Submicron tunnel junctions

We have fabricated a variety of small-area, superconducting tunnel junctions and simple superconducting interferometer circuits using novel e-beam and optical lithographic techniques. These Pb-oxide-Pb(In) tunnel junctions are made using self-aligning processes which involve multiple oblique evaporations through suspended liftoff stencils formed in two-layer resist systems. Oxide barriers are grown in situ immediately after evaporation of base electrode films. Junction areas range from 10^-9cm²(optically patterned) to about 10^-10cm²(e-beam patterned). Current densities as high as 2×10⁶A/cm²have been attained. The high current-density junctions show only small hysteresis at 4K and are completely non-hysteretic at higher temperatures. These junctions have been used to make low-hysteresis interferometers with a current gain of 3. A positive feedback scheme is described which provides sharper switching characteristics in non-latching interferometers.