Yttrium Barium Copper Oxide Films Research Articles

Improvement of the Delamination Strength of Yttrium Barium Copper Oxide (YBCO) Films by the Hamaker Method

Failure of yttrium barium copper oxide (YBCO) coated conductors (CC) tapes usually manifests as delamination occurring majorly in the YBCO films. Because the delamination strength of any material is greatly influenced by its microstructure, a good understanding of the intermolecular interactions in the YBCO films is essential to achieve the desired control of the delamination of YBCO CC tapes. Our previous works on the delamination behavior of multilayered YBCO CC tapes showed that the Hamaker based-models is viable for investigating the damage characteristics of YBCO films. Therefore, in this article, we investigated the intermolecular interactions of the constituent molecules of YBa2Cu3O7 films by Hamaker method. Then, used the deductions for the combining laws of the Hamaker coefficients for the interacting molecules to uncover and eliminate the interactions that cause the microstructural defects in the YBCO films. Our results show that increasing or decreasing the energy of the intervening medium between the interacting molecules to specific critical values eliminates the identified microstructural defects in the YBCO films. In particular, the elimination of the natural separation phenomenon among interacting molecules of the YBCO films improves its delamination strength significantly. Although based on our previous works, this technique had good agreement with the numerical, closed-form solution, and X-rays diffraction methods; further experimental validation is still under construction.

A Displacement-energy Model Approach for Evaluating the Interfacial Stress in Multilayer Film Structures Based on the Interactions of Grains at the Interface

For multilayer film structures, mechanical failure is usually taken place at the interface. To deeply understand the typical issue, it is first essential to know the stress status at the interlayer surface. For this aim, in this work, the author presented displacement-energy models (DEM) for accurately calculating the interfacial stress in multilayer film structures and the impact of the morphology and size of the interacting grains at the interface. The stress-inducing mechanisms are related to the displacement-energy phenomenon of the interacting grains in the structure caused by the deposition technique. In contrast, the interfacial residual stress-evolution in the deposited films is determined from the change in the lattice constant between interacting grains as a function of temperature and time during the deposition and cool-down process. The interacting grains understudied have different morphology with flat and curved surfaces and sizes. Concerning the yttrium barium copper oxide (YBCO) films deposited on the lanthanum aluminum oxide (LaAlO₃) substrate, the computed results showed that the morphology and size of the interacting grains affect the net interfacial residual stresses in the YBCO films significantly. Also, the results of the DEM models agree well with the measured value by the X-ray diffraction method (XRD). Specifically, the computed stress in the YBCO films for the interacting grains with spherical surfaces is 0.18 GPa. Similarly, that measured by the XRD method is 0.178± 0.053 GPa. In the future, the findings of this study could be essential in the defect inspection of several Multilayer Engineering Materials, including composites for various applications, which often consist of grains with different morphology and size.

Experimental Study on the Performance Change of YBCO Tapes Under Repeated Overcurrent

Superconducting cables or fault current limiters may encounter short-circuit currents during operation. When experiencing multiple overcurrent cycles, the critical current degradation of yttrium barium copper oxide (YBCO) tapes may occur. The performance degradation of YBCO tapes under overcurrent is a gradual process. It may take dozens or hundreds of overcurrent or overheating pulses. To get a better understanding of this process, we explored the performance change of YBCO tapes under repeated overcurrent. A life characteristics test platform was established. The electromagnetic performance degradation of YBCO tape under 50 Hz sinusoidal ac operating conditions was investigated, taking the effect of the overcurrent amplitude and duration into account. Meanwhile, the relationship between the number of overcurrent cycles and the I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> degradation is proposed. The reason for this performance change is analyzed by comparing the 2-D current density distribution of the YBCO film before and after experiencing overcurrent. In addition, the U-I property and resistance variations of these tapes are presented. It is inferred that the cracking of the superconducting layer is the main cause of I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> degradation. The experimental results provide meaningful references for the performance degradation of the YBCO tapes and related devices.

