Metalorganic Deposition Process Research Articles

Second Generation HTS Wire Based on RABiTS Substrates and MOD YBCO

The performance of Second Generation (2G) high temperature superconducting wire manufactured by continuous reel-to-reel processes is nearing the 300 A/cm-width (77 K, self field) performance threshold for commercial power cable applications. The 2G manufacturing approach under development at American Superconductor is based on the combination of the RABiTS substrate-buffer technology with metal organic deposition (MOD) of the YBCO layer. The capability of this process has been demonstrated in multiple 10 meter lengths with critical currents exceeding 250 A/cm-width with high uniformity and reproducibility. Critical currents of 380 A/cm-width have been achieved in short length samples prepared by the same basic process. The incorporation of nanoparticles (nanodots) into the YBCO layer using the MOD process has resulted in a 2-fold improvement in the critical current at 65 K in a 3 T field. The research and development focus at ASMC is now directed toward the economical scale-up of the RABiTS/MOD process, optimization of the conductor properties for targeted applications and the use of 2G wire in initial demonstration applications.

Improvement in crystallization and electrical properties of barium strontium titanate thin films by gold doping using metal-organic deposition method

The effect of gold (Au) on the crystallization, dielectric constant and leakage current density of barium strontium titanate (BST) thin films was investigated. BST thin films with various gold concentrations were prepared via a metal-organic deposition process. The X-ray diffraction shows enhanced crystallization as well as expanded lattice constants for the gold-doped BST films. Thermal analysis reveals that the gold dopant induces more complete decomposition of precursor for the doped films than those of undoped ones. The leakage current density of BST films is greatly reduced by the gold dopant over a range of biases (1–5 V). The distribution of gold was confirmed by electron energy loss spectroscopy and found to be inside the BST grains, not in the grain-boundaries. Gold acted as a catalyst, inducing the nucleation of crystallites and improving the crystallinity of the structure. Its addition is shown to be associated to the improvement of the electrical properties of BST films.

Magnetic-Field Properties of High Critical Current Density YBCO Films Deposited by TFA-MOD

The critical current density, Jc, of metal-organic deposition process using trifluoroacetates (TFA-MOD) based YBCO films was measured between 20 K and 77 K in magnetic fields up to 9.5 T as a function of the field direction. C-axis oriented YBCO films was deposited on LaAlO/sub 3/ single crystalline substrates and also on CeO/sub 2/ buffered IBAD (YSZ/Hastelloy) substrates by TFA-MOD method. The obtained Jc values at 77 K and 0 T were 7 and 1.7 MA/cm/sup 2/ for LaAlO/sub 3/ and IBAD substrates, respectively. High Jc values over 10/sup 5/ A/cm/sup 2/ were maintained up to 4 T (B//c-axis) for the LaAlO/sub 3/ substrate and up to 3 T (B//c-axis) for the CeO/sub 2/ buffered IBAD substrate. These results imply that TFA-MOD with simple fabrication process is very promising for the practical YBCO coated conductor. And the dependences on temperature and angular of the Jc at various external magnetic fields for some different thicknesses YBCO films was reported.

Epitaxial growth of La 0.7Ca 0.3MnO 3 thin films by KrF excimer laser assisted metal organic deposition process

Epitaxial La 0.7Ca 0.3MnO 3 (LCMO) films were prepared on SrTiO 3 single-crystal substrates by metal organic deposition (MOD) process. A KrF excimer laser irradiation at a substrate temperature of 500 °C is successfully used instead of thermal annealing at high temperature to perform the epitaxial growth of the LCMO thin films. The epitaxial growth was confirmed by X-ray diffraction (XRD: θ–2 θ scans and pole figure analysis). Morphology and surface properties of the obtained films were investigated by scanning electron microscopy and atomic force microscopy. The temperature coefficient of resistance (TCR) was calculated from the temperature dependence of the resistance measurements. A TCR of about 6% was obtained for the excimer laser annealed films which is considered a good value for bolometric applications.

