Gapless Microlens Array for CMOS Image Sensors
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Solution Overview
Problem
Conventional CMOS image sensors with connected color filter structures suffer from light loss and suboptimal color signal resolution due to gaps between microlenses, limiting light sensitivity and image clarity.
Innovation Solution
A CMOS image sensor with a disconnected color filter structure and a gapless microlens array formed using a thermal process, where the color filters have specific gaps determining the microlens height and slope, allowing for improved light sensitivity and condensing efficiency without the need for additional photolithography.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a connected color filter structure is used, then the manufacturing process is simpler, but gaps between microlenses cause light loss and reduced color signal resolution
Solution Approach 1:
The color filter array is segmented into individually separated color filters rather than a connected structure. This segmentation allows each color filter to be independently positioned and sized, enabling the formation of gaps between adjacent microlenses while maintaining precise alignment. The segmented structure resolves the contradiction by allowing light to pass through all microlenses without being blocked by connecting structures, thereby reducing light loss while still achieving adequate positioning precision through the segmented design.
2Reliability
If gaps are maintained between microlenses to prevent bridge formation, then manufacturing reliability improves, but light sensitivity decreases due to light loss
Solution Approach 1:
The dimensions and positions of the color filters are precisely controlled to create optimal gap sizes between adjacent microlenses. By changing the parameters of the color filter structure (width, spacing, position), the invention achieves a balance where gaps are sufficient to prevent bridge formation during curing and reflowing processes, yet small enough to minimize light loss. This parameter optimization resolves the contradiction between reliability and light sensitivity.
3Manufacturing precision
If photolithography processes are used for microlens formation, then manufacturing precision is achieved, but material selection is limited to photo type materials only
Solution Approach 1:
The invention replaces the photolithography-based microlens formation process with a thermal reflow and curing process. By using heat-induced reflow and UV curing of the photoresist material, the invention achieves precise microlens formation without relying on photolithography exposure patterns. This substitution expands material selection beyond photo type materials to include thermoplastic resins and other materials that can be shaped through thermal processes, thereby resolving the contradiction between manufacturing precision and material versatility.
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 disconnected color filter structure enhances light sensitivity and reduces oblique light incidence, resulting in clearer images and increased flexibility in microlens material selection and profile adjustment.
Implementation Method 1
The transparent material is hardened by a thermal reflow and curing process
Implementation Method 2
The transparent material is hardened by a thermal reflow and curing process
Data Source
AI summary
An image sensor is provided. The image sensor includes a pixel sensor, a color filter array comprising a plurality of color filters formed on the pixel sensor, wherein two adjacent color filters have a gap therebetween, and a gapless microlens array comprising a plurality of microlenses formed on the color filter array. The invention also provides a method for fabricating the image sensor.