High-quality submicron niobium tunnel junctions with reactive-ion-beam oxidation

A new reactive-ion-beam oxidation technique has been applied to the fabrication of rugged, high-quality niobium-lead alloy Josephson tunnel junctions. Control of critical current density over a wide range is possible, and critical current densities exceeding 106 A/cm2 have been obtained. In addition, a process-compatible edge geometry has been developed which allows a junction to be formed on the faceted edge of a niobium base electrode, yielding devices with areas of 10−9 cm2 using 1-μm photolithography.