Microlens Array with Varying Heights for Image Sensor Edge Light Collection
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Solution Overview
Problem
Conventional microlens arrays with uniform microlenses struggle to focus incident light effectively onto the photosensitive regions near the edge of image sensing devices, leading to light field curvature and image distortions due to focal length variations and diffraction issues.
Innovation Solution
A microlens array with microlenses of varying heights arranged in concentric regions over a passivation layer, where each region has microlenses of different heights, allowing for a longer effective focal length and reducing focal length deviations, thereby creating a planar focal plane that improves light collection efficiency near the edges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If microlenses of same radius, shape, height and fixed pitches are used, then manufacturing is simplified, but light focusing capability deteriorates at edge portions causing light field curvature
Solution Approach 1:
The patent applies local quality by varying the height of microlenses based on their position within the pixel array. Central region microlenses have a first height, middle region microlenses have a second height, and edge region microlenses have a third height. This localized variation in microlens parameters compensates for position-dependent optical path differences, enabling uniform focal plane across the entire array while maintaining a relatively simple manufacturing process using standard photolithography and reflow techniques.
2Measurement precision
If pixel size decreases and pixel density increases, then imaging resolution is improved, but light collection efficiency deteriorates due to diffraction effects
Solution Approach 1:
The patent addresses light collection efficiency in high-density pixel arrays by implementing position-dependent microlens heights. Edge region microlenses have reduced height (third height) compared to central microlenses, which compensates for increased diffraction effects at array boundaries. This local optimization ensures that even as pixel density increases and individual pixel dimensions decrease, the microlenses can still effectively focus incident light onto the photosensitive regions without excessive energy loss.
3Device complexity
If uniform microlenses are used across the array, then device complexity is reduced, but image quality deteriorates due to focal length variations
Solution Approach 1:
The patent resolves the contradiction between device simplicity and image quality by implementing a three-region microlens height configuration. The array is divided into central, middle, and edge regions, each with optimized microlens heights (first, second, and third heights respectively). This structured variation maintains reasonable manufacturing complexity while achieving uniform focal plane and high image quality across the entire sensor array.
Solution Approach 2:
The patent applies segmentation by dividing the microlens array into three distinct regions (central, middle, and edge) with different microlens height characteristics. This segmentation allows each region to be optimized for its specific optical requirements while maintaining overall system coherence. The segmented approach enables precise control over focal plane uniformity without requiring completely complex manufacturing processes.
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 solution enhances light collection and reduces image distortions by ensuring that incident light converges effectively onto the photosensors, increasing the percentage of light reaching the edges of the pixels and minimizing focal length deviations, resulting in improved image quality with reduced shielding effects.
Implementation Method 1
A microlens is used to focus light onto the charge accumulation region of the imaging pixels
Data Source
AI summary
A microlens array is provided, including a base layer with a plurality of first microlenses formed over a first region thereof, wherein the first microlenses are formed with a first height. A plurality of second microlenses are formed over a second region of the base layer, wherein the second region surrounds the first region and the second microlenses are formed with a second height lower than the first height. A plurality of third microlenses are formed over a third region of the base layer, wherein the third region surrounds the second and three regions, and the microlenses are formed with a third height lower than the first and second heights.