Yttria-stabilized Zirconia Buffer Research Articles

Growth of epitaxial bismuth ruthenate pyrochlore films on yttria-stabilized zirconia (YSZ) and YSZ-buffered Si substrates by metal–organic chemical vapor deposition

Bismuth ruthenate (Bi2Ru2O7) thin films were deposited on (111) yttria-stabilized zirconia (YSZ) single crystals and (111)YSZ//(111)Si substrates by chemical vapor deposition using Bi(CH3)2[2-(CH3)2NCH2C6H4] and Ru(C7H11)(C7H9) as source materials and oxygen as a reactant gas. The film composition and X-ray diffraction ω-2θ scan profiles for thin films deposited using various source flow rate ratios revealed the existence of a process window to obtain stoichiometric Bi2Ru2O7. Within the process window, the kind of substrates did not strongly affect the deposition rates of Bi and Ru or the Bi/Ru ratio of the deposited films. It was also confirmed that the Bi2Ru2O7 thin films grew epitaxially on both substrates within the process window. In particular, epitaxial Bi2Ru2O7 thin films grew on the Si substrate with a YSZ buffer layer. Scanning electron microscopy revealed the formation of continuous dense Bi2Ru2O7 films without any cracks or voids, and a relatively smooth interface between Bi2Ru2O7 and the YSZ buffer layer on Si. The resistivity of the Bi2Ru2O7 films was almost constant (~550 and ~950 μΩcm for the films deposited on (111)YSZ single-crystal substrates and (111)YSZ//(111)Si substrates, respectively), even when the ratio of Bi and Ru source gas flow rates was changed in the process window. In addition, the resistivity of Bi2Ru2O7 films prepared on both kinds of substrates was almost independent of temperature from 10 to 300 K.

Improvement of Surface Morphology of Yttrium-Stabilized Zirconia Films Deposited by Pulsed Laser Deposition on Rolling Assisted Biaxially Textured Substrate Tapes**Supported by the ITER Project of the Ministry of Science and Technology of China under Grant No 2011GB113004, the Shanghai Commission of Science and Technology under Grant No 11DZ1100402, and the Youth Fund of the National Natural Science Foundation of China

The surface morphology of buffer layer yttrium-stabilized zirconia (YSZ) of YBa2 Cu3 O7-σ (YBCO) high temperature superconducting films relies on a series of controllable experimental parameters. In this work, we focus on the influence of pulsed laser frequency and target crystalline type on surface morphology of YSZ films deposited by pulsed laser deposition (PLD) on rolling assisted biaxially textured substrate tapes. Usually two kinds of particles are observed in the YSZ layer: randomly distributed ones on the whole film and self-assembled ones along grain boundaries. SEM images are used to prove that particles can be partly removed when choosing dense targets of single crystalline. Lower frequency of pulsed laser also contributes to a smoother film surface. TEM images are used to view the crystalline structure of thin film. Thus we can obtain a basic understanding of how to prepare a particle-free YSZ buffer layer for YBCO in optimized conditions using PLD. The YBCO layer with nice structure and critical current density of around 5 MA/cm2 can be reached on smooth YSZ samples.

Ferroelectric domain structures and polarization switching characteristics of polycrystalline BiFeO3 thin films on glass substrates

We investigated ferroelectric characteristics of BiFeO3 (BFO) thin films on SrRuO3 (SRO)/yttria-stabilized zirconia (YSZ)/glass substrates grown by pulsed laser deposition. YSZ buffer layers were employed to grow highly crystallized BFO thin films as well as SRO bottom electrodes on glass substrates. The BFO thin films exhibited good ferroelectric properties with a remanent polarization of 2Pr = 59.6 μC/cm2 and fast switching behavior within about 125 ns. Piezoelectric force microscopy (PFM) study revealed that the BFO thin films have much smaller mosaic ferroelectric domain patterns than epitaxial BFO thin films on Nb:SrTiO3 substrates. Presumably these small domain widths which originated from smaller domain energy give rise to the faster electrical switching behavior in comparison with the epitaxial BFO thin films on Nb:SrTiO3 substrates.

