Fabrication of Bi/sub 2/Sr/sub 2/Ca/sub 2/Cu/sub 3/O/sub x/ thin film grain boundary junctions

As-grown high-quality superconducting thin films of the Bi/sub 2/Sr/sub 2/Ca/sub 2/Cu/sub 3/O/sub x/ were prepared by RF magnetron sputtering with a regulated shuttering technique. 2223 phase films with a 2201 phase buffer layer were deposited on MgO (100) substrates under rigorous control of the bismuth content and valence. As a source of bismuth, Bi(metal) and Bi/sub 2/Sr/sub 2/CuO/sub x/ targets were used. At the preparation no post-treatment steps were performed. The zero resistivity critical temperature of the as-grown film was 107.3 K. Using these films, Bi/sub 2/Sr/sub 2/Ca/sub 2/Cu/sub 3/O/sub x/ step-edge and bicrystal Josephson junctions were prepared. At step-edge junctions, Josephson current was observed up to 41 K, below this temperature I-V curves were RSJ-like. On the other hand, bicrystal junctions were fabricated,on the bicrystal MgO (100) substrate with a misorientation angle of 24/spl deg/. Typical RSJ model I-V curves were observed up to 60 K. The modulation depth goes up to 90%. I/sub c/R/sub n/ values were about 1.0 mV at 4.2 K.<
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