Waveguide Grating Resonance Filters for CMOS Image Sensor Crosstalk Reduction

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Solution Overview

Problem

Conventional CMOS imagers face challenges in efficiently separating and detecting spectral components of incident light, particularly due to increased crosstalk between pixels as they miniaturize, leading to oversaturation and reduced image quality.

Innovation Solution

The implementation of a waveguide grating resonance filter layer with varying effective refractive indices and grating pitches to selectively pass specific wavelengths of light onto photosensors, reducing crosstalk and enhancing optical sensitivity by using materials with different refractive indices and absorption coefficients.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If pixel cells are miniaturized to increase integration density, then device integration is improved, but crosstalk between pixels increases causing oversaturation and reduced image quality

Engineering Contradiction:

Improveintegration densityVSAvoidcrosstalk between pixels

Core Design Contradiction:

ProductivityVSObject-affected harmful factors

Solution Approach 1:

A waveguide layer is introduced as an intermediary component between the color filter array and photosensors. This waveguide layer with grating structures acts as a mediator to guide and separate light wavelengths to specific photosensors, preventing crosstalk while maintaining miniaturized pixel cell dimensions and high integration density

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent modifies optical parameters by implementing a waveguide layer with specific grating pitch values (e.g., 200-400 nm) and refractive index profiles. By changing these physical parameters, the system achieves wavelength-selective light guidance that reduces pixel crosstalk while maintaining small pixel sizes for high integration density

Inventive Principle:

Principle #35Parameter changes

2Measurement precision

If conventional absorptive color filter arrays are used, then color detection is achieved, but spectral separation is insufficient leading to reduced optical sensitivity and increased crosstalk

Engineering Contradiction:

Improvespectral separationVSAvoidcrosstalk and oversaturation

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The patent replaces the conventional absorptive color filter mechanism with a waveguide-based optical guidance system. Instead of relying on material absorption properties, the system uses waveguide physics and grating diffraction to achieve precise spectral separation, thereby improving measurement precision and reducing harmful crosstalk

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The waveguide layer is segmented with periodic grating structures that spatially separate different wavelengths of light. This segmentation approach directs specific wavelength ranges to specific photosensors, achieving superior spectral separation compared to conventional absorptive filters

Inventive Principle:

Principle #1Segmentation

3Area of moving object

If pixel size is reduced to increase array density, then integration capability is improved, but optical sensitivity decreases due to increased crosstalk

Engineering Contradiction:

Improvepixel cell sizeVSAvoidoptical sensitivity

Core Design Contradiction:

Area of moving objectVSReliability

Solution Approach 1:

The waveguide layer serves as an intermediary that compensates for the reduced light collection area of miniaturized pixels. By guiding light through the waveguide structures, the system maintains optical sensitivity despite smaller pixel dimensions, while the grating patterns prevent crosstalk between adjacent pixels

Inventive Principle:

Principle #24Intermediary (Mediator)

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 results in higher transmittance and narrower bandwidths for each color, providing purer color spectra and improved dynamic range, which reduces the complexity of post-processing and enhances image quality.

Implementation Method 1

waveguide grating resonance filter layer with varying effective refractive indices and grating pitches to selectively pass specific wavelengths of light onto photosensors

Methodology Applied

Scientific EffectGuided-mode resonance: Resonance

Implementation Method 2

varying effective refractive indices and grating pitches to selectively pass specific wavelengths of light

Methodology Applied

Scientific EffectRefraction: Refraction

Data Source

PatentUS7858921B2Guided-mode-resonance transmission color filters for color generation in CMOS image sensors

Publication Date: 2010.12.28 APTINA IMAGING CORP

AI summary

Imager pixel arrays and methods for forming imager pixel arrays. An image sensor pixel includes a photosensor and a waveguide grating resonance filter formed over the photosensor. The waveguide grating resonance filter is configured to pass light to the photosensor in a wavelength band and to block light outside of the wavelength band. The waveguide grating resonance filter includes a grating material having a first refractive index and arranged in a grating pattern with a grating pitch, and has an effective refractive index that is a function of the first refractive index. A combination of the grating pitch and the effective refractive index is selected to correspond to the wavelength band.