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.     

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.     

Electrical Properties of the Ta-RuO2 Diffusion Barrier for High-Density Memory Devices

The electrical properties of a Ta layer prepared with and without RuO₂ addition were investigated. The Ta + RuO₂/TiSi₂/poly-Si/SiO₂/Si contact system exhibited lower total resistance and ohmic characteristics up to 800°C. Meanwhile, the Ta/TiSi₂/poly-Si/SiO₂/Si contact system showed higher total resistance and nonohmic behavior after annealing at 650°C, attributed to the oxidation of both Ta and TiSi₂ layers. In the former case, a Ta + RuO₂ diffusion barrier showed an amorphous Ta microstructure and embedded RuO _x nanocrystals in the as-deposited state. The conductive RuO₂ crystalline phase in the Ta + RuO₂ film was formed by reaction between the nanocrystalline RuO _x and oxygen indiffused from air during annealing. When the Ta layer was deposited with RuO₂ addition, therefore, both the electrical properties and the oxidation resistance of the Ta + RuO₂ diffusion barrier were better than those of TiN, TaN, and Ta-Si-N barriers.     

Preparation of Lead Zirconate Titanate Thin Films Derived by Hybrid Processing: Sol-Gel Method and Laser Ablation

Thin films of Pb(Zr_0.52Ti_0.48)O₃ (PZT) were prepared by hybrid processing (sol-gel and excimer laser ablation) on Pt/Ti/SiO₂/Si substrates. Crystalline phases and microstructures of the PZT films were investigated by X-ray diffraction analysis and scanning electron microscopy, respectively. Electrical properties of the films were evaluated by measuring their P - E hysteresis loops and dielectric constants. The temperature of postdeposition annealing in hybrid processing was lower than that in the case of direct film deposition by laser ablation on a Pt/Ti/SiO₂/Si substrate. The preferred orientation of the films derived by hybrid processing could be controlled using the seeding layer deposited by the sol-gel process. The films fabricated by hybrid processing consisted of the perovskite phase with a (111) preferred orientation and had good ferroelectric properties.     

Silicon Carbide Films by Laser Pyrolysis of Polycarbosilane

Thin films of polycarbosilane were deposited on Si and SiO₂ substrates. Instead of conventional oven annealing (high temperatures, inert atmosphere), laser pyrolysis was used to achieve the polymer-to-ceramic conversion. In some conditions, especially when laser radiation absorption was enhanced by depositing a carbon layer on the surface of as-deposited films or by embedding graphite particles, this processing method yielded SiC ceramic coatings, without damaging the substrate. Processing in air or low vacuum did not result in oxidized coatings, contrary to what happens for oven pyrolysis. Laser-converted films were similar to oven-heated films processed at 1000° to 1200°C.     

Microstructure of Molybdenum Disilicide-Silicon Carbide Nanocomposite Thin Films

Composite thin films of molybdenum disilicide-silicon carbide (MoSi₂-SiC) have been deposited via rf magnetron sputtering onto molybdenum substrates. An intermediate layer was deposited in the presence of nitrogen gas and evaluated as a potential diffusion barrier layer. The composite films have been characterized using X-ray diffractometry, scanning electron microscopy, transmission electron microscopy, and Auger electron spectroscopy. The as-deposited films were amorphous but crystallized into nanometer-sized grains after annealing under vacuum at 1000°C for 30 min. There was a significant amount of interdiffusion between the film and substrate, which resulted in the formation of subsilicides such as Mo₅Si₃ and MoSi₃, as well as Mo₂C. The films that were deposited via reactive sputtering in a nitrogen ambient were amorphous in both the as-deposited and annealed conditions. Significantly fewer second phases were detected with the presence of the intermediate layer, which suggests the potential use of the nitrided (MoSi _x N _y C _z ) layer as a high-temperature diffusion barrier layer for the silicon and carbon.     

