The effect of electrode materials on Pb alloy superconducting tunnel junctions for submillimetre wave heterodyne receiver application

Abstract

Submicron superconducting tunnel junctions were fabricated for submillimetre wavelength heterodyne detection. To this end three types of Pb alloy electrodes were investigated. All have shown good I-V do characteristics but only the Pb-In-Au alloy produced stable and reliable junctions in vacuum and thermal cycling. Au-free junctions were found to be unreliable and would fail, i.e would form a short circuit, when placed in vacuum by desorption of water from the oxide barrier. This effect was subsequently stopped by alloying the electrode with 1% wt of Au leading to cathodic corrosion which in turn protects the junction from failing in vacuum.