Characteristics of a NiO barrier layer for high-T/sub c/ superconducting tunnel junction

Characteristics of a NiO barrier layer for high-T/sub c/ superconducting tunnel junctions were investigated. Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub x/ (BSCCO) films were deposited on a MgO or SrTiO/sub 3/ substrate using a dc hollow cathode sputtering system. In situ superconducting BSCCO films deposited in Ar+20%O/sub 2/ gas at T/sub s/=680/spl deg/C on a MgO substrate were c-axis oriented 2212 phase. A NiO layer was formed by reactive sputtering in Ar+20%O/sub 2/ gas using a NiO hollow cathode, and the layer on the BSCCO film was of [100] and [110] orientation. The current-voltage characteristics of an Ag/NiO/BSCCO junction with a NiO barrier layer 5 nm thick were investigated. In the G-V curves of some junctions, a zero bias conductance peak was observed. It is assumed that this behavior is probably due to the nonuniform thickness of the barrier layer. The junction with a thicker barrier layer (18 nm) showed tunnel current characteristics without anomaly.<>