Titanium Diffusion into (K0.5Na0.5)NbO3 Thin Films Deposited on Pt/Ti/SiO2/Si Substrates and Corresponding Effects

Lead-free (K_0.5Na_0.5)NbO₃ (KNN) thin films were prepared on Pt/Ti/SiO₂/Si substrates by a sol–gel processing method, and titanium diffusion from the substrates into the KNN films under different thermal treatment conditions were investigated by the secondary ion mass spectroscopy depth profile and X-ray photoelectron spectroscopy surface analysis. Titanium diffusion was evident in all the KNN thin films, which was further aggravated not only by increasing the annealing temperature, but also surprisingly by higher ramping rate attributed to the resulting larger grain boundaries. The pronounced effects of the titanium diffusion and the resulting substitution of Ti⁴⁺ for Nb⁵⁺ with different valence states on the composition, structure, and electrical properties of the KNN thin films are analyzed and discussed. The results showed that the Ti diffusion from the substrate played a crucial role in affecting the structure and electrical properties of the ferroelectric KNN thin films deposited on Pt/Ti/SiO₂/Si substrate.     

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.     

Preparation of a Monodispersed Suspension of Barium Titanate Nanoparticles and Electrophoretic Deposition of Thin Films

A transparent and stable monodispersed suspension of nanocrystalline barium titanate was prepared by dispersing a piece of BaTiO₃ gel into a mixed solvent of 2-methoxyethanol and acethylacetone. The results of high-resolution transmission electron microscopy (HR-TEM) and size analyzer confirmed that the BaTiO₃ nanoparticles in the suspension had an average size of ∼10 nm with a narrow size distribution. Crystal structure characterization via TEM and X-ray diffraction indicated BaTiO₃ nanocrystallites to be a perovskite cubic phase. BaTiO₃ thin films of controlled thickness from 100 nm to several micrometers were electrophoretic deposited compactly on Pt/Ti/SiO₂/Si substrates. The deposited thin film had uniform nanostructure with a very smooth surface.     

Multiferroic BiFeO3 Thin Films Buffered by a SrRuO3 Layer

Multiferroic BiFeO₃ thin films of huge polarization have been successfully realized by using SrRuO₃ as a buffer layer on a Pt/TiO₂/SiO₂/Si substrate. They consist of a single perovskite phase and are nearly randomly orientated, where the SrRuO₃ buffer layer lowers the crystallization temperature and improves the crystallinity of BiFeO₃. With increasing deposition temperature during magnetron sputtering, they undergo an apparent grain growth and reduction in surface roughness. The multiferroic thin films deposited on the SrRuO₃-buffered Pt/TiO₂/SiO₂/Si substrate at higher temperatures show much improved polarization and reduced coercive field, together with a lowered leakage current. A huge remnant polarization (2 P _r) of 150 μC/cm² and a coercive field (2 E _c) of 780 kV/cm were measured for the BiFeO₃ film deposited at 650°C.     

Synthesis of Highly Oriented Lead Zirconate–Lead Titanate Film Using Metallo-organics

Crack-free Pb(Zr,Ti)O₃ (PZT) thin films with preferred orientation were prepared successfully on MgO (100), SrTiO₃ (100), and Pt/Ti/SiO₂/Si substrates from metal alkoxide solutions. Calcination of precursor films in a H₂O─-O₂ gas mixture was found to be effective not only for low-temperature crystallization of perovskite PZT, but also for obtaining the preferred orientation of PZT films. Single-phase PZT films with high preferred orientation were synthesized on MgO (100) and Pt/Ti/SiO₂/Si substrates at 550° and 600°C for 2 h, respectively. The PZT film on the Pt/Ti/SiO₂/Si substrate showed a permittivity of 520, tan δ of 0.03, a remanent polarization of 24 μC/cm², and a coercive field of 54 kV/cm.     

TEM Characterization of Single- and Multilayer Triol-Based Sol–Gel PZT (53/47) Thin Films

Integrated lead zirconate titanate thin films deposited on Pt/Ti/SiO₂/Si substrates using a novel triol-based route were characterized using X-ray diffraction and transmission electron microscopy. Crack-free single-layer PZT films of up to 200 nm thick were prepared by triol-based sol–gel processing onto Pt/Ti/SiO₂/Si substrates. Films ∼75 nm thick exhibited a microstructure free of pores and second phase. As film thickness increased, film texture changed from {100} to {111} perovskite. Essentially, single-phase multilayer films could be prepared by the deposition and pyrolysis of several 75 nm layers, followed by a single crystallization step. The influence of heat-treatment schedule on the microstructure and orientation of the multilayer films is discussed. Comparison has been made between multilayer films prepared using the triol-based sol and an inverted mixing order/acetic acid-based sol.     