Ni-based anode-supported Al2O3-doped-Y2O3-stabilized ZrO2 thin electrolyte solid oxide fuel cells with Y2O3-stabilized ZrO2 buffer layer

In order to reduce the sintering temperature of Ni-based anode-supported thin 8 mol% yttria-stabilized zirconia (YSZ) elsectrolyte solid oxide fuel cells (SOFCs), alumina, with a weight percent of 1, 3, 5, and 7, is respectively doped into YSZ as sintering aid. A pure YSZ buffer layer is introduced between the Al2O3-doped-YSZ electrolyte and Ni–YSZ anode, to prevent Al2O3 and NiO from forming non-conductive spinel NiAl2O4. The experimental results show that doping proper amount of Al2O3 doping can reduce the sintering temperature of YSZ, e.g., 1 wt.% doping decreases the temperature from 1673 K to 1573 K. Anode-supported SOFCs are prepared with Al2O3-doped-YSZ electrolytes sintered at different temperatures. Electrochemical characterization of the SOFCs shows that the single cell with 1 wt.% alumina-doped YSZ electrolyte sintered at 1573 K gives the highest output. The effect of alumina doping on sintering behavior and electrical performance of YSZ is discussed in detail.

Epitaxial growth of thin films and nanodots of ZnO on Si(111) by pulsed laser deposition

Epitaxial (0001) ZnO thin films were grown on (111) Si substrates buffered with intermediate epitaxial (111) yttria-stabilized zirconia (YSZ) layers by pulsed laser deposition (PLD). X-ray diffraction and transmission electron microscopy characterizations revealed that the YSZ buffer layers enabled the epitaxial growth of structurally high quality ZnO films and an atomically sharp ZnO/YSZ interface, proving to be an effective epitaxial template. The epitaxial orientation relationships were revealed as follows: (0001) ZnO||(111) YSZ||(111) Si and [1¯21¯0] ZnO||[1¯10] YSZ||[1¯10] Si. Room temperature photoluminescence spectrum of the ZnO films showed the excitonic ultraviolet emission with few green emissions relevant to oxygen vacancies in the film. Furthermore, we fabricated ZnO nanostructures on the same (111) YSZ||(111) Si substrates by simply manipulating PLD conditions for the epitaxial film growth. The size control of the ZnO nanodots was realized by varying the number of laser pulses. A blueshift behavior induced by quantum confinement was observed, as the nanodot size decreases.

Grain size of nanocrystalline YSZ buffer layers fabricated by ion beam deposition

Amorphous or nanocrystalline thin films are capable to be efficient diffusion barrier layers for YBCO coated conductors of ion beam assisted deposition route. Nanocrystalline Yttria-Stabilized Zirconia (YSZ) buffer layers were fabricated by the ion beam deposition. Kr and Ar gases were utilized for the dual Kaufman type sputtering ion sources sequently. Both of the ion beams were fixed at 200mA, while the ion energy was in the range of 450–2000eV. The thickness of the YSZ buffer layers was several hundreds of nanometers. The grain size of YSZ thin films, which varied from 2 to 20nm, was calculated by Scherrer Formulation based on the X-ray diffraction measurement results. The grain size always decreased at first and then increased when the ion energy was increased. In the cases Kr gas was utilized and Ar gas was utilized, the grain size reached its minimum value at the ion energy of about 1800eV and 1000eV, respectively. Such phenomenon was discussed using the thermodynamic theory of thin film nucleation. Deposition rate and substrate temperature were the two chief variables of the critical nuclei concentration and grain size.

Epitaxial growth of YSZ buffer layer for YBa 2Cu 3O 7− δ coated conductor by reel-to-reel pulsed laser deposition

Yttria-stabilized zirconia (YSZ) buffer layers were deposited on CeO 2 buffered biaxially textured Ni–W substrate by reel-to-reel pulsed laser deposition (PLD) for the application of YBa 2Cu 3O 7− δ (YBCO) coated conductor and the influence of substrate temperature and laser energy on their crystallinity and microstructure were studied. YSZ thin films were prepared with substrate temperature ranging from 600 to 800 °C and laser energy ranging from 120 to 350 mJ. X-ray diffraction (XRD), scanning electron microscopy (SEM), and atomic force microscopy (AFM) were used to investigate how thin film structure and surface morphology depend on these parameters. It was found that the YSZ films grown at substrate temperature below 600 °C or laser energy above 300 mJ showed amorphous phase, the (0 0 1) preferred orientation and the crystallinity of the YSZ films were improved with increasing the temperature, but the surface roughness increased simultaneously, the SEM images of YSZ films on CeO 2/NiW tapes showed surface morphologies without micro-cracks. Based on these results, we developed the epitaxial PLD-YSZ buffer layer process at the tape transfer speed of 3–4 m/h by the reel-to-reel system for 100 m class long YBCO tapes.

