A novel technique for preparation of tunnel junction barriers using electrochemical anodization

A novel method has been developed for preparing both Josephson and single particle tunnel junctions. This technique has been extensively applied to Sn-SnxOy- metal films where the tin oxide barrier is formed on the surface of a freshly evaporated Sn film by electrochemical anodization. By varying the anodization parameters, the junction resistances can be controlled over more than three orders of magnitude: i.e., from less than 10^-4ohm-cm²to 0.1 ohm-cm². In each instance, high quality junctions with nearly ideal IV characteristics and low leakage currents have been produced. Low resistance Josephson junctions have been fabricated whose critical currents scale with junction resistance and modulate with applied magnetic field in the familiar Fraunhofer-like diffraction pattern. Sn-SnxOyAg-Pb proximity effect samples with the oxide barriers prepared as described above have been used to study magnetic penetration in the Ag layer. We hope to extend this technique to prepare junctions using base electrode superconductors like NbN which then will have considerable technological significance.