HIGH T-C SUPERCONDUCTING STEP-EDGE JUNCTIONS AND THEIR PROPERTIES IN MILLIMETER-WAVE BAND

Superconducting step-edge junctions were fabricated on step-edges in ( 100) LaAlO3 substrates by sputter-deposited epitaxial YBaCuO and TlBaC aCuO thin films. The substrate steps were patterned by ion beam etchin g using metal film as a mask The transport properties of the junctions were characterized by four-probe electrical measurements. The critica l current-normal resistance product (I(c)R(N)) was larger than 0.2mV ( 77K) for most of the junctions. Clear Shapiro steps were observed in t he current-voltage characteristics of the junctions with 36GHz or 95GH z millimeter-wave irradiation. The high frequency properties of these high T-c Josephson junctions showed that they were quite suitable for the Josephson harmonic mixer used in the digital phase locked millimet er and sub-millimeter wave sources.