Characterization of YBCO/Au/YBCO resistors for HTS Josephson noise thermometry

It has been proposed that an absolute thermometer based on the linewidth br oadening of the Josephson oscillation could he realized in the temperature range 10 K to 50 K with the use of high-hemperature-superconducting resisti ve superconducting quantum interference devices (HTS R-SQUIDs). Although th is technique has been successfully demonstrated with LTS devices in the tem perature region below 1 K, there are unresolved problems which have so far prevented ifs translation to higher operating temperatures. A crucial compo nent of a resistive SQUID noise thermometer is the shunt resistor, which is required to have a value < 0.1 m<Omega>. The often excessive and unpredict able contact resistance between normal metal and HTS superconducting thin f ilms has up to now hindered the successful implementation of an HTS resisti ve SQUID. YBCO-Au-YBCO shunt resistors with suitable resistance values of s imilar to 20 mu Omega have recently been manufactured and their characteris tics under cryogenic operating conditions have been measured using the Jose phson frequency-voltage relationship.