Diffractive Pixel Structure for Filter-Free High-Resolution Color Sensing
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Solution Overview
Problem
Conventional color image sensors suffer from lower sensitivity, signal-to-noise ratio, color cross-talk, and spatial resolution due to the use of absorptive color filters, and require complex and costly fabrication processes involving non-complementary metal-oxide semiconductor (CMOS) materials, which degrade quickly.
Innovation Solution
An image sensor with a diffraction layer comprising transparent diffraction features that focus and diffract incident light onto sub-pixels, eliminating the need for color filters and micro lenses, and allowing high color resolution and sensitivity through asymmetric diffraction patterns dependent on light wavelength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If absorptive color filters are used in conventional color image sensors, then color detection capability is provided, but sensitivity and signal-to-noise ratio decrease by 3-4 times at low light conditions
Solution Approach 1:
The patent removes absorptive color filters from the image sensor structure entirely. Instead of filtering light before detection, the system uses a diffraction grating to spatially separate wavelengths, allowing all light to reach photodetectors without absorption losses. This extraction of the filtering function resolves the contradiction by maintaining color detection while eliminating the sensitivity penalty of absorptive filters.
Solution Approach 2:
The patent replaces the absorptive filtering mechanism with a diffractive optical system. Rather than using materials that absorb specific wavelengths, the system employs a diffraction grating that physically redirects different wavelengths to different spatial locations. This substitution eliminates the 3-4 times sensitivity loss while preserving color discrimination capability.
2Measurement precision
If absorptive color filters are used, then color information is captured, but color cross-talk and color shading occur at high chief ray angles
Solution Approach 1:
The patent substitutes absorptive filters with a diffraction-based spatial separation system. The diffraction grating directs different wavelengths to distinct spatial positions on the sensor array, eliminating the spectral overlap that causes color cross-talk. This mechanical redirection of light paths resolves color shading issues at high chief ray angles by maintaining precise wavelength-to-position mapping regardless of incident angle.
Solution Approach 2:
The patent segments the color detection function across multiple spatially separated photodetectors. Each detector receives a specific wavelength range directed by the diffraction grating, creating distinct detection zones. This segmentation eliminates color cross-talk by ensuring that each detector responds primarily to its assigned wavelength band, preventing the mixing of color signals that occurs with absorptive filters.
3Measurement precision
If absorptive color filters are used, then color imaging is enabled, but spatial resolution decreases due to color filter patterning
Solution Approach 1:
The patent segments the color detection function by wavelength rather than by spatial position in the traditional Bayer pattern. The diffraction grating separates colors in the optical domain, allowing all photodetectors to be sensitive to all wavelengths. This approach achieves color imaging without the spatial sampling limitations of filter arrays, thereby preserving full spatial resolution.
Solution Approach 2:
The patent makes all photodetectors universal by rendering them sensitive to the full spectrum. The diffraction grating performs the color discrimination function that filters would otherwise require, allowing each detector to contribute to all color channels. This multi-functionality eliminates the need for color filter patterning and maintains maximum spatial resolution.
4Measurement precision
If non-CMOS materials such as polymers are used for filters and micro lenses, then color filtering and light focusing are achieved, but fabrication becomes more time-consuming and expensive
Solution Approach 1:
The patent removes the need for separate polymer-based color filters and micro lenses. The diffraction grating structure performs both the wavelength separation and focusing functions that previously required multiple specialized components. This extraction of functions simplifies the bill of materials and fabrication process, eliminating the need for non-CMOS materials.
Solution Approach 2:
The patent merges the functions of color filtering and light focusing into a single diffraction grating structure. Rather than requiring separate filter layers and lens elements made from different materials, the grating combines these optical functions in one component that can be integrated into standard CMOS manufacturing processes.
5Use of energy by moving object
If non-CMOS materials are used for filters and micro lenses, then optical functionality is provided, but reliability and operational life are compromised due to weathering
Solution Approach 1:
The patent changes the material parameter from organic polymers to inorganic CMOS-compatible materials for the diffraction grating. This parameter change eliminates the weathering and degradation issues associated with polymer-based optical components. The inorganic materials used in CMOS fabrication provide superior environmental stability and operational life while maintaining the required optical functionality.
6Measurement precision
If uniform non-focusing metal gratings are used to diffract light, then wavelength characteristics can be determined, but light loss occurs before light reaches the substrate
Solution Approach 1:
The patent changes the grating material from metal to transparent dielectric material. This parameter change allows light to pass through the grating structure rather than being reflected or absorbed by metal surfaces. The transparent material maintains the wavelength-dependent diffraction capability while eliminating the light loss that occurs with metallic gratings.
Solution Approach 2:
The patent substitutes metal reflection-based diffraction with dielectric transmission-based diffraction. Instead of using metal surfaces to reflect and separate wavelengths, the system employs transparent dielectric structures that refract and diffract light as it passes through. This substitution eliminates absorption losses inherent in metal gratings while preserving spectral discrimination capability.
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 provides high sensitivity, spatial resolution, and wide spectral range with reduced manufacturing complexity, enabling accurate color identification within 25 nm and maintaining performance across a broad wavelength range without the need for micro lenses or color filters.
Implementation Method 1
The diffraction features operate to focus and diffract incident light onto the sub-pixels. The diffraction pattern produced across the area of the pixel by the diffraction features is dependent on the color or wavelength of the incident light.
Implementation Method 2
The diffraction features can be configured to focus the incident light by providing a higher effective index of refraction towards a center of an associated pixel, and a lower effective index of refraction towards a periphery of the associated pixel.
Implementation Method 3
Each pixel can include a photodiode that generates charge in an amount that is generally proportional to the amount of light (i.e. the number of photons) incident on the pixel during an exposure period.
Data Source
AI summary
Color image sensors and systems are provided. A color image sensor as disclosed includes a plurality of pixels disposed within an array, each of which includes a plurality of sub-pixels. A diffraction layer is disposed adjacent a light incident surface side of the array of pixels. The diffraction layer provides a set of transparent diffraction features for each pixel. The diffraction features focus and diffract light onto the sub-pixels of the respective pixel. Color information regarding light incident on a pixel is determined by comparing ratios of signals between pairs of sub-pixels to a calibration table containing ratios of signals determined using incident light at a number of different, known wavelengths. A wavelength with signal ratios that result in a smallest difference as compared to the observed set of signal ratios is assigned as a color of the light incident on the pixel.