Electrical Characterization of Nb/Al-Oxide/Nb Josephson Junctions with High Critical Current Densities

Transport in Nb/AlOx/Nb junctions involves two parallel channels, barrier defects (pinholes) with sub-nanometer dimensions and nearly-ideal tunneling regions. We fit junction characteristics using only a single parameter, the ratio of the normal state conductances of these current paths. Our barrier model accounts for the excellent Josephson behavior and highly non-ideal quasiparticle characteristics of junctions with critical current densities as high as 4 mA/µm2. It appears to be quite generally applicable to tunnel junctions. © 1995 IEEE