Fabrication of NbCN/PbBi edge junctions with extremely low leakage currents

High-quality submicron NbCN edge junctions were fabricated using two separate plasma processes. A bilayer NbCN/SiO₂ edge is cut with an ion gun, using a photoresist mask for each process. The first plasma technique involves lightly cleaning the bilayer surface with a low-energy argon plasma which does not completely remove the thermally oxidized barrier formed after cutting the edge. The second technique involves a CF₄/Ar plasma cleaning; the existing barrier is apparently beneficially modified by the plasma. These two methods have resulted in extremely high-quality junctions with V_m (3 mV)>150 mV and 250 mV, respectively at 4.2 K. These V_m (3 mV) figures are much higher than other reports for edge junctions. It was also found that the junction quality was not dependent on the ion beam voltage used to cut the bilayer edges for these thermally oxidized barriers, in strong contrast to previous results with ion beam oxidation