Barrier formation in lead-based tunnel junctions studied by surface techniques

A process is described for the production of Pb(In) - oxide barrier - Pb Josephson tunnel junctions. The junctions are predictable in resistance to within 30%, and have excellent leakage, storage and ageing properties. Critical currents and magnetic behaviour agree well with theory. Investigation of the deposited films by surface techniques shows that the presence of In suppresses the formation of ´hillocks´ which occur during annealing and during sputter etching. The distribution of In through the films is investigated by Ion Scattering Spectroscopy, which shows In enrichment at the free surface. There is some, as yet inconclusive, evidence that In plays an important role in the barrier formation (oxidation) process.