New fabrication process for Josephson tunnel junctions with (niobium nitride, niobium) double‐layered electrodes

All hard Josephson tunnel junctions, whose base and counter electrodes are composed of double‐layered niobium nitride (NbN) and niobium (Nb) films, have been successfully fabricated by isolating a junction sandwich formed on a whole silicon wafer with a reactive ion etching technique. The reactive ion etching technique has been used for patterning both base and counterelectrodes, and self‐aligning definition of junction areas has been performed. The fabricated junctions show good quality single‐particle tunneling characteristics and excellent uniformity in critical currents.