Characteristics of YBCO Josephson Junction Prepared by a Focused Ion Beam Technique

In order to clarify the formation and working mechanism of the YBCO Josephson junction, the dependence of the junction characteristics on the oxygen pressure during YBCO deposition was observed. An MgO substrate was damaged by a focused ion beam (FIB) and then a YBCO film was deposited on the substrate. When the oxygen pressure during depositions was 200 mTorr, the junction did not show the Josephson effect. At 100 mTorr, the junction showed the Josephson effect. The transition temperature (T c) and the c-axis lattice constant of the film did not change from 200 to 100 mTorr. Therefore, we considered that the oxygen was lacking more at the junction than in the film and a Josephson junction was formed without film degradation.