Acid-catalysed Al2O3 sol and its gel material: influence of HNO3 content and stability

Abstract

A series of Al₂O₃ sols were prepared by HNO₃ catalysis of aluminum isopropoxide (AIP), using different molar ratios of HNO₃/AIP (n_H). The changes in sol densities, viscosities, refractive indices, stability and particle sizes were reported. Derived properties such as Gibbs energies (ΔG*) and the reaction rate constant (k) have been calculated from the experimental density and viscosity data. The phase-chemical structures of Al₂O₃ materials were characterized using Fourier transform infrared (FTIR) and X-ray diffraction (XRD) measurement. The results show that, when the molar ratio of HNO₃/AIP is 0.25, the prepared Al₂O₃ sol was transparent, uniform and stable, and the sol average particle size gets the minimum. The chemical structure of the non-calcined Al₂O₃ gel material is dominated by Al–O–H and Al–O bonds. After calcination at 350?°C, the Al–O–H bond will break and is transformed into Al–O bonds, and the phase structure is changed from γ-AlOOH to γ-Al₂O₃.     

Comparison of ZrO2-SiO2 sols synthesized by two methods: Preparation,stability and physical-chemical structure

Abstract

In the present work, zirconium nitrate pentahydrate (Zr(NO₃)₄·5H₂O) was used as ZrO₂ precursors. The ZrO₂-SiO₂ sols with the Zr/TEOS molar ratios (n_Zr) ranging from 0 to 2.0 were synthesized by two different methods, which were called ZrO₂-SiO₂-1 and ZrO₂-SiO₂-2 sols, respectively. The Gibbs energies of activation for viscous flow (ΔG*) and reaction rate constants (k) of the sol system were calculated. The effects of n_Zr, ΔG* and k on the sol stability were investigated. The phase, chemical and pore structures of the two ZrO₂-SiO₂ materials calcined at 400?°C were investigated. The results show that, with the increase of n_Zr, the ρ, η and ΔG* values of the sol system increase, and the sol stability deteriorates. The ZrO₂-SiO₂-1 sol has a better stability than ZrO₂-SiO₂-2 sol. The Zr-O-Si bond was found in the ZrO₂-SiO₂-1 and ZrO₂-SiO₂-2 materials. The ZrO₂-SiO₂-2 material fired at 400?°C clearly showed sharp peaks corresponding to a crystalline tetragonal structure of zirconia, while ZrO₂-SiO₂-1 material didn’t. The ZrO₂-SiO₂-2 material has a smaller pore size than ZrO₂-SiO₂-1 material. The result reveals that preparation method of sol plays an important role in the physicochemical properties of ZrO₂-SiO₂ sol.     

Anodizing Properties of High Dielectric Oxide Films Coated on Aluminum by Sol-Gel Method

In order to obtain the high capacitance in aluminum electrolytic capacitor, ZrO₂ and Nb₂O₅ films were coated on aluminum foils by sol-gel method, and then the properties of anodized films were examined. The triple layer of ZrO₂/Al-Zr(Nb)O_x/Al₂O₃ was formed on aluminum substrates after anodizing of ZrO₂(Nb₂O₅)/Al film. The thickness of Al₂O₃ layer decreased with increasing the annealing temperature due to the densification of ZrO₂ film and the capacitance of ZrO₂ coated aluminum foil annealed at low temperature was higher than that at high temperature. The increase of capacitance was due to the high capacitance of ZrO₂ film annealed at low temperature. The capacitance of ZrO₂ and Nb₂O₅ coated aluminum increased about 3 and 1.7 times compared to that of Al₂O₃ layer anodized with 400 V, respectively. From these results, the aluminum foils with composite oxide layers are found to be applicable to the aluminum electrolytic capacitor.     

