We have prepared electrically tunable and active microwave devices incorporating (superconducting YBa2Cu3O7-x)/(nonlinear dielectric SrTiO3) or (normal metal Au)/(nonlinear dielectric Sr0.5Ba0.5TiO3) bilayers. The dielectric layer thickness for these samples varied between 0.5 μm and 2 μm. The top electrode layer for each sample was patterned into a coplanar waveguide device structure. We have configured these devices as voltage-tunable resonators, voltage-tunable phase shifters, voltage-tunable mixers, and voltage-tunable filters. Under dc voltage bias, these prototype devices have exhibited up to 30% resonant frequency modulation, about 1°/mm-GHz phase shift, more than 40 dB change in mixed microwave power, and finetunable symmetric filter profile with less than 2% bandwidth and more than 15% adaptive range.

Ion implantation is used to modify the properties of oxide (YBCO and YSZ) thin films. Both superconducting and dielectric epitaxial oxide films, grown by laser ablation, are studied. The properties of the implanted oxide films are characterized by SIMS, XPS, DC resistivity and AC susceptibility measurements. By introducing reactive ions into superconducting oxide films, the conductivity of the material is inhibited possibly due to the interaction of the implanted ions with oxygen originally bound to the copper atoms. Al, Si, Ag and Ca ions are implanted into epitaxial YBCO films with injection energies ranging from 50 - 100 KeV and doses ranging from 1×1015 - 1×1016/cm2. XPS analysis shows that the implanted Si ions form SiOx. The inhibition method has been applied to the fabrication of superconducting electronic devices, such as SQUIDs. Dielectric oxide films are doped by the implantation of conductive and non-conductive ions. YSZ films are doped with Ag and Si ions and the ions are found to increase the conductivity.

Thin films of the Bi-2212 and T1–2212 compounds were prepared by MOCVD deposition techniques. Resistivity versus temperature and critical current density measurements were used to characterize the electrical properties. An analysis of the data based on a proposed model determined the influence of intragranular weak links. Thin film samples in both systems with near optimum oxygen doping showed a correlation between the slope and magnitude of the resistivity in the normal state. Samples with reduced oxygen content displayed a strong increase in the intragrain boundary resistance, consistent with weak link defects. The results agree with a similar analysis of YBCO samples and support a common mechanism for the development of weak links in cuprates.

Different aspects of interfacial interactions during the growth of epitaxial oxides are illustrated in a BaxSr1-xTiO3/YBa2Cu3O7-x/CeO2/Y-ZrO2/Si/Al2O3 heteroepitaxial multilayer. The effect of chemical interaction, interdiffusion, epitaxial strain and thermal strain are exemplified. It is shown how buffer layers can be used to compensate for otherwise detrimental interactions. Considerations necessary for annealing following the film depositions are also addressed. Even if the described structures are specific for this system, similar considerations need to be made for other oxide systems as well. The present description can provide help to identify suitable material combinations.

In the eight years since its discovery, numerous materials have been identified as being compatible with YBa2Cu3O7-δ (YBCO). Investigation of potentially compatible compounds requires a knowledge of both the chemistry and microstructure of the interface between the superconductor and the material. In this work, spectroscopic ellipsometry (SE) is being developed as a rapid and non-destructive characterization tool for investigating these interfaces. In addition, SE was used to determine reference optical data for common YBCO substrate materials. These include BaZrO3, 9.5 mol% Y2O3-ZrO2 (YSZ), NdGaO3 and LaSrGaO4.

SE measurements of epitaxial YBCO on YSZ substrates have shown that it is possible to identify the formation of the known BaZrO3 reaction layer. The modeled thickness of the reaction layer, as well as the modeled thickness of the YBCO film, are as expected. SE measurements as a function of temperature for YBCO/SrTiO3 have also been obtained. The SE data shows dramatic changes from room temperature to high temperature. This is due to the strong dependence of the dielectric function of YBCO on the oxygen content of the film.

The structure of CeO2 films grown on (1102) sapphire and on YBCO thin films was investigated. The films reported on here were grown by pulsed excimer laser deposition and their surface structure was probed using atomic force microscopy. We found that CeO2 films grown on sapphire were epitaxial with a granular structure which is smooth on an atomic scale. We see evidence of a surface reconstruction on a very smooth CeO2 (100) oriented surface. At higher growth temperatures, three dimensional islands begin to form. When a CeO2 film is grown on top of a YBCO film, the growth mode is two dimensional. The steps in this layer by layer growth are a surprisingly large 2 nm. This is about equal to 4 times the CeO2 lattice constant. This step height appears to be temperature dependent.

