Effect of Precursor Pyrolysis on the Dielectric Properties of Hydrothermally Derived Barium Titanate Thin Films

BaTiO₃ thin films were processed hydrothermally on Ag-coated quartz substrates at 90°C by reacting films of titanium dimethoxy dineodecanoate (TDD) in aqueous solutions of Ba(OH)₂. Two reaction sequences were used: either the TDD was reacted directly in aqueous Ba(OH)₂, or the TDD was first pyrolyzed in air at temperatures ranging from 200° to 500°C before hydrothermal reaction. Depending on the processing conditions, the dielectric constant of the thin films ranged from 5 to 170, the dielectric constant increasing with increasing pyrolysis temperature. Thin film porosimetry data suggest that the improvement in film dielectric performance is related to decreases in thin film residual porosity after hydrothermal reaction.     

Ruddlesden–Popper Planar Faults and Nanotwins in Heteroepitaxial Nonstoichiometric Barium Titanate Thin Films

Nonstoichiometric 10-mol%-excess-BaO–BaTiO₃ (Ba_1.1TiO_3.1) thin film grown on a (100) SrTiO₃ substrate consisted of heteroepitaxial c -axis-oriented BaTiO₃ perovskite crystals including Ruddlesden–Popper planar faults and nanometer-scale multiple (111) twin lamellae. High-resolution electron microscopy and electron energy-loss spectroscopy revealed that nanotwins with coherent (111) Σ3 coincident site lattice boundaries were terminated in the BaTiO₃ matrix to form incoherent (211) Σ3 boundaries accommodating excess barium ions. Both Ruddlesden–Popper planar fault and incoherent (211) boundary formation were proposed as possible accommodation mechanisms of excess barium ions in the perovskite film.     

Hydrothermal Synthesis of Thin Films of Barium Titanate Ceramic Nano-Tubes at 200°C

A novel, low-temperature synthesis method for producing BaTiO₃ thin films patterned in the form of nano-tubes ("honeycomb") on Ti substrates is reported. In this two-step method, the Ti substrate is first anodized to produce a surface layer (∼200–300-nm thickness) of amorphous titanium oxide nano-tube (∼100-nm diameter) arrays. In the second step, the anodized substrate is subjected to hydrothermal treatment in aqueous Ba(OH)₂, where the nano-tube arrays serve as templates for their hydrothermal conversion to polycrystalline BaTiO₃ nano-tubes. This opens the possibility of tailoring the nano-tube arrays and of using various precursor solutions and their combinations in the hydrothermal bath, to produce ordered, patterned thin-film structures of various Ti-containing ceramics. These could find use not only in a variety of electronic device applications but also in biomedical applications, where patterned thin films are also desirable.     

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.     

Preparation of Tetragonal Barium Titanate Thin Film on Titanium Metal Substrate by Hydrothermal Method

Tetragonal BaTiO₃ thin films were prepared directly on Ti metal substrates in Ba(OH)₂ solutions by a hydrothermal method at temperatures 400° to 800°C for 5 to 240 min. The film thickness estimated from weight gain of Ti plate was in the range from 0.5 to 2.5 μm, and it increased with increasing treatment temperature, treatment time, and Ba(OH)₂ concentration. Rectangular crystals having {100} and {001} faces grew idiomorphically with approximate crystal size of 0.3 to 2.0 μm. The tetragonality of the BaTiO₃ films became apparent when the average crystal size exceeded about 1 μm. Lattice parameters of the films were a = 3.994 Å, c = 4.035 Å, and c/a = 1.010. The films formed above 600°C had preferred orientation showing stronger XRD peaks of h 00 and 00 l than the other peaks.     

Nucleation and Inhibition Control during the Hydrothermal–Electrochemical Growth of Barium Titanate Films

The control of the microstructure of BaTiO₃ films grown on titanium by the hydrothermal–electrochemical method was investigated. Experiments were conducted in a three-electrode high-pressure electrochemical cell in a 0.1 M Ba(OH)₂ electrolyte at 150°C. Results showed that the spontaneous initial nucleation linked to pure hydrothermal BaTiO₃ formation can be inhibited by cathodically protecting the titanium electrode from the moment it is immersed in the electrolyte. The application of initial nucleation pulses of varying cathodic potentials affected the grain size of the deposit. It is suggested that the formation of a titanium oxide layer is a necessary step previous to the nucleation of BaTiO₃.     

