Optimization and magnetic field behavior of sputtered submicron YBa/sub 2/Cu/sub 3/O/sub 7/ step-edge Josephson-junctions

Abstract

YBa/sub 2/Cu/sub 3/O/sub 7/ step-edge junctions with widths down to 0.5 /spl mu/m are fabricated on SrTiO/sub 3/-substrates by Ar ion-beam milling of the steps, high-pressure on-axis magnetron sputtering and, finally, electron beam patterning and ion-beam etching of the microbridge. For ratios of film thickness to step height of about 1/2 the current-voltage characteristics show Shapiro steps under microwave irradiation and RSJ (resistively shunted junction)-like behavior. The periodic dependence of the critical current upon the magnetic field resembles a Fraunhofer-pattern. The period of the current variation /spl Delta/B/sub 0/ depends upon the width w of the junction according to the theoretical prediction for planar thin Josephson junctions: /spl Delta/B/sub 0/=1.84/spl phi//sub 0//w/sup 2/. Junctions with widths of 0.7 /spl mu/m possess a large magnetic field stability with /spl Delta/B/sub 0//spl ap/100 G. Small junctions (w<1 /spl mu/m) exhibit voltage jumps in the Fraunhofer pattern, which are explained by flux penetration of single vortices into the superconducting electrodes.