The effect of crystallographic orientation and solution aging on the electrical properties of sol–gel derived Pb(Zr0.45Ti0.55)O3 thin films

Lead zirconate titanate—Pb(Zr_0.45Ti_0.55)O₃ thin films are grown on Pt_1 1 1/Ti/SiO₂/Si_1 0 0 substrates by a sol–gel method with 1 0 0/0 0 1 and 1 1 1 preferred orientations. Film orientation was controlled mainly by the annealing process and temperature. Films with 1 0 0/0 0 1 orientation consist of a uniform microstructure with micron size grains, whereas films with 1 1 1 orientation contain sub-micron grains. The electrical properties were influenced markedly by the microstructure and orientation of the films. The 1 1 1 oriented films exhibit a square-like hysteresis loop with remnant polarization (P_r) reaching 46 μC/cm² under 550 kV/cm, whereas 1 0 0/0 0 1 oriented films have a P_r of 20 μC/cm² with more slim hysteresis curves. Aging of the precursor solutions resulted in films growing with 1 0 0/0 0 1 texture and displaying inferior electrical properties.     

Enhanced dielectric tunability properties of Ba(ZrxTi1−x)O3 thin films using seed layers on Pt/Ti/SiO2/Si substrates

The compositionally graded and homogeneous Ba(Zr_xTi_1−x)O₃ (BZT) thin films were fabricated on LaNiO₃ (LNO) buffered Pt/Ti/SiO₂/Si and Pt/Ti/SiO₂/Si substrates by a sol–gel deposition method, respectively. These films crystallized into a single perovskite phase. The BZT thin films deposited on LaNiO₃/Pt/Ti/SiO₂/Si substrates had a highly (1 0 0) preferred orientation and exhibited a preferred (1 1 0) orientation when the thin films were deposited on Pt/Ti/SiO₂/Si substrates. The LNO and Ba(Zr_0.30Ti_0.70) served as seed layer on Pt/Ti/SiO₂/Si substrates and analyze the relationship of seed layer, microstructure and dielectric behavior of the thin films. The compositionally graded thin films from BaTiO₃ to BaZr_0.35Ti_0.65O₃ were fabricated on LNO/Pt/Ti/SiO₂/Si substrates. The tunability behavior of compositionally graded films was analyzed in order to produce optimum effective dielectric properties. The dielectric constant of BaZr_xTi_1−xO₃ compositionally graded thin films showed weak temperature dependence. This kind of thin films has a potential in a fabrication of a temperature stable tunable device.     

The dielectric properties and optical propagation loss of c-axis oriented ZnO thin films deposited by sol–gel process

The c-axis oriented ZnO thin films were prepared on various substrates by sol–gel processes. The stability of solution was examined through solvent and stabilizer. The c-axis orientation and grain size of films were increased with increasing of heat treatment temperature. The optical propogation losses of ZnO films deposited SiO₂/Si(111) substrates were measured using end-coupling method. The losses result in the scattering of the interface of ZnO/SiO₂, and the ZnO grain. Dielectric constant and resistivity of thin films deposited on Pt/SiO₂/Si(111) substrates are, respectively, in the range of 7–13 and 1.7×10⁴9.8×10⁵Ω cm.     

Spectroscopic ellipsometry characterization of TiO2 thin films prepared by the sol–gel method

TiO₂ thin films were prepared on SiO₂/Si(100) substrates by the sol–gel process. XRD results indicate that the major phase of TiO₂ thin films is anatase. The surface morphology and cross-section are observed by FE-SEM. The surface of thin films is dense, free of cracks and flat. The average grain size is about 60–100 nm in diameter. The thickness of single layer TiO₂ thin films is about 60 nm, which increases with the concentration of solution. Ellipsometric angles ψ, Δ are investigated by spectroscopic ellipsometry. The optical constant and the thickness of TiO₂ thin films are fitted according to Cauchy dispersion model. The results reveal that the refractive index and the extinction coefficient of TiO₂ thin films in wavelength above 800 nm are about 2.09–2.20 and 0.026, respectively. The influences of processing conditions on the optical constants and thicknesses of TiO₂ thin films are also discussed.     

