BaTbO/sub 3/ as a new material for insulation and junction barriers in High-T/sub c/ devices

Abstract

It is shown that BaTbO/sub 3/ has a high degree of chemical and structural compatibility with YBa/sub 2/Cu/sub 3/O/sub 7/ and that this new material has many properties beneficial for different device applications. The growth morphology of several YBa/sub 2/Cu/sub 3/O/sub 7//BaTbO/sub 3//YBa/sub 2/Cu/sub 3/O/sub 7/ multilayer films was investigated by high-resolution transmission electron microscopy (HRTEM). Depending on the deposition temperature two types of interface between YBa/sub 2/Cu/sub 3/O/sub 7/ and BaTbO/sub 3/ 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 /sup 18/O//sup 16/O tracer experiments it was shown that significant oxygen diffusion in a BaTbO/sub 3/ layer is possible at temperatures below 500/spl deg/C. The diffusion rate is much higher than in conventionally used insulators like e.g. SrTiO/sub 3/ and even higher than in YBa/sub 2/Cu/sub 3/O/sub 7/. Insulating properties of BaTbO/sub 3/ were successfully tested for crossovers in multilayer devices. Furthermore field effect devices and Josephson junctions using BaTbO/sub 3/ 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 characteristic voltage of about 0.2 mV at 77 K were observed.