Plasma enhanced chemical vapor deposition of low dielectric constant SiOC(-H) films using MTES/O2 precursor

Low dielectric constant SiOC(-H) thin films were deposited by plasma enhanced chemical vapor deposition (PECVD) using methyltriethoxysilane (MTES) and oxygen as precursors. The SiOC(-H) films were prepared with MTES/O₂ flow rate ratio of 80%, rf power of 700 W and the working pressure was varied from 110 to 150 mTorr. Then the films were annealed at different temperatures in an Ar ambient for 30 min in order to study their thermal stability. Film thickness and refractive index were measured by SEM and ellipsometry, respectively. Bonding characteristics of the films were investigated by Fourier transform infrared (FTIR) spectroscopy. The dielectric constant of SiOC(-H) film was evaluated by C-V measurements using Al/SiOC(-H)/p-Si structure. The dielectric constants as low as 2.4 have been obtained for the film annealed at 500 °C with the working pressure of 150 mTorr. The annealing treatment was found to reduce dielectric constant significantly due to abundant incorporation of methyl group into the Si-O network. These results demonstrated the promising characteristics of SiOC(-H) thin films deposited by using oxygen and MTES precursor.     

YBa2Cu3O7−x Thin Films by Citrate-Based Non-fluorine Precursor

A new fluorine-free chemical solution deposition route has been developed for YBa₂Cu₃O_7−x (YBCO) thin films. The precursor was formed by dissolving metal nitrates and citric acid in ethylene glycol. Polyethyleneimine was used to modify the solution. The preparation of YBCO thin films consisted of repeated dip coating, drying, heat-treating in air and annealing in flowing argon with a small addition of oxygen and with final treatment in pure oxygen. The films were characterized by XRD and SEM and show dominating and well-textured YBCO phase. The AC susceptibility and magnetization measurements reveal a critical temperature about 90 K and a high critical current density, comparable with that of pulse laser deposited films. The simplicity and high performance of the method may be attractive for large-scale superconducting applications.     

Influence of O<Subscript>2</Subscript> Pressure on the Structure and Surface Morphology of YSZ Layer for YBCO Coated Conductor Deposited by PLD on Ni-W Tape

Yttria-stabilized ZrO₂ (YSZ) buffer layers were prepared on Ni-5%W tapes coated with CeO₂-seed layers by a pulsed laser deposition (PLD) technique. The influences of oxygen pressure on the structure and surface morphology of YSZ buffer layers for YBCO coated conductors was investigated. X-ray diffraction (XRD), scanning electron microscopy (SEM) and Atomic Force Microscope (AFM) were used to characterize YSZ films. It was found that the structure and surface morphology were sensitive to the oxygen pressure. When the O₂ pressure was higher than 1 mTorr, the YSZ film had mixed orientation and rugged surface. When the oxygen pressure was reduced to 0.5 mTorr, YSZ film had the pure (001) orientation. The surface became smooth as the oxygen pressure decreased. However, when the pressure was low to 0.1 mTorr, X-ray diffraction peaks form YSZ (002) were weak and the rough surface appeared again. The results could be explained either by plume stoichiometric changes, gas and ions interaction, or atomic rearrangement on the substrate.     

Effect of Oxygen Pressure on the Surface Roughness and Intergranular Behavior of YBCO Thin Films

YBa₂Cu₃ O _7?δ (YBCO) thin films were deposited by pulsed laser deposition on single-crystal LaAlO₃ (100) substrates in O₂ partial pressure (P _O2) from 400 to 500 mTorr. The XRD data shows the presence of a-axis-oriented grains in the YBCO films deposited at P _O2 = 500 mTorr. The a-axis grains lead to increase of strain. Atomic force microscopy images show as oxygen pressure has increased, average surface roughness of the films and size of droplets were increased. The grain misorientaion could be the reason for high average roughness. However, surface analysis by statistical methods reveals that three surfaces have multi-affine structure irrespective of oxygen pressure. Analysis of the temperature dependence of the AC susceptibility near the transition temperature indicates that with increasing oxygen pressure, intergranular critical current density has decreased. It is also suggested that the nature of weak links in the samples is of superconductor-normal-superconductor (SNS) type irrespective of the oxygen pressure.     

Effect of PbO<Subscript>2</Subscript> on the Formation of YBCO Films Fabricated Via Sedimentation Deposition and Partial Melting Technique

PbO₂ addition in sedimentation deposition prepared films was investigated by SEM, EDX, and RT measurements to determine its effect on the formation of YBCO films. YBCO films on SrTiO₃ (STO) (100) substrates of varying amounts of PbO₂ were partially melted at 980 ^°C, annealed, and oxygenated in flowing oxygen atmosphere. In addition, a YBCO sample partially melted at higher temperature was also done for comparison. From the SEM, EDX, and RT analyses, it was found that the film having 8 wt% PbO₂ produces a film with the highest superconducting transition temperature comparable to that of a YBCO sample partially melted at peritectic point. Moreover, it was observed that addition of PbO₂ enhances matter transport between Y123 particles and lowers the processing temperature for the fabrication of YBCO films via the sedimentation deposition method.     

