Embedded Micro-Lenses for CMOS Image Sensor Crosstalk Reduction
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Solution Overview
Problem
The reduction in size of CMOS image sensor pixels leads to alignment errors between micro-lenses and photodiodes, causing optical crosstalk and a decrease in optical efficiency.
Innovation Solution
Embedding micro-lenses with a convex-like or hemispherical cross-section under the color filter sheets directly on the concave surfaces of the buffer oxide layer, which aligns with photodiodes, replacing the conventional micro-lens layer to gather incident light effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If pixel size is reduced to improve image resolution, then image resolution is improved, but optical efficiency decreases and optical crosstalk increases
Solution Approach 1:
The micro-lens layer is merged with the color filter layer to form a single integrated module. The micro-lenses are embedded directly within the color filter layer structure, eliminating the need for separate micro-lens modules and their associated alignment processes. This merging ensures precise alignment between micro-lenses and photodiodes while maintaining optical efficiency even as pixel sizes decrease.
Solution Approach 2:
The micro-lenses are nested within the color filter layer structure. The color filter layer serves as both the filter medium and the housing for the micro-lenses, with micro-lenses positioned at specific depths within the layer. This nesting approach ensures precise spatial relationship between micro-lenses, color filters, and underlying photodiodes.
2Ease of manufacture
If conventional separate micro-lens modules are used, then manufacturing flexibility is maintained, but alignment errors occur between micro-lenses and photodiodes
Solution Approach 1:
The micro-lens layer and color filter layer are merged into a single integrated module that is formed and manufactured together as one unit. This eliminates the need for separate alignment processes between independently manufactured micro-lens modules and color filter layers, thereby eliminating alignment errors while maintaining manufacturing efficiency.
Solution Approach 2:
The integrated module serves multiple functions simultaneously: it acts as both the color filter layer for wavelength selection and the micro-lens layer for light focusing. This multi-functionality eliminates the need for separate alignment between distinct functional layers, as both functions are achieved within a single manufactured structure.
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 solution enhances quantum efficiency and reduces optical crosstalk by ensuring precise alignment and efficient light confinement onto photodiodes, maintaining image resolution without significant signal-to-noise ratio degradation.
Implementation Method 1
A typical micro-lens may be a single element with one plane surface and one spherical convex surface to refract the incident light
Data Source
AI summary
A backside illuminated CMOS image sensor and a manufacturing method thereof are provided. Embedded micro-lenses disposed respectively on concave surfaces of a buffer oxide layer, wherein the concave surfaces are positioned to respectively align with photodiodes of pixel array of the CMOS image sensor. The embedded micro-lenses can confine incident light to the photodiodes to reduce optical crosstalk between adjacent pixels.