Fabrication of submicron YBCO Josephson junctions by a sample mosaic navigation assisted laser etching process

Taking advantage of a New Wave 213nm laser system, equipped with high-precision submicron resolution sample mosaic navigation, we are able to laser-etch and fabricate planar submicron-size Josephson junctions on YBa ₂Cu₃O_7-x thin films successfully. The entire process of laser etching and sample navigation is software controlled. The widths were measured by atomic force microscopy (AFM), and they range from 0.7 to 1.4νm. We report on the observed I-V characteristics and Shapiro steps, which confirm the Josephson effect in these junctions. The measured critical current dependence on temperature shows a linear relationship for micron-size constrictions. In the case of submicron constrictions, the dependence is an exponential decay type, consistent with diffusive long S-N-S junction behaviour. It is believed that the observed behaviour can be ascribed to laser heating of the constriction material, changing the superconducting phase to the normal one.