Graphene Hall Sensor Cryogenic Sensitivity and Contamination
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Solution Overview
Problem
Existing Hall sensors face challenges in maintaining sensitivity and linearity at cryogenic temperatures, and are prone to contamination and doping issues due to atmospheric interactions, which affect their performance and stability over time.
Innovation Solution
A graphene Hall sensor with a specific sheet carrier density range of 2×10^11 cm^-2 to 1×10^13 cm^-2 is developed, featuring a plasma-resistant dielectric layer for protection and encapsulation, allowing for improved performance at cryogenic temperatures and resistance to magnetic field variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If graphene is used to improve sensitivity, then carrier mobility increases, but the device becomes more susceptible to atmospheric contamination and doping
Solution Approach 1:
The patent applies inert atmosphere by encapsulating the graphene layer with dielectric layers (such as aluminum oxide or silicon oxide) that create a protective barrier against atmospheric oxygen and water vapor. This prevents contamination and doping of the graphene while maintaining its high carrier mobility and sensitivity.
Solution Approach 2:
The dielectric layers serve as intermediary protective barriers between the graphene and the atmospheric environment. These intermediate layers block harmful atmospheric molecules from directly contacting the graphene, thereby preventing contamination while allowing the graphene to maintain its electrical properties.
2Ease of manufacture
If standard lithographic processes with polymer coatings are used, then patterning is achieved, but doping and contamination are introduced
Solution Approach 1:
The patent replaces the chemical lithographic process (using polymer coatings like PMMA that can dope the graphene) with a direct laser writing process. This substitution eliminates the need for photolithographic materials that introduce contamination and doping, while still achieving precise patterning of the graphene structure.
Solution Approach 2:
The patent extracts and removes the problematic polymer coating step from the manufacturing process. By using direct laser writing, the harmful intermediary material (polymer) is completely eliminated from the patterning process, preventing the associated doping and contamination issues.
3Ease of manufacture
If silicon-based Hall sensors are used, then manufacturing is straightforward, but operational temperature range is limited to 230K-350K
Solution Approach 1:
The patent changes the material parameter from silicon to graphene, which fundamentally alters the temperature dependence of the material. Graphene's unique electronic properties allow it to maintain high carrier mobility and linear response at cryogenic temperatures below 120K, expanding the operational temperature range while maintaining manufacturability through direct laser writing processes.
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 graphene Hall sensor achieves sensitivity comparable to silicon-based sensors at cryogenic temperatures, maintains linearity across a wide magnetic field range, and reduces contamination and doping, ensuring long-term stability and performance.
Implementation Method 1
The 'Hall-effect' occurs when a current flowing through the conductor interacts with a magnetic field orientated perpendicular to the direction of the current. Charge carriers flowing through the conductor experience a Lorentz force due to the magnetic field. The Lorentz force is perpendicular to the direction of current flow and perpendicular to the magnetic field. This force causes the flow of charge carriers through the conductor to bend, such that charge carriers accumulate on one side of the conductor. The separation of the charge carriers across the conductor establishes an electric field that opposes further charge separation. This potential is the Hall voltage, which can be measured across the conductor.
Implementation Method 2
The dielectric layer is provided on the graphene sheet. The graphene sheet and the dielectric layer share a continuous outer edge surface.
Data Source
AI summary
A graphene Hall sensor for operation at cryogenic temperatures is provided. The graphene Hall sensor comprises a substrate, a graphene sheet, a dielectric layer, a first pair of electrical contacts, and a second pair of electrical contacts. The graphene sheet is provided on the substrate. The dielectric layer is provided on the graphene sheet. The graphene sheet and the dielectric layer share a continuous outer edge surface. The first pair of electrical contacts are in electrical contact with the graphene sheet and spaced apart along a first direction. The second pair of electrical contacts are in electrical contact with the graphene sheet and spaced apart along a second direction. The first direction is perpendicular to the second direction, wherein a path along the first direction between the first pair of electrical contacts crosses a path along the second direction between the second pair of electrical contacts. The graphene sheet has a sheet carrier density in the range of 2×1011 cm−2 to 1×1013 cm−2.