Femtosecond laser-induced breakdown spectroscopy: Elemental imaging of thin films with high spatial resolution

We investigate femtosecond laser-induced breakdown spectroscopy (fs-LIBS) for the spectrochemical imaging of thin films with high spatial resolution. Chemical images are obtained by recording LIBS spectra at each site of 2D raster-scans across the samples employing one fs-laser pulse per site. The diffraction images of the Echelle spectrometer are binned to reduce the read-out time of the intensified CCD detector and to increase the stability of the emission signals against peak drifts in the echellograms. For copper thin films on glass the intensities of Cu I emission lines and the size of ablation craters vary non-monotonously with the film thickness hCu=5–500nm. The emission efficiency, defined as the Cu I line intensity per ablated volume, strongly decreases for films thicker than the optical penetration depth. The Na I line intensity from glass increases exponentially with decreasing Cu film thickness. For yttrium barium copper oxide (YBCO) thin films on MgO various atomic and molecular emission lines of the laser-induced plasma are measured (film thickness hYBCO=200–1000nm). The obtained element (Y, Ba, Cu, Mg) and molecular (Y-O) fs-LIBS images match the structure of the micro-patterned YBCO films very well. The achieved lateral resolution δr=6μm is among the best values reported for spectrochemical LIBS imaging.

The Influence of the Microstructure and Morphology of CeO 2 Buffer Layer on the Properties of YBCO Films PLD Grown on Ni Tape

YBa2Cu3O7−δ films were deposited on CeO2-buffered nickel substrates, with different buffer thickness. Full width at half maximum of rocking curve, Δω, of CeO2 and yttrium barium copper oxide (YBCO), as well as the critical temperature, T c, of YBCO were shown to be strongly dependent on buffer thickness. They behave similarly but not proportional to the buffer thickness increase. This and the fact that Δω vs. buffer thickness and T c vs. buffer thickness for YBCO behave similar with RMS roughness vs. thickness of CeO2 indicates that the surface peculiarity of buffers is responsible for YBCO properties. More precisely, the surface of CeO2 films prepared by the chemical solution route based on propionic acid is prone to agglomerate (de-wet) and the degree of agglomeration depends in an intricate way on buffer thickness. We showed that nor RMS roughness neither (00 l) texture degree can define alone the surface suitable for c-axis YBCO nucleation. The {111} faceted grains (even in the case of high (00 l) texture) and other defects generated by agglomeration supply a low fraction of (00 l) flat terminations of buffer that affect the nucleation of c-axis-oriented YBCO phase. Moreover, the thermal instability of the surface morphology of CeO2 buffers (further development of de-wetting process, {111} faceted grains, etc. during superconducting layer deposition) influence the quality of YBCO films.

Complex Conductivity of YBCO Films in Normal and Superconducting States Probed by Microwave Measurements

We report on microwave frequency characterization of yttrium barium copper oxide (YBCO) thin films in both normal and superconducting states. A microwave single-post dielectric resonator technique using two different resonators was used for the complex conductivity determination of YBCO samples deposited on dielectric substrates. The intrinsic complex conductivity of YBCO films was determined from the measured resonator quality factor Q and resonant frequency values employing rigorous electromagnetic modeling of the resonant structures with the mode-matching and Rayleigh-Ritz techniques. Such approach allowed us to determine the intrinsic properties of the films (conductivity, permittivity, and penetration depth) without any simplifications and errors associated with approximate modeling employing perturbation theory. We describe the superconducting material only through its intrinsic material properties, such as the complex conductivity, which does not depend on the thickness of the sample and other parameters. From both simulations and experimental results, we show that the proposed method of intrinsic complex conductivity determination is particularly useful for the characterization of very thin YBCO layers. To support the novelty of our approach, it is shown that significant differences appear between the rigorous and perturbation computations for thin superconducting films (below 50 nm).

YBCO step-edge junctions with highIcRn

Step-edge junctions represent one type of grain boundary Josephson junctionemployed in high-temperature superconducting junction technology. To date, themajority of results published in the literature focus on [001]-tilt grain boundaryjunctions (GBJs) produced using bicrystal substrates. We investigate the stepmorphology and YBCO (yttrium barium copper oxide) film structure of YBCO-basedstep-edge junctions on MgO [001] substrates which structurally resemble [100]-tiltjunctions. High-resolution electron microscopy reveals a clean GBJ interface of width ∼ 1 nm and a single junction at the top edge. The dependence of the transport propertieson the MgO step-edge and junction morphology is examined at 4.2 K, to enabledirect comparison with results for other junction studies such as [001]-tiltand [100]-tilt junctions and building on previously published 77 K data. MgOstep-edge junctions show a slower reduction in critical current density withstep angle compared with [001]-tilt junctions. For optimized step parameters,transport measurements revealed large critical current and normal resistance (IcRN) products(∼3–5 mV), comparable with the best results obtained in other kinds of [100]-tilt GBJs inYBCO at 4.2 K. Junction-based devices such as SQUIDs (superconducting quantuminterference devices) and THz imagers show excellent performance when MgO-basedstep-edge junctions are used.

