Submicron YBa₂Cu₃O_7 x bicrystal grain boundary junctions by focused ion beam

Submicron YBa2Cu3O7-x bicrystal grain boundary junctions have been fabricated, for the first time, by a focused ion beam process. Although such a process has always been considered detrimental to the YBa2Cu3O7-x because of gallium contamination, high quality 24degrees [001] tilt junctions characterized by RSJ current-voltage characteristics, ICRN products of the order of 1-4 x 10(4) A cm(-2) at 77 K and Fraunhofer-like modulation patterns have been obtained. No significant degradation has been observed over more than 3 months. The critical current density J(C) and the characteristic voltage ICRN show a clear maximum for widths of the order of the Josephson penetration depth. The asymptotic normal resistance shows a typical (width)(-1) dependence, indicating that the FIB process does not increase the grain boundary resistivity of submicron junctions. Experimental results clearly show that FIB is a very powerful tool for the fabrication of high critical temperature superconducting circuits, requiring a small number of submicron Josephson junctions, and for fundamental physics analysis. it also allow the final turning or repair of superconducting or more complex integrated superconducting-semiconducting devices.