Multiferroic Properties of Highly c-Oriented BiFeO[sub 3] Thin Films on Glass Substrates

BiFeO 3 (BFO) thin films were deposited on SrRuO 3 (SRO)/yttria-stabilized zirconia (YSZ)/glass substrates by pulsed laser deposition. To grow highly a- and (110)-oriented SRO bottom electrodes, we used YSZ buffer layers between SRO bottom electrodes and glass substrates. On the highly a- and (110)-oriented SRO bottom electrodes, we obtained highly c- and (011)-oriented BFO thin films in which the structures of BFO thin films were confirmed by X-ray diffraction experiments. The highly c-oriented BFO thin film exhibited a higher ferroelectric polarization (about 40 μC/cm 2 ) than the highly (011)-oriented BFO thin film. The highly c-oriented BFO thin film also showed a ferromagnetic hysteresis loop while the highly (011)-oriented BFO thin film exhibited a superparamagnetic hysteresis loop.

Substrate surface treatment and YSZ buffer layers by IBAD method for coated conductors

In this work, an Ion Beam Assisted Deposition (IBAD) system was utilized to fabricate Yttria-Stabilized Zirconia (YSZ) template films for coated conductors. The surface of the Hastelloy C276 substrate was modified by rolling and electropolishing. The effect of the electropolishing parameters of the substrate on the texture of the YSZ buffer layers was studied. The electropolishing current and time were optimized for short samples of 1 cm×1 cm square shape as 1 A and 60 s, respectively. And the relationship between the roughness of the substrate surface and the texture of the YSZ layer is discussed. Reel-to-reel metal tape moving apparatus was installed and used to produce meter-long buffer layer for coated conductors. The YSZ template film was deposited by IBAD method on meter-long Hastelloy tape with tape shifting speed of 15–20 m/h, and the thickness of the buffer layer was up to about 1.7 μm. The Hastelloy substrate surface was measured by Atomic Force Microscope. The thickness of the YSZ films over length was measured by Thermal Field Emission Scan Electronic Microscopy. X Ray Diffraction Ω-scan and ϕ-scan measurements were performed in order to examine the out-of-plane and in-plane texture of the YSZ buffer layers, respectively.

Highly c-Oriented PbZr[sub 0.48]Ti[sub 0.52]O[sub 3] Thin Films on Glass Substrates

We obtained preferentially (220)-oriented yttria-stabilized zirconia (YSZ) buffer layers on glass substrates by pulsed laser deposition. These preferentially (220)-oriented YSZ buffer layers enabled us to grow preferentially (100)-oriented bottom electrodes. On the preferentially (100)-oriented bottom electrodes, we obtained preferentially -oriented (PZT) thin films, which were confirmed by an X-ray diffraction experiment. The highly -oriented PZT thin films exhibited a high ferroelectric polarization of about . We also checked a high storage density of about with a minimum bit size below with the highly -oriented PZT thin films by electric force microscope.

Epitaxial Growth of Ferromagnetic Iron Silicide Thin Films on Silicon with Yttria-Stabilized Zirconia Buffer Layer

(110)-oriented epitaxial Fe3Si films were grown on (100) and (111) Si substrates with an epitaxial yttria-stabilized zirconia (YSZ) buffer layer by rf-magnetron sputtering. The epitaxial Fe3Si films contained a two-domain structure on the (100) substrate with a YSZ buffer layer, and a three-domain structure on the (111) substrate with a YSZ buffer layer. The coercive forces (Hc) of both epitaxial films were each approximately 40 Oe, and the saturation magnetizations (Ms) were each 850 emu/cm3, which are almost at the same level as those of bulk Fe3Si.

Buffer-Enhanced Electrical-Pulse-Induced Resistive Memory Effect in Thin Film Perovskites

A multilayer perovskite thin-film resistive memory device composed of a Pr0.7Ca0.3MnO3 (PCMO) perovskite oxide epitaxial layer on a YBa2Cu3O7-δ (YBCO) thin-film bottom electrode, a thin yttria-stabilized zirconia (YSZ) buffer layer grown on the PCMO layer, and a gold thin-film top electrode has been developed. With the addition of the YSZ buffer layer, the pulse voltage needed to switch the device is significantly reduced and the resistance-switching ratio is increased compared to a non buffered resistive memory device, which is very important for device fabrication. The magnetic field effect on the multilayer structure resistance at various temperatures shows colossal magnetoresistance (CMR) behavior for both high and low resistance states, implying a bulk material component in the switch behavior. The multilayer thin-film lattice structure has been further characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM) analyses, which indicate a high-quality heterostructure. Current imaging atomic force microscopy (I-AFM) analysis indicated nanogranular conductivity distributed uniformly throughout the PCMO film surface.

