CMOS Image Sensor Color Filter for Microlens Focusing Efficiency
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Solution Overview
Problem
In solid-state imaging elements, the use of color filters with a higher refractive index than microlenses can lead to a decrease in light focusing efficiency toward photoelectric conversion elements.
Innovation Solution
A solid-state imaging element with a color filter that has a transmittance maximum between 400 nm to 500 nm, 50% transmittance between 460 nm to 490 nm, and a refractive index lower than the microlenses, containing blue pigment, violet dye, and violet pigment, with specific ratios and thickness, is employed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If color filters made of dye are used to improve sensitivity and color separation, then color characteristics are improved, but refractive index control becomes more difficult
Solution Approach 1:
The patent changes the refractive index parameter of the color filter by selecting specific resin materials (acrylic, polycarbonate, polyethylene terephthalate) with inherently lower refractive indices, and by controlling the dye concentration and distribution, achieving refractive index matching while maintaining superior color separation properties of dye-based filters
Solution Approach 2:
The patent uses composite material structures by combining specific resin matrices with dispersed dye particles, creating a color filter that achieves both the desired optical filtering characteristics and refractive index properties through the synergistic combination of material components
2Use of energy by moving object
If the refractive index of the color filter is increased to improve light extraction, then light extraction efficiency improves, but light focusing efficiency decreases
Solution Approach 1:
Instead of increasing the refractive index of the color filter to improve light extraction, the patent inverts the approach by using a color filter with lower or matched refractive index relative to the microlens, thereby maintaining focusing efficiency while achieving sufficient light extraction through the inverse refractive index relationship
3Illumination intensity
If the refractive index of the color filter matches or exceeds the microlens, then light extraction is improved, but light focusing efficiency decreases
Solution Approach 1:
The patent applies local quality control by optimizing the refractive index of the color filter material specifically in the blue wavelength region (400-500 nm) to be lower than the microlens, while allowing other regions to have different properties, thereby achieving localized refractive index matching that improves focusing efficiency without compromising overall light extraction
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 prevents a decrease in light focusing efficiency and improves light focusing performance, enhancing peak sensitivity between 400 nm to 500 nm.
Implementation Method 1
incident light is focused by microlenses, and then delivered to a photoelectric conversion element
Implementation Method 2
the color filter has a transmittance that exhibits a maximum value between wavelengths of 400 nm to 500 nm, while also exhibiting a transmittance of 50% between wavelengths of 460 nm to 490 nm
Implementation Method 3
solid-state imaging elements such as charge-coupled devices (CCDs) and complementary metal-oxide-semiconductor (CMOS) devices, which use photoelectric conversion elements such as photodiodes
Data Source
Figure 1~2
Figure 3
AI summary
A solid-state imaging element comprises: a semiconductor substrate (11) having a plurality of photoelectric conversion elements (12); a microlens layer (16) having a plurality of microlenses (17) that each cause light (γ) to enter the photoelectric conversion elements (12) of the semiconductor substrate (11); and color filters (14A to 14C) provided between the semiconductor substrate (11) and the microlens layer (16); wherein the color filter (14C) has a transmittance that exhibits a maximum value between wavelengths of 400 nm to 500 nm, while also exhibiting a transmittance of 50% between wavelengths of 460 nm to 490 nm, and has a refractive index that is a smaller value than that of the microlenses (17) at a wavelength in which the transmittance becomes the maximum value.