Plasma nitridation process for the fabrication of all-refractory Josephson junctions

A process for the fabrication of high-quality, all-refractory Josephson junctions of the type Nb/Six Ny /Nb is described in detail. The junctions have been fabricated using the selective niobium anodization process with a tunnel barrier consisting of an amorphous Si film converted to its nitride by the application of a rf plasma of nitrogen. An attractive feature of these junctions is their comparably low specific capacitance C/A=3.9±0.1 μF/cm2 (for Jc =6 A/cm2 ). Junctions of this type having critical current densities up to Jc =2000 A/cm2 and Vm =16 mV have been fabricated. Excellent magnetic field threshold curves have also been observed for these junctions, indicating that the critical current density is very uniform.