Ultraviolet light assisted oxygenation process for submicron $YBa2Cu3O7−δ$ thin film devices

We have successfully fabricated superconducting nanobridges and grain-boundary junctions from epitaxial $YBa2Cu3O7−δ$ thin films with thickness between 20 and 30 nm and width down to $∼100$ nm. The patterning process turned out to severely deteriorate the transport properties resulting in structural damage, corrosion, and oxygen loss. The most crucial steps are the baking procedure used to cure the electron beam resist, the resist development, and the ion beam etching process. By optimizing these steps and applying a suitable post-treatment procedure a significant enhancement of the sample quality could be achieved. An ultraviolet light assisted oxygenation procedure after the patterning process enabled us to achieve superconducting transition temperatures between 80 and 87 K and critical current densities at 4.2 K up to $4×107 A cm−2$ for the nanobridges and $5×103–2×105 A cm−2$ for the grain boundary junctions. At 4.2 K junctions with width down to 100 nm corresponding to a junction area down to $2.3×10−3$ $μm2$ showed superconductivity.