Properties Of YBCO Thin Films Research Articles

Enhanced dual superconducting and ferromagnetic properties of YBCO film tuned with boron and oxygen partial pressures

This study reports the dual enhancement of superconductivity and ferromagnetic properties of YBCO films for the first time. These dual enhanced properties have been achieved by tunning YBCO films with dopant boron and oxygen partial pressures. Thin films of YBa2Cu3-xBxO7-y with different B concentrations and oxygen partial pressures were fabricated by electro-spin coating. The systematic optimization of B concentration and oxygen partial pressure of YBCO films were studied through microstructural, electrical, optical, and magnetic properties. In particular, YBCO film doped with 20 mol% B and 20 SCCM O2 pressure showed excellent superconducting and magnetic properties. The breakthrough of this study in the films YBa2Cu2.4B0.6O7−y/20 SCCM, not only displayed enhanced superconducting properties but also ferromagnetic properties at near transition temperature (Tc) (i.e., 109 K). The magnetic moment values YBa2Cu2.4B0.6O7−y/20 SCCM films achieved ≈ 0.65 μB/mol, which is two order increment of films prepared without oxygen partial pressure. The dopant boron and oxygen partial pressure provide a new pathway for tuning the superconducting and ferromagnetic properties of YBCO thin films.

Composition effect on transport and microwave properties of YBCO thin films prepared by metalorganic chemical vapor deposition

YBa2Cu3O7−δ (YBCO) thin films deposited on LaAlO3 single-crystal substrates have great potential for application in microwave field due to their low microwave surface resistance (Rs). In order to prepare high-performance films and facilitate adjustment of experimental parameters, we designed novel metalorganic chemical vapor deposition system. This system adopts single liquid-source pulse feed that provides facile control over film composition through the adjustment of Y, Ba, and Cu ratios in precursors. Here, we thoroughly study influence of film composition on performance. By conducting energy-dispersive spectroscopy measurements, Y, Ba, and Cu composition ranges of 21–24%, 28–31%, and 46–54%, respectively, are found to optimize YBCO film transport and microwave properties. Composition affects purity of film phase which in turns determines film performance. To confirm this observation, we adjust ratio through input–output relationship to obtain film with composition ratio within abovementioned optimal range. Obtained YBCO film has critical current density of 2.8 MA/cm2 at 77 K and 0 T and Rs of 0.285 mΩ at 77 K and 10 GHz. The full width at half maximum of YBCO (005) peak and (103) plane, measured via X-ray diffraction, are 0.235° and 0.762°, respectively.

Mechanical characterization of YBCO thin films using nanoindentation and finite element method

Abstract The mechanical properties of YBCO thin film deposited on SrTiO3 (100) substrates by magnetron sputtering were determined using Berkovich nanoindentation and scanning electron microscopy. Hardness and elastic modulus were determined via the Oliver–Pharr method from indentation load–depth curves. The hardness values of the YBCO thin film show depth dependence, i. e., indentation size effect, which arose from the surface roughness as detected by scanning electron microscopy. Multiple pop-in events were observed on the loading curves, however, no obvious pop-out takes place during the elastic recovery. In addition, an effective analytical method accommodating the indenter imperfection was proposed and validated against experimental data in terms of elastic modulus, yield stress and friction angle using the Drucker–Prager yield criterion for the YBCO thin film.

Effects of electron beam irradiation on the superconducting properties of YBCO thin films

The effects of electron beam (EB) irradiation on the superconducting critical temperature (Tc) and critical current density (Jc) of YBCO films were studied. The YBCO thin films were irradiated using a KAERI EB accelerator with an energy of 0.2 MeV and a dose of 1015–1016 e/cm2. A small Tc decrease and a broad superconducting transition were observed as the EB dose increased. The value of Jcs (at 20 K, 50 K and 70 K) increased at doses of 7.5×1015 and 2.2×1016 e/cm2. However, Jcs decreased as the dose increased further. The X-ray diffraction (XRD) analysis showed that the c axis of YBCO was elongated and the full width at half maximum (FWHM) increased as the dose increased, which is strong evidence of the atomic displacement by EB irradiation. The transmission electron microscopy (TEM) showed that the amorphous layer formed in the vicinity of the surfaces of the irradiated films. The amorphous phase was often present as an isolated form in the interior of the films. In addition to the formation of the amorphous phase, many striations running along the a-b direction of YBCO were observed. The high magnification lattice image showed that the striations were stacking faults. The enhancement of Jc by EB irradiation is likely to be due to the lattice distortion and the formation of defects such as vacancies and stacking faults. The decrease in Jc at a high EB dose is attributed to the extension of the amorphous region of a non-superconducting phase.