The microstructure of YBa2Cu3O7-δ(YBCO)/Ag bilayers sputter deposited in situ on step-edge SrTiO3 (STO) substrates, was carefully examined by transmission electron microscopy (TEM). Considerable variation in the YBCO film growth morphology is found near steps, including film protrusions beyond the step edges and film growth on slopes. Lattice images recorded near steps unveil a high density of crystalline defects in the film. An increased density of defects is also found near the substrate interface for film grown on etched STO surface. However, these defects are confined to the interface region and do not propagate beyond the scale of the STO surface roughness. Comparison of TEM lattice images of YBCO(100)/Ag and YBCO(001)/Ag junctions from the same specimen unveils a distinct difference in the interfacial microstructure of those two junctions. Whereas the former exhibits a sharp crystalline interface, the latter typically features a thin ( ∼ 20 Å ) interfacial layer of amorphous material. The YBCO film morphology and the high density of defects in the step edge region uncovered in this study suggest that manufacture of reproducible and uniform YBCO/Ag (Au)/YBCO (SNS) Josephson junctions using the step-edge technique, will prove a difficult task.

Two 123 thin films grown by e-beam evaporation have been studied using Raman microscopy. The films were grown under different conditions of temperature and oxygen partial pressure and show different levels of cation disorder as determined from the ‘c’ axis lattice parameter in combination with x-ray data. The oxygen stoichiometry in each film was changed by controlled anneals using a coulometric titration apparatus. As a result we report on the sensitivity of the 500cm−1 and 585cm−1 Raman peak to the oxygen stoichiometry and how the intensity and position of these peaks can be used to detect or confirm the presence of a small amount of cation disorder.

Thin films of the orthorhombic perovskite GdAlO3 were grown on R-plane sapphire single crystals. Two different film growth methods were used, viz. (i) a chemical reaction of a Gd-O plasma with the sapphire crystals, and (ii) the reactive radio frequency (r.f.) sputtering of a GdAlO3 target. Subsequently, YBa2Cu3O7-δ (YBCO) films were deposited onto the GdAlO3 buffer by pulsed laser deposition (PLD). The GdAlO3 and YBCO films were investigated by Xray diffraction pole figure analysis and transmission electron microscopy (TEM), including highresolution transmission electron microscopy of cross sections. Independent of the deposition method the GdAlO3 films grew according to the nearly equivalent orientation relationships The GdAlO3 grains are additionally tilted by angles up to ± 3° around the sapphire [11.1] axis. On top of these buffer layers the YBCO films grew with c-orientation and with an in-plane rotation of 45°. YBCO films of 200 nm thickness on GdAlO3 buffer layers with a thickness of 10 to 20 nm showed a Tc > 87 K and a jc(77 K) > 3×106 A/cm2.

We 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.

Epitaxial single layer (001) SrTiO3 films and an epitaxial Yba2Cu3O7-x/SrTiO3 multilayer were dc and rf sputtered on (110)rhombohedral LaAIO3 substrates. The microstructure of the films was characterised using transmission electron microscopy. The single layer SrTiO3 films exhibited different columnar morphologies. The column boundaries were due to the lattice mismatch between film and substrate. The boundaries were associated with interfacial dislocations at the film/substrate interface, where the dislocations relaxed the strain in the a, b plane. The columns consisted of individual subgrains. These subgrains were misoriented with respect to each other, with different in-plane orientations and different tilts of the (001) planes. The subgrain boundaries were antiphase or tilt boundaries.

The individual layers of the Yba2Cu3O7-x/SrTiO3 multilayer were relatively uniform. A distortion of the SrTiO3 unit cell of 0.9% in the ‘001’ direction and a Sr/Ti ratio of 0.62±0.04 was observed, both in correspondence with the single layer SrTiO3 films. Areas with different tilt of the (001)-planes were also present, within each individual SrTiO3 layer.

The results of a transmission electron microscopic (TEM) and X-ray microanalysis (EDS) study of Yba2Cu3O7-x (YBCO) films grown on vicinal (011) SrTiO3 substrates are presented. The YBCO films tend to be single crystalline grown in single variant orientation with c-axis =;45° from the surface. Cracks, second phase precipitates (CuO and Y2O3), and a few small YBCO grains in other orientations were revealed in the films.

Superconducting Yba2Cu3O7 -x(YBCO) films were prepared by dipping-pyrolysis process on SrTiO3 (001) or on MgO (001) substrates covered with a metal (Au or Ag) buffer layer, and the effects of these metal layers on the growth of YBCO films were investigated. Epitaxial growth of YBCO was found to be suppressed by the Au buffer layer, which crystallized to exhibit (111) orientation, after heat treatment at 700°C and higher. On the other hand, epitaxial YBCO films were obtained starting with Ag buffer layer by heat treatment at 700°C and higher, after which most of Ag was accumulated to particles. It was also found that the annealing temperature required for the epitaxial growth of YBCO films on MgO was lowered to 850°C by adopting the Ag buffer layer.

