Image Sensor Microlens Array Uniformity
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Solution Overview
Problem
Electronic image recording apparatuses suffer from non-uniform sensitivity of photosensitizing devices due to varying incident light angles across the image sensor chip, leading to distortion in image recording.
Innovation Solution
A method of fabricating an image sensor by forming microlenses in a specific array pattern on the substrate, where the distance between microlenses decreases towards the edge, and their focal lengths increase, ensuring all incident light is focused at the photosensitizing plane, thereby uniformizing sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If microlenses with uniform curvature and focal length are used, then manufacturing is simplified, but sensitivity becomes non-uniform toward the chip edge
Solution Approach 1:
The patent applies local quality by varying the curvature and focal length of microlenses according to their position in the array. Microlenses at different locations have different optical properties - specifically, those at the edge have different curvature than those at the center - to compensate for the increased incident angle of light at the edges, thereby achieving uniform sensitivity across the entire chip surface.
Solution Approach 2:
The patent changes the optical parameters (curvature and focal length) of microlenses based on their position in the array. By adjusting these parameters systematically from center to edge, the patent compensates for the varying incident angles of light, ensuring that all microlenses focus light uniformly onto the photosensitizing plane despite their different locations.
2Manufacturing precision
If microlenses with increased focal length toward the edge are used, then sensitivity uniformity is improved, but device complexity increases
Solution Approach 1:
The patent applies preliminary action by pre-calculating and pre-configuring the different curvatures and focal lengths for each microlens position in the array before fabrication. This systematic pre-planning of optical parameters allows the complex varying sensitivity compensation to be achieved through a standardized fabrication process, reducing the operational complexity despite the varied lens specifications.
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 uniform sensitivity across the image sensor chip, reducing distortion in image recording by effectively focusing incident light from the center to the edge, improving image quality.
Implementation Method 1
a thermal reflow step is performed to convert the photoresist patterns into a plurality of microlenses arranged in a second array
Implementation Method 2
The focal length of microlens increases from the center of the array toward the edge of the array. Thus, all incident lights from the array center to the array edge can be focused at the photosensitizing plane
Data Source
AI summary
A method for fabricating an image sensor is provided. A substrate is provided, and then a plurality of photoresist patterns is formed on the substrate. The photoresist patterns are arranged in a first array and defined by a plurality of photomask patterns arranged as a photomask pattern array, wherein a top view of each photoresist pattern has a substantially square shape and a distance between two neighboring photoresist patterns decreases from a center of the first array toward an edge of the first array. Besides, each photomask pattern includes a transparent portion and an opaque portion, wherein an area proportion of the transparent portion included in a photomask pattern increases from the center toward the edge of the photomask pattern array. Then, a thermal reflow step is performed to convert the photoresist patterns into a plurality of microlenses arranged in a second array.