Air-Gap Pixel Shielding for CMOS Crosstalk Reduction
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Solution Overview
Problem
Optical crosstalk between adjacent pixel regions in CMOS image sensors degrades spatial resolution, reduces sensitivity, causes color mixing, and leads to image noise, and existing shielding structures either absorb photons or increase crosstalk.
Innovation Solution
Implementing a hybrid shielding structure with air gaps enclosed within a metal and dielectric layer grid structure between pixel sensors to reduce crosstalk while maintaining high quantum efficiency and signal-to-noise ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a metal shielding structure is used between pixel sensors, then crosstalk is reduced, but quantum efficiency decreases due to photon absorption
Solution Approach 1:
The patent applies porous materials by creating an air gap structure within the shielding grid. The air gaps (porous spaces) allow incident photons to pass through without being absorbed by metal, while still providing optical isolation between adjacent pixel regions. This resolves the contradiction by eliminating photon absorption (improving quantum efficiency) while maintaining crosstalk reduction through the physical barrier of the air gaps enclosed by metal and dielectric layers.
2Loss of energy
If a hybrid shielding structure with air gaps is implemented, then quantum efficiency increases, but device complexity increases
Solution Approach 1:
The shielding structure is segmented into discrete air gap regions enclosed by metal and dielectric layers. Rather than using a continuous solid metal shield, the structure is divided into isolated air-filled compartments positioned between pixel regions. This segmentation approach maintains the optical isolation function while minimizing material usage and reducing overall device complexity compared to solid shielding alternatives.
Solution Approach 2:
The patent introduces an intermediary air gap structure between the metal and dielectric layers. This air gap acts as a mediator that provides optical isolation without absorbing photons, enabling the system to achieve both crosstalk reduction and high quantum efficiency. The intermediary air gaps simplify the overall design by eliminating the need for complex multi-material composite shields.
3Object-affected harmful factors
If air gaps are used for shielding, then crosstalk is reduced and quantum efficiency is maintained, but manufacturing precision requirements increase
Solution Approach 1:
The air gaps are formed preliminarily during the semiconductor fabrication process by defining recesses in the substrate before subsequent dielectric layer deposition. This preliminary action ensures that air gaps are precisely positioned and sized according to design specifications, reducing the need for post-fabrication adjustments and simplifying manufacturing while maintaining the required optical isolation performance.
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 air gaps provide total reflection of incident light, reducing photon loss and crosstalk, thereby increasing quantum efficiency and signal-to-noise ratio of the pixel array.
Implementation Method 1
The air gaps provide total reflection of incident light, reducing photon loss and crosstalk, thereby increasing quantum efficiency and signal-to-noise ratio of the pixel array.
Data Source
AI summary
A shielding structure of air gaps, formed on a grid structure between pixel sensors in a pixel array, reduces crosstalk. Efficiency and signal-to-noise ratio of the pixel sensors is increased because crosstalk is reduced. The shielding structure also increases quantum efficiency of the pixel array because the air gaps do not adsorb photons.