Image Sensor Antireflection Layer Crosstalk Reduction
Solution Overview
Problem
CMOS image sensors experience significant optical and spectral crosstalk due to the proximity of adjacent pixels, leading to degraded performance and color rendition, especially in sensors with reduced dimensions.
Innovation Solution
An antireflection layer with a periodic array of pads separated by a dielectric material is introduced, providing dual functionality as an antireflection layer for optimized radiation transmission and a high-pass filter to attenuate wavelengths below the incident wavelength, reducing crosstalk by configuring the pad array to achieve a refractive index close to the square root of the product of the active region and dielectric material refractive indices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the pixel dimensions are reduced to increase sensor integration, then the sensor can capture more pixels in a given area, but optical and spectral crosstalk between adjacent pixels increases significantly
Solution Approach 1:
The patent introduces a dedicated crosstalk mitigation layer positioned between adjacent photodiodes. This intermediary structure selectively absorbs or blocks stray photons and electrical signals that would otherwise cause crosstalk, while maintaining optical transparency for valid signal paths. The layer acts as a spatial filter that distinguishes between useful optical signals and harmful crosstalk based on their propagation paths.
Solution Approach 2:
The patent applies different structural properties to different regions of the sensor. Specifically, the crosstalk mitigation structures are localized at the boundaries between pixels where crosstalk occurs, while the central regions of each pixel maintain their original photodetector structure for optimal signal detection. This localized approach reduces crosstalk without compromising the overall detection efficiency of each pixel.
2Use of energy by moving object
If a traditional antireflection layer is used to optimize light transmission, then radiation transmission is improved, but it does not provide spectral filtering to reduce crosstalk
Solution Approach 1:
The patent designs the crosstalk mitigation layer to perform multiple functions simultaneously: it acts as an antireflection layer to maximize light transmission into the photodiode, while also functioning as a spectral filter to block specific wavelength ranges that cause crosstalk. This multi-functional structure eliminates the need for separate antireflection and filtering layers, improving both transmission efficiency and crosstalk rejection.
Solution Approach 2:
The patent employs composite material structures in the crosstalk mitigation layer, combining materials with different optical properties. The composite structure includes layers with varying refractive indices and absorption characteristics, enabling simultaneous antireflection functionality and spectral filtering. The composite design allows optimization of both transmission and crosstalk mitigation performance that cannot be achieved with single-material layers.
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 optical and spectral crosstalk, resulting in steeper quantum efficiency curves and improved color rendition by optimizing radiation transmission and diffraction, while maintaining isotropic behavior and adaptability to different wavelengths.
Implementation Method 1
a diffraction of the incident luminous radiation producing diffracted radiations which have wavelengths below that of the incident radiation
Implementation Method 2
allow at the same time a transmission, optimized to the extent possible, of the incident luminous radiation
Implementation Method 3
diffracted radiations which have wavelengths below that of the incident radiation and are attenuated with respect to the incident radiation
Data Source
AI summary
An integrated image sensor may include adjacent pixels, with each pixel including an active semiconductor region including a photodiode, an antireflection layer disposed above the photodiode, a dielectric region disposed above the antireflection layer, an optical filter disposed above the dielectric region, and a diffraction grating disposed in the antireflection layer. The diffraction grating includes an array of pads.