YBaCuO Thin Films Research Articles

Rectifying differences in transport, dynamic, and quasi-equilibrium measurements of critical current density

The dependence of the critical current density (Jc) on electric field criteria (Ecr) is studied for high-quality YBCO (YBa2Cu3O7) thin films over the entire applied magnetic field (Ba) range. The quantitative model describing the Jc(Ba) dependence is compared and explained for the critical current densities obtained by different measurement techniques. Transport current and quasi-equilibrium magnetization measurement data can successfully be fitted by the model with appropriate electric field criteria. The dependence of the irreversibility field on the Ecr criterion can be obtained within the model. At the same time, the dynamic magnetization measurements of the Jc(Ba) curves strongly depend on instrumentally defined parameters, introducing inconsistencies in the experimental results. Therefore, the model calculations are able to explain the Jc(Ba) curves only if the instrumental vibrations affecting vortex behaviour are taken into account. However, the nature of the observed dependence on the vibration of the samples is unclear. Different frequencies of the sample vibrations have been investigated. It is revealed that if the frequency tends to zero, the Jc(Ba) curves are well described by the model. We have outlined a number of possibilities which may be responsible for the behaviour observed. However, none of the existing theories can explain the effect of the vibrations, which exponentially degrade the irreversibility field to a certain tampered Birr value at frequencies larger than ≃25 Hz.

Integration of atomic layer deposition CeO2 thin films with functional complex oxides and 3D patterns

We present a low-temperature, <300°C, ex-situ integration of atomic layer deposition (ALD) ultrathin CeO2 layers (3 to 5 unit cells) with chemical solution deposited La0.7Sr0.3MnO3 (LSMO) functional complex oxides for multilayer growth without jeopardizing the morphology, microstructure and physical properties of the functional oxide layer. We have also extended this procedure to pulsed laser deposited YBa2Cu3O7 (YBCO) thin films. Scanning force microscopy, X-ray diffraction, aberration corrected scanning transmission electron microscopy and macroscopic magnetic measurements were used to evaluate the quality of the perovskite films before and after the ALD process. By means of microcontact printing and ALD we have prepared CeO2 patterns using an ozone-robust photoresist that will avoid the use of hazardous lithography processes directly on the device components. These bilayers, CeO2/LSMO and CeO2/YBCO, are foreseen to have special interest for resistive switching phenomena in resistive random-access memory.

A simple solution to the problem of effective utilisation of the target material for pulsed laser deposition of thin films

The factors determining the efficiency of the target material utilisation for pulsed laser deposition of films are considered. The target volume is calculated, which is evaporated in the ablation process by the focused laser radiation having a rectangular form. The new device is suggested and developed for obtaining thin films by the method of laser deposition, which is specific in the employment of a simple optical system mounted outside a deposition chamber that comprises two lenses and the diaphragm and focuses the laser beam onto a target in the form of a sector-like spot. Thin films of CuO and YBaCuO were deposited with this device. Several deposition cycles revealed that the target material is consumed uniformly from the entire surface of the target. A maximal spread of the target thickness was not greater than both prior to deposition and after it. The device designed provides a high coefficient of the target material utilisation efficiency.

Study of the pinned vortex fraction in the single crystal YBaCuO films

In this work we intend to study the pinned vortex fraction in type II superconductors. The sample used is the YBa2Cu3O7-γ. In continuation one will study the variations of this fraction according to the transport current density for two values of magnetic field (H = 0.6 T and H = 1.2 T) , and different values of temperature. The studied sample is a monocristalline YBaCuO thin film deposited by the ablation laser method on the surface (001) of a SrTiO3 substrate. In zero magnetic field, the resistance vanished a Tc = 90 K. The C-axis of YBaCuO is perpendicular to surface of the film. Electrodes of measurement are in gold and deposited on the surface of the sample in situ by evaporation. The film has a thickness of 400 nm, and a width 7.53 μm. The distance between electrodes of power measurement is 135 μm. Contact resistances were less than 1Ω.

Ca Doped YBCO Films in THz Frequency range

Ca doped YBaCuO thin films were investigated using frequency and time domain THz spectroscopy. A non-monotonic behavior was observed in with a maximum at about 1.8 meV and 1.2 meV depending on Ca concentration. Two batches of thin films 500–600Å thick where used; one of 5% and the other of 10% Ca concentration. The films show a clear c-axis orientation and 77K for the 5% Ca and 10% Ca respectively. Both thin film batches show a decrease in plasma frequency as temperature increases and superconducting transition is approached. The quasiparticles scattering rate decreases in the normal state and drops when Tc is approached. The imaginary part of the conductivity was found to be proportional to 1/ω, known from the delta-function response.

