PREPARATION AND CHARACTERIZATION OF GRAIN-BOUNDARY JOSEPHSON JUNCTION FROM AMORPHOUS THIN-FILM

To prepare the grain boundary Josephson junction, Y-Ba-Cu-O amorphous thin film was first etched into a bridge shape and then annealed at a high temperature, 990-degrees-C, to form grain boundaries. The bridge thus prepared showed clear Shapiro steps under the irradiation of microwaves at 4.2 K. Grains of the films sensitively varied their structures, sizes and electric properties with annealing temperature. The grains annealed at a lower temperature, 960-degrees-C, were as small as a few micrometers or less. Large grains appeared when the annealing temperature became higher, and the higher the annealing temperature, the greater the number of large grains, untill 990-degrees-C. The bridge of 5-mu-m in width that had grains over 10-mu-m in size exhibited a.c. Josephson effect, but the effect was not observed with the bridge which consisted of only small grains of a few-mu-m.