Preparation of BaPbO3 Electrode Thin Films by RF Magnetron Sputtering

For electrode materials of Pb(Zr,Ti)O₃ (PZT) thin films in ferroelectric random access memory (FeRAM), various materials have been studied. As new electrode material with which the polarization and fatigue properties are improved, we take notice of barium metaplumbate BaPbO₃ (BPO). Because the BPO contained lead (Pb) and oxygen is conductor that adopted same perovskite structure as PZT. BPO thin films were prepared by rf magnetron sputtering on various substrates. (SiO₂/Si, MgO, Al₂O₃ and Pt-coated substrates), and influence of growth conditions (sputtering gas, rf power, the substrate-heating temperature and post anneals) on crystallization and conductivity were investigated. In case of post anneal after sputtering at room temperature, perovskite single phase was obtained above 400°C. In case of substrate heating while sputtering, without post anneal, perovskite single phase was obtained at 350–500°C on SiO₂/Si substrates (110) preferred orientation BPO films obtained at low temperature, and resistivity of the films decreased at decreasing sputtering temperature. Resistivity of the film at substrate temperature 350°C was 3 × 10^?3 Ω cm. In the case of single crystal substrate, the BPO films were epitaxially grown. Orientation of the films was varied with the sputtering condition. The epitaxial PZT thin films were also grown on the BPO, revealing that PZT(111)[011] //BPO(111)[011] //Pt(100)[011] //MgO(100)[011] and PZT(111)[011] //BPO(111)[011] //Pt(111)[011] //Al₂O₃(001)[100] structures were obtained, and their ferroelectric properties were also evaluated.     

Rf Sputtered Na0.5K0.5NbO3 Films on Oxide Substrates as Optical Waveguiding Material

Highly crystalline Na_0.5K_0.5NbO₃ (NKN) thin films of 1–2 μm thickness were deposited by rf-magnetron sputtering of a stoichiometric, ceramic target on single crystal LaAlO₃(001) and Al₂O₃(0112) substrates. X-ray diffraction measurements revealed epitaxial quality of NKN/LaAlO₃ film structures, whereas NKN films on sapphire substrates were found to be preferentially c-axis oriented. A prism-coupling technique was used to characterize optical and waveguiding properties. A bright-line spectrum at λ = 632.8 nm, revealed sharp peaks, corresponding to transverse magnetic (TM) and electric (TE) waveguide propagation modes in NKN/LaAlO₃ and NKN/Al₂O₃ thin films. Using a least mean square fit the refractive index for the films and film thickness were calculated. The extraordinary and ordinary refractive indices were determined to n _e = 2.207 ± 0.002 and n _o = 2.261 ± 0.002, and n _e = 2.216 ± 0.002 and n _o = 2.247 ± 0.002 at λ = 632.8 nm for 2.0 μm thick NKN films on LaAlO₃ and Al₂O₃, respectively. This corresponds to a birefringence Δn = n _e ? n _o = ?0.054 ± 0.003 and Δn = ?0.031 ± 0.003 in the films, where the larger Δn for the NKN/LaAlO₃ structure can be explained by the superior crystalline quality compared to NKN/Al₂O₃. Atomic force microscopy images of the film surfaces revealed rms roughnesses of 2.5 nm and 8.0 nm for 1.0-μm thick NKN/LaAlO₃ and NKN/Al₂O₃ films, respectively. We believe surface scattering is one of the main sources of waveguide losses in the thin films.     

Development of Low Temperature Al2O3 MOCVD for Ferroelectric Film Passivation on 8″ Wafers

A long-term consideration in the application of ferroelectrics in device production is hydrogen-induced failures. Subsequent to ferroelectric formation, post-capacitor processes of inter-level dielectric layers contain hydrogen and are performed at elevated temperatures. Free hydrogen may react with the ferroelectric oxides, reducing portions of the dielectric layer and creating leakage paths. For optimum ferroelectric film performance, protection against hydrogen infusion is needed. In part, a design solution to this problem is to employ an Al₂O₃ hydrogen diffusion barrier in the device structure. We have focused on MOCVD of the barrier layer using an array of precursors—including trimethylaluminum (TMAl) and aluminum iso-propoxide (Al i-Pr) among others. We have successfully lowered the Al₂O₃ deposition temperature from 600°C to 350°C without sacrificing film quality or deposition rate. We have produced Al₂O₃ MOCVD films in a SpinCVD? cluster tool rotating disk low-pressure reactor. The Al₂O₃ films are uniform and reproducible. The MOCVD process provides uniform precursor and temperature distributions necessary for coverage over topology in stacked architectures. This paper describes the MOCVD process and resultant film properties.     

