FABRICATION OF TUNNEL JUNCTIONS ON NIOBIUM FILMS

High background currents, often observed in tunnel junctions when the barrier is formed by oxidizing niobium, probably stem from the fact that one oxide of niobium (NbO) is not an insulator. The fabrication process described in this paper uses an active layer of gas adsorbed on the niobium surface that reacts with the upper film (e.g., lead) and forms the junction barrier. This technique avoids the problem above and results in tunnel junctions with low background currents. © 1969 The American Institute of Physics.