Fabrication of high-temperature superconductor Josephson junctions by focused ion beam milling

We have fabricated high-critical-temperature Josephson junctions using a focused ion beam (FIB) milling to define the gap, in a-axis oriented YBa₂Cu₃O₇ (YBCO) films. A good quality normal metal/YBCO interface is obtained by in situ Au deposition. The effect of FIB milling has been studied with different milling conditions and the resulting devices exhibit different I–V characteristics, i.e., flux flow or superconductor/normal/superconductor Josephson junction behavior. The junctions exhibit Shapiro steps in their I–V characteristics under microwave irradiation. The critical current and normal resistance product (I_cR_n) of the order of 1 mV has been obtained. We also show that there is a voltage modulation in the superconducting quantum interference devices as a function of an applied magnetic flux up to 80 K. © 1997 American Vacuum Society.