BaTbO3 as a new material for insulation and junction barriers in high-T-c devices

It is shown that BaTbO3 has a high degree of chemical and structural compat ibility with YBa2Cu3O7 and that this new material has many properties benef icial for different de tice applications. The growth morphology of several YBa2Cu3O7/BaTbO3/YBa2Cu3O7 multilayer films was investigated by high-resolu tion transmission electron microscopy (HRTEM). Depending on the deposition temperature two types of interface between YBa2Cu3O7 and BaTbO3 were found. At relatively high deposition temperatures the misfit strain is mainly res tricted to a narrow (smaller 1 nm) interface layer, whereas at lower temper ature a semi coherent interface with well-localized misfit dislocations was observed By O-18 / O-16 tracer experiments it was shown that significant o xygen diffusion in a BaTbO3 layer is possible at temperatures below 500 deg rees C. The diffusion rate is much higher than in conventionally used insul ators like e.g. SrTiO3 and even higher than in YBa2Cu3O7. Insulating proper ties of BaTbO3 were successfully tested for crossovers in multilayer device s. Furthermore field effect devices and Josephson junctions using BaTbO3 as dielectric or barrier material hale been investigated. The ramp-type Josep hson junctions included chemically as well as ion beam etched ramp-edges. I n both cases the normal resistance decreases with decreasing temperature fo r a barrier thickness of 10 nm. For chemically etched junctions well define d Shapiro steps and a characteristic voltage of about 0.2 mV at 77 K were o bserved.