Praveen Chaudhari

An innovator in the field of thin films and high-temperature superconductors, Praveen Chaudhari died of cancer on 13 January 2010 at his home in Briarcliff Manor, New York.Praveen was born on 30 November 1937 in Ludhiana, India, and grew up in Calcutta, where he lived through the scarring times of the Indian partition and witnessed the bloodshed of the 1947 riots. Sent to boarding school because he would play truant and go fishing, he eventually received his bachelor’s degree in metallurgy from the Indian Institute of Technology Kharagpur in 1961 and a PhD from MIT in 1966 in physical metallurgy. His thesis, under adviser Michael Bever, was on the irradiation effects on bismuth telluride.Praveen then began his 37-year career at IBM Research in Yorktown Heights, New York. He quickly became the source of inspiration in many areas of thin-film physics, including dislocation interactions and superplasticity, stability of Josephson junctions, and coincidence boundaries between crystals. He was a crucial contributor to IBM’s product development and provided fundamental research in improving reliability for products such as the IBM 370 and 3081 computers. During the early 1970s, he and colleagues Dick Gambino and Jerry Cuomo worked on amorphous gadolinium cobalt films that were successfully integrated into IBM’s magnetic bubble memory devices and adopted later as the basis for read-write media for the magneto-optic disk industry. In recognition of that work, the trio received the 1995 National Medal of Technology.Appointed vice president of science in 1982, Praveen shaped the evolution of IBM’s science research programs in the 1980s. Basic research flourished under his management, and in 1986 and 1987, IBM scientists were awarded the Nobel Prize in Physics for the invention of the scanning tunneling microscope and the discovery of high-temperature superconductivity, respectively.Throughout his professional life, Praveen successfully united careers as an executive and a scientist. During the time that high-T c superconductivity was discovered, Praveen carried out his responsibilities as vice president during the day and then worked in the lab during nights and weekends. Initially, the cuprate superconductors possessed minute critical current densities, and their potential utility was questioned. Guided by his intuitive understanding of materials, Praveen’s team succeeded in growing the first epitaxial yttrium barium copper oxide films with critical current densities two orders of magnitude higher than the earlier results; that increase allayed the utility concerns.Understanding the role of grain boundaries then became important for polycrystalline high-T c superconducting cable applications. Praveen conceived the idea of using bicrystalline substrates, in which crystals of two different orientations share a long, controlled grain boundary; a small group that shared his infectious enthusiasm started using that approach to control-lably study the effects of the films’ grain boundaries. The charismatic IBM vice president did not hesitate to drop by the shielded measurement room at midnight to share cookies and discuss the latest data.The bicrystal research ultimately resulted in the most widely used technology that employs high-T c oxides — Josephson junctions. Bicrystal junctions also provided a foundation for the tricrystal-based experimental confirmation of d-wave pairing in cuprates, which Praveen, remarkably, did not endorse. With the discovery that the critical current decreases with increasing grain boundary angle, bicrystals also became the basis for the development of high-T c coated-conductor technology.In 2003 Praveen retired from IBM and joined Brookhaven National Laboratory as its director. He put BNL on a firm foundation of stability and growth that continues today. His vision led to many successes, including the creation of BNL’s Center for Functional Nanomaterials. In 2006 he stepped down as director and, true to form, returned to the lab; he published a paper on superconducting oxides in Physical Review Letters in 2008. He continued to work part-time at BNL, joined Columbia University as an adjunct professor, and returned to his old laboratory at IBM in Yorktown, where he could often be found running his experiments in the afternoon. He remained active in scientific work up to a few months before his death.Deeply involved in national science policy, Praveen was on the advisory council on superconductivity to Presidents Ronald Reagan and George H. W. Bush and served on the US National Critical Technologies Panel in 1992-93. He advised the government of India and reported on science and technology to two prime ministers, Rajiv Gandhi and P. V. Narasimha Rao.Praveen was a gifted speaker and an excellent motivator who could get others excited about his ideas. He cherished competition, yet he maintained an open door for science discussions and went out of his way to help others with their careers. He switched with ease between hands-on science and demanding management positions, never losing his touch in the lab nor his skills in the conference room. He is greatly missed.Praveen ChaudhariPPT|High resolution© 2010 American Institute of Physics.

