Yttria-stabilized Zirconia Buffer Layers Research Articles

Properties of sprayed YSZ buffer layers on alumina substrates for YBCO thick films

Yttria-stabilized-zirconia (YSZ) buffer layers on polycrystalline alumina substrate were fabricated by spraying a suspension consisting of ultrafine YSZ powders. It was found that the spraying conditions such as the flow rate of carrier gas and the aperture of spray nozzle had a great influence on the mechanical properties of the sprayed buffer layers and also on the J c values of YBCO thick films processed on these buffer layers. The maximum J c value of screen-printed YBCO film, fired by the solid-phase sintering method, was about 470 A cm −2 at 77 K, 0 T. This value was about four-fifths of those for films on single-crystal YSZ substrates.

Enhancement of critical current density in Tl 2Ba 2CaCu 2O y superconducting thin film on polycrystalline Al 2O 3 substrates using textured YSZ buffer layers

Tl 2Ba 2CaCu 2O y superconducting thin films on polycrystalline Al 2O 3 substrates with and without textured yttria-stabilized-zirconia(YSZ) or CeO 2/YSZ buffer layers were fabricated. Ion beam-assisted laser deposition was used to obtain the textured YSZ buffer layers. The Tl 2Ba 2CaCu 2O y thin films grown on the YSZ buffer layers were highly c-axis oriented with respect to the film surface and strongly in plane textured. The zero resistance temperature of these films was 100–108K. The critical current density (J c) of the films grown on the YSZ buffer layers was 10 5A/cm 2. J c of the films grown on the CeO 2/YSZ buffer layer or on Al 2O 3 substrates directly was less than 10 4A/cm 2.

Improvement of in-plane alignment of YBa 2Cu 3O 7−x films on polycrystalline alumina substrates using biaxially aligned CeO 2/YSZ buffer layers

Biaxially aligned superconducting YBa 2Cu 3O 7−x thin films have been fabricated on ceramic alumina substrates. Yttria-stabilized zirconia buffer layers were first deposited on alumina using ion-beam assisted pulsed laser deposition. CeO 2 and YBCO films were subsequently deposited on the YSZ layer using pulsed laser deposition (PLD). All three layers were (001) oriented and biaxially textured. The YBCO films have T c values of 89 K and J c of 1×10 5A/cm 2 at 77 K.

YBCO and YSZ buffer layer growth on metallic tape using sputtering method

Yttria-stabilized zirconia(YSZ) thin films with the c-axis texturing and partial in-plane texture were deposited on polycrystalline metallic tape (Hastelloy-C) by modified dc bias sputtering. YBCO films were deposited by using dc magnetron sputtering on Hastelloy tape with YSZ buffer layer. Microstructure of the YBCO/YSZ/substrate was studied using transmission electron microscopy and scanning electron microscopy.

Film thickness effect on the properties of interconnection between YBCO and Si for superconductor and semiconductor integration

Abstract YBa2Cu3O7−δ (YBCO) films were grown on Si using a buffer layer of yttria-stabilized zirconia (YSZ) by pulsed laser deposition. Interconnections between the YBCO film and the Si substrate using Au have been fabricated by lithography. The YBCO films showed zero-resistance critical temperatures in the range of 80–85 K and were found to be grown in the c–axis orientation. The structural properties of the films of various thicknesses were analyzed by XRD, SEM and Raman spectroscopy. Because of very different thermal expansion coefficients of Si and YBCO, there is a tendency to crack formation for films. The crack formation interrupts the current flow and increases the normal state resistance of the films. The effect of cracks on the contact resistances between YBCO films of various thicknesses and Si substrates through Au interconnections is reported.

