RF-sputter-deposited magnesium oxide films as high-quality adjustable tunnel barriers

High-quality RF-sputtered MgO films as tunnel barriers to fabricate small-area nitride tunnel junctions. A magnetism oxide barrier deposited as a single layer or as a multilayer film results in devices with similar characteristics. Annealing trilayers at temperatures in excess of 250°C for several hours decreases junction current density and improves device quality, presumably by increasing barrier heights through reducing resonant tunneling states. A self-aligned process utilizing only two mask levels is used to produce junctions as small as 0.5 μm² with excellent critical current uniformity. These junctions exhibit energy gaps of 5.1 mV and low subgap currents at current densities in excess of 1000 A/cm², which make them suitable for a variety of applications such as SIS (superconductor-insulator-superconductor) mixers and logic circuits