Low-temperature synthesis of barium titanate thin films by nanoparticles electrophoretic deposition

The nanoparticles electrophoretic deposition (EPD) of barium titanate (BaTiO₃ or BTO) thin films was investigated. BTO nanocrystallites in a pseudocubic perovskite phase with an average particle size of about 10 nm were synthesized at a low temperature of 90°C by a high-concentration sol–gel process. By using a mixed solvent of 2-methoxyethanol and acetylacetone as dispersing medium, transparent and well-dispersed BTO nanocrystallites suspensions within the concentration range of 0.0125 to 0.20 mol/l was successfully prepared for nanoparticles EPD. A uniform microstructure and a smooth surface were observed on the deposited films. The film thickness of the deposited films increased rapidly with increasing EPD time in the initial period of EPD, and thereafter gradually increased to a limited thickness. With increasing applied EPD voltage, the limited film thickness increased. A near linear relation between the film thickness of films and the concentration of suspensions was observed under the same EPD conditions. The microstructures of the deposited BTO thin films were investigated.     

Influence of substrate orientation on structural,ferroelectric and piezoelectric properties of hexagonal YFeO<Subscript>3</Subscript> films

In this study, we fabricated hexagonal YFeO₃ films on Si(100) and Si(111) substrates by a sol-gel method, and investigated the effect of substrate orientation on the structural, ferroelectric and piezoelectric properties of the YFeO₃ films. Grazing incidence X-ray diffraction reveals that the YFeO₃ films on Si(100) and Si(111) have slight preferred-orientation in (110) and (004) direction, respectively. Both films possess granular microstructure with good crystallization, as well as low surface roughness. The (004)-oriented film has higher density than the (110)-oriented film, resulting in lower leakage current. The two films show weak ferroelectric properties and different domain structures. Local amplitude and phase response loops manifest that the film on Si(111) possesses larger phase change and coercive field. While influenced by polarization rotation towards the applied field direction, larger effective piezoelectric coefficient d₃₃ of 67 pm/V has been found in the film on Si(100). These findings suggest that preferred orientation can account for the physical properties of multiferroic YFeO₃ films.     

Properties of (001)-textured Pb(Mg1/3Nb2/3)O3–PbTiO3 thin films

Relaxor ferroelectric Pb(Mg_1/3Nb_2/3)O₃–PbTiO₃ (PMN–PT) thin films with [001] preferential orientation were deposited on platinized silicon wafers by a sol–gel method, in which a PbO seeding layer was involved. The influences of annealing temperature on the crystal phase, microstructure, and electrical properties of the PMN–PT films were investigated. Pyrochlore-free perovskite PMN–PT films could be formed on PbO-seeded Pt(111)/Ti/SiO₂/Si wafers at 800 °C, which was also the optimal annealing temperature for endowing the film with the best ferroelectric and dielectric properties. The enhanced properties were attributed to the improved crystallinity and microstructure. The leakage behaviors of the PMN–PT films annealed at different temperatures were also measured and discussed.     

EFFECTS OF DEPOSITION PARAMETERS AND FILM THICKNESS ON THE PHASES AND ELECTRICAL PROPERTIES OF Pb(Mg1/3Nb2/3)O3 THIN FILMS MADE BY MOCVD USING ULTRASONIC NEBULIZATION

ABSTRACT

PMN thin films were deposited by MOCVD using ultrasonic nebulization and the effects of deposition parameters and film thickness on the phases and electrical properties of the PMN films were investigated. The low deposition temperature and RTA treatment were favorable to deposit the PMN films with a low content of pyrochlore phase. Excess Mg enhanced the formation of perovskite phase of PMN films also. As the film thickness was increased, the portion of pyrochlore phase in PMN films was decreased. The dielectric constant of PMN films increased with the film thickness and showed the value of 25–230.     