Power-dependent microwave properties of superconducting YBa2Cu3O7−x films on buffered polycrystalline substrates

We have studied the microwave properties of 0.4 μm thick YBa2Cu3O7−x (YBCO) films on polycrystalline substrates with ion-beam-assisted-deposited yttria-stabilized zirconia buffer layers using a parallel-plate resonator technique at 10 GHz. The YBCO films with similar in-plane texture grown on both forsterite and Ni-based alloy substrates show similar microwave properties. We measure low-power surface resistance Rs values of about 0.5 mΩ at 76 K and 0.15 mΩ at 4 K for films with an in-plane mosaic spread of about 7°. Single-tone power-dependence measurements show that the surface resistance and the surface reactance increase linearly and by the same amount with increasing microwave field level. At intermediate power levels, the intermodulation measurements show odd-order intermodulation products that increase quadratically with two-tone input power. These results indicate a hysteretic vortex penetration mechanism in the weak links as the most plausible source of the observed nonlinearities in these films.

In situ reflection high energy electron bombardment analysis of biaxially oriented yttria-stabilized zirconia thin film growth on amorphous substrates

Yttria-stabilized zirconia (YSZ) thin films were prepared on thermally oxidized Si-wafer substrates using ion-beam assisted laser deposition (IBALD). Biaxially oriented crystal growth with the [001]-axis parallel to the substrate normal and the [111]-axis parallel to the impinging argon ion beam was obtained for a range of deposition parameters. The film growth and crystallite orientation were observed in situ by reflection high-energy electron diffraction (RHEED). During film deposition, the crystal structure and crystallite orientation were monitored in the diffraction pattern. The in-plane orientation of the grown film surface was determined quantitatively by evaluating changes in intensity of selected spots in diffraction patterns recorded while rotating the sample around the substrate normal. The obtained intensity distribution is a convolution of crystallite orientation and beam broadening effects due to crystal strains and crystallite dimensions. The effects of limited crystal size and mosaic spread are evaluated from a recorded diffraction pattern and deconvoluted from the spot intensity distribution over the rotation angle, giving the crystallite in-plane alignment. The results are in good agreement with X-ray diffraction. A possible explanation for the improved in-plane alignment of YBa 2Cu 3O 7− δ films compared with the YSZ buffer layers is given. The grown films were analysed ex situ by X-ray diffraction for crystal analysis and by atomic force microscopy for characterization of the surface roughness and crystallite size. Film strains were related to argon implantation into the films during deposition.

Growth of biaxially aligned buffer layers for YBCO tapes by ion-beam assisted laser deposition and in situ RHEED texture analysis

Biaxially oriented yttria-stabilized zirconia (YSZ) buffer layers were grown at room temperature by Pulsed Laser Deposition (PLD) and Ion-Beam Assisted Laser Deposition (IBALD) on amorphous substrates. Dependent on deposition parameters, IBALD grown films showed in-plane orientations of up to 20° FWHM (full-width at half maximum). Film in-plane alignment increases with film thickness. Film growth at room temperature without assisting ion-beam was polycrystalline with a growth-rate dependent preferred orientation. (011)- and (001)-oriented films were obtained for growth rates of 10 A/s and 14 A/s, respectively. YSZ film growth orientation was monitored in situ with reflection high-energy electron diffraction. A quantitative analysis of the in-plane orientation of the IBALD grown YSZ film surfaces was established.

YBaCuO thick films on planar and curved technical substrates

For high-current applications, homogeneous well-textured high-temperature-superconducting Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBaCuO) films on technical ceramic or metallic substrates are required. The ion-beam-assisted deposition (IBAD) of yttria-stabilized zirconia (YSZ) buffer layers, which serve as templates for the YBaCuO, was extended to large planar areas (20 cm/spl times/20 cm) as well as curved or cylindrical (diameter /spl les/15 mm) substrates. For both types of substrates a pronounced in-plane alignment is observed. A deposition equipment is developed to grow high-quality YBaCuO films also on tubes by pulsed laser deposition (PLD), which is characterized by a high long-term stability both of the deposition rate and of the surface temperature of the growing film. Current densities up to 0.9/spl times/10/sup 6/ A cm/sup -2/ at 77 K in self fields are observed in films on planar Ni foils with biaxially aligned YSZ buffers (bi-YSZ). For the coating of long lengths of tubes and tapes a translation and a rotation of the samples are incorporated both in the buffer as well as in the YBaCuO-deposition process. Furthermore, the dependence of the critical transport current densities, J/sub c/, of the HTS layer on magnetic fields and on mechanical stresses are investigated.