Growth and Characterization of YBCO Thin Films by Sequential Deposition and Annealing

A novel thin film growth procedure, sequential deposition and annealing (SDA), which contains the advantages of both in situ and ex situ procedures, was proposed. Y₁Ba₂Cu₃O_{7 – x} (YBCO) high temperature superconducting thin films were grown and characterized by the SDA procedure. Purely c-axis-oriented YBCO thin films with no foreign phases and other oriented grains were successfully prepared. The superconducting transition properties of SDA-grown YBCO thin films were measured by measurement of inductance and resistance. The inductance measurements gave a T _c ^onset of 85 K and a T _c of 5 K. The resistance measurements gave a T _c ^onset of 90 K and a T _c of 5 K. Atomic force microscopy studies showed that SDA-grown YBCO thin films had micrometer-size grains surrounded by many nanometer-size grains. The nanometer-size grains in SDA-grown YBCO thin films are responsible for degradation of superconducting transition properties.     

Preparation and characterization of highly <Emphasis Type="Italic">c</Emphasis>-axis textured MgO buffer layer grown on Si(100) substrate by RF magnetron sputtering for use as growth template of ferroelectric thin film

Highly c-axis textured MgO thin films were grown directly on Si(100) substrates without any buffer layer by RF magnetron sputtering for use as growth template of ferroelectric film. We fixed the target-to-substrate spacing of 40 mm and then changed the substrate temperature, deposition pressure, and RF power to study the effect of deposition parameters on the growth of c-axis textured MgO thin films. The as-grown films were post-annealed by the rapid thermal annealing (RTA) and furnace annealing to improve the film quality. The experimental results show that the optimum deposition parameters are substrate temperature of 350 °C, oxygen pressure of 15 mTorr and RF power of 75 W. The full width at half maximum intensity (FWHM) of MgO(200) peak obtained from the XRD measurement was 0.8°, and it was further reduced to 0.5° and 0.27° after annealing by RTA and furnace, respectively. Highly c-axis textured PZT and BaTiO₃ films could be obtained on this template. Hysteresis loops of the BaTiO₃ films deposited on MgO(100) single crystalline substrate and MgO(200)/Si(100) template were measured for comparison. The results show that MgO/Si templates thus obtained are suitable for the synthesis of perovskite ferroelectric thin films.     

Spray Pyrolysis of MgO Templates on 321-Austenitic Stainless Steel Substrates for YBa2Cu3O7 Deposition by PLD

Spray pyrolysis was used to deposit MgO films on polycrystalline 321-austentic stainless steel substrates using magnesium nitrates and magnesium acetates as precursors. The MgO films deposited from the nitrate precursors were amorphous; however, MgO (200) oriented films were obtained when the acetates precursors were used. The texture of the films was improved with increasing the concentration and the deposition temperature. To evaluate the performance of the MgO buffers, PLD was used to deposit YBCO on MgO-buffered 321 substrates. Only the smoothest MgO films were found as good buffers for the deposition of c-axis oriented YBCO films. The superconducting transition temperature was broad and the T _C onset was 83.6 K. Austenitic 321 steel is an alternative for C276 as a substrate for thin film deposition.     

Superconducting behavior of high-T c YBa2Cu3O7 thin films with BaO impurity produced by pulsed laser deposition

We have investigated the superconducting behavior of high-T _c YBa₂Cu₃O₇ (YBCO) thin films containing BaO impure phase produced by pulsed laser deposition. The thin films were characterized by the standard four-probe method, X-ray diffraction (XRD), and scanning electron microscopy (SEM). XRD showed that all these thin films contained BaO impurity, with thec-axis normal to the surface of the substrates. The presence of impurity existed from substrate temperatureT _s of 727 to 796°C. When these thin films with BaO impurity were measured under the magnetic fields, it was found that the critical current densityJ _c increased slightly with increase in magnetic fieldB within the range ofB≤500 G, in the case ofB perpendicular to thec-axis of the film.     

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.     