Thermal and dielectric properties of ZnO-B2O3-MO3glasses (M = W, Mo)

Glasses in the ZnO-B₂O₃-MO₃(M = W, Mo) ternary were examined as potential replacements to PbO-B₂O₃-SiO₂-ZnO glass frits with the low firing temperature (500–600^∘C) for the dielectric layer of a plasma display panels (PDPs). Glasses were melted in air at 950–1150^∘C in a narrow region of the ternary using standard reagent grade materials. The glasses were evaluated for glass transition temperature (T _g ), softening temperature (T _d ), the coefficient of thermal expansion (CTE), dielectric constant (ε _r ), and optical property. The glass transition temperature of the glasses varied between 470 and 560^∘C. The coefficient of thermal expansion and the dielectric constant of the glasses were in the range of 5–8 × 10^{− 6}/^∘C and 8–10, respectively. The addition of MO₃to ZnO-B₂O₃binary could induce the expansion of glass forming region, the reduction of T _g and the increase in the CTE and the dielectric constant of the glasses. Also, the effect of the addition of MO₃to ZnO-B₂O₃binary on the transmittance in the visible-light region (350–700 nm) was investigated.     

Influence of B2O3/SiO2 Ratio on the Fabrication of Nd:YAG Ceramics

B₂O₃/SiO₂ are used as composite sintering aids to fabricate Nd:YAG ceramics by solid-state reaction and vacuum sintering method at 1750°C for 5h using Nano-Al₂O₃, Y₂O₃, Nd₂O₃ as starting materials. In this article, we focus on the influence of B₂O₃/SiO₂ ratio on grain size, porosity and relative density. Finally, with the increase of B₂O₃/SiO₂ ratio, the density and shrinkage rate of transparent ceramics increase, the grain size becomes uniform and the porosity reduces, for the reason that B³⁺ begins to vaporize at 1300°C and is reduced to trace levels by 1600°C. The best B₂O₃/SiO₂ ratio is 4: 1.     

Control of Microwave Dielectric Properties in the System BaO ⋅ Nd<Subscript>2</Subscript>O<Subscript>3</Subscript> ⋅ 4TiO<Subscript>2</Subscript>—BaO ⋅ Al<Subscript>2</Subscript>O<Subscript>3</Subscript> ⋅ 4TiO<Subscript>2</Subscript>

BaO ⋅ Nd₂O₃ ⋅ 4TiO₂—based ceramics were prepared by the mixed oxide route. Specimens were sintered at temperatures in the range 1200–1450^∘C. Microstructures were investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM); microwave dielectric properties were determined at 3 GHz by the Hakki and Coleman method. Product densities were at least 95% theoretical. The addition of up to 1 wt% Al₂O₃ to the starting mixtures reduced the sintering temperatures by at least 100^∘C. Incorporation of small levels of Al into the structure (initially Ti sites) led to an increase in Q × f values, from 6200 to 7000 GHz, a decrease in relative permittivity (ε_r) from 88 to 78, and moved the temperature coefficient of resonant frequency (τ_f) towards zero. The addition of 0.5 wt% Al₂O₃ with 8 wt% Bi₂O₃ improved densification, increased both ε_r (to 88) and Q× f (to 8000 GHz) and moved τ_f closer to zero. Ceramics in the system (1 − x)BaO ⋅ Nd₂O₃ ⋅ 4TiO₂ + xBaO ⋅ Al₂O₃ ⋅ 4TiO₂ exhibited very limited solid solubility. The end member BaO ⋅ Al₂O₃ ⋅ 4TiO₂ was tetragonal in structure with the following dielectric properties: ε_r = 35; Q× f = 5000 GHz; τ_f = −15ppm/^∘C. Microstructures of the mixed Nd-Al compositions contained two distinct phases, Nd-rich needle-like grains and large Al-rich, lath-shaped grains. Products with near zero τ_f were achieved at compositions of approximately 0.14BaO ⋅ Nd₂O₃ ⋅ 4TiO₂ + 0.86BaO ⋅ Al₂O₃ ⋅ 4TiO₂, where Q× f = 8200 GHz and ε_r = 71.     

