Color-Filter-Free Image Sensor With ARL for Small-Pixel Color Separation
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Solution Overview
Problem
Existing image sensors suffer from low light use efficiency due to the use of color filters, which absorb two-thirds of the incident light, and pixel size reduction limits color separation, leading to resolution deterioration.
Innovation Solution
An image sensor design that incorporates multiple photodiodes for different wavelength bands without a color filter, utilizing an anti-reflection layer (ARL) with a refractive index between 1 and 1.08 times the square root of the product of the sensing layer and air indices, and a thickness ratio of 1/50 to 1/2.5, to enhance light absorption and reduce reflectance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a color filter is used to detect light color, then color detection function is achieved, but light use efficiency is lowered due to absorption of two-thirds of incident light
Solution Approach 1:
The patent removes the color filter component from the image sensor structure and replaces it with multiple photodiodes having different bandgap energies that directly absorb specific wavelength bands. This extraction of the color filter eliminates the 2/3 light absorption loss while maintaining color detection capability through direct photodiode absorption.
Solution Approach 2:
The patent substitutes the mechanical/optical color filter system with a semiconductor-based photodiode absorption system. Instead of using a color filter to selectively transmit or absorb light wavelengths, the invention uses photodiodes with different bandgap energies to directly convert specific wavelength bands into electrical signals, achieving color detection through semiconductor physics rather than optical filtering.
2Manufacturing precision
If pixel size is reduced to increase resolution, then more pixels can be packed, but color separation function is limited
Solution Approach 1:
The patent divides each pixel into multiple photodiodes with different bandgap energies, where each photodiode is responsible for detecting a specific wavelength band. This segmentation allows color separation to occur at the photodiode level within each pixel, maintaining color detection capability even when pixel sizes are reduced for higher resolution.
Solution Approach 2:
The patent changes the fundamental parameter used for color separation from spatial filtering (color filters) to material property differences (bandgap energies of photodiodes). By utilizing photodiodes with different bandgap energies, the system achieves wavelength-selective absorption based on material physics rather than optical filtering, enabling color separation to function effectively at smaller pixel dimensions.
3Loss of energy
If an anti-reflection layer is added to reduce surface reflectivity, then light absorption is enhanced, but device structure becomes more complex
Solution Approach 1:
The patent introduces an anti-reflection layer as an intermediary component between the incident light and the photodiodes. This intermediate layer reduces the reflectivity at the air-semiconductor interface, allowing more light to enter the photodiodes and be absorbed. The anti-reflection layer acts as a mediator that improves light coupling without fundamentally changing the core photodiode detection mechanism.
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
Improves light use efficiency and maintains color separation performance, reducing artifacts like flares and ghosts, while enabling high-resolution imaging without the need for color filters.
Implementation Method 1
an anti-reflection layer (ARL) provided on a light incident surface of the sensing layer to lower reflectance of light incident on the sensing layer
Implementation Method 2
A refractive index of the ARL satisfies 1ARL≤1.08×√{square root over (nS×nAIR)}, when nARL denotes the refractive index of the ARL is nARL, nS denotes a refractive index of the sensing layer is nS, and nAIR denotes a refractive index of air
Implementation Method 3
a first photodiode configured to absorb light in a red wavelength band, a second photodiode configured to absorb light in a green wavelength band, a third photodiode configured to absorb light in a blue wavelength band
Implementation Method 4
a filling material provided around the first photodiode, the second photodiode, and the third photodiode
Data Source
AI summary
An image sensor includes a plurality of pixels arranged two-dimensionally and each having a size less than or equal to a diffraction limit. Each of the plurality of pixels includes a sensing layer including two or more photodiodes, and a surrounding material filling an area around the first, second, and third photodiodes. The two or more photodiodes include first, second, and third photodiodes that selectively absorb lights in red, green, and blue wavelength bands, respectively. An anti-reflection layer (ARL) is located on a surface of the sensing layer. The ARL lowers reflectance of light incident on the sensing layer.