Critical Current Density and Temperature Dependence of Nb-Al Oxide-Nb Junction Resistance and Implications for Room Temperature Characterization

Room temperature junction resistance measurements are commonly used for screening Josephson-based circuits because testing is much easier than at cryogenic temperatures and can even be carried out at the wafer level. The value of ambient testing depends on the existence of a strong correspondence between the measured resistance at room temperature and the resistance and critical current obtained at the ultimate operating temperature. We have systematically studied the temperature dependence of junction resistance in order to quantify the emergence, with increasing critical current density, of parasitic contributions from non-uniform currents flowing in the Nb films, which tend to limit the value of room temperature screening. We will describe our measurements and our approach to correcting for these parasitic effects.