Fabrication and Analysis of Tri-layer YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript><Emphasis Type="Italic">O</Emphasis><Subscript>7−<Emphasis Type="Italic">δ</Emphasis></Subscript> Thick Films by Low-Fluorine MOD Method

Improving the thickness of superconducting layer in coated conductors is an effective way to enhance its critical current. In this work, tri-layer YBCO/YBCO/YDyBCO films were successfully deposited on buffered Hastelloy substrate using the multi-coating lowfluorine metal-organic decomposition (LF-MOD) method and the thickness of the films can be up to 2.4 μ m. The effects of high-temperature annealing time on microstructures and superconducting properties of the films were systematically studied. Energy dispersive X-ray spectroscopy (EDS) results reveal that there remains a large amount of F element in the upper layer of the film when the annealing time is too short. With increasing the annealing time, the fluoride-containing precursor converts to YBCO grains completely. But the coarsening of grains appeared, and the critical current density (J _c) of the film dropped slightly when the annealing time is too long. The cross-sectional scanning electron microscope (SEM) image and EDS plane analysis were applied to investigate the microstructure and element distribution of the final triple-layer YBCO films, respectively. The critical current of the final YBCO superconducting film could reach 316 A (77 k, self-field) for 1.2-cm-wide tapes with the optimal annealing conditions.     

High-temperature superconducting dual-mode resonator on (100) MgO substrate

We report, for the first time to our knowledge, a clear resonant peak split in the range of 7.7–9.7 GHz in a perturbed dual-mode disk-type resonator (DMDR) made of YBa₂Cu₃O_7–x (YBCO) superconducting thin film on MgO substrate. Epitaxial YBCO superconducting thin films were grown on (100) MgO substrates by pulsed laser deposition technique. The critical temperature of superconducting thin film on MgO substrate was 85 K. Superconducting dualmode disk resonators were designed by microwave design software, EEsof, and patterned by photolithography and a wet-etch process. The unloaded quality factor (Q_UL) of the superconducting DMDR was found to be 1,312 at 77 K. We believe this type of DMDR can be utilized for dual-mode resonator-based filters for satellite communications.     

Structural and optical characterization of c-axis textured BaTiO<Subscript>3</Subscript> thin films on MgO fabricated by RF magnetron sputtering

In this paper, BaTiO₃ thin films were prepared by RF magnetron sputtering on MgO substrates and their properties such as the crystal structure and optical waveguide properties were investigated. The optimum deposition parameters, such as substrate temperature, deposition pressure, gas flow ratio, the RF power and the after annealing temperature, were obtained in order to get the best BaTiO₃ film quality. The XRD results show that highly c-axis textured BaTiO₃ thin films were successfully grown on MgO substrate. Films obtained under the optimum deposition parameters, substrate temperature of 650°C, RF power of 50 W, deposition pressure 18 mTorr and gas flow ratio O₂/(Ar+ O₂) of 15% namely, reaches a full width at half maximum intensity (FWHM) of BaTiO₃ (002) XRD peak of 0.25°. The FWHM of BaTiO₃ (002) XRD peak was further reduced to 0.24° via post-treatment with furnace annealing (at 800°C for 2 h) which indicates the film crystal quality is further improved. The bright and sharp TE modes measured by m-line spectroscopy of the BaTiO₃ film were observed indicating its possible application in optical waveguide.     

Influence of Heat Treatment on Structure and Superconducting Properties of YBCO Film by Chemical Solution Deposition Method

YBCO films have been fabricated on a (00l) LaAlO₃ single-crystal substrate via self-developed fluorine-free polymer-assisted metal organic deposition (PA-MOD) method. The influence of heat treatment on texture, microstructure and superconducting properties of YBCO films has been investigated. After a pyrolysis process ranging from 145 °C to 500 °C with different heating rates, the samples were fired at 760–780 °C in Ar and O₂ mixture gas followed by annealing at 450 °C in pure O₂. The results indicate the film fired at 770 °C after decomposition at the rate of 0.5 °C/min showed the highest T _c of 90.4 K and J _c (77 K, 0 T) over 2 MA/cm². According to the XRD patterns, phi-scan and omega-scan curves as well as SEM images, the good properties may be attributed to better biaxial texture and purer YBCO phase as well as better grain connectivity.     

Structure and Electrical Properties of NdBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript> Thin Films by Laser Ablation at Low Oxygen Partial Pressure

A deposition process for NdBa₂Cu₃O _y thin films by laser ablation at decreased deposition temperature was developed using substitution of oxygen with argon in the chamber during deposition. A low deposition rate is the crucial factor to obtain high-quality NBCO films. The Nd/Ba cation disorder in the film can be suppressed by an increase of the deposition temperature or by a decrease of the oxygen partial pressure during deposition. The presence of Nd/Ba disorder during deposition stimulates the introduction of oxygen into the growing film. A simple model is proposed for estimation of oxygen contents in the film using structural parameters measured with XRD techniques. Studies of the post-deposition annealing process showed ordering of the Nd/Ba sub-lattice and intense oxygen in- and out-diffusion. The temperature of the post-deposition annealing step should be chosen low enough (～400 °C) to avoid oxygen diffusion out of the NBCO film.     