Effects of Al2O3 on the piezoelectric properties of Pb(Mn1/3Nb2/3)O3-PbZrO3-PbTiO3 ceramics

Piezoelectric properties of Al₂O₃-doped Pb(Mn_1/3Nb_2/3)O₃-PbZrO₃-PbTiO₃ ceramics were investigated. The constituent phases, microstructure, electromechanical coupling factor, dielectric constant, piezoelectric charge and voltage constants were analyzed. Diffraction peaks for (002) and (200) planes were identified by X-ray diffractometer for all the specimens doped with Al₂O₃. The highest sintered density of 7.8 g/cm³ was obtained for 0.2 wt% Al₂O₃-doped specimen. Grain size increased by doping Al₂O₃ up to 0.3 wt%, and it decreased by more doping. Electromechanical coupling factor, dielectric constant, piezoelectric charge and voltage constants increased by doping Al₂O₃ up to 0.2 wt%, and it decreased by more doping. This might result from the formation of oxygen vacancies due to defects in O^{2 −} ion sites and the substitution of Al³⁺ ions.     

Current Conduction and Dielectric Behavior of High k-Y2O3 Films Integrated with Si Using Chemical Vapor Deposition as a Gate Dielectric for Metal-Oxide-Semiconductor Devices

Integration of Y₂O₃ high-k thin film over Si as gate dielectric in high performance CMOS and high-density MOS memory storage capacitor devices is described. Y₂O₃ film growth by low-pressure chemical vapor deposition induces interfacial reactions and complex SiO_{2 – x} layer growth. It has a graded structure, in crystalline-SiO₂ form at Y₂O₃ side and amorphous SiO_{2 – x} form at Si side. MIS devices based on Y₂O₃/SiO₂-SiO_{2 – x} composite dielectric integrated with Si show high frequency C-V behavior indicative of inversion to accumulation changes in capacitance. Observed bi-directional hysterisis in C-V is detrimental to the functioning of storage capacitor in memory function. Detailed investigation of this effect led to understanding of gate bias controlled emission of carriers as responsible mechanism. Observed anomalous increase in inversion capacitance at low frequency is attributed to additional charges transferred from SiO_{2 – x}/Si interface states. Leakage current and injected charge carrier transport across bilayer interface is dominated by Poole-Frankel (PF) process at low fields and by Fowler-Nordhiem (FN) at high fields. This investigation provides a greater understanding of the complex nature of integration of Y₂O₃ films.     

Preparation and characterization of LiNi0.80Co0.20– x Al x O2 as cathode materials for lithium ion batteries

LiNi_0.80Co_{0.20− x} Al _x O₂ samples (x = 0.025, 0.050 and 0.100) were prepared by a solid-state reaction at 725^∘C for 24 h from LiOH⋅H₂O, Ni₂O₃, Co₂O₃ and Al(OH)₃ under oxygen flow. LiNiO₂ simultaneously doped by Co-Al has been tried to improve the cathode performance. The results showed that substitution of optimum amount Al and Co at the Ni-site in LiNiO₂ improved cycling performance. As a consequence, LiNi_0.80Co_0.15Al_0.05O₂ has 178.2 mAh/g of the first discharge capacity and 174.0 mAh/g after 10 cycles. Differential capacity vs. voltage curves indicated that the Co-Al co-doped LiNiO₂ showed suppression of the phase transitions compared with pure LiNiO₂.     

Thick Film Planar CO<Subscript>2</Subscript> Sensors Based on Na β-Alumina Solid Electrolyte

Practical small-sized thick film CO₂ sensor with self-heater was fabricated with Na β -Alumina (NBA), Na₂Ti₆O₁₃-TiO₂, and Na₂CO₃ as a solid electrolyte, reference electrode, and a sensing electrode, respectively. The measured EMF from the sensor followed the Nernstian behavior with CO₂ concentration change in the range of 400 to 600^∘C (350–580 mW power consumption). However, in the aspect of stability, densification of the NBA thick film and prevention of Na₂CO₃ evaporation were needed. In this study, an Al₂O₃ porous layer deposited on Na₂CO₃ was effective in improving the durability during operation of the sensor. It is thought that Al₂O₃ suppresses evaporation of Na₂CO₃.     

