours.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If microlenses of the same radius of curvature are used throughout the image sensor, then the manufacturing process is simple, but the sensitivity is reduced due to vertical shifts in focus caused by varying incident light angles
Solution Approach 1:
The patent applies local quality by varying the radius of curvature of microlenses based on their position on the sensor. Central microlenses have a different radius of curvature than peripheral microlenses, allowing each region to be optimized for its specific optical requirements. This resolves the contradiction by maintaining manufacturing simplicity through a systematic variation rather than complete customization, while significantly improving sensitivity across different incident light angles.
Solution Approach 2:
The patent changes the optical parameter (radius of curvature) of microlenses to optimize performance. By adjusting this parameter across different locations and for different color pixels, the system compensates for varying incident light angles and wavelengths, thereby improving sensitivity without requiring entirely new manufacturing approaches.
2Reliability
If microlenses of different radii of curvature are used for different locations and color pixels, then the sensitivity and optical performance are improved, but the manufacturing complexity increases
Solution Approach 1:
The patent segments the microlens array into different groups based on location (central vs. peripheral) and color pixel type. Each segment is assigned a specific radius of curvature optimized for its requirements. This segmentation allows the complex manufacturing process to be broken down into manageable steps using standard semiconductor fabrication techniques, thereby reducing overall manufacturing complexity while maintaining sensitivity improvements.
Solution Approach 2:
The patent introduces asymmetry in the microlens design by using different radii of curvature for different locations and color pixels. This asymmetric design is implemented through asymmetric photoresist patterning and reflow processes, which, while adding some complexity, enable precise control over the final microlens shapes to achieve the desired optical performance.
3Ease of manufacture
If a symmetrical microlens structure is used, then the manufacturing process is straightforward, but the focus shifts vertically for oblique incident light at peripheral areas
Solution Approach 1:
The patent applies asymmetry to the microlens structure itself, particularly for peripheral microlenses that receive oblique incident light. By designing asymmetric microlens shapes that match the angular distribution of incoming light, the system eliminates vertical focus shifts while maintaining a manufacturing process that builds upon standard symmetric fabrication techniques with targeted asymmetric modifications.
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
Improves optical performance by ensuring better light focus onto the focal plane, enhancing sensitivity and compensating for different wavelengths and oblique incident light angles.
Implementation Method 1
The photoresist layer is exposed according to a pattern on a photomask
Implementation Method 2
the semi-finished substrate with the photoresist layer thereon is subject to a temperature of above 150 degree centigrade for 10 minutes, so that the photoresist layer is partially melted
Implementation Method 3
due to viscosity of the photoresist material, the melted photoresist layer has the contour as the microlenses
Implementation Method 4
an image sensor chip usually includes a layer of multiple microlenses, so that incident light may better focus on a focal plane
Data Source
AI summary
The present invention provides an image sensor which comprises improved microlenses to cope with different optical requirements for oblique incident light or different components of light. In one embodiment, the image sensor comprises at least two microlenses having different radii of curvature. In another embodiment, the image sensor comprises at least one asymmetrical microlens.