Waveguide Tube Image Sensor Crosstalk Reduction
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Solution Overview
Problem
Conventional CMOS image sensors suffer from crosstalk effects due to light scattering, which degrade signal-to-noise ratio and reduce imaging sensitivity, particularly when incident light strikes the surface at non-perpendicular angles.
Innovation Solution
The integration of a wave-guide tube with a straight sidewall and a filler embedded in a dielectric layer, featuring an optical barrier with a different refractive index, prevents crosstalk by ensuring total internal reflection of incident light, thereby enhancing light collection and sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If conventional CIS structure with metal lines and dielectric layers is used, then integration and miniaturization are achieved, but light scattering and crosstalk occur when incident light strikes at non-perpendicular angles
Solution Approach 1:
The patent extracts the problematic metal lines from the optical path by placing them in the peripheral electronic circuit area outside the light sensing area. The light sensing area uses a simplified structure without metal lines, eliminating the source of light scattering and crosstalk while maintaining integration through separate peripheral circuits for signal processing.
Solution Approach 2:
The patent divides the CIS structure into distinct functional areas: a light sensing area with photodiodes arranged in an array without metal lines, and a peripheral electronic circuit area containing metal lines for interconnects. This segmentation isolates the light-sensitive region from sources of optical interference while maintaining electrical connectivity through dedicated peripheral circuits.
2Productivity
If photodiodes are arranged in an array with multilevel interconnects, then signal processing capability is improved, but light scattering from metal lines degrades signal-to-noise ratio
Solution Approach 1:
The patent segments the device into a light sensing area containing only photodiodes for optimal light reception and signal generation, and a peripheral electronic circuit area containing metal lines and transistors for signal processing. This spatial separation ensures that metal lines do not interfere with incident light while still providing full signal processing capability through the peripheral circuits.
Solution Approach 2:
The patent introduces a specialized structure at the boundary between light sensing and peripheral areas that acts as an intermediary. This structure allows electrical signals to be transferred from photodiodes to peripheral circuits while preventing optical interference from metal lines from reaching the photodiodes, thus maintaining both signal processing capability and high signal-to-noise ratio.
3Object-affected harmful factors
If light passageway with metal barriers is used to prevent crosstalk, then light scattering is reduced, but the discontinuous surface causes light scattering and reduces light reception
Solution Approach 1:
The patent removes metal barriers from the light passageway structure entirely. Instead, it uses a planarized dielectric surface with optional transparent filler materials to define the light reception area. This eliminates the discontinuous surface caused by metal barriers while still preventing crosstalk through proper structural design and material selection.
Solution Approach 2:
The patent applies different material properties to different regions: the light passageway uses transparent or translucent filler materials with appropriate refractive indices to guide light, while the peripheral areas use metal lines for electrical connectivity. This local differentiation allows optimal light reception in the sensing area while maintaining electrical functionality in peripheral circuits.
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 effectively reduces surface defects and leakage currents, improves image sensing efficiency, and increases sensitivity by minimizing light scattering and crosstalk, leading to enhanced imaging performance.
Implementation Method 1
The wave-guide tube includes a filler embedded in the dielectric layer and an optical barrier disposed on a sidewall of the filler. The dielectric layer, the filler, and the optical barrier have a refractive index n1, a refractive index n2, and a refractive index n3, respectively. In addition, the refractive index n2 is larger than the refractive index n3.
Data Source
AI summary
An image sensor includes a substrate, at least an optical device, at least a dielectric layer, and at least a wave-guide tube disposed upon the optical device. The wave-guide tube has an optical barrier disposed on a sidewall thereof and a filter layer filled in the wave-guide tube. The structure of the wave-guide tube has the advantages of shortening light path, focusing, and preventing undesirable crosstalk effect between different optical devices.