Effect of Oxygen Content in Atmospheres of Heat Treatment on the Properties of YBCO Thin films

YBa 2 Cu 3 O 7- x (YBCO) films were prepared on single-crystal LaAlO 3 (100) substrate using a low-fluorine sol-gel method. The effect of the oxygen content in the atmospheres of heat treatment at 725 °C on the critical current density ( J c ) of the obtained YBCO films was investigated. Results show that all the films heat-treated in the oxygen content range of 100∼1700 µL/L exhibit good biaxial-texture characteristics. However, high- J c YBCO films are not obtained at the oxygen contents of 100 and 200 µL/L due to the lower density of the surfaces. With increasing the oxygen content, the film surface becomes dense gradually. When the oxygen content is 300 µL/L, the surface of the film is very dense and J c reaches 4.3 MA/cm 2 . Furthermore, many copper-rich second phases grow up on the surfaces with further increasing oxygen content up to 800 and 1700 µL/L, which is a dominant reason for the decline in J c of the films.

Co-doping effects of Gd and Ag on YBCO films derived by metalorganic deposition

Y1–xGdxBa2Cu3O7–δ-Ag (x = 0, 0.25, 0.5, 0.75, 1) thin films were prepared on oxide buffered Hastelloy substrates by low fluorine metalorganic depostion (MOD) process. The effects of co-doping of Ag and Gd on the microstructures and superconducting properties of YBCO thin films are investigated with respect to improvement on texture and superconducting performance in case of optimized doping content. It is found that optimum addition of Ag and Gd may lead to better c-axis orientation, superior surface microstructure and finally give rise to much improvement of superconducting performance.

Performance Analysis of Direct Gold Wire Bonding on Superconducting <inline-formula><tex-math notation="LaTeX">$\mbox{YBa}_{2}\mbox{Cu}_{3}\mbox{O}_{7\mbox{-}x}$</tex-math></inline-formula> Thin Films and Devices

The performance analysis of direct gold (Au) wire bonding on 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">7-x</sub> (YBCO) thin films was performed. In a number of applications, YBCO thin films and devices are wire bonded on chip carriers or printed circuit boards for further electronic connections via the metallization of the contact pads of YBCO thin films. Although metallization for contact wiring is generally performed by thermal evaporation or sputtering at room temperature, the surface of a film is generally exposed to high temperatures by evaporated material or sputtering plasma. Moreover, an additional lithographic process (i.e, the application of a photoresist, baking, developing, and dry or wet etching) is necessary after the metal layer deposition in order to define contact pads. Since the superconducting properties of YBCO thin films and Josephson junctions are very sensitive to temperature and a humid environment, the metallization and additional lithographic processes during the fabrication cause significant degradation in the performance of the devices. In order to eliminate these additional steps, we performed a direct wire bonding process on YBCO thin films. Films of various thicknesses were deposited onto (100) SrTiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> (STO) substrates by direct-current magnetron sputtering, and 20-μm-wide meander-type microbridges were patterned. The contact pads of the devices were wire bonded onto chip carriers by a thermosonic wedge bonder without using any metallization layer. The reliability and performance analyses of the bonds were performed under several aggressive thermal cycling conditions from liquid nitrogen (LN, 77 K) up to 450 K. The superconducting properties of the samples were then analyzed by means of resistance-temperature (R-T) and current-voltage (I-V ) measurements. A resistance model was developed for the bonding layout, and a specific contact resistivity was derived as ~3 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-6</sup> Ω · cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> .

