Improved process for high-T_c superconducting step-edge junctions

We have developed a process for the fabrication of YBaCuO high-T c junctions based on the step-edge weak-link concept. The process emphasizes the creation of sharp and straight step edges on a substrate, and the restoration of oxygen content for superconducting materials at the step edges. A diamond-like carbon film is used as an ion milling mask for the creation of steps on substrates such as LaAlO3 and SrTiO3. Room-temperature plasma oxidation is shown to be effective in restoring T c from processing related degradation for grains residing at the step edge. Using this process, dc SQUIDs were fabricated with 77 K electrical performances matching, and in certain cases exceeding, similar SQUIDs made using bicrystal-based tilt-boundary weak-link junctions.