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 t he ramp edge surfaces with ion beams and heat-treated them under various co nditions prior to the deposition of counter-electrode layers. After pattern ing the samples into ramp edge junctions using photolithography and ion bea m etching, we measured their electrical properties, such as current-voltage characteristics, magnetic field modulation of the critical current, and mi crowave responses. Some showed resistively shunted junction (RSJ)-type curr ent-voltage (I-V) characteristics, while others exhibited flax-flow behavio rs, depending on the details of interface treatment. Junctions fabricated u sing optimized conditions showed fairly uniform distribution of junction pa rameters. Their I-V curves were RSJ-type, which was also proved by the micr owave-induced constant voltage steps. IcRn values of typical RSJ-type junct ions were about 0.07 mV at 77 K.