Deposition of Pb(Zr,Ti)O3 Thin Films by Metal-Organic Chemical Vapor Deposition Using β-diketonate Precursors at Low Temperatures

Lead zirconate titanate (PZT) thin films were deposited by metal-organic chemical vapor deposition (MOCVD) using β-diketonate precursors and 0₂ at temperatures below 500°C on variously passivated Si substrates. PZT thin films could not be deposited on bare Si substrates, owing to a serious diffusion of Pb into the Si substrate during deposition. Pt/SiO₂/Si substrates could partially block the diffusion of Pb, but a direct deposition of PZT thin films on the Pt/SiO₂/Si substrates resulted in a very inhomogeneous deposition. A TiO₂ buffer layer deposited on Pt/SiO₂/Si substrates could partially suppress the diffusion of Pb and produce homogeneous thin films. However, the crystallinity of PZT thin films deposited on the TiO₂-buffered Pt/SiO₂/Si substrate was not good enough, and the films showed random growth direction. PZT thin films deposited on the PbTiO₃-buffered Pt/SiO₂/Si substrates had good crystallinity and a- and c-axis oriented growth direction. However, the PZT thin film deposited at 350°C showed fine amorphous phases at the grain boundaries, owing to the low chemical reactivities of the constituent elements at that temperature, but they could be crystallized by rapid thermal anneaiing (RTA) at 700°C. PZT thin film deposited on a 1000-å PbTiO₃,-thin-film-buffered Pt/SiO₂/Si substrate at 350°C and rapid thermally annealed at 700°C for 6 min showed a single-phase perovskite structure with a composition near the morphotropic boundary composition.     

Effect of Substrate Texture on Orientations of rf-Sputtered Ba2Si2TiO8 Thin Films

Radio-frequency-sputtered barium silicon titanate, Ba₂Si₂TiO₈ (BST), thin films were grown on various substrates at substrate temperatures ranging from 750° to 955°C. The asdeposited films were characterized using X-ray diffraction, optical microscopy, and scanning electron microscopy (SEM). The results of the morphology analysis and X-ray diffraction analysis show no crystalline structure for films deposited on the fused quartz and unetched Si (100) substrates at temperatures lower than 865°C. At a substrate temperature of 900°C, tiny tetragon-like grains were observed for the film grown on the fused quartz, and the grains grew at a rate of 0.18 μm/min in the initial deposition stage. Optical and SEM micrographs reveal (001)-oriented, tetragon-like grains grown on HF-etched Si (100) wafers in the initial deposition stage and in later stages at substrate temperatures from 822° to 865°C. The results of X-ray diffraction analysis show a high (001) orientation for the thicker films, which corresponds to the tetragon-like configuration of the grains in the initial stage. Triangle-like grains were observed on the films deposited on etched Si (111) substrates in a temperature range from 822° to 899°C, but the grain configuration changed from the initial triangle shape to a tetragon shape as the films grew thick. The X-ray diffraction spectra show a high (001) orientation for the thicker films, which indicates an orientation transformation during the deposition due to a very low interfacial energy between the (001)-oriented BST overgrowth and the BST substrates in the later stage of deposition. Both the tetragon-like and the triangle-like grains have quasi-two-dimensional polygon shapes and have nonliquid-like characteristics in coalescence, which suggests a strong interaction between the BST deposits and the Si substrates.     

Microstructural Model on the Evolution of Domain Structure during Processing of PbTiO3 Thin Films on MgO(100) Substrates

A two-dimensional microstructural model is proposed to explain the origin of the 90° domain structure of epitaxial PbTiO₃ thin films grown on MgO(100) substrates by radio frequency sputter deposition. During film deposition at or above 600°C, the film grows epitaxially in a cubic phase without any domain structure. At or just below the Curie temperature, the film mainly consists of α-domains with a small portion of c -domains nucleated in a triangular shape. The c -domains gradually expand with decresasing temperature to relax the strain energy caused by the difference in thermal contraction rate between the c -axis of α-domains and the substrate, forming consequently thin strips of α-domains distributed in the matrix of c -domains at room temperature.     