高分子辅助沉积法在镍基片上制备的钛酸钡薄膜的漏电机制

采用高分子辅助沉积法在多晶镍衬底上,以氧化镍作为缓冲层,生长了多晶钛酸钡(BaTiO3,BTO)薄膜。对其漏电特性测试及分析发现,在测试电压区间和极性不同时,分别具有不同的漏电机制,可分别用Frankel-Pool emission,space charge limited current(SCLC)与Schottky emission等机制来描述。由于界面缓冲层分解以及界面扩散等原因,BTO/Ni界面呈现Ohmic接触,而Au/BTO界面呈现Schottky势垒接触。通过测量不同温度下的漏电流大小,得到Au/BTO界面的有效势垒为0.32eV,从而得到Au/BTO/Ni能带结构图。利用一阶线性电路模型对其界面电阻与体电阻进行计算,得到的界面电阻与体电阻大小及变化趋势与实验及理论相符合。     

Crystallization of Sol–Gel-Derived Barium Strontium Titanate Thin Films

Microstructural development of thin-film barium strontium titanate (Ba _x Sr_{1– x} TiO₃) as a function of strontium concentration and thermal treatment were studied, using transmission electron microscopy (TEM) and X-ray diffractometry (XRD). Thin films, ∼250 nm thick, were spin-coated onto Pt/Ti/SiO₂/Si substrates, using methoxypropoxide alkoxide precursors, and crystallized by heat-treating at 700°C. All films had the cubic perovskite structure, and their lattice parameters varied linearly with strontium content. Films with higher strontium concentrations had a larger average grain size. In situ TEM heating experiments, combined with differential thermal analysis/thermogravimetric analysis results, suggest that the gel films crystallize as an intermediate carbonate phase, Ba _x Sr_{1– x} TiO₂CO₃ (with a solid solution range from x = 1 to x = 0). Before decomposition at 600°C, this carbonate phase inhibits the formation of the desired perovskite phase.     

Optical Properties of Barium Strontium Titanate (BST) Ferroelectric Thin Films

Barium strontium titanate (Ba_0.05Sr_0.95TiO₃) ferroelectric thin films have been prepared on single crystal [001] MgO substrates using the pulsed laser deposition method. The X-ray diffraction (XRD) analysis show the films were oriented with the [001] direction perpendicular to the plane of the substrate. The refractive index of Ba_0.05Sr_0.95TiO₃ is determined from model fitting with the calculated data of the reflectivity of Ba_0.05Sr_0.95TiO₃ in the wavelength 1450-1580 nm at the room temperature. The dispersion curve decreases gradually with increasing wavelength. The average value of the refractive index is found to be 1.985 in the wavelength 1450-1580 nm which is important for optoelectronic device applications.     

Dielectric Properties of Fluxed Barium Titanate Ceramics with Zirconia Additions

BaTiO₃ compacts, when fluxed with <2 vol% of a complex borate glass phase, were sintered to near theoretical density at temperatures <1175°C in 2 h. Microstructural analysis showed a uniform grain size <1.0 μm with 0.75 wt% ZrO₂ added to the flux phase as a grain growth inhibitor. TEM analysis revealed a microcrystalline grain-boundary phase with the ZrO₂ resident along the grain boundaries. These samples displayed an essentially flat dielectric profile, low dissipation factors (<2%) over the range 25° to 125°C, a near linear dependence (≅±15%) between 25° and −55°C, and significantly increased voltage stability. X-ray diffraction analyss of these small-grained materials indicated a suppression of the tetragonal structure toward a more cubic modification.     

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.     

钽掺杂对钛酸钡基陶瓷介电性能影响的研究

研究了微量钽掺杂对钛酸钡基陶瓷介电常数、介电损耗以及温度稳定性等介电性能的影响.利用XRD、SEM等现代分析手段分析了材料的显微结构,分析了显微结构与材料介电性能的关系,得到了性能较为优良的电容器基料配方.     

