Pixel Separation Wall Geometry for Color Mixing and Quantum Efficiency
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Solution Overview
Problem
Imaging devices with color filters and on-chip lenses face challenges in improving quantum efficiency and reducing color mixing due to light penetration and scattering issues caused by separation walls.
Innovation Solution
The imaging device incorporates a semiconductor substrate with a matrix of pixels, featuring color filters and condensing lenses on one surface, and a separation wall with a narrower line width on the light incident side than on the substrate surface, reducing light penetration between adjacent pixels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a separation wall is provided between adjacent color filters to reduce color mixing, then color mixing is reduced, but light penetration and scattering occur which decreases quantum efficiency
Solution Approach 1:
The separation wall is designed with non-uniform line width, being narrower on the light incident side and wider on the substrate side. This local variation in geometry allows the separation wall to effectively block oblique light paths that cause color mixing while minimizing interference with directly incident light, thus preserving quantum efficiency in light-receiving regions.
Solution Approach 2:
The separation wall employs an asymmetric cross-sectional shape where the line width differs between the light incident side and the substrate side. This asymmetric design creates an optical path that effectively blocks scattered and oblique light from entering adjacent pixels while allowing maximum light transmission to the photoelectric converters, resolving the contradiction between color isolation and light collection efficiency.
2Measurement precision
If the separation wall line width is increased to improve color isolation, then color mixing is reduced, but light blockage increases which decreases quantum efficiency
Solution Approach 1:
The separation wall's line width is optimized locally - narrower where light incident (to minimize blockage) and wider where it contacts the substrate (to maximize color isolation). This spatially varying geometry achieves effective pixel separation without sacrificing quantum efficiency, as the narrow portion allows light transmission while the wide portion prevents light leakage.
Solution Approach 2:
The separation wall design transitions from a uniform two-dimensional cross-section to a three-dimensional structure with varying line width. This dimensional complexity allows the wall to perform dual functions: blocking light laterally to prevent color mixing while maintaining transparency to directly incident light, thereby resolving the energy loss issue.
3Loss of energy
If the separation wall line width is decreased to improve light transmission, then quantum efficiency is improved, but color mixing increases between adjacent pixels
Solution Approach 1:
The separation wall implements different line widths at different locations: a narrow line width on the light incident side minimizes blockage to incident light, preserving quantum efficiency; while a wider line width on the substrate side provides sufficient separation to prevent color mixing between adjacent pixels. This local differentiation resolves the contradiction between light transmission and color isolation.
Solution Approach 2:
The asymmetric line width design of the separation wall creates an optimized optical path where the narrow upper portion allows maximum light transmission to photoelectric converters, while the wider lower portion effectively blocks oblique and scattered light from adjacent pixels, simultaneously achieving high quantum efficiency and effective color isolation.
4Ease of manufacture
If a conventional uniform separation wall is used, then manufacturing is simplified, but oblique light and scattered light penetrate into adjacent pixels causing color mixing
Solution Approach 1:
The separation wall design introduces local variation in line width rather than uniform geometry. This can be implemented using standard photolithography techniques with appropriate mask design, making the manufacturing process relatively simple while achieving superior optical performance in blocking oblique and scattered light compared to uniform separation walls.
Solution Approach 2:
The asymmetric line width profile of the separation wall is achieved through controlled fabrication processes. The wider base provides effective light blocking at the substrate interface, while the narrower top minimizes impact on incident light transmission. This asymmetric geometry can be manufactured using conventional semiconductor processing techniques, balancing manufacturing ease with improved color isolation performance.
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 enhances quantum efficiency and minimizes color mixing by effectively blocking oblique light and scattered light, improving image quality.
Implementation Method 1
a plurality of photoelectric converters that each generates, through photoelectric conversion, electric charge corresponding to an amount of received light
Implementation Method 2
a plurality of condensing lenses provided on a light incident side of the plurality of color filters in the respective ones of the plurality of pixels
Data Source
AI summary
An imaging device according to an embodiment of the present disclosure includes: a semiconductor substrate having a first surface and a second surface opposed to each other, the semiconductor substrate including a plurality of pixels disposed in a matrix, and a plurality of photoelectric converters that each generates, through photoelectric conversion, electric charge corresponding to an amount of received light for each of the pixels; a plurality of color filters provided on a side of the first surface in respective ones of the plurality of pixels; a plurality of condensing lenses provided on a light incident side of the plurality of color filters in the respective ones of the plurality of pixels; and a separation wall provided between the plurality of color filters adjacent to each other on the side of the first surface, the separation wall having a line width on the light incident side narrower than the line width of the separation wall on the side of the first surface.