Pb-Diffusion Barrier Layers for PbTiO3 Thin Films Deposited on Si Substrates by Metal Organic Chemical Vapor Deposition

The interfaces between metal organic chemical vapor deposited PbTiO₃ thin films and various diffusion barrier layers deposited on Si substrates were investigated by transmission electron microscopy. Several diffusion barrier thin films such as polycrystalline TiO₂, amorphous TiO₂, ZrO₂, and TiN were deposited between the PbTiO₃ thin film and Si substrate, because the deposition of PbTiO₃ thin films on bare Si substrates produced Pb silicate layers at the interface irrespective of the deposition conditions. The TiO₂ films were converted to PbTiO₃ by their reaction with diffused Pb and O ions during PbTiO₃ deposition at a gubstrate temperature of 410°C. Further diffusion of Pb and O induces formation of a Pb silicate layer at the interface. ZrO₂ did not seem to react with Pb and O during PbTiO₃ deposition at the same temperature, but the Pb and O ions that diffused through the ZrO₂ layer formed a Pb silicate layer between the ZrO₂ and Si substrate. The TiN films did not seem to react with Pb and O ions during the deposition of PbTiO₃ at 410°C, but reacted with PbTiO₃ to form a lead-deficient pyrochlore during postdeposition rapid thermal annealing at 700°C. However, TiN could effectively block the diffusion of Pb and O ions into the Si substrate and the formation of Pb silicate at the interface.     

The Effect of Deposition Temperature and Postanneal on the Bi3.63Pr0.3Ti3O12 thin Films Prepared by RF-Magnetron Sputtering Method

Praseodymium doped Bi₄Ti₃O₁₂ (BTO) thin films with composition Bi_3.63Pr_0.3Ti₃O₁₂ (BPT) were successfully prepared on Pt/Ti/SiO₂/Si substrates by RF-magnetron sputtering method at substrate temperatures ranging between 500° and 750°C. The structural phase and orientation of the deposited films were investigated in order to understand the effect of the deposition temperature on the properties of the BPT films. As the substrate temperature was increased to 700°C, the films started showing a tendency of assuming a c -axis preferred orientation. At lower temperatures, however, polycrystalline films were formed. The Pt/BPT/Pt capacitor showed an interesting dependence of the remnant polarization (2 P _r) as well as dc leakage current values on the growth temperature. The film deposited at 650°C showed the largest 2 P _r of 29.6 μC/cm². With the increase of deposited temperature, the leakage current densities of films decreased at the same applied field and the film deposited at 750°C exhibited the best leakage current characteristics. In addition, the ferroelectric fatigue and Raman measurements were carried out on the as-prepared, postannealed in air and postannealed in oxygen BPT films. It was revealed that the BPT film postannealed in air exhibited the weakest fatigue-resistance characteristics and highest frequency shifted Raman vibration modes, indicating the highest oxygen vacancy concentration in this film.     

Excimer Laser Crystallized (Pb,La)(Zr,Ti)O3 Thin Films

A KrF pulsed excimer laser (248 nm) was utilized to crystallize sputtered La-modified Pb(Zr,Ti)O₃ (3:30:70) (PLZT) films on LaNiO₃-coated silicon substrates. The film surface was irradiated with defocused laser pulses in an oxygen ambient at various substrate temperatures. Polycrystalline, phase pure perovskite PLZT thin films were produced for substrate temperatures of 250°C and higher. The dielectric constant and loss tangent values of laser-assisted crystallized (10 min exposure at 10 Hz using a substrate temperature of 400°C) PLZT thin films at 10 kHz were 406 and 0.027; in comparison, rapid thermal annealed films (annealed at 700°C for 1 min) showed values of 400 and 0.021, respectively. Laser crystallized films exhibited a remanent polarization value of 14 μC/cm² with a coercive field |( E _+c+ E _−c)|/2 of 95 kV/cm.     