Substrate effect on low‐field transport properties of La–Pb–Mn–O granular‐type thin films

AbstractThis paper studied the low‐field tunnel‐type transport characteristics of polycrystalline and c‐axis‐oriented La0.7Pb0.3MnO3 (LPMO) thin films. Polycrystalline thin films were fabricated on SiO2/Si(100) substrate (film A), on SiO2/Si substrate with yttria‐stabilized zirconia (YSZ) buffer layer (film B), and on c‐axis‐oriented thin film grown on LaAlO3(001) (LAO) single crystal substrate (film C) using the soft‐chemical deposition method. A YSZ buffer layer acts as a barrier against inter‐diffusion. As a result, it decreases the amount of dead layers generated from the interface and helps to produce qualitative films for application of magnetoresistive elements. The magnetoresistance (MR) ratio was 0.52%, 0.7%, and 0.4% for film A, film B, and film C under the applied field of 500 Oe at 300 K, respectively. The polycrystalline film had denser boundaries than the c‐axis oriented film, i.e., the polycrystalline film gave more effective potential barrier regions than the c‐axis oriented film. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Proposal of general rule to prepare epitaxial ceramic thin films at low temperature from the point of crystal chemistry

We have succeeded to prepare epitaxial yttria stabilized zirconia (YSZ) thin films at room temperature (27 °C) by the use of nm thick YSZ buffer layer deposited at 800 °C on Si(0 0 1) substrate. Room temperature epitaxial growth was realized on 0.8 nm thick ultra thin YSZ buffer layer, however, to achieve high crystallinity, 6.7 nm thick was needed. On the 6.7 nm thick YSZ buffered Si(0 0 1) substrate, we have tried to prepare epitaxial oxide ceramic thin films. As the result, epitaxial CeO 2, In 2O 3, and MnZn-ferrite thin films were successfully deposited even at room temperature. The conditions of epitaxial growth at such low temperature was considered from the point of crystal chemistry. As the result, following conditions were proposed: (1) Materials with both small lattice mismatch and small electronegativity difference; or (2) Materials with small lattice mismatch and composed of single component. These proposed conditions will helpful to design epitaxial growth of oxide ceramic thin film at low temperature.

Sol–gel derived LaNiO 3 thin films on ZrO 2-buffered (1 0 0) Si substrates

Perovskite LaNiO 3 (LNO) thin films with a strong (1 0 0)-orientation were fabricated on yttrium-stabilized-zirconia (YSZ)-buffered silicon substrates using a sol–gel method. The YSZ buffer layer showed a stable tetragonal phase, and proved to be effective to suppress inter-diffusion between the Si substrates and the LNO films. Our obtained LNO films on the YSZ buffer layer exhibited a homogenous and smooth surface, with an average grain size below 0.1 μm. The resistivity of the LNO films was in the magnitude order of 10 −4 Ω cm. The crystallographic orientation and low resistivity make the sol–gel derived LNO films very attractive as the bottom electrode layer for perovskite oxide ceramic thin films.

Analysis of coplanar LiNbO3 waveguide structures applicable to electrooptic modulator with FDTD method

AbstractThe 3D finite‐difference time‐domain (FDTD) method and the 2D quasi‐static formulation have been used to calculate the characteristic impedance and the microwave effective index of coplanar waveguide structures on lithium niobate (LiNbO3) single‐crystal substrates with a yttria‐stabilized zirconia (YSZ) or SiO2 buffer layer. The results shown can be a good source to predict the modulator characteristics. The effects of the thin buffer layer and anisotropy of the LiNbO3 crystal (x‐cut and z‐cut) are discussed. The comparison between the FDTD and quasi‐static results shows good agreement. In this paper, the efficient modeling technique of the FDTD method for the coplanar waveguide (CPW) structures based on an anisotropic substrate with a thin buffer layer is developed. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 39: 234–237, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.11178

Fabrication of YSZ buffer layer by single source MOCVD technique for YBCO coated conductor