Preparation of tin oxide films on various substrates by excimer laser metal organic deposition

Tin oxide (SnO 2) thin films were prepared on various substrates by the excimer laser metal organic deposition (ELMOD) and the thermal metal organic deposition (MOD) processes. When the amorphous SnO 2 film prepared at 300 °C on (1 0 0) Si, and (1 0 1 0) sapphire substrates was irradiated by the KrF excimer laser at a fluence of 200 mJ/cm 2 and 25 °C, polycrystalline SnO 2 films were obtained. When the amorphous SnO 2 film prepared at 300 °C on the (1 0 0) SrTiO 3 and (1 0 0) TiO 2 substrates was irradiated by the KrF excimer laser at the same conditions, a (1 1 0) oriented SnO 2 film on the SrTiO 3 substrate and a (1 0 0) oriented SnO 2 film on the TiO 2 substrate were obtained. Using the pole–figure measurements, a SnO 2 film on TiO 2 substrate was found to be epitaxially grown. On the other hand, when a thermal MOD process was used, all the product films on their substrates were of the polycrystalline phase whereas the orientation of the films depended on the substrate. Polycrystalline and epitaxial growth of the SnO 2 films by the ELMOD process are also discussed.

Numerical Analysis of YBCO Crystal Growth in the TFA-MOD Process

Numerical analyses of YBa 2 Cu 3 O 6 . 5 + x (YBCO) polycrystalline film growth in the metal organic deposition (MOD) process using precursor solution containing metal trifluoroacetates (TFA) have been performed. This process is accompanied with both consuming H 2 O and releasing HF at the growth interface. At first, a one-dimensional numerical growth model of the YBCO was proposed in consideration of the growth kinetics at the interface between the precursor and the YBCO crystalline layers together with the conservation of the gas components, H 2 O and HF, in the precursor layer. This numerical model was treated as a boundary condition for the convective multi-component diffusion equations in the gas region. Subsequently, the convective multi-component diffusion equations and Navier-Stokes equation in the gas region were solved in a two-dimensional manner by the finite difference method. It was found that this numerical model calculation could make a good estimate for the growth rate distribution in the film and the molar fractions of the components in the gas region. Finally, it was confirmed that the supplied water vapor molar fraction dependence, the positional dependence and the inlet gas velocity dependence of the calculated YBCO growth rate were in good agreement with the experimental results.

Critical current density and microwave surface resistance of 5-cm-diameter YBCO films on LaAlO 3 substrates prepared by MOD using an infrared image furnace

Inductive critical current density ( J c) and microwave surface resistance ( R s) were investigated for 0.7-μm-thick epitaxial YBa 2Cu 3O 7− y (YBCO) films on 5-cm-diameter LaAlO 3 substrates prepared by a chemical solution-based metal organic deposition (MOD) process using an infrared image furnace. By varying the heating rate at ramp during the final heat treatment, we obtained various orientations of YBCO; the c- and a-axis orientation at a slower rate, i.e., 20–100 °C/min while the pure c-axis orientation at a faster rate, 200 °C/min. The c-axis-oriented YBCO films showed excellent superconducting properties; for example, a high inductive- J c (77 K) of 2.6 MA/cm 2 and low R s (12 GHz)’s of 0.24 and 0.52 mΩ at 50 and 77 K, respectively, by a sapphire rod resonator method. The c- and a-axis-oriented films exhibited a lower J c and a higher R s. It was found that the J c and R s values of MOD-derived YBCO films showed a strong correlation; approximately, R s is inversely proportional to J c. This correlation is in good agreement with a previous report by Ohshima et al. for sputtered-YBCO films on BaSnO 3-buffered MgO substrates.

Detection of quasimolecular ion of Cu(hfac)(tmvs) by ion attachment mass spectrometry

A molecular ion of (trimethylvinylsilane)(1,1,1,5,5,5-hexafluoroacetyl-acetonato)Cu(I) [Cu(hfac)(tmvs)], which could not be detected by mass spectrometry with conventional ionization techniques such as electron impact ionization because of weak coordination bonds, has been successfully detected as a quasimolecular ion, Cu(hfac)(tmvs)Li+, for the first time by recently developed ion-attachment mass spectrometry (IAMS). Cu(hfac)(tmvs) is a material widely used in the metal organic chemical vapor deposition (MOCVD) process. In the thermal decomposition of Cu(hfac)(tmvs), trimethylvinylsilane (tmvs) and hexafluoroacetylacetone (Hhfac) were observed by IAMS as the reaction products. We also evaluated the dependence of the decomposition process on temperature. We found IAMS to be an effective tool in monitoring and clarifying MOCVD processes.