Low-temperature synthesis in vacuum of c-axis oriented ferroelectric YMnO3 thin films using alkoxy-derived precursors

Abstract

Hexagonal YMnO₃ thin films were prepared on Pt(111)/TiO_x/SiO₂/Si and Pt(111)/Al₂O₃(0001) substrates using alkoxy-derived precursor solutions. The films were prepared by spin coating the YMnO₃ precursor solutions and then, the films were calcined and crystallized via rapid thermal annealing in oxygen or vacuum ambient. The annealing conditions and substrates were critical for crystallization of ferroelectric YMnO₃ films. When annealed in vacuum, the films both on Pt(111)/TiO_x/SiO₂/Si and Pt(111)/Al₂O₃(0001) substrates crystallized to hexagonal YMnO₃ and the orientation depended on the substrates. The film on Pt(111)/Al₂O₃(0001) had c-axis orientation and the film on Pt(111)/TiO_x/SiO₂/Si had no preferred orientation. In addition, it was found that crystallization behavior, orientation and morphology of YMnO₃ films on Pt(111)/TiO_x/SiO₂/Si substrates depended on the annealing condition. The heat-treatment in vacuum at initial stage for crystallization affected the restraint of perovskite phase and formation of hexagonal phase. The following heat-treatment in oxygen promoted the c-axis orientation and grain growth. The optimum annealing procedure for crystallization of the c-axis oriented YMnO₃ films on Pt(111)/TiO_x/SiO₂/Si was addressed.     

Modification on PTCR behavior of (Sr0.2Ba0.8)TiO3 materials by post-heat treatment after microwave sintering

Abstract

Effect of post-sintering treatment on PTCR behavior of (Sr_0.2Ba_0.8)TiO₃ materials prepared by microwave-sintering (ms) process was compared to that prepared by rapid thermal sintering (RTS) process. The microwave-sintering process needed only 1130°C-40 min to effectively densify (Sr_0.2Ba_0.8)TiO₃ materials. The grain size was around 6 μm and PTCR characteristics was around ρ_max/ρ_min≈ 10^1.75, with T_c = 50°C. Lowering the cooling rate after sintering substantially increases the resistivity jump (ρ_max/ρ_min) from 10² to 10^3.4, without altering the microstructure. The annealing at 1250°C for 2 h markedly increased the resistivity jump to (ρ_max/ρ_min)≈10⁶. On the other hand, the rapid thermal sintering (RTS) process required 1320°C-30 min to fully develop the good microstructure (～15 μm) and PTCR property (ρ_max/ρ_min ～ 10^3.0). Post-sintering process, including cooling rate control and annealing, did not improve the electrical properties of these samples, that is ascribed to the slow-cooling rate characteristics of RTS-process for a temperature lower than 800°C.     

Crystallization of Zr Based Oxide with Glass Forming Additives for Gate Dielectric Applications

In this study, Si, Al, and Bi have been investigated as a glass forming additive. Addition of glass forming materials is effective on stabilization of amorphous phase for Zr based films. The higher crystallization temperature results from the more additives. Addition of heavier atom is more effective on enhancing dielectric constant but results in lowering crystallization temperature. Addition of Si results in the most stable amorphous with significant reduction of dielectric constant. When the atomic ratio of Si over (Si + Zr) of about 0.55 is annealed at 950°C for 1 min, any crystallization behaviors are not noticed with dielectric constant of 12. On the other hand, addition of Al causes moderate improvement of crystallization behavior with small sacrifice of dielectric constant. The amorphous films of Zr_{1 ? x} Al _x O _y (X = 0.55) remain amorphous up to 800°C anneals with dielectric constant of 15.     

