Improved process for high- T c superconducting step-edge junctions

We have developed a process for the fabrication of YBaCuO high-Tc 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 Tc 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.