Effect of ion damage on the crystallization of PZT thin films

Abstract

Effects of Ar ion damage prior to the phase transformation from pyrochlore to perovskite structure of PZT thin films have been investigated. As the degree of damage increased by increasing the acceleration voltage in the ion mass doping system, the phase transformation temperature decreased such that the temperature could be lowered down to 550°C when the film was damaged at 15kV for 5 minutes. When the films were damaged prior to the heat treatment, the final grain size of the perovskite thin films became less than 300Å. The microstructure showed the granular type rather than columnar structure after ion damage treatment and annealing. It turned out that relatively high value of the remanent polarization (about 30 μC/cm²) as well as improvement of the fatigue characteristics to a large extent are closely related to the fine grain size of thus obtained PZT films.     

Effect of Zr/Ti Ratio on Microstructure and Electrical Properties of Lead Zirconate Titanate Thin Films Derived by Pulsed Laser Deposition

PZT films were fabricated using various targets of Pb(Zr_xTi_{1 – x})O₃ with Zr/Ti ratios of 70/30, 58/42, 52/48, 45/55 and 30/70, and with excess PbO of 20 wt% on Pt/Ti/SiO₂/Si(100) substrates. The rosette structure was observed in the films derived from the target with a Zr/Ti ratio of 70/30 and disappeared with increasing titanium composition. The observations on surface and cross-sectional microstructure were consistent with a higher perovskite nucleation for the higher Ti content films. The PZT films derived from the target with a Zr/Ti ratio of 45/55 had a polycrystalline columnar microstructure extending throughout the thickness of the film and no pyrochlore phase on the surface was observed. The PZT films derived from the target with a Zr/Ti ratio of 45/55 exhibited better electric properties than those derived from the target with a Zr/Ti ratio of 52/48.     

Structural and electrochemical properties of Nichrome anode thin films for lithium battery

Low cost anode materials having a high electrochemical efficiency have been critical in the success of thin film batteries that are applicable in ubiquitous environments as a portable energy source. Nichrome thin films are ideally suited for use in hybrid assemblies but their applications include precision integrated circuits in fields of telecommunications, instrumentation, power supplies, military and medical equipment where low noise and good power dissipation are required. With such a wide spectrum of applications, it is important to understand the electric behavior of the Nichrome alloy thin films by their microstructure. In this work, nanocrystalline films of nickel chromium alloys were deposited on alumina substrate by radio frequency (RF) magnetron sputtering technology. High purity nickel and chromium sputtering target were used for the deposition. First, aluminum was deposited on ceramic substrate acts as a current collector and over that NiCr was deposited by RF sputtering method. Both the layers were analyzed for structural and electrical properties using X-ray diffraction (XRD), energy dispersive X-ray analysis (EDS), atomic force microscopy (AFM), scanning electron microscopy (SEM) and cyclic voltammetry. The XRD peak confirms that deposited NiCr and Aluminum have tetragonal and cubic structures, respectively. The crystallite size was determined by full width at half maximum of XRD peaks. Structure, composition and the properties of the film are the major focus of this paper. Composition ratio between nickel and chrome obtained by EDS is 1:1. Particle size and microstructure of the film have been studied by SEM and AFM. Electrochemical properties of the films were analyzed. Reaction mechanism for the insertion and excretion is reported. After Lithium insertion and extraction the effect on the surface and structure of the thin film has been studied. The composition of equilibrium phases of NiCr as useful as attracting anode for the thin film battery. Nichrome on aluminum thin films as an anode has been attracted because it provides practical advantages including low cost production and competitive electrical performance.     

Perovskite phase formation in sol-gel derived Pb(ZrxTi1−x)O3 thin films

Abstract

Thin films of lead zirconate titanate having the composition Pb_1.05(Zr_0.53Ti_0.47)O₃ were deposited by a solgel method on a set of crystalline and amorphous substrates. The thickness of the film was varied by controlling the sol concentration or by repeated coatings. Factors controlling phase formation in the films such as nature of the substrate material, film thickness, chemical composition of the film, heating rate and gaseous atmosphere during the heat treatment were studied. On glass substrates the pyrochlore phase was obtained in thin (0.4 um) films and the perovskite phase in thicker (>1.5 um) films. Crystalline substrates (except Si and stainless steel) yielded a perovskite phase in 0.6 um thick film. Low Zr/Ti ratio, rapid heating and introduction of nitrogen in the later stage of heat treatment also favoured the formation of the perovskite phase. It is shown that Pb deficiency in the film caused by diffusion of Pb into amorphous substrates or by other mechanisms is primarily responsible for inhibiting the pyrochlore to perovskite transformation. The initial crystallisation of the amorphous film into pyrochlore rather than a perovskite phase (as in powders) is proposed to be due to higher strain energy barrier which exists for the amorphous to perovskite transformation in the film.     