Structure and conducting properties of La0.5Sr0.5CoO3−δ films on YSZ

La_0.5Sr_0.5CoO_3−δ (LSCO) thin films were deposited on yttria stabilized zirconia (YSZ) substrates by pulsed laser deposition (PLD) for application to thin film solid oxide fuel cell electrodes. During the deposition, the substrate temperature was varied from 450 to 750°C, and the oxygen pressure in the chamber was varied from 80 to 310 mTorr. Films deposited at 650°C and an oxygen background pressure of 150 mTorr were mostly (100) oriented. Deposition at higher temperatures or under lower oxygen pressures lead to mostly (110) oriented films. Films with low electrical resistivity of 10⁻³ Ω·cm were obtained.     

Nano Techniques for Enhancing Critical Current in?Superconducting YBCO Films

A range of nano techniques is explored in order to increase the critical current in pulsed laser deposited (PLD) superconducting YBa₂Cu₃O _x (YBCO) thin films. The structural measurements are linked with magnetic and transport measurements of the films. The effectiveness of PLD techniques is analyzed from the point of view of the dimensionality of nanostructures formed prior to and during the film growth. It is shown that a combination of two-dimensional substrate decoration with nanoparticles before the film deposition and one-dimensional growth of external phase nanorods during the deposition offers a high critical current in magnetic field both along the c-axis and in the ab-plane of YBCO.     

Photoluminescence behaviors in ZnGa2O4 thin film phosphors deposited by a pulsed laser ablation

ZnGa₂O₄ thin film phosphors have been deposited using a pulsed laser deposition technique on Si (1 0 0) and Al₂O₃ (0 0 0 1) substrates at a substrate temperature of 550 °C with various oxygen pressures 100, 200 and 300 mTorr, and various substrate temperatures of 450, 550 and 650 °C with a fixed oxygen pressure of 100 mTorr. The films grown under different deposition conditions have been characterized using microstructural and luminescent measurements. Under the different substrate temperatures, ZnGa₂O₄ thin films show the different crystallinity and luminescent intensity. The crystallinity and photoluminescence (PL) of the ZnGa₂O₄ films are highly dependent on the deposition conditions, in particular, oxygen pressure, substrate temperature, a kind of substrates. The luminescent spectra show a broad band extending from 350 to 600 nm peaking at 460 nm. The PL brightness data obtained from the ZnGa₂O₄ films grown under optimized conditions have indicated that the sapphire is one of the most promised substrates for the growth of high quality ZnGa₂O₄ thin film phosphor.     

Effect of annealing pressure on structure and properties of ferroelectric Bi3.25La0.75Ti3O12 thin films prepared by sol�Cgel method

The effect of annealing pressure was investigated for Bi_3.25La_0.75Ti₃O₁₂ (BLT) thin films prepared on Pt/TiO₂/SiO₂/p-Si(100) substrates by sol?Cgel method. The amorphous films were annealed at 750 °C for 30 min under different oxygen pressures varying from 10^?4 to 3 atm. The largest P _r of 17.8 ??C/cm² with the E _c of 73.6 kV/cm was obtained for the film annealed under 0.1 atm P_O2. Then the structure, crystallization degree, and morphology were characterized by X-ray diffraction (XRD), Raman spectroscopy, and field-emission scanning electron microscope (FSEM) to clarify the effect of annealing pressure on the ferroelectric properties. The XRD and Raman spectroscopy results indicated a clear decreasing of the crystallization degree of the films annealed under 10^?4 and 3 atm P_O2. FSEM results showed the different growth orientation of grains under different oxygen pressures. This study indicated some important effects of annealing pressure on the physical properties of BLT thin films.     

Effect of post-annealing on thin YBCO films deposited from a nanocrystalline target

Pulsed laser deposition is used to ablate thin superconducting YBCO films on SrTiO ₃ substrates. The most important parameters of thin superconducting films are high critical current density, ability to stand magnetic fields and smoothness of surfaces. Smoothness is important in fabrication of layered structures and for research of basic properties of thin superconducting structures. The target sintered from YBCO nanopowder is a promising material for making films which meet most of the requirements above. Investigations by AFM show that our target has grains about one order of magnitude smaller than usual grain size of commercial targets. At optimal deposition parameters, the oxygen pressure of 0.4 torr in the chamber and the substrate temperature 725°C, films with T _c = 90 K, J _c =8 × 10⁶ A/cm ² (77 K) and RMS surface roughness = 1.5 nm are obtained. Thermal annealing of the deposited films for 18 h at 900°C further increases the value of J _c .