Magnetic pinning effects of epitaxial LaxSr1−xMnO3 nanostructured thin films on YBa2Cu3O7−δ layers

The present paper presents the effects of a nanostructured, ferromagnetic La1−xSrxMnO3(LSMO) thin film on the pinning characteristics of an epitaxial YBa2Cu3O7(YBCO) thin film deposited on top. Ordered arrays of LSMO grains were obtained upon growing the film on a terraced (001) SrTiO3 substrate. The analyses of magnetic measurements revealed the presence of a complex vortex pinning mechanism within the YBCO film. With respect to a reference single YBCO layer, an additional pinning potential was observed. Its temperature evolution suggests that a magnetic pinning mechanism is responsible for improved pinning characteristics in the high temperature and field region. Based on the morphology of the underlying LSMO buffer, a strong pinning force is expected to arise due to the anti-dot formations, where a high magnetization gradient exists.

Evolution of ferromagnetic clustering in Pr0.5Ca0.5MnO3 and its effect on the critical temperature of YBa2Cu3O7 thin film

A thin film bilayer of Pr0.5Ca0.5MnO3 and YBa2Cu3O7 has been deposited on LaAlO3 substrate by pulsed laser deposition. XRD pattern confirms the formation of the bilayer. Current and magnetic field dependent resistance measurements have been carried out to study the proximity effect. These measurements have shown that the superconducting transition temperature (Tc) of YBa2Cu3O7 is suppressed to lower temperatures with a progressive increase in current. In addition, a hump like feature appears in resistivity near Tc with increase in applied current. The results are explained on the basis of the formation and growth of ferromagnetic clusters on account of charge order melting in Pr0.5Ca0.5MnO3 upon application of high current and magnetic field.

Structural defects in trifluoroacetate derived YBa2Cu3O7 thin films

We present an accurate description of the structural defects occurring within YBa2Cu3O7 (YBCO) films grown by chemical solution deposition (CSD) based on metal trifluoroacetates (TFA). Transmission electron microscopy (TEM) is the essential tool to identify and evaluate the microstructural defects that might act as natural pinning centers. Our study of TFA–YBCO thin films shows that the YBCO thin films contain a variety of extended defects, such as intergrowths, twin boundaries and dislocations, mainly in the basal plane. These extended defects and their interaction make up a rich variety of key microstructural features that play an important role in the YBCO thin films physical properties and performance.

Temperature dependence of magnetic-field angle dependent critical current density and the flux pinning in YBa2Cu3O7 thin films

The magnetic-field angle dependence of the critical current density Jc(H, θ) was measured over a wide temperature range (20–85K) in high-Jc YBa2Cu3O7 (YBCO) and DyBa2Cu3O7 (DyBCO) epitaxial films belonging to two categories. The films in the first category were prepared by thermal co-evaporation and were characterized by a high density of nanometer-sized precipitates (mostly<7nm), which act as small random (point) pins. The films in the second category were prepared by fluorine-free metalorganic deposition (FF-MOD), whose primary pinning centers were recently revealed to be dislocations (linear pins) associated with stacking faults parallel to the ab-plane. Relatively broad Jc(θ) peaks around H//ab in the shape of a stratovolcano were observed at 77–80K in the co-evaporated YBCO and DyBCO films in the first category, and the Jc(H, θ) data were scaled to be a single curve when plotted against scaled fields using an effective anisotropy parameter. However, the Jc(θ) curves became more gradual at 60–70K and the scaling behavior was broken because the radius of nano-precipitates was not sufficiently smaller than the temperature dependent Ginzburg–Landau coherence length ξ(T) at these temperatures. In contrast, sharp Jc(θ) peaks around H//ab were observed in the FF-MOD YBCO films in the second category at all temperatures in the range 20–85K. Anisotropic scaling analysis showed that the pinning was apparently due to small random pins and pins correlated with the ab-plane, and the linear pins whose radius is sufficiently smaller than ξ(T) can cause the observed Jc(H, θ). The temperature dependence of Jc due mainly to the random pinning was approximately ∼(1−T/Tc)2(1+T/Tc)2 for the FF-MOD thin films (dislocation pins), which is consistent with a simple theoretical model based on core pinning interactions. The T dependence of Jc for the co-evaporated films (nano-precipitate pins) was ∼(1−T/Tc)m (1+T/Tc)2 (m=2.1–2.6), which deviates from m=2.5 expected from the simple theoretical model because nano-precipitates are not sufficiently smaller than ξ(T) at T⩽70K.