YBCO Film With Sm Addition Using Low-Fluorine TFA-MOD Approach

Yttrium barium copper oxide (YBCO) film was synthesized by a metal-organic deposition (MOD) process with fluorine-free Y and Cu precursor. The precursor solution with Sm addition enabled further improvement of the thickness and uniformity of precursor films. The calcination and firing processes were studied, and the precursor film was successfully converted to dense and uniform YBCO film on LaAlO3 (LAO) substrate after annealing in a wet Ar and O2 atmosphere. The measured critical current density (J c) value was about 80 A/cm-w (2.66 MA/cm2). The trifluoroacetate (TFA) reduced MOD process has the advantage that it has a larger tolerance for variations in the gas flow rate and path. The results on a Sm-YBCO film deposited on LAO with a CeO2 buffer layer fabricated by MOD are also presented.

Effect of texture dispersion on the effective biaxial modulus of fiber-textured hexagonal, tetragonal, and orthorhombic films

The effective biaxial modulus (Meff) of fiber-textured hexagonal, tetragonal, and orthorhombic films is estimated by using the Voigt–Reuss–Hill and Vook–Witt grain-interaction models. The orientation distribution function with Gaussian distributions of the two Euler angles θ and ϕ is adopted to analyze the effect of texture dispersion degree on Meff. Numerical results that are based on ZnO, BaTiO3, and yttrium barium copper oxide (YBCO) materials show that the Vook–Witt average of Meff is identical to the Voigt–Reuss–Hill average of Meff for the (001) plane of ideally fiber-textured hexagonal and tetragonal films. The ϕ distribution has no influence on Meff of the (hkl)-fiber-textured hexagonal film at any θ distribution in terms of the isotropy in the plane perpendicular to the [001] direction. Comparably, tetragonal and orthorhombic films represent considerable actions of ϕ dispersion on Meff, and the effect of ϕ dispersion on Meff of a (001)-fiber-textured YBCO film is smaller than that for a (001)-fiber-textured BaTiO3 film since the shear anisotropic factor in the (001) shear plane of a YBCO film more closely approaches 1. Enhanced θ and ϕ distributions destroy the perfect fiber textures, and as a result, the films exhibit an evolution from ideal (hkl) fiber textures to random textures with varying full widths at half maximums of θ and ϕ.

Interaction of magnetic field and magnetic history in high-temperature superconductors

Yttrium barium copper oxide (YBCO) coated conductors are now the most promising high-temperature superconducting tapes in terms of current capacity and price. One form of these conductors utilizes YBCO films on Ni–W metallic tapes and is being considered for a number of power engineering applications. In these applications, the conductor will carry an ac current, leading to energy losses, which are the focus of significant technical and experimental efforts. Our measurements of the ac losses of YBCO/Ni–W conductors carrying ac currents in applied dc magnetic fields have revealed a complex interaction between the magnetic materials present, the geometry of the conductor, the ac and dc magnetic fields, and the electromagnetic “history” of the sample. The investigation of this interaction is the main subject of this paper.

Thickness control of solution deposited YBCO superconducting films by use of organic polymeric additives

We show that the thickness of yttrium–barium–copper–oxide (YBCO) superconducting films grown from trifluoroacetate precursors can be strongly modified using polymeric additives, while deposition conditions by spin or dip coating remain unchanged. A screening of different families of organic additives has been performed, and the best results have been achieved using polymers having an oxygen functionalized backbone. Two different polymeric additives, polyvinyl pyrrolidone (PVP) and poly(ethylene glycol) (PEG), have been more thoroughly investigated, and thermal analysis suggests that PEG is the most promising alternative because the pyrolysis step of the new complex precursors remains sharp and narrow and hence the final homogeneity of the film is preserved. The combination of anhydrous trifluoroacetic acid (TFA) solutions and poly(ethylene-glycol) (PEG8000) as additive can produce an increase of the YBCO film thickness up to 300%, while keeping a fast pyrolysis process and high critical current densities.