Tl 2Ba 2CaCu 2O y superconducting thin films on polycrystalline Al 2O 3 substrates with textured YSZ buffer layers

We report for the first time the successful fabrication of Tl 2Ba 2CaCu 2O y superconducting thin films on polycrystalline Al 2O 3 substrates using yttria-stabilized-zirconia (YSZ) buffer layers. Ion beam-assisted laser deposition was used to obtain the textured YSZ buffer layers. The Tl 2Ba 2CaCu 2O y thin films were shiny, highly c-axis oriented with respect to the film surface and strongly in plane textured. The zero resistance temperature of these films was as high as 108 K with a critical current density of ∼ 10 5 A/cm 2 at 77 K.

Influence of the process parameters on the growth of YSZ-layers prepared by Ion Beam Assisted Deposition (IBAD)

Cubic yttria stabilized zirconia (YSZ) thin films were grown on amorphous quartz, r-plane sapphire and stainless steel substrates by ion beam sputtering from a planar target under simultaneous ion bombardment (IBAD) during film growth and sputtering employing the inverted cylindrical magnetron (ICM) gun. The formation and modification of preferred orientations was studied by X-ray diffraction and TEM investigations as a function of different deposition parameters like substrate temperature, total pressure, deposition rate, ion beam energy and current. A preferred (100)-orientation could be achieved on untextured substrates by ICM-deposition at substrate temperatures above 800°C and by IBAD without external heating of the substrates. In-plane orientation of YSZ films on untextured substrates was only achieved with IBAD for an ion impact angle α s between 30° and 70°. For α s = 55° the best mosaic spread was observed. The observation of significantly smaller texture distribution widths for epitaxially post-deposited material than measured at the basic YSZ buffer layer was found to be due to a gradual improvement of YSZ growth under ion bombardment with increasing layer thickness.

Biaxially textured yttria stabilized zirconia buffer layers on rotating cylindrical surfaces

Biaxially textured yttria stabilized zirconia (YSZ) buffer layers are prepared on rotating cylindrical surfaces by an ion-beam-assisted deposition (IBAD) process. A large fraction of the cylinder surface can be coated at the same time, resulting in an effective deposition rate of 40 nm/h for the whole tube circumference (diameter of the tube 12 mm). The in-plane alignment depends on the total film thickness and the rotation velocity. The best in-plane textures achieved so far with a full width half maximum (FWHM) value of 27° are sufficient for the preparation of YbaCuO films with critical current densities above 105 A cm−2 at 77 K and self-fields.

Y-123 Films on technical substrates

Abstract For high-current applications, homogeneous well-textured high-temperature superconducting Y 1 Ba 2 Cu 3 O 7− δ (Y-123) films on technical ceramic or metallic substrates are required. The ion-beam-assisted deposition (IBAD) of yttria-stabilized zirconia (YSZ) buffer layers, which serve as a template for Y-123, was extended to large-area substrates as well as differently shaped long substrates. TEM, as well as XRD investigations, was performed to observe the relevant growth mechanisms. The influence of nucleation, growth selection, and homoepitaxial growth on the development or the maintenance of a preferential orientation of the YSZ buffer is discussed. Y-123 films were prepared by a modified pulsed-laser-deposition (PLD) technique based on a quasi-equilibrium substrate heating and variable azimuth scanning of the target. The method allows a PLD coating of long pieces of tapes and tubular substrates because no direct mechanical contact of a substrate with the heater is required. Critical current densities, J c , above 10 6 A cm −2 were achieved on polycrystalline Ni tapes as well as on polycrystalline YSZ sheets at 77 K and self fields. The dependence of J c on magnetic field resembles that of Y-123 deposited on single-crystalline substrates and demonstrates the absence of weak links due to grain boundaries. The thickness dependence of J c is interpreted in terms of a nucleation layer appearing in the early stage of film growth. A growth model is proposed which seems to be in agreement with the experimental observations. The measured strain tolerance of the films does not impede their application.

