Stacked-Refractive-Index Microlens Array for CMOS Pixel Sensitivity Uniformity
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Solution Overview
Problem
In solid-state imaging devices, variations in pixel separation portion width, position, and microlens overlay deviations can cause light to deviate from photoelectric conversion units, leading to inter-same-color sensitivity differences and reduced quantum efficiency.
Innovation Solution
A solid-state imaging device with a microlens array featuring two or more lens layers of different refractive indices, where the layer closer to the substrate has a lower refractive index, and a lattice-shaped trench portion surrounding each photoelectric conversion unit, to enhance light condensation and reduce sensitivity differences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the curvature radius of the microlens is increased to widen the light-condensed spot, then the inter-same-color sensitivity difference is reduced, but the quantum efficiency decreases due to reduced light condensing power
Solution Approach 1:
The patent changes the refractive index parameter distribution within the microlens by introducing multiple lens layers with different refractive indexes. The first lens layer has a higher refractive index and the second lens layer has a lower refractive index, allowing the system to achieve both wide light condensation and high quantum efficiency through parameter optimization rather than simply increasing the curvature radius
Solution Approach 2:
The microlens is constructed as a composite structure with two or more lens layers having different refractive indexes. This composite design allows the outer layer to provide strong light bending capability while the inner layer maintains a larger effective aperture, resolving the contradiction between light condensing power and light-receiving area
2Ease of manufacture
If the width or position of the pixel separation portion varies, or if overlay deviation occurs between the pixel separation portion and microlens, then manufacturing is simplified, but the light-condensed spot center deviates from photoelectric conversion unit centers causing sensitivity differences
Solution Approach 1:
The patent uses refractive index gradient design in the multi-layer microlens structure to reduce the sensitivity of light condensation position to manufacturing variations. The gradual transition of refractive indexes helps maintain stable light condensation characteristics even when pixel separation portion dimensions or positions vary
Solution Approach 2:
The multi-layer microlens structure with different refractive indexes acts as a compensatory mechanism that pre-adapts to potential alignment deviations. The optical path design inherently compensates for overlay deviations between the pixel separation portion and microlens, reducing the impact of manufacturing tolerances on final positioning accuracy
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 configuration improves quantum efficiency while minimizing inter-same-color sensitivity differences by widening the light-condensed spot and ensuring reliable light condensation, even with variations in pixel separation and microlens alignment.
Implementation Method 1
two or more lens layers having different refractive indexes are laminated in the microlens
Implementation Method 2
a plurality of photoelectric conversion units formed on the substrate
Data Source
AI summary
Provided is a solid-state imaging device capable of improving the quantum efficiency while reducing an inter-same-color sensitivity difference. Provided are: a substrate; a plurality of photoelectric conversion units formed on the substrate; a microlens array including a plurality of microlenses formed on one surface side of the substrate for a photoelectric conversion unit group including at least two or more of the adjacent photoelectric conversion units; and a trench portion which has a lattice shape and is formed in the substrate to surround each of the photoelectric conversion units. Furthermore, the microlens is formed by laminating two or more lens layers having different refractive indexes. Furthermore, out of the two or more lens layers, a lens layer closer to the substrate has a lower refractive index.