NbN-MgO-NbN Josephson junctions prepared by window isolation process

NbN-MgO-NbN Josephson junctions prepared by the window isolation process are investigated with the aim of setting up a reliable fabrication process for integrated thin-film superconducting quantum interference device (SQUID) applications. Compared to the SNAP, SNIP, and other related processes, the trilayer is built up in two separate steps, which has the advantage that the base- and the counter-electrode can be formed without affecting the junction edges, and therefore leakage currents at the edges can easily be prevented. The critical current density can be varied between 0.1 and 4.0 kA/cm/sup 2/ with values of V/sub M/ on the order of 40 mV. For the integration of the junctions into a multilayer SQUID system, the authors developed for each relevant material (Nb, NbN, SiO) a specific reactive ion etching process to produce oblique edges of the structures. This facilitates the crossing of narrow current leads of moderate film thickness without any reduction in cross section or even interruptions.<>