ARTIFICIAL YBCO GRAIN-BOUNDARY JUNCTIONS ON SRTIO3 AND SI BICRYSTALS

Bicrystal substrates of SrTiO3 and Si were made and artificial angled-grain boundary Josephson junctions were made on both substrates. In order to form an angled-grain boundary structure artificially, which contributes effectively as a Josephson junction, (0 0 1)SrTiO3 and (0 0 1)Si bicrystal substrates were fabricated by diffusion bonding of the two single crystals. YBCO films were epitaxially grown by MOCVD and RF magnetron sputtering on SrTiO3 and Si bicrystal substrates, respectively. The bridges crossing the boundaries were patterned by excimer laser etching. Both types of bridge responded to microwave irradiation. A bridge with 20-degrees angled-grain boundary and I(c) of about 100-mu-A on an SrTiO3 bicrystal showed Shapiro steps up to the fourth order for RF = 8.4 GHz at 69 K, and a bridge with 10-degrees boundary and I(c) of about 0.8 mA on an Si bicrystal showed Shapiro steps up to 0.5 mV for RF = 9.6 GHz at 77 K.