SrTiO3 thin films by mocvd for 1 gbit DRAM application

Abstract

Three important aspects of the preparation of SrTiO₃ thin films by MOCVD are discussed in detail in view of the application of these films as the capacitor dielectric of Gbit-scale DRAMs: CVD reactions in the Sr(DPM)₂-Ti(i-OC₃H₇)₄-O₂ system, step coverage and relations between microstructure and electrical properties. The effect of the substrate temperature on the Sr and Ti deposition rates was first investigated for thermal and ECR CVD SrTiO₃ films. SrO and TiO₂ deposition by thermal CVD above 550°C were found to be controlled by the surface reaction and gas transport, respectively, whereas both SrO and TiO₂ deposition are controlled by gas transport for ECR CVD at 450 to 600°C. The influence of the Sr and Ti deposition regimes on the step coverage of SrO, TiO₂ and SrTiO₃ were then assessed. SrO films prepared by thermal CVD at 600°C exhibited the best step coverage, indicating that a relation exists between reaction controlled deposition and good step coverage. The effect of the film composition and film thickness on the microstructure of SrTiO₃ thin films were finally investigated and correlations were made to other analyzed physical and electrical properties. Polycrystalline perovskite phase SrTiO₃ films were obtained for a composition 0.7 ≤ Sr/Ti ≤ 1.2. The best crystallinity, maximum permittivity and maximum refractive index were obtained for Sr/Ti = 0.95. Titanium rich films are thought to be composed of a mixture of a titanium rich amorphous phase and crystalline SrTiO₃, and strontium rich films are believed top correspond to a (SrTiO₃)_m (SrO)_n structure. The dielectric constant slowly decreased as the film thickness was reduced. The sharp decrease observed near 400–500 Å could be due to the existence of some perturbed layer at the interface with one or both of the electrodes     

纳米晶化对Co-FeNbZr薄膜结构及阻抗的影响

用直流磁控溅射法制备非晶Co-FeNbZr软磁膜,再用独特的快速循环纳米晶化技术(RRTA)对其进行纳米晶化.研究了不同的纳米晶化工艺条件下薄膜的微观结构和阻抗性能.结果表明,500℃退火的Co-FeNbZr软磁薄膜晶粒细化到30～40nm,阻抗值从28Ω增加到110Ω(1400MHz),阻抗共振峰向低频移动200～220 MHz左右,薄膜的软磁性能极大改善.     

Excess Bismuth-Dependent Characteristics of Chemical Solution Deposited Bi3.15La0.85Ti3O12 Thin Films

The phase formation and electrical properties of (Bi_3.15La_0.85)Ti₃O₁₂ (BLT) thin films prepared by the chemical solution deposition method on Pt/Ti/SiO₂/Si substrates have been investigated. It was observed that the microstructure and electrical properties of BLT thin films dramatically varied with the excess Bi content. The crystallographic orientation of BLT films was varied with excess Bi content and the intermediate rapid thermal annealing (RTA) process. While BLT thin films prepared without intermediate RTA process have ?117? orientation irrespective of excess Bi content, BLT thin films with RTA process at 450°C have an orientation change with excess Bi content. The leakage current of BLT thin films slightly increased with increasing excess Bi content up to 6.5% and then considerably decreased in BLT film with 10% Bi, where was revealed to be almost stoichiometric composition.     