Yttria stabilized zirconia (YSZ) buffer layers were deposited by a metal organic chemical vapor deposition technique using a single liquid source for the application of YBa 2Cu 3O 7− δ (YBCO) coated conductor. Y:Zr mole ratio was 0.2:0.8, and tetrahydrofuran (THF) was used as a solvent. The (1 0 0) single crystal MgO substrate was used for searching the deposition conditions. Bi-axially oriented CeO 2 and NiO films were fabricated on {1 0 0} 〈0 0 1〉 textured Ni substrate by the same method and used as templates. At a constant working pressure of 10 Torr, the deposition temperatures (660–800 °C) and oxygen flow rates (100–500 sccm) were changed to find the optimum deposition condition. The best (1 0 0) oriented YSZ film on MgO was obtained at 740 °C and O 2 flow rate of 300 sccm. For a YSZ buffer layer with this deposition condition on a CeO 2/Ni template, full width half maximum values of the in-plane ( ϕ-scan) and out-of-plane ( ω-scan) alignments were 10.6° and 9.8°, respectively. The SEM image of YSZ film on CeO 2/Ni showed surface morphologies without microcracks. The film deposition rate was about 100 nm/min.

New approach to depositing yttria-stabilized zirconia buffer layers for coated conductors

A new approach for the production of yttria-stabilized zirconia (YSZ) oxide buffer layers directly on metal rolling-assisted biaxially textured substrates (RABiTS) is described in this paper. This represents a significant advance over existing techniques and avoids the need for complicated steps to avoid substrate oxidation during direct deposition of oxides. Current densities of about 1 MA/cm2 have been achieved for YBa2Cu3O7-δ layers on the YSZ buffer, with an intermediate CeO2 layer. The process consists of reactive sputtering of a YxZr1−xN film directly on the RABiTS, which adopts its biaxial texture. This nitride film is then converted to YSZ via a thermal oxidation step. The YSZ films retain the texture of the nitride film (and of the RABiTS) through local syntaxy. In many cases, YSZ films exhibit improved biaxial texture over that of the RABiTS substrate. Nitrides can be sputter deposited at much higher rates relative to oxides, making the approach industrially scalable and economical.

YSZ buffer layers and YBCO superconducting tapes with enhanced biaxial alignment and properties

Commercial applications of YBa 2Cu 3O 7 (YBCO) superconducting cables require viable and scalable manufacturing processes. We have investigated the evolution of the biaxial alignment of yttria-stabilized zirconia (YSZ) buffer layers with increasing film thickness (50–900 nm) and report on a method of fabricating highly aligned YBCO tapes using a thin epitaxial YSZ buffer layer as template. The method employs magnetron and ion beam assisted deposition (IBAD) techniques followed by epitaxial growth to produce the buffer architectures IBAD-YSZ and epi-YSZ/IBAD-YSZ onto optically polished hastelloy metal substrates. Subsequent in situ deposition of YBCO films is used to determine the biaxial alignment at the surface of the buffer architecture, and to show that 100–200 nm thick epi-YSZ layers suffice to yield YBCO tapes that have enhanced biaxial alignment (Δ φ=9–10°) and high critical current densities: J c (77 K)=(1–2)×10 6 A cm −2 and J c (5 K,1 T)=8×10 6 A cm −2. Atomic force microscopy of the surface microstructure of the YSZ buffer layers and YBCO films reveals some grain coarsening in the epi-YSZ layers compared to the IBAD-YSZ layers while the YBCO tapes show significant outgrowths (∼200 nm) and large grains (800–1200 nm) that are similar to high- J c YBCO films grown on single crystal MgO(1 0 0) substrates.

Texture and surface morphology of yttria-stabilized zirconia buffer layer on Ni-based tapes by electron beam evaporation

Biaxially textured buffer layers of yttria-stabilized zirconia (YSZ) have been fabricated on metal Ni-based tapes by electron beam evaporation technique. The high deposition rate of the electron beam evaporation presents an advantage in making long coated tape. Various materials including cubic textured Ni, Cu–Ni, and Hastelloy tapes were used as substrates. The grown YSZ films were characterized by X-ray diffraction, scanning electron microscopy, etc. It was found that the YSZ buffer layers were highly c-axis oriented on Ni or Ni-based tapes. The YSZ (1 1 1) pole figure revealed a cubic texture. The full width at half maximum of ϕ-scan of YSZ (1 1 1) deposited on Ni, Cu–Ni, and Hastelloy tapes was 15°, 14° and 20°, respectively. The surface of YSZ film is dense. Such YSZ buffer layers are promising for making YBCO coated conductors on metal tapes.