Preparation of in-plane textured buffer layers for YBa2Cu3Oy film growth by modified bias sputtering

Abstract A modified bias sputtering technique has been proposed to grow in-plane textured yttria-stabilized zirconia buffer layers on polycrystalline metallic substrates for deposition of YBa2Cu3Oy films. The principle of developing an in-plane texturing by this technique is basically the same as that of ion beam assisted deposition; an in-plane texturing occurs by off-normal ion beam bombardment because of the higher sputtering yields of all orientations other than the channelling direction. In our process, however, a flux of energetic particles impinging on the growing film is generated using specially devised negatively biased electrodes installed in a magnetron sputtering system instead of a separate ion-source in IBAD. So far an X-ray phi-scan width of 18° was attained for YSZ films on Hastelloy tapes. Epitaxial YBCO films grown on these buffer layers using pulsed laser deposition showed the Jc’s exceeding 105 A cm−2 (77 K, 0 T). In this paper, we present variation of the bias sputtering technique also used to obtain the textured films on large area substrates. Although the proposed process offers a very convenient method to grow textured films, more efforts must be made to increase growth rates of the films (currently ∽0.1 nm s−1) for large-scale applications of YBCO films.

Fabrication of biaxially aligned YBa 2Cu 3O 7− x thin films on glass substrates

Biaxially aligned YBa 2Cu 3O 7− x thin films have been fabricated on glass substrates with an in-plane aligned yttria-stabilized zirconia (YSZ) buffer layer. Ion-beam assisted pulsed laser deposition was used to prepare the YSZ buffer layers on amorphous glass substrates. The YSZ films deposited at room temperature exhibited (001) orientation, whereas at temperatures higher than 300°C, YSZ grew with high degree of (111) orientation. Both the (001) and (111) YSZ films were biaxially aligned. YBa 2Cu 3O 7− x films deposited using pulsed laser deposition on biaxially aligned (001) YSZ on glass were highly c-axis oriented and strongly a- b plane aligned. A critical temperature T c0 ( R = 0) of 87.1 K was routinely achieved and J c was in the range of ∼ 10 4 A/cm 2. The limitation in J c was found to be due to microcracks in the YBCO film caused by the tensile stress resulting from the thermal expansion mismatch between the glass and YBCO. The results suggest that glass with a better thermal expansion match to YBCO would lead to higher J c values.

Crystal and Electrical Characterizations of Oriented Yttria-Stabilized Zirconia Buffer Layer for the Metal/Ferroelectric/Insulator/Semiconductor Field-Effect Transistor

Using reflection high-energy electron diffraction (RHEED), X-ray diffraction (XRD) and X-ray pole figure measurements, we evaluated the crystallinities of yttria-stabilized zirconia (YSZ) thin films as an intermediate layer for metal/ferroelectric/insulator/semiconductor-structure field-effect transistors (MFIS-FETs). A highly oriented YSZ film was grown on a Si(100) substrate by the vacuum evaporation method. The [100] axes of the YSZ crystals were aligned parallel to [100] axes of Si crystals in the plane. In addition, electrical characterizations of the highly oriented YSZ thin films on Si(100) were evaluated from current–voltage ( I–V ) and capacitance–voltage ( C–V ) measurements. The I–V measurement indicated a breakdown field of about 3 MV/cm (at I=1 nA/cm2). The C–V measurement results suggest that mobile ions were present in the YSZ films. Oriented perovskite PbTiO3 films were deposited on YSZ crystal and YSZ/Si(100) substrates by the digital chemical vapor deposition (CVD) method. These PbTiO3 films included many PbTiO3 grains with their [100] axes parallel to the [100] or [110] axis of YSZ crystals in the plane of the PbTiO3/YSZ interface.

