Characterization of grain boundaries in YBa/sub 2/Cu/sub 3/O/sub y/ bicrystal junctions [SQUIDs]

I-V, V-/spl Phi/ characteristics and atomic force images of grain boundary Josephson junctions fabricated on SrTiO/sub 3/ bicrystal substrates were investigated. The half integer Shapiro steps and I/sub c/ versus B curves show evidence of the inhomogeneous current distribution along the grain boundary junction. The dc SQUID formed on the grain boundary shows the expected V-/spl Phi/ curve. The AFM images, R-T curves and I/sub c/R/sub n/ product reveal sequential destructive deterioration of the junction originating from the underlying grooved substrate. The results are discussed.