Structural Variation of the BaTi4O9 Thin Films Grown by RF Magnetron Sputtering

BaTi₄O₉ thin films were grown on a Pt/Ti/SiO₂/Si substrate using rf magnetron sputtering and the structure of the thin films were then investigated. For the films grown at low temperature (≤350°C), an amorphous phase was formed during the deposition, which then changed to the BaTi₅O₁₁ phase when the annealing was conducted below 950°C. However, when the annealing temperature was higher than 950°C, a BaTi₄O₉ phase was formed. On the contrary, for the films grown at high temperature (>450°C), small BaTi₄O₉ grains were formed during the deposition, which grew during the annealing. The homogeneous BaTi₄O₉ thin films were successfully grown on Pt/Ti/SiO₂/Si substrate when they were deposited at 550°C and subsequently rapid thermal annealed at 900°C for 3 min.     

Metal Propionate Synthesis of Magnetoresistive La1−x(Ca,Sr)xMnO3 Thin Films

A flexible chemical solution deposition (CSD) method for the preparation of magnetoresistive La_1−x (Ca,Sr)x MnO₃thin films based completely on metal propionates is pre-sented.A number of polycrystalline thin films with varying stoichiometries were deposited on different substrate ma-terials at temperatures between 550° and 850°C. The crys-tallization behavior on selected substrates was found to de-pend on the thin film stoichiometry. Magnetoresistivity and magnetization were measured as a function of temperature. For the selected samples, a magnetic Curie temperature TC, a metal–semiconductor transition, and magnetoresistive behavior were observed. These measurements demon-strated that La_1−x(Ca,Sr)x MnO₃ thin films with properties well known from films deposited by PLD or sputtering can be prepared by a simple, propionate-based CSD method.     

Pulsed-Laser Deposition of Barium Titanate Thin Films

Barium titanate (BaTiO₃) thin films have been deposited on single-crystal magnesia (MgO) substrates by pulsed-laser ablation. Temperature dependence of capacitance measurements show a peak of 110°C, indicative that a ferroelectric phase transition has occurred at this temperature. This value is lower than that determined for single-crystal BaTiO₃, but consistent with that found for BaTiO₃ thin films produced by other methods. It has been demonstrated that the microstructure of the films can be varied by changes in the deposition parameters. Optimizing these variations permits the formation of thin films with controlled microstructures and properties.     

Formation of High-Quality, Epitaxial La2Zr2O7 Layers on Biaxially Textured Substrates by Slot-Die Coating of Chemical Solution Precursors

Crystallization studies were performed of epitaxial La₂Zr₂O₇ (LZO) films on biaxially textured Ni–3at.%W substrates having thin Y₂O₃ (10 nm) seed layers. LZO films were deposited under controlled humid atmosphere using reel-to-reel slot-die coating of chemical solution precursors. Controlled crystallization under various processing conditions has revealed a broad phase space for obtaining high-quality, epitaxial LZO films without microcracks, with no degradation of crystallographic texture and with high surface crystallinity. Crack-free and strong c -axis aligned LZO films with no random orientation were obtained even at relatively low annealing temperatures of 850°–950°C in flowing one atmosphere gas mixtures of Ar–4% H₂ with an effective oxygen partial pressure of P(O₂)∼10⁻²² atm. Texture and reflection high-energy electron diffraction analyses reveal that low-temperature-annealed samples have strong cube-on-cube epitaxy and high surface crystallinity, comparable to those of LZO film annealed at high temperature of 1100°C. In addition, these samples have a smoother surface morphology than films annealed at higher temperatures. Ni diffusion rate into the LZO buffer film is also expected to be significantly reduced at the lower annealing temperatures.     

Surface Oxidation of Ge33As12Se55 Films

Ge₃₃As₁₂Se₃₃ films deposited by ultrafast pulse laser deposition were annealed at various temperatures and pressures, and the dependence of the surface oxidation on the processing conditions was investigated by X-ray photoelectron spectroscopy (XPS). We found that even as-grown film contains a thin oxidized surface and the oxygen distribution exponentially decays along the normal direction of the films regardless of different processing conditions. The critical thicknesses of the oxidized layers were 6.5, 11, 48, and 98 nm, respectively, for the as-grown, 250°C annealing sample for 4 h under 1 × 10⁻⁶ Torr, and 150° and 250°C annealing samples for 15 h under 20 mTorr.     

