Fabrication and Characterization of NdBaCuO-Josephson Junctions on MgO-Substrates Damaged by a Focused Ion Beam

We have fabricated a NdBa 2 Cu 3 O 7 Josephson junction using a narrow-focused Ga-ion beam to damage MgO(100) substrates prior to film deposition. NdBa 2 Cu 3 O 7 films with smooth surface morphology and without particulates have been deposited by RF magnetron sputtering under rather low oxygen partial pressures. I c values at 4.2 K of several junctions with the same fabricating conditions vary from several µA to several mA. The junctions with higher I c exhibit flux-flow type I-V curves and Fraunhofer-like diffraction patterns of I c under magnetic field. The junctions with lower I c show RSJ type I-V curves and SQUID-like diffraction patterns of I c under magnetic field.