Low-temperature growth of SnO2 film prepared by XeCl excimer laser MOD process

A SnO2 film has been prepared by an excimer laser metal organic deposition (ELMOD) process using an XeCl laser. The effects of the laser fluence, shot number, and the pretreatment temperature of the Sn acetylacetonate (Sn-acac) on the crystallization of the SnO2 film were investigated by X-ray diffraction and infrared spectroscopy. When the MO spin-coated film preheated at room temperature on a Si substrate was irradiated by the laser at a fluence of 100 mJ/cm2 and at a repetition rate of 10 Hz for 5 min, a crystallized SnO2 film was successfully obtained without heat treatment. At a fluence of 260 mJ/cm2, the highest crystalline film was formed. On the other hand, when the amorphous SnO2 film was irradiated by the laser at 260 mJ/cm2, the crystallinity of the SnO2 film was improved. SnO2 films were also prepared by conventional thermal MOD in a temperature range from 300 to 900 °C. The crystallinity of the SnO2 films prepared by the ELMOD process at room temperature was higher than that of the films prepared by heating at 900 °C for 60 min.

Advanced TFA-MOD process of high critical current YBCO films for coated conductors

Although the metalorganic deposition (MOD) process using metal trifuluoroacetete (TFA) is considered to be a strong candidate due to its low cost and high J c performance as a fabrication process for coated conductors of YBa 2Cu 3O 7 − x (YBCO), the long calcination time of 10 h for 300 nm YBCO thickness was a problem that needed to be solved in the case of the MOD process using the TFA salts for all elements (all TFA solution). In this study, in order to shorten the calcination time, a new combination of starting materials was developed. Through the investigation of the generation rate of hydro fluoride (HF) gas during calcination, it was found that the high generation rate at a high heating rate is the reason for the bubbling which prevents an increase of the heating rate. Therefore, the amount of fluorine (F) in the starting material was reduced by using the Cu-salt without F while maintaining the basic crystallization reaction in this process. A new heating process using these materials has been developed. Consequently, the calcination time was shortened to 40% using the All TFA solution and an overall transport I c value of 292 A for 1 cm width was obtained (77 K in self-field).

Fabrication of YBa 2Cu 3O 7 films on {1 1 0}〈1 1 0〉 textured Ag tapes by MOD process

The YBa 2Cu 3O 7 films were prepared on polycrystalline {1 1 0}〈1 1 0〉 textured Ag substrates without any buffer layers using a MOD (metal organic deposition) method in various heat treatment condition. The Y:Ba:Cu cation ratio of the precursor solution was 1:2.6:4.5 molar ratio. The deficient of a Cu element was observed in the films prepared under a low oxygen partial pressure ( p(O 2)=0.0002 atm). The amount of Cu element was decreased with increasing the annealing temperature. From X-ray pole figure measurements, we confirmed a weak biaxial crystal orientation in the YBCO films prepared on a {1 1 0}〈1 1 0〉 textured polycrystalline Ag substrates at 900 °C for 2.5 h in air. On the polycrystalline {1 1 0}〈1 1 0〉 textured Ag substrates, the observed epitaxial relationship with YBCO lattice is 〈1 1 0〉 YBCO ∥ 〈1 1 0〉 Ag.

Low-temperature growth of La 0.8Sr 0.2MnO 3 thin films on LaAlO 3 and SrTiO 3 substrates by an excimer laser metal organic deposition (ELMOD) process

The preparation of La 0.8Sr 0.2MnO 3 (LSMO) films on LaAlO 3 (LAO) and SrTiO 3 (STO) substrates was examined by an excimer laser MOD processes (ELMOD). Epitaxial LSMO films on the LAO substrate were obtained by the ArF laser irradiation at a fluence of 100 mJ/cm 2 for 10, 30, 60 and 90 min with heating at 500 °C. In the case of the STO substrate with heating at 500 °C, epitaxial LSMO was obtained by the ArF laser irradiation at 70 mJ/cm 2 whereas no film was formed at 100 mJ/cm 2. The effects of the laser fluence, irradiation time and film thickness on the temperature dependence of the resistance and TCR (defined as 1/R·dR/DT) of the LSMO films on the LAO substrate were investigated. It was found that the resistance of the 80 nm thick LSMO film that was irradiated by the ArF laser at a fluence of 100 mJ/cm 2 for 60 min showed a metallic temperature dependence from 310 to 100 K, and the maximum temperature coefficient of resistance of the film (TCR: defined as 1/R·dR/DT) was 3.4% at 265 K. In the case of the STO substrate, the resistance of the 80 nm thick LSMO film that was irradiated by the ArF laser at a fluence of 70 mJ/cm 2 for 60 min showed a Tc at 280 K, and the maximum TCR of the film was 2.9% at 220 K. The formation mechanisms of the epitaxial LSMO films obtained by the ELMOD process also are discussed.