厚度对Ni_(25)Fe_(75)-ZnO颗粒膜阻尼因子和软磁特性的影响

采用磁控溅射制备了(Ni_(25)Fe_(75))-ZnO颗粒膜,研究了其高频动态磁性与薄膜厚度的关系,用Landau-Lifshitz-Gilbert方程计算出阻尼因子,并用一个幂函数拟合与外场的关系曲线。实验结果和拟合结果表明,动态磁化时有效阻尼系数αeff和内禀阻尼系数αint均随着样品厚度减小而增大。αint和αeff变化的物理起源应该与微结构的不均匀性、薄膜与衬底之间的界面效应和薄膜中的混杂物有关。     

Phase Formations and Electrical Properties of Various (Bi, La)4Ti3O12 Thin Films by Chemical Solution Deposition

The phase formation and electrical properties of (Bi, La)₄Ti₃O₁₂ (BLT) thin film and V-, Sm-doped BLT thin films prepared by the chemical solution deposition method on Pt/TiO₂/SiO₂/Si substrates have been investigated. It was observed that the microstructure and electrical properties of BLT thin films dramatically varied with V- and Sm-doping. The crystallinity and grain size of BLT thin films were definitely increased by V- and Sm-doping into BLT films, which resulted in the enhancement of remanent polarization in doped BLT films. The remanent polarization (Pr) of Sm-doped BLT films annealed for 3 min by an RTA system was about 9 C/cm². The V- and Sm-doped BLT films also exhibited good fatigue characteristics under bipolar stressing to 10¹⁰ cycles.     

Strong thickness dependence of aurivillius phase formation in SrBi2Ta2O9 thin films

Sr_0.7Bi_2.4Ta₂O₉ (SBT) thin films were studied for the dependence of Aurivillius phase formation kinetics on their film thickness. SBT thin films were fabricated using a sol-gel process and spin coating, and their thickness was varied controlling the number of spin coating. The films were first heated at a low temperature for the complete crystallization of amorphous film to fluorite phase and then further heated at different elevated temperatures for the phase transformation to Aurivillius for 40 min. It was found that the phase transformation kinetics apparently increased with thickness up to ∼390 nm, and then it sharply decreased at higher values. The Aurivillius crystal size decreased and the density of crystals increased with the increase of film thickness up to ∼390 nm, implying increasing number of nuclei due to the reduced energy barrier for nucleation. Above the critical value both the size and density of crystals decreased. It is suggested that up to ∼390 nm the tensile strain energy in the films, which was stored by the shrinkage of thin films during the removal of remaining organic components from sol-gel chemistry, plays a major role for determining the phase transformation kinetics and above the critical value SBT films act as a free bulk material without substrate constraints.     

Epitaxy and interfacial phase in thin films of lead scandium tantalate deposited by reactive sputtering on a platinum interlayer

Abstract

Lead scandium tantalate (PST) films with a lead-rich composition were deposited at 500°C by RF sputtering on sapphire substrates coated with Pt and were investigated by cross-sectional transmission electron microscopy. The films consisted almost entirely of the perovskite phase. The grains of perovskite PST had a crystallographic orientation almost parallel to that of the underlying Pt. Some elongated voids were observed. The presence of an interfacial phase, with interplanar spacings consistent with a pyrochlore phase, was demonstrated by electron diffraction and dark-field imaging. The crystallographic orientation of this phase is also nearly parallel to that of the Pt. Energy-dispersive X-ray microanalysis showed that the interfacial phase is lead-deficient. The interfacial phase is irregular in thickness. A reduction in the Pb content of the film leads to a thicker interfacial layer. The implications for the mechanism of growth of PST on Pt and for improvement of the film quality are discussed.     

PROPERTIES OF FERROELECTRIC P(VDF-TrFE) 70/30 COPOLYMER FILMS AS A GATE DIELECTRIC

ABSTRACT

We directly formed the organic ferroelectric P(VDF-TrFE) 70/30 copolymer film by the spin coating for making the MFS structure in the silicon wafer. To understand the crystallization behavior of P(VDF-TrFE) 70/30 copolymer, the morphologies of copolymer thin films were studied by AFM and XRD. AFM studies revealed that as grown and annealed films showed surface roughness greater than amorphous films due to crystallization. The XRD spectrum of the films subjected to various annealing temperatures showed β -phase and this phase content was maximum at 140°C annealing. The capacitance shows hysteresis behavior like a buttery shape due to the polarization reversal in the film and this result indicates clearly that the film has a ferroelectric property. The dielectric constants of the P(VF₂-TrFE) copolymer films calculated from the capacitance at the two peak points of the C-V characteristics were about 8.7.     

