THE QUANTUM HALL-EFFECT AND RESISTANCE STANDARDS

Following the discovery of the quantum Hall effect in 1980 metrologists were eager to develop the effect as a resistance standard in a similar manner to the development, a decade earlier, of the Josephson effects in superconductors as a voltage standard. This article reviews the progress made by many national laboratories to assess and compare the quality and limitations of semiconductor devices, mainly silicon MOSFETs and GaAs/AlGaAs heterostructures, as quantized Hall resistance standards with values R(H) (i) = R(K)/i = h/ie2, where R(K) = 25812,807-OMEGA is the von Klitzing constant and i is an integer. Potentiometric and cryogenic current comparator bridge techniques for the measurement of R(K) in terms of conventional resistance standards with 1-sigma relative accuracies better than 1 part in 10(8) are compared, and determinations of R(K) in ohms with accuracies as high as 2,4 parts in 10(8) using calculable capacitors are described. The comparison of direct determinations of R(K) with alternative derivations of h/e2 leading to the CCE recommendations and subsequent international adoption, from 1 January 1990, of the value 25812,807 +/- 0,005-OMEGA for R(K) are also described.