Josephson Junctions and SQUIDs Created by Focused Helium-Ion-Beam Irradiation of Y Ba 2 Cu 3 O 7

To fabricate high-${T}_{c}$ Josephson junctions, YBa${}_{2}$Cu${}_{3}$O${}_{7}$ (YBCO) bicrystal grain-boundary junction technology is used most frequently, as it is simple and yields junctions of reasonable quality. This technique only allows placement of junctions along a single line on a chip, though. The authors instead use a focused helium-ion beam (He-FIB) to ``draw'' Josephson junctions anywhere on the chip. High FIB doses can also produce highly resistive walls that can be used as circuit boundaries, avoiding extra lithography. A SQUID drawn by He-FIB on a YBCO bridge is presented as proof of principle. These results should enable development of more complex YBCO circuits at sub-$\ensuremath{\mu}$m scale.