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Quantum Conductance

Summary:

Graphene, discovered in 2004, has truly extraordinary electronic properties that enable new approaches in many areas where conventional materials are running into obstacles, ranging from the macro to nanoscale. Our efforts are currently focused on developing graphene to advance NIST’s core mission – specifically, the development of intrinsic quantum electrical standards to enable the development of innovative future electronics. Graphene represents a rare opportunity to dramatically improve metrology based on the fundamental constants by utilizing an inherently 2D conductive material made entirely of carbon atoms. However, application of the truly unique characteristics of graphene requires perfecting new fabrication methods as a route to better quantum Hall resistance (QHR) standards, single electron devices, and efficient quantum computing.

Description:

Since the quantum Hall effect was discovered over 35 years ago, fabrication of improved GaAs-GaAlAs heterostructures has been a goal of leading National Metrology Institutes (NMIs) around the world; however, they are consistently in short supply because of the difficulty and expense involved in their production. Monolayer graphene’s unique electrical properties will allow QHR standards to work efficiently at lower magnetic field strength, higher temperature, and higher current levels than semiconductor-based structures. Moreover high-quality graphene and the QHR standards themselves can be produced at NIST for rapid progress in research and development.

For electrical standards, monolayer graphene grown on insulating SiC substrates easily surpasses GaAs in performance at high temperature and current. Large monolayer graphene devices fabricated at NIST can operate at current levels and temperatures ten times higher than most existing QHR standards, while maintaining a precision of one part in a hundred million. This material was grown by annealing chips diced from SiC wafers in a Si-rich argon atmosphere at 1900°C, resulting in a graphene layer with highly uniform electrical properties. The devices were fabricated with a metal coating that shields the exposed graphene surface from unintentional contamination. We are working with collaborators at NIST and at several universities to improve such devices even further and to build a detailed understanding of their functional principles. Better and easier QHR traceability for customers who use room-temperature measurement systems is an initial goal of the project.

In microelectronics, it is well known that the continuation of Moore’s Law is already facing major challenges in power management and is being confronted by the discreteness of matter itself. The U.S. semiconductor industry spends billions of dollars to make incremental advances and desperately needs technology that transcends CMOS limitations. The major semiconductor industries have established consortia such as the Nanoelectronics Research Initiative (NRI) to direct various laboratories (academic, national, and corporate) to come up with visionary solutions to the foreshadowed limitations in silicon. Graphene promises to be one of these potential solutions, offering new opportunities for discovery to extend the availability of accurate electrical standards, high-frequency and quantum-based devices.

Interested in Reading More About Graphene?

Additional Technical Details:

Major Accomplishments:

  • Restricted the epitaxial growth to single-domain Dirac-carrier graphene over 50 mm2 areas
  • Eliminated high carrier density by molecular doping to obtain desirable QHR characteristics
  • Fabricated robust, large-scale devices while maintaining excellent electronic characteristics
quantum conductance
Graphene quantized Hall resistance device (inset) shown with a contrast-enhanced, magnified image of the device channel region (background). The device, including eight gold contact pads, is about one square mm in size.

Start Date:

January 1, 2008

End Date:

ongoing

Lead Organizational Unit:

pml

Facilities/Tools Used:

Advanced Measurement Laboratory

  • SiC annealing facility
  • Device characterization lab
  • NIST GaAs QHR standard
  • Cryogenic current comparators

CNST Nanofabrication Facility

Staff:

Randolph Elmquist
David Newell

Associates:

Yanfei Yang
Jiuning Hu
Chieh-Wen Liu

Related Programs and Projects:

Contact

Randolph Elmquist
(301) 975-6591

100 Bureau Drive, MS 8170
Gaithersburg, MD 20899-8170