Sr2AlTaO6 Research Articles

Deposition of YBCO Thin Films in View of Microwave Applications

In preparation for the future characterization of the microwave properties of pulsed laser deposited high-temperature superconductor YBa <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6+x</sub> (YBCO) thin films, a YBCO growth optimization is performed using different substrate materials that have both a small dielectric constant and a small dielectric loss tangent. At first, the effect of thermal contact between a SrTiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> substrate and the sample holder is investigated by comparing silver paste and a mechanical attaching mask as fixing techniques. Hence, the thermal contact is observed to be a crucial parameter for successful growth, while the effect of lattice mismatch when using, e.g., MgO, SrLaAlO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> , NdGaO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> , and (LaAlO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> ) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.3</sub> (Sr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> AlTaO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> ) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.7</sub> , is seen to be less important. In addition, the preliminary reflectiontype measurements for a meander-type coplanar stripline YBCO resonator are implemented and a comparison between the calculated and experimentally determined field-dependent frequency values is obtained.

Preparation of Sr2AlTaO6 Insulating Films on YBa2Cu3O7-δ by Metalorganic Chemical Vapor Deposition with Purified Sr Source

200-nm-thick Sr2AlTaO6 (SAT) insulating films were prepared on 10-µm-thick superconducting YBa2Cu3O7-δ (YBCO) films by metalorganic chemical vapor deposition (MOCVD). By employing a purified Sr(thd)2 metalorganic source, instead of Sr(thd)2-2tetraene, and a higher evaporation temperature, we could reproducibly obtain stoichiometric SAT films with high crystallinity as revealed by the full-width at half maximum value of the SAT (004) X-ray rocking curve which was as small as 0.2°. Moreover, a 200-nm-thick c-axis-oriented YBCO film with a Tc of 90 K and a Jc higher than 107 A/cm2 below 60 K could be grown on the SAT film. These results confirm that the SAT films prepared by MOCVD are suitable for use as insulating layers in high-Tc multilayer electronic devices.

Effect of the deposition conditions and annealing process on the crystallinity and superconducting properties of high-Tc multilayers

On the basis of successful fabrications of multilayers based on NdBa2Cu3O7- (NBCO) using Sr2AlTaO6 (SAT), Sr2AlNbO6 and lanthanum doped SAT, LaxSr2-xAlTaO6 (LSAT) as insulators, we have systematically investigated the effect of deposition conditions and the annealing process on the crystallinity and superconducting properties of multilayers. It was found that the superconducting properties of the bottom NBCO layers were dependent on both the post-annealing process and the deposition conditions of multilayers. The insulator layers deposited at the same substrate temperature for growth of NBCO films had very good crystallinity. However, the bilayers showed relatively low Tc0 (~80-85 K) even after annealing and rough surfaces. Since both the smooth surface and the epitaxial quality are the essential requirements for further epitaxial growth in multilayer technology, it is necessary to balance the crystallinity against the surface and superconducting properties by optimizing deposition conditions. High-Tc multilayers with excellent superconductivity have been fabricated at a relatively low substrate temperature and high oxygen partial pressure.

Oxygen Diffusion Coefficients for Sr2AlTaO6: Ramifications on Htsc Multilayer Processing

AbstractWe have studied the rate of oxygen diffusion through Sr2AlTaO6 (SAT), a buffer and dielectric layer used in high critical temperature superconducting (HTSC) structures. An epitaxial bilayer film of SAT on YBa2Cu3O7-δ (YBCO) was deposited onto an (001) oriented single crystal LaAlO3 substrate using the pulsed laser deposition technique. The rate of oxygen diffusion through the bilayer was investigated over the temperature range 415 to 675 °C by post deposition annealing individual sections of the bilayer in 1/3 atm of 18O enriched molecular oxygen gas. Secondary ion mass spectroscopy was used to depth profile 18O and 16O in each sample. Oxygen diffusion coefficients for SAT at 418, 510, 570 and 673 °C were determined to be roughly (0.93, 6.31, 26.6 and 75.3) × 10−16 cm2 s−1, respectively. Since these diffusion rates can limit oxygen intake into underlying YBCO films, SAT may be an inappropriate choice as a dielectric candidate for use in an HTSC multilayer device technology and will at best require development of suitable post annealing schemes to oxygenate underlying YBCO layers.

Sr2AlTaO6 films for multilayer high-temperature superconducting device applications

Thin films of Sr2AlTaO6 (SAT) and multilayers of YBa2Cu3O7 (YBCO)/SAT have been grown by pulsed laser deposition on [001] LaAlO3 substrates. X-ray diffraction shows that SAT grows on [001] LaAlO3 with the c-axis oriented normal to the substrate plane. X-ray rocking curve and Rutherford backscattering channeling measurements on SAT films yield full width at half maximum of &amp;lt;0.3° and minimum backscattering yield χmin of 5%–7%, respectively, indicating good crystallinity. The real part of the dielectric constant εr is found to be ∼23–30, with ∼6×107 V/m static breakdown electric field. Both the dielectric constant and the static breakdown field show negligible temperature dependence between 10 and 300 K. A 100 nm×10 μm×50 μm YBCO film on SAT shows zero-field critical current density of ∼1.3×106 A/cm2 at 77 K, with a superconducting transition temperature Tc0 of ∼89.2 K.