NIOBIUM TRILAYER JOSEPHSON TUNNEL-JUNCTIONS WITH ULTRAHIGH CRITICAL-CURRENT DENSITIES

We describe the fabrication and properties of Nb-AlO(x)-Nb Josephson t unnel junctions having critical current densities as high as 400 kA/cm 2, roughly an order of magnitude larger than any previously reported f or this materials system. The quality of the junction characteristics, as indicated by the current level at subgap voltages, is considerably lower in high-J(c) than in low-J(c) junctions. However, over the enti re high-J(c) range of 20-400 kA/CM2, the quality of our junctions rema ins the same (i.e., subgap current scales with critical current).