A fully automated system for the characterization of standard reference resistors using the quantum Hall effect

The authors have constructed a self-contained, fully automatic system for the characterization of laboratory transfer resistance standards. A novel feature is the integration of all elements into a single cryogenic system. The instrument allows direct comparison of standard resistors with the quantum Hall resistance in GaAs/GaAlAs heterostructures. At low temperature the Hall voltage exhibits plateaux of constant value as the external magnetic field is increased, corresponding to a quantum Hall resistance equal to h/e/sup 2/n, where h is Planck's constant, e the electron charge and n an integer. The resistance of the transfer standard can therefore be determined from fundamental physical constants. The system comprises a /sup 3/He insert capable of producing temperatures down to 300 mK, a 14T superconducting magnet to allow resistance plateaus of up to n=2 to be attained, and a Cryogenic Current Comparator (CCC) mounted in a common cryostat to minimise liquid helium consumption. Use of an RF SQUID as a null detector allows DC currents in the CCC to be balanced with a precision of better than 1 part in 10/sup 9/. The system operates under PC control using the LABVIEW programming environment.