Back-Illuminated CMOS Sensor Structure for Lower Pixel Color Mixing
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Solution Overview
Problem
Existing solid-state imaging elements, such as CMOS image sensors, suffer from decreased image quality due to color mixing between pixels, which occurs when light transmitted through a color filter of one pixel is incident on an adjacent pixel's photodiode.
Innovation Solution
A solid-state imaging element is designed with a color filter on a semiconductor substrate, a low-refractive-index waveguide between adjacent filters, and a metal layer with a narrower width closer to the substrate, configured to reflect oblique light and suppress color mixing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a barrier metal with narrow width is provided below the low-refractive-index wall portion, then color mixing between pixels is suppressed, but pixel sensitivity decreases
Solution Approach 1:
The metal layer is designed with an asymmetric cross-sectional shape where the lower portion width (closer to semiconductor substrate) is narrower than the upper portion width (closer to waveguide). This asymmetric configuration allows the upper wider portion to effectively block oblique light and suppress color mixing, while the lower narrower portion minimizes light absorption and preserves pixel sensitivity
Solution Approach 2:
Different portions of the metal layer are given different widths to perform different functions: the upper wider portion is optimized for light blocking to suppress color mixing, while the lower narrower portion is optimized to minimize light absorption and maintain pixel sensitivity
2Object-affected harmful factors
If the metal layer width is increased to suppress color mixing, then color mixing is reduced, but light absorption by the metal layer increases and pixel sensitivity decreases
Solution Approach 1:
The asymmetric width configuration of the metal layer allows the upper portion to be wider for effective light blocking while the lower portion remains narrower to minimize light absorption, resolving the contradiction between color mixing suppression and light absorption reduction
Solution Approach 2:
The metal layer's different portions have different widths optimized for different purposes: the upper wider portion handles light blocking function while the lower narrower portion minimizes light absorption, achieving both color mixing suppression and light absorption reduction simultaneously
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 solution effectively reduces color mixing and maintains pixel sensitivity, thereby enhancing image quality.
Implementation Method 1
a waveguide disposed between adjacent ones of the color filters, the waveguide being formed of a low-refractive-index material having a refractive index lower than a refractive index of the color filters
Implementation Method 2
a metal layer disposed on a semiconductor substrate side of the waveguide and in the insulating layer on the semiconductor substrate side of a semiconductor-substrate-side surface of the color filters
Data Source
Figure 1A~1B
Figure 2
Figure 3
AI summary
The present disclosure relates to a solid-state imaging element, a manufacturing method, and an electronic apparatus that can further improve image quality. The solid-state imaging element includes a color filter provided, for each of a plurality of pixels, on a back surface side of a semiconductor substrate with an insulating layer interposed between the color filter and the semiconductor substrate, the back surface side of the semiconductor substrate being illuminated with light, a waveguide disposed between adjacent ones of the color filters, the waveguide being formed of a low-refractive-index material having a refractive index lower than a refractive index of the color filters, and a metal layer disposed on a semiconductor substrate side of the waveguide and in the insulating layer on the semiconductor substrate side of a semiconductor-substrate-side surface of the color filters, the metal layer being configured in a shape in which a width of a lower portion closer to the semiconductor substrate is narrower than a width of an upper portion closer to the waveguide. The present technology can be applied to, for example, a back-illuminated CMOS image sensor.