Anomalous Grain Growth in Donor-Doped Barium Titanate with Excess Barium Oxide

Grain growth and semiconductivity of donor-doped BaTiO₃ceramics with an excess of BaO and additions of SiO₂or B₂O₃were studied. The microstructures and electrical measurements on sintered samples revealed that their electrical properties are related to the microstructure development of the sintered samples. Samples heated with an excess of BaO developed a normal microstructure during sintering, as a consequence of normal grain growth (NGG), and were yellow and insulating. In contrast, samples with an excess of BaO and an addition of SiO₂or B₂O₃exhibited anomalous grain growth (AGG) and were dark blue and semiconducting after sintering. When some BaTiO₃seed grains were embedded in a sample of donor-doped BaTiO₃with an excess of BaO (without SiO₂or B₂O₃), AGG was observed, i.e., some seed grains grew into large grains and were blue and semiconducting. An explanation is given for why AGG is responsible for the oxygen release and the formation of semiconducting grains in donor-doped BaTiO₃and not NGG.     

Properties of Lead Zirconate Titanate Thin Films Prepared Using a Triol Sol–Gel Route

Microstructure and phase development during the thermal decomposition of sol–gel precursor coatings of PbZr_0.53Ti_0.47O₃ on platinized silicon substrates have been investigated for a triol sol–gel route. The single-layer, 0.4 μm PZT films were heated from below the substrate, over the temperature range 350–600°C, using a calibrated hot plate. The first crystalline phase to appear was a PbPt₃ intermetallic phase at the Pt/PZT interface. Although perovskite PZT formed at ca. 500°C, heating at higher temperatures, for example 550°C for 30 min, was required to develop ferroelectric hysteresis loops. However, the rather low value of remanent polarization, P _r= 11 μC·cm⁻², was consistent with incomplete crystallization at 550°C. The values of remanent polarization increased with increasing processing temperatures, reaching 21 μC·cm⁻² for samples heated at 600°C, with a corresponding E _c value of 57 kV·cm⁻¹. Distinctive spherical precipitates up to ca. 50 nm in size have been identified by TEM in the lower portions of otherwise amorphous coatings, after heating at around 350–400°C. Although their precise composition could not be identified, they were mostly Pb-rich, and it is speculated that they form due to reduction of some of the lead(II) acetate starting reagent, to atomic Pb during the early stages of thermal decomposition of the organic components of the gel; it is possible that subsequent reactions occur to form lead oxides or carbonates. High levels of porosity were present in many of the fully crystallized films. The possible reasons for this are discussed.     

Effect of Lead Zirconate Titanate Seeds on PtxPb Formation during the Pyrolysis of Lead Zirconate Titanate Thin Films

Lead zirconate titanate (PZT) thin films were prepared on platinized silicon substrates by dip-coating using a modified diol-based sol–gel route without and with up to 5 mol% PZT nanometric seeds dispersed in the precursor sol. A metastable intermetallic Pt _x Pb phase formed at the early stages of heat treatment. XRD, TEM, and RBS revealed that the thickness and stoichiometry of the Pt _x Pb layer varied with the concentration of seeds and heat treatment of the films. The relation of the Pt _x Pb layer to the final crystalline texture of the PZT thin films is reported and discussed.     

Effects of Excess Barium Ions on Aqueous Barium Titanate Tape Properties

The effects of excess free barium ions in aqueous barium titanate slip on the resulting BaTiO₃ tape properties were investigated in terms of the slip behavior, green/sintered tape density and morphology, and dielectric properties. The excess free barium ions expressed by means of the Ba/Ti ratio adversely affected most tape properties. Increase in the slip viscosity, green porosity, and agglomeration along with a decrease in mechanical properties and green/sintered density were found with the increase in the Ba/Ti ratio. However, dielectric permittivity was increased with increase in the Ba/Ti ratio. An effort was made to correlate these phenomena with Ba²⁺ leaching in water for realistic multilayer ceramic capacitor applications.     