Design and fabrication of center frequency and bandwidth tunable HTS filter

We have developed a bandwidth and a center frequency tuning method for use in high-temperature superconducting microstrip filters. A pair of waveguide is placed between the resonators, and the bandwidth is adjusted by changing the switch states of the waveguides. Additional electrical pads are placed open ends of the resonators for tuning the center frequency. Pads are also placed around the input/output coupled-line elements to enable the external quality factors to be adjusted, thereby reducing the insertion loss caused by tuning. A prototype three-pole tunable bandpass filter was fabricated by depositing YBa2Cu3O7 thin film on an MgO substrate and has a measured center frequency of 4.83GHz and bandwidth of 121MHz. Use of the waveguides to adjust the coupling coefficients, the electrical pads to adjust the effective lengths of the resonators and the pads to adjust the external quality factors resulted in 120-MHz bandwidth tuning and 400-MHz center frequency tuning without increased insertion loss.

Critical current behaviour of YBCO thin films described by vortex pinning on low-angle domain boundaries and vortex creep

A pinning potential for vortices was introduced assuming plastic pinning of vortex lattice on chains of out-of-plane individual edge dislocations that form low-angle domain boundaries in high quality YBa2Cu3O7 thin films. Using this pinning potential with the classical Kim–Anderson vortex creep approach a model for critical current dependence on field has been successfully developed. The model shows a plausible description of Jc(Ba) over the entire field range. Electrical field criterion is incorporated providing the ability to compare measurements made with different criteria (including different measurement techniques). Applicability of this model has been verified by experimental data obtained by direct transport and magnetisation measurements on high quality films grown by pulsed laser deposition. Pinning potential obtained from the fitting procedure is consistent with theoretical predictions. The model showed that the effective pinning landscape changes under influence of external conditions.

Inhomogeneities in YBa2Cu3O7 thin films with reduced thickness

Morphology and physical properties of mono- (YBa2Cu3O7) and multilayered (YBa2Cu3O7/SmBa2Cu3O7/ YBa2Cu3O7) superconducting thin films with thickness ranging from 90nm to 28nm have been investigated. For both types of samples, the superconducting properties degraded with reduction of film thickness. Structural and electromagnetic properties were visualized through scanning electron microscopy and magneto-optical imaging, respectively, and revealed high level of inhomogeneity for thinner (<58nm) samples. However, samples with thickness above 58nm showed enhanced homogeneity, which explains better superconducting characteristics observed in these films. Results of this work demonstrate that multilayering approach performed by conventional laser ablation results in degradation of superconducting properties in films with thickness below 90nm, although has positive impact on morphology of these films, which is crucial for device fabrication process.

Development of Energy-Efficient Cryogenic Leads with High Temperature Superconducting Films on Ceramic Substrates

Abstract High temperature superconductor (HTS) material can be used for the implementation of high-speed low-heat conduction data links to transport digital data from 4 K superconductor integrated circuits to higher-temperature parts of computing systems. In this work, we present a conceptual design of energy efficient interface and results in fabricating such HTS leads. Initial calculations have shown that the microstrip line cable geometry for typical materials employed in production of HTS thin films can be a two-layered film for which the two layers of about 10 cm long are separated by an insulation layer with as low permittivity as possible. With this architecture in mind, the pulsed laser deposition process has been designed in a 45 cm diameter vacuum chamber to incorporate an oscillating sample holder with homogeneous substrate heating up to 900°C, while the laser plume is fixed. This design has allowed us to produce 200 nm to 500 nm thick, 7 cm to 10 cm long YBa2Cu3O7 thin films with the homogeneous critical temperature (Tc) of about 90 K. The critical current density (Jc) of the short samples obtained from the long sample is of (2 ± 1) × 1010 A/m2. Lines of 3-100 μm wide have been successfully patterned along the length of the samples in order to directly measure the Tc and Jc values over the entire length of the samples, as well as to attempt the structuring of multichannel data lead prototype.

Effect of coupling state on power handling capability of HTS transmit filters with stripline structure

The effect of the coupling state on the power handling capability of a superconducting transmit filters with a stripline (SL) structure was investigated by comparing the performances of such a filter with combline configuration with that of one with an interdigital configuration. The coupling states between the resonators used with these filters are inherently different. The filters had three-pole half-wavelength straight-line resonators, a 5.0-GHz center frequency, and a 100-MHz bandwidth. They were fabricated using YBa2Cu3O7 thin films on an r-Al2O3 substrate. Measurement of their responses and maximum current densities using electromagnetic simulator showed that their power levels were 33.6 and 36.5 dBm, respectively. This indicates that the power handling capability depends on the coupling state, and that an interdigital filter has higher power handling capability than a combline filter.

