Tunneling Studies On Thin Film Nb-Al Alloys

Relatively high quality Josephson tunnel junctions have been fabricated using e-beam coevaporated Nb-Al thin film alloys as the base electrode. Alloys of various Al concentrations, and deposited at several substrate temperatures, have been studied. Structure analysis indicates that these alloys contain metastable disordered bee and/or amorphous phases. Low excess tunneling currents and a small barrier dielectric constant (er~5) can be achieved by oxidizing an aluminum layer which is deposited on the base electrode as the tunnel barrier. © 1979 IEEE