FABRICATION OF NBCN/PBBI EDGE JUNCTIONS WITH EXTREMELY LOW LEAKAGE CURRENTS

We have fabricated high-quality submicron NbCN edge junctions 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 edge junctions with V(m)(3mV) > 150mV and 250mV respectively at 4.2K. These V(m)(3mV) figures are much higher than any reports for edge junctions of which we are aware. It was also unexpectedly 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 with our previous results with ion beam oxidation.