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.