Surface etching of YBCO films by xenon difluoride

We have demonstrated that xenon difluoride (XeF2) etches thin films of YBa2Cu3O7−x, the superconducting form of yttrium–barium–copper–oxide (YBCO), during dry etch processing. Both c-axis and mixed a∕c-axis YBCO films show evidence of such etching with a axis being more reactive. Profiles of YBCO films examined by ESCA show that the surfaces of both etched and unetched films are barium rich at the expense of yttrium. After XeF2 etching, fluorine was found to be present to a depth of at least 40nm. Despite the etching and the presence of fluorine in the YBCO films, the superconducting transition temperature, Tc, was unaffected by the XeF2 treatment.

Fluorine Analysis and Microstructural Evolution in Coated YBCO Conductor Deposited by Metal Trifluoroacetate Process

A solution based processes using metal trifluoroacetate (TFA) precursors is being developed for commercialization of Yttrium Barium Copper Oxide (YBCO) coated conductors. This nonvacuum technique uses inexpensive precursors and has the advantage of easy scalability, ease of composition control, eliminates carbonate formation during decomposition, and helps maintain film uniformity during heat treatment. However, fluorine remains incorporated in the YBCO film, depending on process conditions, and may result in a reduction of Jc. An appropriate heat treatment schedule ensures reduction of fluorine in the YBCO films as well as an improvement in microstructural properties. The aim of this work was to investigate the fluorine depth profile, density, and microstructural evolution of metal organic deposited (MOD) YBCO films with heat treatment using focused ion beam (FIB) microscopy, nuclear reaction analysis (NRA), and Rutherford backscattering spectroscopy (RBS). Multilayer structures studied consisted of 0.7 /spl mu/m to 2.0 /spl mu/m-thick YBCO layers deposited on a NiW alloy substrate buffered with CeO/sub 2//YSZ/Y/sub 2/O/sub 3/.

Integration of Pb(Zr0.52Ti0.48)O3 epilayers with Si by domain epitaxy

High-quality lead zirconate titanate films (PZT) have been grown on yttrium barium copper oxide (YBCO) bottom electrode by domain epitaxy where integral multiples of lattice constants match across the interface. The YBCO films were epitaxially fabricated on Si (100) by introducing epilayer geometry of strontium titanate/magnesium oxide/titanium nitride. Pulsed-laser ablation was used to evaporate these five stoichiometric targets in a high vacuum chamber. X-ray diffraction and high-resolution transmission electron microscopy techniques were employed to gain understanding of the structure, crystallinity, and interfaces in these epilayers. The electrical characterization of the PZT films with evaporated silver contacts resulted in superior values of spontaneous polarization, remnant polarization, and coercive fields. This heterostructure opens a way for integration of epitaxial single-crystal PZT-based capacitors with silicon-based devices.

Double-sided sputtering deposition of YBa/sub 2/Cu/sub 3/O/sub 7-δ/ thin films on 2" LaAlO/sub 3/ wafers for microwave applications

Superconducting yttrium barium copper oxide films were prepared on 2" lanthanum aluminate substrates by sputtering from a cylindrical and stoichiometric target. The deposition parameters were studied in order to obtain in a reproducible manner a sufficiently low value of the surface resistance for microwave applications. The typical value at 10 GHz and 77 K was 0.35 m/spl Omega/ down to 0.2 m/spl Omega/. The purpose of this work was the subsequent deposition of YBa/sub 2/Cu/sub 3/O/sub 7-z/ on the LaAlO/sub 3/ backside without degradation of the first deposit. The fabrication of the subsequent deposit was made with the same deposition parameters as the first film after turning over the substrate at room temperature. The physical and structural properties of both side deposits were analyzed (RBS, ion channeling, MEB, XRD, Rs and electrical resistivity). Although the first film underwent a second thermal process during the subsequent deposition, the surface resistance value was not degraded. This unexpected result is discussed in the frame of the mechanism of oxygenation in YBa/sub 2/Cu/sub 3/O/sub 7-x/ film by changing the conditions of sample cooling. An example of a microwave filter using this double-sided structure is presented.

