A self-aligned nano-fabrication process for vertical NbN-MgO-NbN Josephson junctions

摘要

We present a new process for fabricating vertical NbN-MgO-NbN Josephson junctions using self-aligned silicon nitride spacers. It allows for a wide range of junction areas from 0.02 to several 100 mu m(2). At the same time, it is suited for the implementation of complex microwave circuits with transmission line impedances ranging from <1 Omega to >1 k Omega. The constituent thin films and the finished junctions are characterized. The latter are shown to have high gap voltages (>4 mV) and low sub-gap leakage currents.