BaTbO₃ as a new material for insulation and junction barriers in High-T_c devices

It is shown that BaTbOs has a high degree of chemical and structural compatibility with YBajCuaO? and that this new material has many properties beneficial for different device applications. The growth morphology of several YBazCuaCVBatbOj/YBajCujO? multilayer films was investigated by high-resolution transmission electron microscopy (HRTEM). Depending on the deposition temperature two types of interface between YBajCuiO? and BaTbOj were found. At relatively high deposition temperatures the misfit strain is mainly restricted to a narrow (smaller 1 nm) interface layer, whereas at lower temperature a semi coherent interface with well-localized misfit dislocations was observed. By 18O / 16O tracer experiments it was shown that significant oxygen diffusion in a BaTbOj layer is possible at temperatures below 500°C. The diffusion rate is much higher than in conventionally used insulators like e. g. SrTiCh and even higher than in YBajCujCK Insulating properties of BaTbOj were successfully tested for crossovers in multilayer devices. Furthermore field effect devices and Josephson junctions using BaTbOs as dielectric or barrier material have been investigated. The ramp-type Josephson junctions included chemically as well as ion beam etched ramp-edges. In both cases the normal resistance decreases with decreasing temperature for a barrier thickness of 10 nm. For chemically etched junctions well defined Shapiro steps and a characteristic voltage of about 0. 2 mV at 77 K were observed.