Growth of bismuth oxide films by direct liquid injection-metal organic chemical vapor deposition with Bi(tmhd) 3 (tmhd: 2,2,6,6-tetramethyl-3,5-heptanedione)

Bismuth oxide films were deposited at 225–425 °C by direct liquid injection (DLI)-metal organic chemical vapor deposition (MOCVD) process with Bi(tmhd) 3 (tmhd : 2,2,6,6-tetramethyl-3,5-heptanedione) dissolved in n-butylacetate. The deposition rate of Bi 2O 3 film was determined by surface reaction with the apparent activation energy of 15 kcal/mol. The growth rate was decrease above 325 °C because of the gas phase dissociation of the precursor. The Bi 2O 3 film deposited at 300 °C was amorphous, while the film annealed at temperatures above 550 °C showed monoclinic α-phase. The grain size and surface roughness of the annealed film were increased with the increase of the annealing temperature up to 650 °C. At 750 °C, the monoclinic α-Bi 2O 3 film was changed into the cubic bismuth silicate due to the reaction with Si substrate. The dielectric constant of Bi 2O 3 films deposited at 300 °C was about 32 and the film showed a leakage current of 3.15×10 −7 A/cm 2 at 3 V (0.33 MV/cm). The thickness of Bi oxide Bi silicate films used in the C– V and I– V measurement was 92 and 140 nm, respectively.

High critical current YBCO films using advanced TFA-MOD process

As a method of the fabrication process of YBa 2Cu 3O 7− x (YBCO) coated conductors, the metalorganic deposition (MOD) process using metal trifluoroacetates (TFA) has been considered to be a strong candidate as a low cost fabrication process for coated conductors with high J c. In the case of the MOD process using the TFA salts for the all three elements, it requires several tens hours in the calcination process for each single coated film to minimize the generation of pores in the film. In order to shorten the calcination time, a new combination of starting materials was developed. In this study, the new heating process for these new materials has been investigated. Consequently, the calcination time was shortened to be about 17%. Also, the overall transport I c of 292 A and the J c value of 2.0 MA/cm 2 were achieved with 1.48 μm in thickness at 77 K in self-field.

Low temperature growth of epitaxial complex oxide films by an excimer laser MOD process

Epitaxial La0.7Sr0.3MnO3 (LSMO) and Pb(ZrTi)O3 (PZT) thin films on various substrates were prepared by excimer laser metal organic deposition (ELMOD) process. The effect of the substrate on the formation of these films was investigated by X-ray diffraction (XRD: theta-2theta scans, pole-figure analysis). For the LSMO films, epitaxial grown LSMO films on SrTiO3 (STO) and LaAlO3 (LAO) substrates were formed by ArF laser irradiation at 400 and 500°C, respectively. The temperature dependence of the resistance (R/R300) of the LSMO film on LAO substrate prepared at 500°C showed a metallic behavior from 310 to 100K, and the maximum TCR of the LSMO film on LAO was 2.5%. For the PZT films, epitaxial grown PZT films on the STO and La-doped STO (LSTO) substrates were obtained by the ELMOD process without heat treatment. The formation mechanisms of the epitaxial complex oxide films using the ELMOD process are also discussed.

Nonlinear optical properties of neodymium-doped bismuth titanate thin films using Z-scan technique

Bi 3.75 Nd 0.25 Ti 3 O 12 (BNT0.25) thin film with good surface morphology and layered perovskite structure was fabricated by a metalorganic solution deposition process. Their fundamental optical constants (the band gap, linear refractive index, and absorption coefficient) were obtained through optical transmittance measurements. The nonlinear optical properties of the film were investigated by using a top-hat Z-scan method. Large positive nonlinear refractive index n2 and two-photon absorption coefficient β were determined to be 4.52×10−7 esu and 5.24×10−7 m/W, respectively. All of the results show that the BNT0.25 thin film is promising for applications in nonlinear optical devices.