Synthesis of Oriented Ba2NaNb5O15 (BNN) Thin Films from an Alkoxy-derived Precursor

Ba₂NaNb₅O₁₅ (BNN) thin films with a tungsten bronze structure were fabricated using a precursor solution that was synthesized from barium, sodium, and niobium alkoxides. Highly (002)-oriented BNN films were prepared successfully on Pt(100)/MgO(100) substrates at 700°C, using a BNN underlayer. X-ray pole-figure measurement showed that the BNN films that crystallized on Pt(100)/MgO(100) substrates had two in-plane orientations. The remanent polarization and coercive field of the BNN film (thickness of 1.0 µm) that was crystallized at 700°C were 12.3 µC/cm² and 101 kV/cm, respectively, at –150°C (123 K). BNN films on fused silica substrates exhibited second harmonic generation upon irradiation with 1064 nm light.     

Doped Lanthanum Gallate Film Solid Oxide Fuel Cells Fabricated On a Ni/YSZ Anode Support

A colloidal deposition without any binder was developed to prepare a dense La_0.8Sr_0.2Ga_0.85Mg_0.15O_3−δ (LSGM) film on porous NiO/YSZ substrates, using an incompletely crystallized LSGM powder as starting material. Both the dense LSGM film with a thickness of 15 μm and the required phase composition of the LSGM were achieved simultaneously by sintering at 1400°C for 6 h. The conductivity of the supported LSGM film attained 0.102 S/cm at 800°C, which was comparable with those of the self-supported LSGM films. The maximum power density of the LSGM film cell was 480 at 800°C and 614 mW/cm² at 850°C, respectively.     

Structural Characterization of Lanthanum Chromite Perovskite Coating Deposited by Magnetron Sputtering on an Iron-Based Chromium-Containing Alloy as a Promising Interconnect Material for SOFCs

Chromium-containing stainless steel (SS) is a prospective material for use as an interconnect in solid oxide fuel cells (SOFCs). However, during operations at high temperatures, the growth of oxide scales causes the performance of the interconnect and SOFC as a whole to deteriorate. The coating of SS 446 with a conducting perovskite is a potential method of slowing the growth of oxide scale and, therefore, improving overall SOFC performance. In the present research, the structural characterization of a pure LaCrO₃ thin film on the SS 446 substrates has been performed as a model material that can be used as a barrier coating for the metallic interconnect. The deposition of an amorphous La-Cr-O thin film on SS 446 was performed using radio-frequency (rf) magnetron sputtering. The deposited amorphous film was annealed in air to form the desired perovskite phase. The film underwent an amorphous to LaCrO₄ phase transition during annealing at 500°C with further transformation to LaCrO₃ orthorhombic phase during annealing at 700°C. A self-organized dendritic structure was reported as a result of the perovskite-phase formation. Although formation of various oxides, such as Fe₂O₃ and Fe₃O₄, was observed during the annealing of uncoated SS 446 in air, the coating of SS 446 surface with LaCrO₃ film prevented formation of various oxide phases at the interconnect surface. The structural characterization of the films and SS 446 surfaces was accomplished using scanning electron microscopy with energy-dispersive X-ray analysis, X-ray diffractometry, micro-Raman spectroscopy, and nanoindentation.     

Liquid Precursor Route for Hetero-epitaxy of Zr(Y)O2 Thin Films on (001) Cubic Zirconia

ZrO₂–3 mol% Y₂O₃„single-crystal” thin films with multiple variants were epitaxially formed on (100) cubic zirconia substrates. The films were prepared by spin-coating an aqueous zirconium acetate/yttrium nitrate solution onto the cubic zirconia substrates and subsequently heat-treated at temperatures between 1100° and 1400°C. Electron diffraction and dark-field TEM observations showed that the film has tetragonal symmetry and consists of 50–100 nm variants with their c-axes aligned with one of the three substrate cube axes. Unrelaxed strain energy estimates indicate that the two variants with their c ₁-axis parallel to the substrate/thin film interface are energetically favorable.     