For the in situ growth of cuprate superconductors and related oxides by vacuum deposition methods it is desired to achieve as high a flux of oxidizing species as possible at the growing surface and as little as possible elsewhere within the reaction chamber. The well known gas flow equations derived by Knudsen, Clausing, and others which apply to the molecular flow regime were implemented in a computer algorithm to simulate the gas flow upon a substrate from hypothetical nozzles of several different geometries. The optimal design for a particular MBE chamber and substrate size was determined and such a nozzle was fabricated and characterized. A dysprosium-coated quartz crystal monitor was used to determine the oxidant flux. The measured result matches predictions of the computer model within a factor of three. The computer algorithm was also used to model the spatial distribution of ozone gas through a nozzle of another reported geometry, where measurements of the resulting flux had been made. The shape of the calculated flux distribution agrees to within a few percent and the absolute values of flux reported agree within a factor of two.

For the first time, epitaxial c-axis oriented lithium niobate (LiNbO3) films were grown on MgO (001) substrates. This orientation is relevant to the monolithic integration of LiNbO3 with GaAs for waveguiding, frequency doubling, and other opto-electronic applications. The epitaxial orientation relationship is (001 ) LiNbO3 parallel to (001) MgO and [100] LiNbO3 parallel to [110] MgO. Four equivalent in-plane orientations were observed, such that the lithium or niobium atoms along the [100] axis of LiNbO3 are bonded to the oxygen atoms on diagonal comers of the MgO unit cell. These epitaxial films were prepared by off-axis pulsed laser deposition at substrate temperatures of 775–800 °C in a 15–50 mTorr mixture of 5% O3 in O2.

Total Reflection Angle X-Ray Spectroscopy with Reflection High Energy Electron Diffraction (RHEED-TRAXS) is a highly sensitive method for surface analysis. Yba2Cu3O7-x films of less than 1 unit cell average coverage can be detected by its characteristic x-rays. We grew YBCO films on MgO substrates by laser-ablation with two different kinds of surface morphology; one had few particles on a flat surface and the other had many long and narrow islands on the surface which we call linear islands. We measured the take-off angle dependence of TRAXS on these films. For the YBCO films with linear islands the intensities of YLα, BaLα and CuKα x-ray lines have shoulders at the critical angles given by a theoretical formula. For the YBCO films with smooth surfaces, only the BαLa intensity had a sharp peak at the critical angle. The result suggests that a BaO layer terminates YBCO films, or that a chemical reaction occurs at the surface and Ba compounds is produced.

MicroRaman spectroscopy allows to identify the presence of c| and c⊥ oriented grains in YBCO thin films. This is achieved by the observation of two Raman modes associated with the oxygen sublattice vibrations, ˜500 cm−1 and ˜338 cm−1. The relative intensity of these Raman modes is related to the presence of c⊥ and c⊥;. oriented grains. Using the high lateral resolution of the Raman microprobe (<1 μm) some needle shaped grains of the films were scanned. The different Raman parameters were analyzed, showing noteworthy transformations at the [c|;]/[c⊥] boundaries. In particular the Raman mode corresponding to the out of phase O (2)– O(3) in plane vibrations (˜338 cm−1) was found to be narrowed, which should account for a decoupling of the phonon with the electronic continuum.

The magneto-optical Faradayeffect [MOFE] is known to be an excellent tool for the spatially resolved analysis of the flux distribution in superconductors. We use three examples to demonstrate the power of this technique for device oriented investigations. It is shown that homogeneous Yba2Cu3O7 thin films with different shape show a flux pattern strongly depending on the geometry of the sample; model calculations for the flux distribution are in excellent agreement with the experimental results. Furthermore, we show, that crystallographic defects as well as imperfections due to pattern delineation are affecting the flux pattern on macroscopic scale. In a third example we use the MOFE to demonstrate that pulsed laser irradiation of Yba2Cu3O7 thin films with UV photons of moderate flux causes an enhancement of the critical current.

A series of compounds in the system A4MeSb13O12 where A=Ba, Sr and Me=Li, Na &K were prepared by solid state reaction at elevated temperature. A new form of Sr4NaSb3O12 was prepared. The compounds were characterized with regard to their lattice parameters, density and dielectric properties. Thin films were prepared by PLD from dense targets and epitaxial relationships identified between YBCO and these compounds.

Large area uniform deposition of Yba2Cu3O7 (YBCO) thin films on 8 inch diameter wafers, using a 3 inch diameter sputtering target and optimized substrate rotation in a single target 90° off-axis sputtering technique, is reported. The variation in thickness, composition and superconducting properties was studied as a function of substrate position on stationary and rotating substrates. The films deposited from a 3” target on rotating substrates displayed uniform thickness (< ±5% variation) and composition (< 2.3% deviation from target stoichiometry) and a consistently high transition temperature ( Tc > 88.3°K) over an 8” diameter area.