Preparation of 0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 Thin Films Via a Polyvinylpyrrolidone-Assisted Aqueous Sol–Gel Process and Dielectric Properties

Pb(Mg_1/3Nb_2/3)O₃–PbTiO₃ (PMN–PT) thin films were prepared by spin coating using aqueous solutions of metal salts containing polyvinylpyrrolidone, where niobium oxide layers and lead—magnesium–titanium oxide layers were laminated on Pt(111)/TiO _x /SiO₂/Si(100) substrates and fired at 750° or 800°C. 250 ± 20 nm thick 0.7PMN–0.3PT thin films of a single-phase perovskite could be prepared, and the film fired at 750°C had dielectric constants and dielectric loss of 1900 ± 350 and 0.13 ± 0.03, respectively, exhibiting polarization-electric field hysteresis with a remanent polarization of 5.1 μC/cm² and a coercive field of 21 kV/cm.     

Texture Control of Sol-Gel Derived Pb(Mg1/3Nb2/3)O3–PbTiO3 Thin Films Using Seeding Layer

Lead magnesium niobium titanate (PMNT) thin films with a composition near the morphotropic phase boundary were prepared on conventional Pt(111)/Ti/SiO₂/Si substrates using a modified sol-gel process. A PbO seeding layer was introduced to the interface between the PMNT layer and the substrate to enhance the [001]-preferential orientation of the PMNT film. Single-phase perovskite PMNT films with highly [001]-preferential orientation were obtained at reduced annealing temperatures compared with the PMNT films directly deposited on the same substrates. The dielectric and ferroelectric properties of the prepared PMNT films were evaluated as a function of annealing temperature.     

Lead Zirconate Titanate Thin Films by Aerosol Plasma Deposition: Microstructure Analysis

Lead zirconate titanate (Pb(Zr,Ti)O₃, PZT) thin films were grown on silicon 〈100〉 substrate by aerosol plasma deposition (APD) using solid-state-reacted powder containing donor oxide Nb₂O₅ when keeping the substrate at room temperature and 200°C. Crystalline phases of the deposited films have been analyzed via X-ray diffractometry (XRD), and microstructure via scanning and transmission electron microscopy (SEM and TEM). Cross-sectional TEM revealed that the microstructure comprised several layers including the deposited PZT film and the platinum-electrode-and-titanium-buffered layers on SiO₂–Si substrate. The Pt-electrode layer contained (111)_Pt twinned columnar grains with a slight misorientation and forming low-angle grain boundaries among them. The PZT layer contained randomly oriented grains embedded in an amorphous matrix. Some of the PZT grains, oriented with the zone axis Z = [[Twomacr]11]_PZT parallel to Z = [111]_Pt, were grown epitaxially on the Pt layer by sharing the (111)_PZT plane with the (111)_Pt twinned columnar Pt crystals. However, the existence of such an orientation relationship was confined to several nanosize grains at and near the PZT-Pt interface, and no gross film texture has been developed. An amorphous grain boundary phase, generated by pressure-induced amorphisation (PIA) in the solid state, was identified by high-resolution imaging. Its presence is taken to account for the densification of the PZT thin films via a sintering mechanism involving an amorphous phase on deposition at 25° and 200°C.     

Effect of Orientation on the Ferroelectric Behavior of (Pb,Sr)TiO3 Thin Films

Pb_0.6Sr_0.4TiO₃ (PST) ferroelectric thin films were prepared on two different substrates by sol–gel methods. Films derived on the LaNiO(LNO)/Pt/Ti/SiO₂/Si substrates showed a strong (100) preferred orientation. The PST thin films grown on the LNO/Pt/Ti/SiO₂/Si(100) substrate showed a non-uniform rounded grain size distribution and have a larger polarization and lower coercive field E _c. The dependence of electrical properties derived on the Pt/Ti/SiO₂/Si and LNO/Pt/Ti/SiO₂/Si substrates has been studied, with a focus on the change of dielectric constant versus direct current (DC) bias field. The dielectric and ferroelectric properties of the Pb_0.6Sr_0.4TiO₃ thin films deposition on two kinds of substrates were investigated as a function of temperature, frequency and DC bias field.     

