RF properties of overdamped SIS junctions

A new type of nonhysteretic Josephson junction suitable for applications in voltage metrology has been developed. These junctions derive from the Nb/Al-AlO_x/Nb SIS junctions using a relatively thick Al layer oxidized at a low value of oxygen exposure. This produces junctions with reproducible and spatially homogeneous I-V characteristics, having current densities ranging from 10³ to more than 2×10⁴ A/cm² and characteristic voltages up to 0.40 mV. The authors report here the rf response of these junctions at 70 GHz. The authors have measured the dependence of the rf-induced steps on the microwave power and the stability of the steps, in view of a future application of these junctions to an AC Josephson voltage standard.