Effect of ion beam damage and heat treatment on interface-modified junctions

We have fabricated Josephson junctions by modifying ramp edges of the base electrodes without depositing any artificial barrier layer. We irradiated the ramp edge surfaces with ion beams and heat-treated them under various conditions prior to the deposition of counter-electrode layers. After patterning the samples into ramp edge junctions using photolithography and ion beam etching, we measured their electrical properties, such as current-voltage characteristics, magnetic field modulation of the critical current, and microwave response. Some showed resistively shunted junction (RSJ)-type current-voltage (I-V) characteristics, while others exhibited flux-flow behavior, depending on the details of interface treatment. Junctions fabricated using optimized conditions showed fairly uniform distribution of junction parameters. Their I-V curves were RSJ-type, also shown by the microwave-induced constant voltage steps. I/sub c/R/sub n/ values of typical RSJ-type junctions were about 0.07 mV at 77 K.