Fabrication of All-Nb Josephson Junctions Using Oxidized Zr Overlayers

Fabrication of all-Nb Josephson tunnel junctions using artificial barriers of oxidized Zr overlayers is described. Thin Zr overlayers are sputter-deposited onto polycrystalline Nb films and then thermally oxidized. The tunneling characteristics of these junctions are found to be greatly affected by the occurrence of Zr diffusion into the grain boundaries of the base Nb films during Zr deposition, which is confirmed by XPS analysis. Paying particular attention to the rapid substrate cooling, high quality junctions with V m =47 mV are obtained.