Portable quantum resistance standards: Making quantum resistance standards more widely available in industry
Resistors are used to manage the current flow in many electrical systems, whilst accurate resistance measurements underpin the precise control needed for sophisticated electronics and sensors. Highly accurate NMI resistance standards based on the Quantum Hall Effect (QHE) are used to link industrial instruments that characterise electronic components to the Ohm - the SI unit of resistance.
When electrical current passes through a magnetic field at right angles to the current’s flow a voltage difference is generated across the conductor. This is called the Hall Effect. In very high magnetic fields and at extremely low temperatures, two dimensional structures produce the quantum version of the Hall Effect. Two-dimensional graphene has the potential to simplify the experimental conditions needed by today’s NMI QHE standards. New methods for manufacturing suitable graphene, and ways to reliably characterise its performance are required before graphene can be considered for precise NMI resistance standards.
This project investigated the use of graphene to create more practical resistance standards.
• Developed methods for fabricating graphene suitable for use as a resistance standard, by growing graphene films on a substrate, and developed approaches to confirm its quality
• Confirmed graphene produced the QHE at higher temperatures and lower magnetic fields than existing resistance standard materials, whilst also identifying the further work needed to improve flow of electrons
• Demonstrated the potential for using graphene for impedance standards, the equivalent to resistance for AC current, which can confirm the performance of AC sensors and electronics such as touch screens
• Developed a room temperature instrument for scaling QHE resistance values, providing an alternative to cryogenic current comparators which rely on liquid helium to create very low temperatures.
As a result of this project, more European NMIs can now fabricate resistance grade graphene, and easier to use resistance standards have been developed. These are increasing the availability of highly precise resistance calibrations across the EU. Shortening the resistance calibration chain and bringing high quality resistance standards closer to industrial users will help innovation in electronic devices and supports increased competitiveness.
The project’s manufacturing method for high-quality large-area graphene wafers is proving valuable for developing new graphene technologies, such as sensors for small magnetic fields, as well as those for radiation and gas detection.
Simpler resistance standards, and in the future potential impedance standards, will spur innovation in a wide range of technologies where the electrical resistance of materials is important, including sensors, electronics and communications.
Coordinator: Franz Josef Ahlers (PTB)
For more information, please contact the EURAMET Management Support Unit
Phone: +44 20 8943 6666