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.
In high temperature superconductors (HTS) the coherence length along non-c axis directions is longer. This feature can be useful wh en designing electronics devices based on HTS. Therefore growth and characterization of non-c axis oriented thin HTS films is of great interest. In this paper we present a short review of our data regarding (119) Bi-2223 thin films grown by MOCVD on (100) NdGaO3 and (110) SrTiO3. The emphasis is made on improvement and control of the quality of the films by the "two-temperature" technological approach and/or use of the vicinal substrates. Phase and morphology evolution for different processing conditions, substrate's type and off-angle are presented. The highest critical temperatures of Tc0=67.2 K and Tc0=74 K for the "single" and "two-"temperature routes were obtained on vicinal SrTiO3 with the off-angle of 20°. A higher off-angle promoted the formation of a specific step-like morphology with lower roughness. For the films grown on flat substrates the morphology was of mountain-range shape. Surface morphology as a result of two types of growth mechanisms (two-dimensional (2D), assisted by a so-called "twin"-growth and step-flow growth) for the (119)Bi-2223 filmes are discussed.
KEYWORDS: Atomic force microscopy, Metalorganic chemical vapor deposition, Magnetism, Superconductors, Technetium, Thin films, Crystals, Oxygen, Scanning electron microscopy, Temperature metrology
Bi-Sr-Ca-Cu-O superconducting films consisting of 2223-high Tc single phase have been prepared on LaAlO3(100) and Nd:YAlO3(001) substrates without post-annealing by MOCVD. As-deposited films exhibited the highest Tc(zero) of 97 K and the highest Jc of 3.8 X 105 Acm-2 at 77 K under zero magnetic field as reported so far. It also showed little degradation of Jc under high magnetic field up to 8 T at 77 K. It was speculated through the measurement of the angular dependence of Jc that the origin of such high Jc is primarily attributed to the intrinsic pinning mechanism. AFM observations of these film surfaces have been carried out to elucidate the crystal growth mechanism and the effect of surface structures on superconducting properties. AFM images of the film surfaces grown on LaAlO3(100) (off angles <EQ 0.3 deg.) and on Nd:YAlO3(001) (off angle approximately 2.7 deg.) clearly showed a 2D nucleation growth and a step flow growth mechanism, respectively. The magnetic-field dependence of Jc and the observed surface morphologies strongly suggest that these as-grown films have no weak-links, which is a promising characteristic for device applications.
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