Effect of Pyrolytic Film Thickness on the Texture Evolution of PZT Thin Films

This paper describes the effects of pyrolysis temperature and film thickness before annealing on the orientation and microstructure of the lead zirconate titanate (PZT) thin films prepared by chemical solution deposition method (CSD). Different thickness of the pyrolytic films were obtained by repeating deposition and pyrolysis with different times. The orientation and microstructures of the PZT thin films were characterized by X-ray diffractometry (XRD) and field-emission scanning electron microscope (SEM). The results show that the thickness of the pyrolytic films was the principal factor that affects the crystalline structures in PZT thin films.     

Solution chemistry effects in Pb(Zr,Ti)O3 thin film processing

Ferroelectric thin films in the PZT compositional family were prepared by two different solution deposition methodologies. The approaches were based on the use of carboxylate and alkoxide precursors, and acetic acid. Solution aging and mixing order effects on thin film microstructure and ferroelectric properties were studied. Films prepared from 15 day old solutions had a lower remanent polarization (1.4 μC/cm2) and higher coercive field (256 kV/cm) than films prepared from 1 day old solutions (Pr = 18.7 μC/cm2; Ec = 55.2 kV/cm). Raman, FTIR, and NMR spectroscopies were employed to confirm the role of acetic acid in the process, and to begin to understand why changes in solution chemistry can so dramatically affect the resulting film microstructure and properties. FTIR spectroscopy indicated that in addition to acting as a solvent, acetic acid also serves as a chemical modifier in the two processes. That is, it reacts with the alkoxide precursors on a molecular level, replacing the alkoxy ligands. Ester formation was also observed by both FTIR and NMR spectroscopy. The formation of this by-product implies the simultaneous formation of water, and therefore, in-situ hydrolysis and condensation of the precursors.     

Study on the ZnO-based ceramic films for low-voltage varistors with high stability

ZnO-based ceramic films for low-voltage varistors were fabricated by a novel sol-gel process. The stability of ZnO-based ceramic films has been studied by improving the degradation properties and increasing the microstructure compactness of the films. The degradation of the film varistors was improved via doping with Na⁺ and heat-treating in oxygen ambient. The microstructure compactness was increased via eliminating the microspores and improving uniformity of the grain size of ZnO by doping with B₂O₃. The results indicated that ZnO-based ceramic films for low-voltage varistors with high stability can be obtained while the concentration of doped Na⁺ is 20–40 ppm, B₂O₃ is 0.25–0.5 mol.% and being heat-treated in oxygen ambient for 2 h.     

Ceria-Zirconia Composite Electrolyte for Solid Oxide Fuel Cells

Ceria-zirconia-ceria sandwich structured composite filmelectrolytes were designed in order to offer high ionic and low electronicconductivity electrolyte films. Calculation of oxygen potential profile inthe composite film electrolyte indicates that a very thin zirconia filmkills the electronic current of ceria without affecting the ionicconductivity. The composite films were successfully prepared by a co-fireprocess. The main problem was the fact that the ceria and zirconia greenfilms had different shrinkage behaviors. Successful co-firing was achievedby controlling the temperature program and amount of binder. De-laminationbetween yttria stabilized zirconia(YSZ) and gadolinia doped ceria(GDC)layers was overcome by the formation of a solid solution phase at theinterface of the two films. The resultant composite films, however, showedpoor electrical conductivity compared with theoretical values. The formationof a solid solution phase can have a negative effect on compositeelectrolytes. Also, the composite film is unsatisfactory in terms ofmechanical strength. This could be due to the lattice expansion in reducingatmospheres, thermal expansion coefficient mismatch, or the intrinsicweakness of the ceria texture.