Superconducting YBa2Cu3O7 Films Research Articles

Millimeter-wave detection by GBJJ using high-T/sub c/ superconducting YBaCuO films

Millimeter-wave detection in the heterodyne mixing mode has been carried out using the high-T/sub c/ superconducting GBJJ (grain boundary Josephson junction). The GBJJ was fabricated from high T/sub c/ superconducting Y-Ba-Cu-O films, prepared on YSZ and SrTiO/sub 3/ substrates using an RF sputtering technique. The junction was patterned by chemical wet etching with phosphoric acid solution. The authors carried out experiments in the heterodyne mixing mode for a signal of 35 GHz with local oscillation at 34.97 GHz. The detected IF (intermediate frequency) output power was obtained at a bias voltage lying midway between the zeroth and first Shapiro steps. A mixer conversion efficiency of -15 dB was obtained with a dynamic range of about 20 dB at 35 GHz. This result strongly implies that high-T/sub c/ superconducting GBJJ works well as a detector at millimeter-wave frequencies.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

High Tc Superconductor Films Grown by the Liquid Phase Epitaxial Technique

AbstractHigh Tc superconducting YBa2Cu3O7 films have been prepared by the Liquid Phase Epitaxial (LPE) technique. The x‐ray diffraction patterns displayed a high degree of (00l) preferred orientations with c‐axes perpendicular to the film surfaces. The in‐situ grown YBa2Cu3O7 films showed zero‐resistivity at 76*K. Examination of the film cross sections by SEM revealed a growth mechanism.

Structural studies of the effects of silver and gold on the YBaCuO superconducting films formed from layer structures

Superconducting YBaCuO films have recently been formed using both Ag/Cu/BaO/Y2O3/MgO and Au/Cu/BaO/Y2O3/MgO structures, where MgO is the substrate. The addition of a silver layer in the starting structure improves the film resistances from those using the Cu/BaO/Y2 O3 /MgO structure, especially at lower annealing temperatures. This allows the formation of superconducting films between annealing temperatures of 750 and 900 °C, all with an onset above 85 K. The transition into full superconductive state, however, broadens with decreasing annealing temperatures, with zero resistance between 80 and 60 K. This dependence on annealing temperatures is studied by x-ray diffraction, which shows the diminishing signals of the superconducting YBa2 Cu3 O7 phase at reduced annealing temperatures. A study of the surface morphology provides further information regarding the roles of silver and gold on the superconducting films formed.

Deposition and characterization of superconducting YBaCuO films

Films of YBa 2Cu 3O y have been prepared on sapphire substrates by rf sputtering from a single nonconducting target made by hot-pressing unreacted powders of Y 2O 3, BaCO 3 and CuO and by e-beam deposition of multilayers of Cu, Y and BaF 2. After post-growth annealing in oxygen, these films exhibited superconducting properties with T c onsets above 90 K and with zero resistances and diamagnetic susceptibilities above 60 K. Resistivity, ac magnetic susceptibility and reverse ac Josephson effect measurements indicate a very weak Josephson coupling between the superconducting grains of these polycrystalline films.

Formation of high T c superconducting films by organometallic chemical vapor deposition

The first growth of superconducting YBaCuO films by organometallic chemical vapor deposition is described. Metal β-diketonates were decomposed thermally on MgO substrates in an oxygen-rich atmosphere to produce amorphous brown films. Subsequent annealing in oxygen yielded dull gray films whose thickness corresponded to deposition rates of approximately 8 nm min−1. These films showed semiconductor-like behavior at higher temperatures, followed by a broad resistive transition from 80 to 36 K with the resistance becoming zero at ∼20 K. Analysis of x-ray data indicated the presence of the orthorhombic superconducting phase and various other metal oxides. Profilometer measurements yielded film thicknesses up to 950 nm, and scanning electron microscopy revealed faceted grains from 0.5 to 1.0 μm in size.

Effects of silver and gold on the YBaCuO superconducting thin films with the use of Ag/Cu/BaO/Y2O3 and Au/Cu/BaO/Y2O3 structures

Superconducting YBaCuO films have been fabricated from the Ag/Cu/BaO/Y2O3 and Au/Cu/BaO/Y2O3 layer structures on MgO substrates. Compared to those using only the Cu/BaO/Y2O3 structure, the addition of a silver layer to the starting structures improves the film resistances, especially at reduced annealing temperatures, allowing the study of the dependence of the superconducting transition on the annealing temperatures between 900 and 750 °C. Zero resistance is observed at 80 K for the Ag/Cu/BaO/Y2O3 structure annealed at 900 °C. The use of a gold layer, on the other hand, reduces the temperature for zero resistance to 75 K for a similarly annealed film. All the superconducting films are composed of the YBa2Cu3O7 and the Y2BaCuO7 phases, with starting compositions off that of the former. Structural and morphological analysis of the films is performed to explore the roles of silver and gold in the films formed.

Growth and properties of YBaCu-oxide superconducting thin films prepared by magnetron sputtering

Thin superconducting YBaCuO films have been reproducibly deposited by dc-magnetron sputtering from sintered targets in an oxygen-argon atmosphere. The growth has been studied on different single crystalline substrates like ZrO, Al 2 O 3 and SrTiO 3 as a function of T s . Best zero resistance values on the different substrates were 87 K and 89 K, respectively with transition widths s 3 at 77 K was 10 S A/cm 2 . On SrTiO 3 the films grow epitaxially in the single crystalline phase.