An all-field-range description of the critical current density in superconducting YBCOfilms

A new critical current density (Jc) model forhigh-quality YBCO (YBa2Cu3O7) thin films has been proposed, combining thermally activated flux creep with a vortex pinningpotential for columnar defects. The pinning for thermally activated vortices has been describedas strong pinning on chains of individual edge dislocations that form low-angle domainboundaries in high-quality YBCO thin films. The model yields an adequate description of theJc behaviour over the whole applied field range, as verified by direct measurements ofJc in YBCO thin films grown by pulsed-laser deposition. It also indicates that theeffective pinning landscape changes under the influence of the external conditions.Remarkably, the pinning potential obtained from the model is consistent with the valuesobtained for columnar defects, which confirms the validity of the overall approach.

Mesoscopic inhomogeneity creation in YBa2Cu3O7−y thin film by swift heavy ion irradiation at low temperature

In the present study, we report the modification of pulsed laser deposited c-axis oriented thin films of YBa2Cu3O7−y (YBCO) in a cylindrical region around the path of swift heavy ions (SHIs). Our in situ temperature-dependent resistivity measurement and in situ low-temperature X-ray diffraction (XRD) study on YBCO irradiated at liquid nitrogen temperature with 200 MeV Ag ions shows that the SHI-induced secondary electrons selectively create point defects at CuO basal chains of YBCO. Beyond a critical fluence (∼1012 ions/cm2), the radially strained region around the amorphous latent tracks estimated from full width at half-maximum of (00l) XRD peaks tends to overlap, and a two-step superconducting transition evolves instead of a single transition in the in situ resistivity measurement.

Influence of CeO2-Cap Layer on the Texture and Critical Current Density of YBCO Film

YBa2Cu3O7 (YBCO) thin films have been fabricated on different textured CeO2-cap layers by pulsed laser deposition (PLD). The texture and critical current density Jc of YBCO thin films have been systematically investigated. Both in-plane and out-of-plane textures of YBCO films and CeO2-cap films were characterized by X-ray diffraction (XRD). And the critical currents of YBCO films were measured by the conventional four-probe method. It was found that the texture and Jc of YBCO films were largely dependent on the texture of CeO2-cap layers under the optimized deposition conditions. With increasing the degree of in-plane and out-of-plane texture of CeO2-cap layers, Jc of YBCO films decreased from 4.23×106 A/cm2 to 0.47×106 A/cm2. The FWHM values of the omega scan rocking curves of YBCO films decreased from 3.71 to 1.84° and the phi scan rocking curves from 6.68 to 4.91° with improvement of CeO2-cap layer texture. Our results indicated that the fabrication of high texture quality of CeO2-cap layer was necessary for the epitaxial growth of high-Jc YBCO films. The high-quality YBCO films which are comparable with those grown on single crystal substrates could be achieved on high textured CeO2-cap layers buffered metal substrates.

Microwave Dependence of $a$-Axis Oriented ${\rm YBa}_{2}{\rm Cu}_{3}{\rm O}_{7}$ Thin Film

The <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">a</i> -axis oriented 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</sub> thin films were grown on SrLaGaO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> (100) substrate with a buffer layer of 50 nm thick Gd <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> CuO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> using pulsed laser deposition technique. The thickness of Y-123 thin film was about 500 nm. Intrinsic Josephson junctions (CuO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> planes) were aligned perpendicular to the substrate in the thin films. The bridge type pattern was fabricated using focused ion beam milling technique in such a way so that the current flow along the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</i> -axis in thin film. The dimensions of bridge were 1 μm in length along the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</i> -axis and 5 μm in width along the b-axis. The resistance vs. temperature characteristics showed transition temperature of about 89 K. The critical current density (J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> ) of 2×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> was measured from current-voltage (I-V) characteristics at 10 K. The samples were irradiated with external microwave at 20 GHz and the J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> was suppressed with increase in power. This suppression in J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> indicates the formation of layered structure with strong coupling. The voltage steps were appeared with microwave irradiation in I-V characteristics. The values of voltage steps were irregular and change with increase in power. We have also studied all <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">a</i> -axis oriented multilayered thin films 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">7</sub> (Y123) and PrBa <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</sub> (Pr123). We fabricated a submicron stack in which Josephson junctions were forming by Y123 and Pr123. The submicron stack showed response with microwave irradiation of different frequency and power. The transport characteristics of these thin films are discussed in detail.

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.

Ultrafast linear kinetic inductive photoresponse of YBa2Cu3O7−δ meander-line structures by photoimpedance measurements

We report the experimental demonstration of the linear kinetic-inductive photoresponse of thin-film YBa2Cu3O7−δ meander line structures, where the photoresponse amplitude, full-width-half-maximum, and rise time are bilinear in the incident optical power and bias current. This bilinear behavior reveals a trade-off between obtaining high responsivity and high speed photodetection. We also report a rise time as short as 29 ps in our photoimpedance measurements.