In-Plane Polarized 0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 Thin Films

Ferroelectric 0.7Pb(Mg_1/3Nb_2/3)O₃–0.3PbTiO₃ (PMN-PT) thin films were deposited on ZrO₂/SiO₂/silicon substrates using a chemical-solution-deposition method. Using a thin PZT film as a seed layer for the PMN-PT films, phase-pure perovskite PMN-PT could be obtained via rapid thermal annealing at 750°C for 60 s. The electrical properties of in-plane polarized thin films were characterized using interdigitated electrode arrays on the film surface. Ferroelectric hysteresis loops are observed with much larger remanent polarizations (∼24 μC/cm²) than for through-the-thickness polarized PMN-PT thin films (10–12 μC/cm²) deposited on Pt/Ti/Si substrates. For a finger spacing of 20 μm, the piezoelectric voltage sensitivity of in–plane polarized PMN-PT thin films was ∼20 times higher than that of through-the-thickness polarized PMN-PT thin films.     

Effects of deposition temperature on the crystallinity of Ba0.5Sr0.5TiO3 epitaxial thin films integrated on Si substrates by pulsed laser deposition method

Epitaxial Ba_0.5Sr_0.5TiO₃ (BSTO) thin films were grown on TiN buffered Si (0 0 1) substrates by PLD method and the effects of deposition temperature on their crystallinity and microstructure were studied. BSTO thin films were prepared with substrate temperature ranging from 350 to 650 °C. The BSTO films grown at below 400 °C showed amorphous phase and the film grown at 450 °C showed mixed phase of crystalline and amorphous, where crystalline phase was observed only at the top surface portion of the film. The BSTO films with fully crystalline phase were obtained in the samples deposited at above 500 °C. The (0 0 l) preferred orientation and the crystallinity of the BSTO films were improved with increasing the temperature. The dielectric constant, measured at 100 kHz and at room temperature, of the BSTO film grown at 650 °C was measured to be as high as 1129.     

Synthesis of KTiOPO4 (KTP) Thin Films Using Metallo-organics

Crack-free and highly transparent KTiOPO₄ (KTP) thin films were synthesized by the sol-gel method using a homogeneous precursor solution prepared from ("BuO)₂-P(O)(OH), Ti(OEt)₄, and KOEt in EtOH. Precipitated powders from the solution crystallized directly to KTP above 550°C. Polycrystalline KTP thin films were obtained at 600°C on various substrates. On NdAlO₃(100) substrates, KTP films with (101) and (240) preferred orientations were formed at 600°C. KTP films on glass substrates showed a refractive index of 1.75 and an absorption edge of 350 nm. KTP films exhibited the second harmonic generation of the 532 nm light on irradiaton with 1064 nm light.     

PbTiO3–PbO–SiO2 Glass-Ceramic Thin Film by a Sol–Gel Process

PbTiO₃(PT)-PbO-SiO₂ glass-ceramic thin films were pro-duced by a sol-gel process. The crystallization of PT oc-curred at ∼700°C and was higher than that in PT-PbO-B₂ O₃ sol-gel glass-ceramics. A pinhole-free thin film was obtained by a rapid thermal annealing process when the designed glass-forming phase content in the thin film was >24 vol%. The measured dielectric constants of the films fairly agreed with the predicted values, based on a parallel mixing model. The dielectric constant was 219 and the di-electric loss was 0.04 in the 0.6PT-0.4(PbO-SiO₂) film that was fired at 700°C.     

Properties of Liquid-Phase Deposited Silica Films for Low-k Dielectric Applications

Both the electrical and mechanical properties of silica thin films deposited by liquid phase deposition (LPD) have been evaluated in this study. Silica thin films have been prepared on glass surface by immersing it in a supersaturated Hexafluorosilicic acid (H₂SiF₆)-based solution at a low temperature of 50°C. The as-deposited LPD silica films exhibit a low dielectric constant ( k ) that varies from 1.7 to 2.7 depending on the film morphology and fluorine content of the film. Young's modulus of these films was measured in the range of 18.9–24.5 GPa by a nanoindentation technique. The combination of extremely low k and fairly high modulus made this low-temperature-processed LPD silica films a very promising candidate for an interlayer dielectric film for the next-generation semiconductor devices.