Josephson junctions of small area formed on the edges of niobium films

Abstract

Niobium-oxide-lead Josephson tunnel junctions formed on the edge of the Nb base electrode are found to have excellent tunnel characteristics up to Josephson current densities of at least 20 kA/cm2. They are made by growing an anodic oxide several hundred angstroms in thickness on the Nb followed by plasma etching of the sandwich using CF4+O2. Only the exposed edges of the Nb films are subsequently oxidized to form the tunnel barrier. Preliminary results show uniform and reproducible Josephson currents, with no evidence of leakage through the surface oxide. The structures combine small capacitance, a well-defined area, and the ability to pattern large arrays of junctions and interferometers, properties which make them attractive for cyrogenic computers and other high-frequency applications.