Fabrication and characterization of all-refractory NbCN/Al/AlO/sub x//Al/Nb junctions

High-quality AlO/sub x/ tunnel barriers have been fabricated on epitaxial niobium carbonitride (NbCN) base layers by the deposition of an Al layer followed by thermal oxidation. By careful control of its uniformity, the thickness of the Al layer has been reduced to less than 3 nm, which results in an average gap voltage, V/sub g/(NbCN), of up to 2.65 mV. Using a self-aligned whole-wafer processing route, high-quality NbCN/Al/AlO/sub x//Al/Nb junctions as small as 0.6 mu m/sup 2/ have been made. These junctions offer considerable advantages over directly deposited barriers in terms of minimal subgap leakage, good control of the barrier conductance, and simple processing procedures. It was shown that submicron junctions can be fabricated with no gap smearing or reduction in quality. Using only Nb counterelectrodes total gap voltages up to 4.0 mV, with widths of 0.6 mV, have been demonstrated in high-quality junctions.>