Josephson junctions fabrication in multi-layer deposition and post annealing MgB<sub>2</sub> thin films

Abstract

Josephson junctions are fabricated by focused ion beam in MgB₂ thin films. The films were prepared by deposite multi-layer Mg and B films at room temperature first and then annealed at about 700°C. These films have <italic>T</italic>_c of 32 K. Strips and SQUID loops were defined by photolithography and Ar ion beam milling. Then nanobridges of 150-300 nm wide were made by focused ion beam etching. The <italic>R-T</italic> characteristics of the strip is the same as that of the raw film while SQUIDs have a “foot” near the critical temperature. The <italic>I-V</italic> curve of one of the SQUIDs is hysteretic below about 10 K. Nanobridges show features of the resistively shunted junction like, and the temperature dependence of the critical current turns out to be of SINS weaklink. At 9.8 K, the critical current density is about 1.5×10⁷ A/cm².