New growth method of high-quality, multicomponent oxide thin films used in strongly correlated electron device applications: impurity-precipitate issues and their problem solving

Abstract

Perovskite-related layered multicomponent oxide films with strongly correlated electrons such as (La, Sr)MnO₃ and HTS are promissing candidates for advanced MRAM, Josephson devices and others. These devices have usually sandwich-type structure with an ultra-thin intermediate layer. Formation of the impurity-precipitates on the surface during the growth of the multicomponent oxide films is a fatal problem working against high-performance of devices. In this study, high quality and surface-clean thin films of multicomponent oxides have been grown by MOCVD on substrates with artificial steps of predefined height and width. The surface of the films grown on the steps having width equal to the 'double of the migration length' of the atomic species depositing on the substrate is totally free of precipitates: precipitates are gathered at the step edges where the free energy is lowest. The method has several advantages: it is simple, universal (it is independent of the materials, substrates, deposition technique or application) and allows control of precipitates segregates so that the quality and growth conditions of the films are the same as for the films grown on conventional substrates. The method is expected to result in new opportunities for the device fabrication, integration, design and performance. As an example we present successful fabrication of a mesa structure showing intrinsic Josephson effect. We have used completely precipitate-free thin films of Bi-2212/Bi-2223 superstructure grown on (001) SrTiO₃ single crystal substrates with artificial steps.