Systematic Variation of Hybrid APCs Into YBCO Thin Films for Improving the Vortex Pinning Properties

The effect of hybrid (columnar and spherical) artificial pinning centers (APCs) on the vortex pinning properties of YBCO thin films is studied in this paper on the basis of variation of critical current density JC with applied magnetic held and also with the orientation of the applied magnetic held. YBCO+BSO3% composite target is used for preparing film with 1-D (columnar) APCs, whereas the same composite target is modified by putting two differently sized (2.2 area% and 3 area%) Y <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> sectored pieces for preparing films having different concentrations of 3-D (spherical) APCs along with 1-D APCs. Film consisting of only 1-D APCs exhibits enhanced in-held J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</sub> values as compared to the one without any APC, and the ones consisting of hybrid APCs exhibit even better J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C-</sub> B characteristics with increase in the fraction of 3-D APCs. Fp max. values increase systematically with incorporation of 1-D and 1-D + 3-D APCs, and it also shifts toward higher applied magnetic fields. Film with 1-D APCs exhibits strong J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</sub> peak at Θ = 0° (H//c-axis), whereas films consisting of hybrid APCs exhibit enhanced J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</sub> at all the investigated angular regime. A possible mechanism of vortex pinning in samples with hybrid APCs is also discussed, suggesting the role of 1-D and 3-D APCs.

Influence of Interfacial LSMO Nanoparticles/Layer on the Vortex Pinning Properties of YBCO Thin Film

YBa2Cu3O7−δ (YBCO) thin films have been deposited on bare and La0.67Sr0.33MnO3 (LSMO) modified single crystal SrTiO3 (STO) substrates. The effect of randomly distributed ferromagnetic LSMO nanoparticles and a complete LSMO layer, present at STO/YBCO interface, on the superconducting properties of YBCO thin films has been investigated by temperature dependent magnetization studies. The YBCO thin film on LSMO nanoparticles decorated STO substrate shows significant improvement in the critical current density and pinning force density as compared to the YBCO thin film deposited on bare STO substrate and this improvement is more significant at higher applied magnetic field. However, the LSMO/YBCO bilayer showed the improved flux pinning properties only up to a magnetic field of 1.5 T above which it deteriorates. In the case of LSMO/YBCO bilayer, the underlying LSMO layer gives rise to magnetic inhomogeneities due to domain structure, which leads to improved flux pinning properties limited to lower field. However, in the case of LSMO nanoparticles decorated substrate, the presence of LSMO nanoparticles at YBCO/STO interface seems to introduce magnetic inhomogeneities as well as structural defects, which might be acting as correlated pinning sites leading to improved flux pinning properties of the YBCO thin film over a wide range of applied magnetic field.

Enhanced critical current density in YBa2Cu3O7−δ thin film deposited on La0.67Sr0.33MnO3 decorated SrTiO3 substrates

Thin films of YBa2Cu3O7−δ (YBCO) have been deposited on undecorated and La0.67Sr0.33MnO3 (LSMO) nanoparticles decorated single crystal SrTiO3 (STO) substrate using laser ablation technique and their flux pinning characteristics have been compared using temperature dependent magnetization studies. Significant improvement in the critical current density of YBCO thin film has been observed even at higher applied magnetic field (∼7T). The improved flux pinning properties of YBCO thin films deposited on LSMO decorated STO substrate has been attributed to the presence of ferromagnetic LSMO nanoparticles at the substrate/film interface which seem to be acting as artificially generated magnetic pinning centres leading to improved flux pinning properties.

