Three terminal, non-equilibrium quasiparticle device experiments with submicron tunnel junctions

A multilayer film edge technique has been developed for the fabrication of dual small area tunnel junctions on the aligned edges of two overlapping thin films separated by a thin insulating layer, with a common electrode shared by the two junctions. Using this technique with electron beam lithography, junction areas as small as 3 × 10-10A/cm2have been produced with separations between the two tunnel barriers of 50-80 nm. Devices of this type have been fabricated with Pb alloy counterelectrodes on Nb edges, using reactive ion beam oxidation to obtain tunnel current densities in the 105A/cm2range. The potential of this multijunction configuration as a high speed, three terminal Josephson device with current and power gain has been investigated. In addition, the edge junctions have been employed to probe non-equilibrium phenomena in the common electrode.