Effects of Heating Profiles on the Orientation and Dielectric Properties of 0.5Pb(Mg1/3Nb2/3)O3-0.5PbTiO3 Thin Films by Chemical Solution Deposition

0.5Pb(Mg_1/3Nb_2/3)O₃-0.5PbTiO₃ thin films were prepared on Pt(111)/Ti/SiO₂/Si(100) substrates by varying the film formation procedures and heating processes. Depending on the multilayer film formation and appropriate heating process, the films were grown with a preferential orientation. The films showed a (100)-preferred orientation and large grain-size distribution when they were directly heat-treated after deposition of amorphous layers. The films showed a (111)-preferred orientation and small grain-size distribution when formed layer-by-layer or directly heating amorphous thin films with a perovskite seed layer. These results were explained by the effect of a seed layer. Saturation polarization of the (111)-preferred films was ∼35 µC/cm², which was somewhat higher than that of the (100)-preferred film. In contrast, the dielectric constant of the (100)-preferred film was ∼1600, which was larger than that of the (111)-preferred film.     

Use of Transmission Electron Microscopy for the Characterization of Rapid Thermally Annealed, Solution-Gel, Lead Zirconate Titanate Films

The microstructure and preferred orientations of rapid thermally annealed Pb(Zr_0.53,Ti_0.47)O₃ films, deposited on Pt/Ti/SiO₂/Si electrode/substrates by solution-gel spinning, have been investigated using analytical and high-resolution electron microscopy and X-ray diffraction. The temperature of pyrolysis of the PZT films was found to influence the preferred orientation of the film: lower temperatures (350°C) favored a (111) orientation, whereas higher temperatures (420°C) favored a (100) orientation. Excess Pb was used to control the A-site stoichiometry of the film particularly at the film surface where Pb-deficient crystals could often be observed. The absence of these crystals was shown to be correlated with an improvement in the dielectric response.     

Effect of Low-Energy Accelerated Ion Bombardment on the Properties of Metal-Organic Decomposition Derived SrBi2(Ta,Nb)2O9 Thin Films Processed at Low Temperature

Ferroelectric SrBi₂(Ta,Nb)₂O₉ (SBTN) thin films were deposited on Pt (200 nm)/TiO _x (40 nm)/SiO₂ (100 nm)/Si substrates by metal-organic decomposition. The effects of bombardment from accelerated argon and oxygen ions on the properties of SBTN thin films were investigated. It was found that the argon ion bombardment could decrease the crystallization temperature owing to the increase of internal energy of the films. Also, the oxygen vacancies at the interface between the SBTN film and platinum bottom electrode or at grain boundaries in the film were passivated through the oxygen ion treatment, resulting in the improved electrical properties. By optimizing the process parameters and using bombardment of accelerated argon and oxygen ions, SBTN films with good ferroelectric and electrical properties could be obtained, at a temperature as low as 650°C.     

Effects of Plasma Bombardment on the Initial Growth of (Ba,Sr)TiO3 Films and Their Properties

Magnetron-sputtered (Ba,Sr)TiO₃ films were grown on Pt/SiO₂/Si and MgO substrates that were located inside and outside the plasma region. The effects of plasma bombardment on the properties of the grown films were observed. The films that were grown outside the plasma region exhibited better crystallinity, higher dielectric constants, higher electrical conductivity, and rougher surfaces than those that were grown inside the plasma region. However, plasma bombardment did not affect the initial growth of the films on Pt/SiO₂/Si or MgO substrates, as explored by atomic force microscopy. The films that were grown on Pt/SiO₂/Si showed island growth characteristics, whereas those that were grown on MgO substrates revealed layer-by-layer growth characteristics. Possible explanations for the different growth mechanisms are provided.