Enhanced Flux Pinning Properties of BaZrO3-doped YBCO Films Grown by Pulsed Laser Deposition on LaAlO3(100) Substrates Decorated with Y2O3 Nanoislands

In this work, we intend to investigate the interaction between two types of nanoscaled artificial pinning centers and their pinning properties in YBCO thin films grown by pulsed laser deposition technique. The two types of artificial pinning centers were prepared in different processes, (1) Y2O3 nanoislands decorated on substrates prior to the deposition of YBCO thin film, and (2) BaZrO3 nanoparticles self-assembled within YBCO matrix during the deposition of YBCO thin film. We compared the transport characteristics of the YBCO thin films containing these two types of artificial pinning centers with those of pure YBCO thin films grown on decorated substrates and BZO-doped YBCO thin films grown on undecorated substrates. It was found that these two types of artificial pinning centers, which are simultaneously present, acted constructively to enhance the pinning properties of YBCO thin films.

The effects of Sm and Y addition on the properties of YBCO thin film prepared by a DCA-MOD method

Off-stoichiometric (Y 1RE x )Ba 2Cu 3O 7− δ ( x = 0–0.4, RE = Y or Sm) films have been prepared on LaAlO 3 (1 0 0) single-crystal substrates by a metal-organic deposition using dichloroacetic acid as chelating solution. Coating solutions with excess Sm or Y were prepared by dissolving Y, Sm, Ba and Cu acetates in dichloroacetic acid and distilled water followed by refluxing, drying to obtain blue gel. The final precursor solution for dip coating was prepared by diluting blue gel in 2-methoxyethanol. Coated films were calcined at low temperature up to 500 °C in flowing humid oxygen atmosphere. Conversion heat treatment was performed at 800 °C for 2 h in flowing Ar gas containing 1000 ppm oxygen with a humidity of 9.45%. The viscosities of the precursor solution were increased as the content of added Sm or excess Y increased. The transport critical current density ( J c ) of (Y 1RE x )Ba 2Cu 3O 7− δ film was enhanced with the addition of excess Sm and Y up to 20% and then decreased with further addition. Scanning electron microscope (SEM) observation showed that surface roughness was increased with the addition of excess Y.

Effect of target density on YBCO thin films deposited from nanograined targets

Nanograined YBa 2 Cu 3 O 6 + x (YBCO) targets with grain sizes of 25–45 nm and different densities were prepared with sol–gel method. The properties of the thin films laser deposited from these targets were systematically studied. It was found that most parameters are not clearly affected by the target density, although the surface roughness decreased with target density. A small effect of decreasing J c with increasing target density was observed, but this can be interpreted as film to film variation. On the other hand, a negative correlation between the accommodation field, B ∗ , and zero field J c was observed and B ∗ was found to increase with increasing number of lattice defects. Thus target density is found not to have a large effects on the superconducting or structural properties of YBCO thin films.

Influence of Inhomogeneous Superconducting Properties of YBCO Thin Film on Current Limiting Characteristics

This paper describes numerical analysis of current limiting characteristics of YBCO thin film with inhomogeneous superconducting properties. The analysis tool uses a finite element method (FEM) based on current vector potentials. First, the validity of the analysis tool was verified by comparing with experimental results using small samples. Then we analyzed large-size meander-shaped thin films and discussed the influence of inhomogeneous superconducting properties of YBCO thin film on current limiting characteristics.

Structural Properties of YBCO Thin Films Deposited From Different Kinds of Targets

The accommodation field of 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+infin</sub> (YBCO) a thin films depends on the microstructure of the films and specifically the amount of pinning sites, which can be controlled by the type of the target used in the laser deposition. Typical values for the accommodation field at 5 K are 40-100 mT, 160 mT and 500 mT for films deposited from a micrograined, nanograined and optimally BaZrO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> (BZO) doped targets, respectively. We present structural data on YBCO thin films prepared by laser deposition from a nanograined target, a micrograined target and nanograined targets with added BZO. The characterizations were done with XRD and TEM and it was found that the main difference in the undoped films (nano and micro) was the stiffer lattice of the nanofilms. The BZO inclusions were found to induce a large amount of dislocations to the YBCO lattice surrounding the BZO. This can explain the increase observed in the accommodation field.

