High-T c
 superconductivity has generated a great deal of interest because of the challenges it presents in the fields of material science, condensed matter physics, and electrical engineering, and because of the potential applications which may result from these research efforts. Thin-film passive microwave components may become the first high-temperature superconducting (HTS) devices available for widespread use and commercialization. In this article, we review aspects of material science, physics, and engineering which directly impact high-T

 c
 superconducting microwave devices and discuss issues which determine the performance of these devices. Methods of growing HTS thin films on large-area substrates, techniques for fabricating single-level HTS passive microwave components, and the relevant properties of high-T

 c
 superconducting films are discussed, with a focus on thin films of the HTS material YBa2Cu3O7−δ. Several known mechanisms for microwave loss in both the superconductor and the dielectric substrate are presented. An overview of the general classes of superconducting passive microwave devices is given, and representative microwave devices which have been recently demonstrated are described in detail. Examples of a select few HTS active microwave components are also presented. Potential microwave applications are illustrated with comparisons to current technology.

High-temperature superconducting microwave devices: Fundamental issues in materials, physics, and engineering

Various orientations of YBa2Cu3O7−x grains in polycrystalline films prepared on (001)MgO substrates by in situ laser deposition were determined using electron diffraction. Eight different types of in‐plane orientations have been observed. These orientations agree well with the prediction of a simplified theory of near coincidence site lattice between YBa2Cu3O7−x and MgO. The YBa2Cu3O7−x grains were found to have a high probability of forming low angle or low Σ boundaries among themselves. These grain boundaries are of low energy and should exhibit a high connectivity of Cu‐O‐Cu chains. Therefore, YBa2Cu3O7−x thin films on MgO can attain a Tc of ∼90 K and a Jc of ∼106 A/cm2 at 77 K.

Application of a near coincidence site lattice theory to the orientations of YBa2Cu3O7−x grains on (001) MgO substrates

https://publikationen.bibliothek.kit.edu/270027933/3813383

Epitaxial growth and properties of YBaCuO thin films

The epitaxy of a thin‐film Y‐Ba‐Cu‐O (YBCO) superconductor deposited on a single‐crystal [001] MgO substrate was examined by transmission electron microscopy. The large lattice mismatch (8–10%) in the basal plane of YBCO and MgO is accommodated mainly by the formation of a polycrystalline, mosaic structure. The grain boundaries correspond to unique crystallographic interfaces, determined by the crystal symmetry of the substrate and the thin film.

Epitaxy of Y-Ba-Cu-O thin films grown on single-crystal MgO

The growth and characterisation of YBa2Cu3O7 thin films are reviewed. The discussion of growth is limited to the physical vapour deposition techniques of laser ablation, sputtering and evaporation. Emphasis is placed on the practical problems of growing epitaxial films in situ and characterising them.

https://iopscience.iop.org/article/10.1088/0953-2048/3/1/006/pdf

Physical vapour deposition techniques for the growth of YBa2Cu3O7 thin films

Ultrathin films of YBa2Cu3O7−x with thicknesses down to 2 nm were grown on(100)SrTiO3 and (100)MgO by inverted cylindrical magnetron sputtering. Metallic behavior and zero resistance temperatures above 4.2 K were obtained in 3‐nm‐thick films on SrTiO3. Thinner films revealed temperature‐activated conductivity and only partial transitions to superconductivity due to inhomogeneities in the film morphology. On MgO, the critical film thickness leading to deteriorations of the transport properties was 6 nm. An analysis of the fluctuation‐enhanced conductivity near Tc in terms of the Aslamazov–Larkin theory [Phys. Lett. A 26, 238 (1968)] revealed three‐dimensional behavior even in the thinnest fully superconducting films.

Preparation and superconducting properties of ultrathin YBa2Cu3O7−x films

The growth features of YBa2Cu3O7−x thin films on (100) MgO substrates were studied by He ion channeling and x‐ray diffraction measurements. A minimum yield value of 7% at 2 MeV He ion energy and a standard deviation of the crystallite misorientation of only 0.1° show that epitaxial growth (c‐axis oriented) is achieved despite a large lattice mismatch of about 9% between the film and the substrate. Detailed studies of the energy dependence of the dechanneling yield at the film‐substrate interface for films of different thickness reveal the presence of dislocations probably formed by strain relief in the initial state of growth. Stacking faults appear as the main defect structure in the bulk of the films.

Growth characterization of YBa2Cu3O7−x thin films on (100) MgO

The growth quality of thin, superconducting YBaCuO films has been compared on random and (100) oriented yttrium‐stabilized zirconia substrates using x‐ray diffraction and ion channeling experiments. Superior growth is observed on (100) substrates with narrow mosaic distributions (0.4°) and a minimum yield value of 10% in the channeling experiment. The lattice matching required for epitaxial growth is achieved by azimuthal adjustment of the film plane with respect to the substrate. The superior growth is reflected in the film properties like the critical current density yielding values of 2×106 A/cm2 at 77 K.

O. Meyer

Papers

Preparation and superconducting properties of ultrathin YBa2Cu3O7−x films

Growth characterization of YBa2Cu3O7−x thin films on (100) MgO

Growth of YBaCuO thin films on random and (100) aligned ZrO2 substrates