Niobium Josephson Junction With a Hf/HfN Double Overlayer

A Nb Josephson junction was fabricated with a Nb/HfOx--Hf/HfN/Nb structure. The junction showed an excellent current--voltage characteristics (V sub m = 40 mV), and these characteristics were degraded with annealing at temperatures up to 350 deg C. Each layer in the Hf/HfN double overlayer plays an important role in the junction structure. The Hf layer acts as a layer for the tunneling barrier formation and as an effective etch stop for a reactive ion etching process in junction fabrication. The HfN layer greatly contributes to the annealing durability of the junction by acting as an effective stop for grain boundary diffusion between the Nb and Hf layers.