Improvements in the quantum Hall resistance standard at VTT

This paper describes improvements in the realisation of the quantum Hall effect (QHE) resistance standard at VTT and presents the results of the latest measurements. A new superconducting magnet and a new QHE sample were used to calibrate standard resistors in terms of R/sub K-90/, (R/sub K-90/=25812.807 /spl Omega/ is the conventional value of the von Klitzing constant R/sub K/). A 100 /spl Omega/ standard resistor was calibrated directly against the quantum Hall resistance (QHR) on i=2 plateau using a low-frequency cryogenic ac resistance bridge based on the cryogenic current comparator (CCC). The same cryogenic ac bridge was used to trace the 1 /spl Omega/ and 10 k/spl Omega/ standard resistors from the 100 /spl Omega/ standard.