MgO sacrificial layer for micromachining uncooled Y-Ba-Cu-O IR microbolometers on Si/sub 3/N/sub 4/ bridges

This paper describes a new micromachining technique for fabrication of semiconducting yttrium barium copper oxide (YBCO) microbolometers using magnesium oxide (MgO) as the sacrificial layer. This type of bolometer can be operated at room temperature, providing a low-cost alternative for more expensive cryogenically cooled thermal detectors used for infrared (IR) imaging. The new micromachining techniques described here would enable the fabrication of YBCO IR focal plane array (FPA) with CMOS signal processing circuitry. Devices were fabricated by growing YBCO films on 4000-/spl Aring/-thick suspended Si/sub 3/N/sub 4/ membranes measuring 40/spl times/40 /spl mu/m/sup 2/ in area and extended over micromachined air gaps, which provide the low thermal conductivity that is required for high responsivity. The gap was created by etching an MgO sacrificial layer. This is the first example of using MgO in this type of application. The MgO sacrificial layer technique is fully CMOS compatible and presents no major fabrication challenges. Thermal conductivities achieved in vacuum with the Si/sub 3/N/sub 4/ suspended structures were on the order of 10/sup -7/ W/K, yielding an effective thermal isolation for bolometer operation. Optical characterization has shown responsivity up to 60 kV/W and detectivity over 10/sup 8/ cm.Hz/sup 1/2//W to black-body IR radiation, indicating that this technology is a suitable candidate for low-cost thermal imaging.

Fabrication and Electrical Characterisation of Superconductor‐on‐Silicon Devices

The objectives of this study are to assess the utility of the high‐Tc superconductor, yttrium barium copper oxide (YBCO), as a gate material in two‐ and three‐terminal superconductor‐insulator‐semiconductor (SulS) devices, and to study the electrical properties of the insulator and the insulator/Si interface. The YBCO and yttria‐stabilised‐zirconia (YSZ) layers were epitaxially grown on Si by pulsed‐laser deposition. The SulS diodes were fabricated using standard lithographic techniques, with evaporated gold providing the gate and substrate contacts. Electrical characterisation of these superconducting devices is performed using current vs. voltage and capacitance vs. voltage (C‐V) measurements under bias‐temperature cycling. It is found that deposition of thicker YBCO films (≥ 1500 A) minimises the leakage current of the devices, resulting in electrically stable capacitors, especially at superconducting temperatures. A thermally activated process in the temperature range 80–295 K, as determined from flat‐band shifts of C‐V curves, is attributed to trapping/detrapping mechanisms in the SiOx interfacial layer between YSZ and Si. The mobile ions present in YSZ, which affect the room‐temperature C‐V behaviour, give rise to adjustable threshold voltages at superconducting temperatures. These findings will have a significant impact on future transistors using this capacitor as the gate structure.

Fabrication of Biaxially Oriented YBCO on (00l) Biaxially Oriented Yttria-Stabilized-Zirconia on Polycrystalline Substrates

AbstractIon-assisted, ion-beam sputter deposition is used to obtain (00l) biaxially oriented films of cubic yttria-stabilized-zirconia (YSZ) on polycrystalline metal substrates. Yttrium-barium-copper-oxide (YBCO) is then heteroepitaxially-pulse-laser deposited onto the YSZ. Phi scans of the films show the full-width-half maxima of the YSZ (202) and the YBCO (103) reflections to be 14° and 10° respectively. Our best dc transport critical current density measurement for the YBCO is 800,000 A/cm2 at 75K and 0T. At 75K, the total dc transport current in a 1 cm wide YBCO film is 23 A.

The effect of deposition conditions on the structure and electrical properties of YBaCuO superconducting thin films

Thin superconducting films of yttrium barium copper oxide (YBCO) grown onto MgO(100) and YSZ(100) substrates have been prepared by rf magnetron sputtering and by chemical sol gel methods. The structure, morphology and compositional properties were studied by X-ray diffraction, scanning electron microscopy and Auger electron spectroscopy, respectively. The electrical resistance was measured by a four-probe dc method. The results indicate that the method of film preparation, the substrate material and the nature of the post-deposition annealing have a significant influence on the microstructure and the superconducting properties of YBCO films.