Abstract: High-Tc Josephson junctions have been fabricated by a focused Ga-ion beam (FIB) with a full width of half maximum of 10 nm. Using two functions of etching and deposition, two types of the junction structures have been made on MgO and SrTiO$-3$/ substrates. The first one is a grain boundary junction formed on the narrow modified area which is ion-irradiated on the substrate prior to film deposition. For this fabrication process, RSJ-type I-V characteristics are observed only on the MgO substrate. The Ic spread of working 30 junctions, $sigma@, is plus or minus 59% on the substrate of 1 cm$+2$/. The second one is a proximity-effect junction with Au barrier layer. The tunneling area has been formed by etching and deposition technique of high-resolution FIB after film deposition. This junction also shows RSJ-type properties. The first type junctions are applied for some integrated circuits, using advantage of freedom of choice in the position of each junction with the high accuracy of the ion-beam control. !16
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