YBCO thick films on alumina substrates with sprayed YSZ buffer layers

YBCO thick films of 10–30 μm thickness were fabricated on polycrystalline alumina substrates using a simple screen-printing method. All films on bare alumina substrate showed very poor or non-superconducting properties above 77 K due to aluminium diffusion from the substrate into the film. We have therefore fabricated yttria-stabilized-zirconia (YSZ) buffer layers on alumina substrates by the screen-printing method or by spraying a suspension consisting of ultrafine YSZ powders. The sprayed buffer layers showed a dense and less cracked structure compared with the screen-printed layers, and were found to act as a successful buffer to aluminium diffusion. The J c values of YBCO films on sprayed layers, fired by the solid-phase sintering method and the liquid-phase processing method, were about 400 and 1300 A cm −2 respectively at 77 K, 0 T. These values are about two-thirds of those for films on single-crystal YSZ substrates.

Epitaxial growth of highly conductive RuO2 thin films on (100) Si

Conductive RuO2 thin films have been heteroepitaxially grown by pulsed laser deposition on Si substrates with yttria-stabilized zirconia (YSZ) buffer layers. The RuO2 thin films deposited under optimized processing conditions are a-axis oriented normal to the Si substrate surface with a high degree of in-plane alignment with the major axes of the (100) Si substrate. Cross-sectional transmission electron microscopy analysis on the RuO2/YSZ/Si multilayer shows an atomically sharp interface between the RuO2 and the YSZ. Electrical measurements show that the crystalline RuO2 thin films are metallic over a temperature range from 4.2 to 300 K and are highly conductive with a room-temperature resistivity of 37±2 μΩ cm. The residual resistance ratio (R300 K/R4.2 K) above 5 for our RuO2 thin films is the highest ever reported for such films on Si substrates.

Electrical properties of laser deposited YBa 2Cu 3O 7−δ films on silicon wafers

YBa 2Cu 3O 7−δ (YBCO) thin films were deposited on n-type (100) silicon wafers with yttria-stabilized zirconia (YSZ) buffer layers by a laser ablation technique. The YSZ layer had a thickness of about 60 nm, and was oriented preferentially in the (100) direction. The YBCO films were found to be preferentially (001) oriented, and had a superconducting critical temperature ( T c) above 85 K. Pure gold ohmic contacts were made on both sides of the YBCO/YSZ/Si structure and its I- V characteristics revealed a diode behavior. The turn-on and breakdown voltages are 1.3 and 20.34 V, respectively, at temperatures below the T c. The ideality factor η had values of 13, 9.5 and 7 at room temperature, 100 and 50 K, respectively. Better superconductivity, lower operation temperature, and thinner buffer layers would result in better rectification.

Microstructural study of yttria stabilized zirconia buffered sapphire for YBa2Cu3O7−δ thin films

Yttria stabilized zirconia (YSZ) buffer layers were grown by rf-magnetron sputtering on the r (11̄02) plane of sapphire for YBa2Cu3O7−δ (YBCO) thin film deposition. Microstructural changes of YSZ buffer layers grown using different sputtering conditions (5, 10, and 20 mTorr; Ar/O2 gas mix ratio of 9:1 and 1:1) were monitored by atomic force microscopy (AFM). Films grown using a lower oxygen partial pressure (5 mTorr) and a higher Ar/O2 ratio (9:1) showed smooth surface morphology and the average surface roughness increased with an increase in oxygen partial pressure. YBCO films in situ grown by pulsed laser deposition on sapphire with a YSZ buffer layer deposited using optimized sputtering parameters (5 mTorr gas pressure, 9:1 Ar/O2 ratio) yielded the highest critical density, Jc≊4.5×106 A cm−2 at 77 K. An excellent correlation between microstructure and Jc has been found and AFM has proved to be important for the study of the microstructure of films.