Microwave Dielectric Properties of Gallium-Doped Hexagonal Barium Titanate Ceramics

High-permittivity and low-loss ceramics with composition BaTi_0.92Ga_0.08O_2.96 have been prepared in the BaO–Ga₂O₃–TiO₂ system using the mixed-oxide route. This compound forms as the hexagonal polymorph (6 H ) of BaTiO₃ with the space group P 6₃/ mmc . The dielectric properties of dense ceramics have been studied, at microwave frequencies, with the ceramics fired at 1450°C under flowing oxygen gas; the results are a relative permittivity, ɛ_r, of ∼74 and a quality factor, Q · f _r, of ∼7815 at 5.5 GHz. The quality factor is strongly influenced by the sintering conditions (temperature and atmosphere), whereas the relative permittivity is not influenced significantly by ceramic processing for pellets ≥93% of the theoretical X-ray density. To our knowledge, this is the first report of microwave dielectric resonance in a perovskite-type BaTiO₃-based ceramic.     

Microstructure of Solution-Processed Lead Zirconate Titanate (PZT) Thin Films

Lead zirconate titanate (PZT) thin films with a composition near the morphotropic phase boundary (Zr/Ti = 53/47) were fabricated by spin deposition of an alkoxide-derived solution and annealed at 650°C for 30 min. A complex microstructure is observed in which micrometer-scale rosettes of the desired perovskite phase are surrounded by nanocrystalline (10 to 15 nm) grains of pyrochlore structure. Transmission electron microscopy (TEM) demonstrates that the perovskite rosettes—features of approximately circular cross section which grow rapidly within the confined conditions of the thin film—are single crystals despite being highly porous. Pockets of lead-deficient pyrochlore extend throughout the thickness of the film. The only effects of Nb (2%) doping on the microstructure are to increase the fraction of the perovskite phase and the perovskite grain size. Despite the highly irregular shape of the perovskite particles and the presence of some pyrochlore, reasonable ferroelectric properties are measured (spontaneous polarization P _s∼ 0.2 C/m²).     

Lead Zirconate Titanate Thin Films on Base-Metal Foils: An Approach for Embedded High-Permittivity Passive Components

An approach for embedding high-permittivity dielectric thin films into glass epoxy laminate packages has been developed. Lead lanthanum zirconate titanate (Pb_0.85La_0.15(Zr_0.52Ti_0.48)_0.96O₃, PLZT) thin films were prepared using chemical solution deposition on nickel-coated copper foils that were 50 μm thick. Sputter-deposited nickel top electrodes completed the all-base-metal capacitor stack. After high-temperature nitrogen-gas crystallization anneals, the PLZT composition showed no signs of reduction, whereas the base-metal foils remained flexible. The capacitance density was 300–400 nF/cm², and the loss tangent was 0.01–0.02 over a frequency range of 1–1000 kHz. These properties represent a potential improvement of 2–3 orders of magnitude over currently available embedded capacitor technologies for polymeric packages.     

Texture Development in Modified Lead Titanate Thin Films Obtained by Chemical Solution Deposition on Silicon-Based Substrates

An advanced method of X-ray diffractometry analysis, the quantitative texture analysis, is used in this work to study the preferential orientations of ferroelectric lanthanum-modified lead titanate thin films, to establish the factors affecting their development. The new, more reliable, texture data obtained allows us to discuss previous models of texture development in chemical-solution-deposited films. The results show that a fiber type, mixed <100>,<001> preferential orientation, is obtained when high heating rates are used during crystallization. The degree of texture of these films decreases when successive layers are deposited before a simultaneous crystallization of the ensemble is conducted. This undesirable effect is avoided through layer-by-layer crystallization, because of the preferential nucleation of <100>,<001> crystals at the interface between layers. The use of a titanium layer on the platinized silicon-based substrate leads to the development of an additional fiber <111> texture component. In this case, the layer-by-layer crystallization process cannot avoid the loss of the degree of orientation (texture index) with the increase of film thickness. This is mainly caused by the appearance of interlayer porosity, which disrupts the growth of <111>-oriented grains into upper layers.