Influence of thermal oxide on leakage current for Pb-alloy Josephson junctions

Abstract

The effects of thermal oxide on leakage current of rf-plasma oxidized Pb-In-Au alloy Josephson junctions are examined. The leakage current is small in junctions with thermal oxide grown at low oxygen pressure and for a long period. Current-voltage characteristics at low temperature show that the leakage current magnitude is closely related to the magnitude of the current steps at the gap voltages of electrode materials. Furthermore, optical property investigations of the oxide show that leakage current decreases with a decrease in the oxide absorption coefficients, which are correlated to carrier density. Based on these experimental data, a leakage current model is proposed for Pb-alloy junctions. This model shows that the tunneling current between superconductor and normal metal regions in the oxide barrier causes leakage current.