Identification of Barrier in the Modified Interface High-Tc Josephson Junction by TEM

The atomic structure and composition of modified interface junctions which showed reproducible critical current Ic (Ic lσ < 8% for series connected 100 junctions) are investigated by transmission electron microscopy. Transmission electron microscopic observations show the existence of a thin barrier (1–2 nm) homogeneously covering the ion milled edge of the base YBa2Cu3Oy film although there is no barrier deposition and annealing process. High-resolution electron microscopy images and energy dispersive x-ray analysis with spot size of 1 nm indicate that the barrier is a Ba-based perovskite-like structure. (Y1-xCux)BaOy. with x < 0.5. A thin amorphous layer whose composition deviates from YBa2Cu3Oy is formed due to the preferential sputtering of Cu. The amorphous layer recrystallizes into the nonequilibrium phase, (Y1-xCux)BaOy after heating up to the deposition temperature. The effect of La in substrate and insulation layer on the junction property was discussed.