MOCVD preparation of SBTN thin films from two organometallic sources bottles

Abstract

SrBi₂(Ta_0.7Nb_0.3)₂O₉ (SBTN) films were first prepared on (111)Pt/Ti/SiO₂/Si substrates by MOCVD from only two organometallic source bottles. Bi(CH₃)₃ and the mixture of Sr[Ta(O°C₂H₅)₆]₂ and Sr[Nb(O°C₂H₅)₆]₂ were used as source materials. High compositional reproducibility was obtained; the Nb/(Ta+Nb) ratio was the same as the mixing ratio of the source. Sr/(Ta+Nb) and Bi/(Ta+Nb) ratios can be controlled by the reactor pressure and the input gas flow rate ratio of the source gases. Almost single phase of SBTN was obtained for the film deposited at 500°C and the following heat-treated at 800°C in O₂ atmosphere. Pr and Ec values of 330 nm-thick SBTN film were 8.5 μC/cm² and 91 kV/cm, respectively and were larger than those of SrBi₂Ta₂O₉ film. There was no degradation after 5x10¹⁰ cycles polarization switching.     

Chemical processing and properties of Sr2(Ta,Nb)2O7 thin films

Abstract

The crystallographic orientation, microstructure and electrical properties of Sr₂(Ta, Nb)₂O₇ thin films strongly depended on the composition (Ta:Nb). Post-annealing at 850°C was effective for the improvement of some properties. The thin films with relatively Nb-rich compositions, such as Sr₂(Ta_0.6Nb_0.4)₂O₇ and Sr₂(Ta_0.5Nb_0.5)₂O₇, showed the (0k0) preferred orientation. The Sr₂(Ta_0.5Nb_0.5)₂O₇ thin film had a lamination layer structure after the post-annealing at 850°C for 6 min in oxygen. The characteristic microstructure originated in the crystallographic orientation of (0k0), which is the cleavage plane, and influenced electrical properties. The dielectric constant little change with the composition, however, the P-E hysteresis properties improved with the Nb content.     

The effect of alumina addition on the electrical conductivity of Gd-doped ceria

Acceptor doped-ceria is a possible electrolyte material for the IT-SOFC (intermediate temperature solid oxide fuel cell) due to its high oxygen-ion conductivity. However, its use has been limited by its mechanical weakness and the appearance of electronic conductivity in reducing condition. In this study, alumina was selected as an additive in the doped-ceria to see if it increases the oxygen-ion conductivity and mechanical strength. Effects of alumina addition in doped ceria were studied as a function of alumina content and acceptor (Gd) content. The electrical conductivity of (Ce_1−x Gd _x O_2−δ)_1−y + (Al₂O₃) _y (x = 0–0.35, y = 0–0.10) was measured by using impedance spectroscopy. The grain conductivity of Ce_0.8Gd_0.2O_2-δ (GDC20) with 5 mol% alumina increased ∼3 times from that of GDC20 at 300^∘C. The grain conductivity was even ∼2 times higher than that of Ce_0.9Gd_0.1O_2−δ (GDC10) at 300^∘C. The electrical conductivity of GDC20 without alumina addition, measured at 500^∘C in air, rapidly decreased after exposure to reducing condition (Po₂∼10⁻²² atm) at 800^∘C. However, the decrease was much slower in GDC20 with alumina addition, indicating the improved mechanical strength. Among the examined compositions, (Ce_0.75Gd_0.25 O_2-δ)_0.95 + (Al₂O₃)_0.05 (GDC25A5) showed the highest conductivity at most temperatures.     

Effect of SnO2 on improvement on the microwave dielectric properties of Ba2Ti9O20

Effect of SnO₂ addition on the crystal structure/microstructure and the related microwave dielectric properties of the Ba₂Ti₉O₂₀ were systematically investigated. Incorporation of SnO₂ markedly stabilized the phase constituent and microstructure for the Ba₂Ti₉O₂₀ such that high quality materials can be obtained in a much wider processing window. The sintered density of the Ba₂Ti₉O₂₀ increased linearly, but the microwave dielectric constant (K) decreased monotonically, with the SnO₂ doping concentration. The quality factor (Qxf) of the materials increased firstly due to the addition of SnO₂, but decreased slightly with further increase in SnO₂ content. The best microwave dielectric properties obtained are K = 38.5 and Qxf = 31,500 GHz, which occurs for the 0.055 mol SnO₂-doped and 1350 °C/4 h sintered samples. These properties are markedly better than those for undoped materials (K = 38.8 and Qxf = 26,500 GHz).