Spectroscopic and X-ray diffraction study of high Tc epitaxial YBCO thin films obtained by pulsed laser deposition

We report spectroscopic characterization of epitaxial YBCO thin films grown on LaAlO 3 by pulsed laser deposition. Raman spectroscopy and spectroscopic ellipsometry were used for film characterization and the results were correlated with X-ray diffraction measurements. The mentioned techniques allowed us to analyze crystallographic, micro-structural, and morphological properties of YBCO thin films. We also demonstrated that relatively low resolution Raman spectroscopy and spectroscopic ellipsometry are reliable techniques for a rapid and non-destructive characterization of epitaxial YBCO thin films.

Effects of Residual Surface Resistance on the Microwave Properties of YBCO Thin Films

The performance of a planar microwave device fabricated from a YBCO thin film is strongly dependent on the quality and uniformity of the film. In this paper we present a full set of results of the microwave surface impedance at 8 GHz of three films deposited on MgO substrates and patterned into coplanar resonators. We use the Modulated Optical Reflectance (MOR) technique as a complementary, noncontacting, room temperature method of assessing the uniformity of the films. The three films studied have highly uniform MOR signals across the whole of their surfaces, indicative of thin films of very good electrical quality. However, although the measured Q factors of all three resonators are high, they vary significantly from 15000 to 30000 at 15 K, a result that is uncorrelated with the observed uniformity of the MOR signals. We interpret this variability as being due to residual surface resistance associated with microstructural defects that are impossible to detect using MOR. On subtracting the residual resistance we find that the intrinsic, linear microwave properties (i.e. quasiparticle conductivity /spl sigma//sub 1/ and penetration depth /spl lambda/) are very similar, consistent with the uniformity of the MOR signals.

Effect of Ca doping on the nonlinear microwave properties of YBCO thin films

We have investigated the microwave properties of a set of four identicalYBa2Cu3O7−δ (YBCO) films. One of the films has a 30% Ca-substituted YBCO overlayer, whereas thethree others are used as references to highlight the effect of the Ca substitution. Themicrowave characterization was carried out using the stripline-resonator technique. TheRs of the sample that has a Ca-rich overlayer increased slightly in the linear regime, whereasno significant effect on the nonlinear components and the intermodulation distortion hasbeen observed. We conclude that Ca doping does not significantly improve the nonlinearmicrowave properties of YBCO films, but the small changes in the linear surface resistancethat we observed are discussed in terms of the physics of Ca doping of YBCO.

The preparation of two inch double-sided YBCO thin films

The preparation of two inch double-sided YBCO thin films by simultaneous sputtering from a single target is reported. The lateral homogeneity of microwave surface resistance of the YBCO thin films, on both sides of the two inch wafer, is characterized by using a Fabry–Perot resonator at 145 GHz and 75 K. Values of microwave surface resistance Rs (75 K, 145 GHz, 0 T) below 55 mΩ were reached over the whole area of YBCO thin films on two inch LaAlO3 wafers. The majority of the wafer area has Rs (75 K, 145 GHz, 0 T) values in the range of 15 mΩ to 40 mΩ. The uniformity of Rs values in the whole two inch wafer is excellent and the properties of YBCO thin films were found to be very similar on both sides of the wafer.

Improvement of the superconducting properties of YBCO thin films upon annealing of CeO 2/Al 2O 3 substrate

To investigate the influence of CeO 2 buffer layer on the subsequent YBa 2Cu 3O x (YBCO) growth superconducting YBCO films were deposited on two types of substrates: as-grown or annealed CeO 2 buffered sapphire. The 0 0 2 CeO 2 rocking curves recorded from the as-grown CeO 2 layer have a two-component shape. Annealing of the CeO 2 layers improves the crystalline quality of the layers and it modifies the two-component shape of the rocking curves. The crystallinity of the YBCO films was characterized by X-ray diffraction and transmission electron microscopy analyses. Microwave investigation of both types of films showed significant difference in temperature dependence of microwave losses between the YBCO films grown on the as-deposited CeO 2 (gradual transition to the superconducting state) and on the annealed CeO 2 layers (simple and sharp transition to the superconducting state). Our results show that used annealing procedure improves the properties of the YBCO films, reduces the presence of high angle grain boundaries and diminishes the dispersion of their critical temperature.