Microstructural and compositional analysis of YBa 2Cu 3O 7−δ films grown by MOCVD before and after GCIB smoothing

The microstructural and compositional evolution of thick (>1 μm) high temperature superconducting YBa 2Cu 3O 7− x (YBCO) films grown on single crystal SrTiO 3 substrates by the metal organic chemical vapor deposition (MOCVD) process was investigated by focused ion beam microscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, and atomic force microscopy. This study showed that as the MOCVD YBCO film thickness increased above 0.5 μm, defects such as second phase particles, pores, and misaligned grains preferentially nucleated and grew at the YBCO surface. A portion of this defective top layer was eliminated from all the samples using a gas cluster ion beam (GCIB) process that first removed material with a focused argon cluster beam. Next, an oxygen cluster beam was used to smooth the surface and re-oxygenate the YBCO. Comparing the critical current ( I c) measured before and after GCIB processing showed that the I c remained the same, and even improved, when part of the defective top layer was removed. This microstructural and electromagnetic “dead layer” is believed to be responsible for the overall I c decrease of MOCVD YBCO films thicker than 0.5 μm.

Electrical properties of the La0.8Sr0.2MnO3 thin films on SrTiO3 substrate by an excimer laser metal organic deposition (ELMOD) process at low temperature

ABSTRACTThe electrical properties of epitaxial La0.8Sr0.2MnO3 films on a SrTiO3(STO) substrate prepared by changing the laser fluence, the irradiation time and the film thickness using excimer laser metal organic deposition(ELMOD) at 500/cm2, the film showed a 3.9 % maximum temperature coefficient of resistance (TCR: defined as 1/R•dR/dT) which was obtained by the ArF laser irradiation at 80mJ/cm2 for 10min. At a constant fluence of 80mJ/cm2, the Tm (temperature of the maximum TCR) of the La0.8Sr0.2MnO3 films increased from 225K to near 250K with an increase in the irradiation time to 90min at which the TCR was almost 3.9%. The La0.8Sr0.2MnO3 film that showed the maximum TCR of 4.0% at 275K was obtained by the ELMOD process at 500°C using the optimum conditions (Flence:80mJ/cm2, Irradiation time: 90min, Film thickness: 80nm).

Real-Time Feedback Control of Carbon Content of Zirconium Dioxide Thin Films Using Optical Emission Spectroscopy

In this work, we present a methodology for real-time carbon content feedback control of a plasma-enhanced metal organic chemical vapor deposition process using optical emission spectroscopy. Initially, an estimation model of carbon content of ZrO2 thin films based on real-time optical emission spectroscopy data is presented. Then, a feedback control scheme, which employs the proposed estimation model and a proportional-integral controller, is developed to achieve carbon content control. Using this approach, a real-time control system is developed and implemented on an experimental electron cyclotron resonance high density plasma-enhanced chemical vapor deposition system at UCLA to demonstrate the effectiveness of real-time feedback control of carbon content. Experimental results of the deposition process under both open-loop and closed-loop operations are shown and compared. The advantages of operating the process under real-time feedback control in terms of higher productivity, reduced process variation and lower carbon content are demonstrated

次世代超電導線材の開発と特性評価 改良型ＴＦＡ‐ＭＯＤ法を用いた仮焼条件の適正化によるＹＢＣＯ線材の高特性化

In order to shorten the calcination time in the metal-organic deposition (MOD) process using metal trifluoroacetate (TFA), a new combination of starting materials was developed using the F-free salt of Cu and TFA salts of Y and Ba as a so-called "new solution". Moreover, a new process temperature profile for this solution was developed as an advanced TFA-MOD process in which a high heating rate was achieved. Consequently, an overall transport Ic value of 210 A and a Jc value of 1.5 MA/cm2 (77 K, Self-field), similar to Ic and Jc values using TFA for all salts, were obtained. In order to obtain higher Jc performance, the effects of process parameters such as the heating rate in the calcination process for the Jc characteristics were investigated. As a result, a YBCO film with a thickness of 1.2μm was fabricated on a CeO2/IBAD-Gd2Zr2O7 layer-buffered Hastelloy substrate with Δφ∼7°. The overall Ic value of 251 A (77 K Self-field) corresponding to the Jc value of 2.1 MA/cm2 was achieved by calcination at a heating rate of 2°C/min.