Effect of pre-sintering temperature on the structural and dielectric properties of (Ba0.5Sr0.5)TiO3 thin films deposited by sol–gel technique

(Ba_0.5Sr_0.5)TiO₃ thin films have been deposited by sol–gel technique and the effect of pre-sintering temperature on the structural and dielectric properties has been studied. The sol was prepared from barium acetate and strontium acetate powders by dissolving them in acetic acid; while titanium isopropoxide was used as titanium source. Acetyl acetone, 2-methoxyethanol, and formamide were used as chelating agent, diluting reagent, and for getting crack free films, respectively. Two sets of films were prepared; one set pre-sintered at 400 °C while the other one at 600 °C. In all the cases, the final sintering temperature was kept fixed at 700 °C for 2 h. These films were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), dielectric constant, and loss measurements and AC conductivity studies. It has been found that with an increase in the pre-sintering temperature from 400 to 600 °C, the dielectric constant increases from 225 to 383 (measured at 100 kHz); whereas, the loss tangent remains nearly constant at 0.03–0.05. The XRD results show better crystallinity and enhanced grain growth in case of films pre-sintered at 600 °C. The FTIR spectra reveals that there is significant removal of organic materials in films with higher pre-sintering temperature as compared to that with lower pre-sintering temperature. The AC conductivity studies show a decrease in the frequency exponent ‘s’ with an increase in the pre-sintering temperature which has been correlated with the reduction in oxygen vacancy densities in the sample with higher pre-sintering temperature.     

Novel electro-optic properties of epitaxially grown (Pb, La)(Zr, Ti)O3 (PLZT) thin films derived by advanced sol–gel methods

Advanced sol–gel methods using a secondary solvent addition into (Pb, La)(Zr, Ti)O₃ (PLZT) sol–gel solution and a methanol pre-treatment of sapphire substrates are demonstrated. For the secondary solvent addition, the additive affected the crystallinity and electro-optic (EO) property of PLZT films and only methanol addition can improve them. In addition, the methanol pre-treatment is also appeared to be effective to improve film characteristics.

Through these optimizations, epitaxially grown PLZT thin films on r-cut sapphire are obtained and a high Pockels coefficient which is comparable to those of bulk PLZTs is achieved. It is believed that these PLZT thin films are applicable for integrated EO devices and open the door for the future data communication systems.     

Preparation and dielectric properties of B2O3–Li2O-doped BaZr0.35Ti0.65O3 ceramics sintered at a low temperature

BaZr_0.35Ti_0.65O₃ (BZT) ceramics have been fabricated via a traditional ceramic process at a relatively low sintering temperature using liquid-phase sintering aids B₂O₃ and Li₂O. The dielectric properties of BZT ceramics have been investigated with the emphasis placed on the dielectric properties under an applied dc electric field. The temperature-dependent dielectric constant reveals that the pure BZT and B₂O₃–Li₂O-doped BZT ceramics all have a typical relaxor behavior and diffuse phase transition characteristics. The temperature-dependent dielectric constant under the applied dc electric field shows that the Curie temperature is slightly shifted to higher temperature and the peaks are suppressed and broadened. The dielectric loss is still under 0.005 and tunability is above 20% at an applied dc electric field of 30 kV/cm.     

Magnetic properties of nanosize NiFe2O4 particles synthesized by sol–gel auto combustion method

A nitrate–citrate gel was prepared from metal nitrates and citric acid by sol–gel auto combustion process, in order to synthesize NiFe₂O₄ ferrite. X-ray diffraction showed the formation of NiFe₂O₄ and the inclusion of -Fe₂O₃. However, with increasing the calcination temperature, this inclusion phase (-Fe₂O₃) decreased. TEM was also used to characterize the microstructure of the nanosize NiFe₂O₄. Magnetization hysteresis of the nickel ferrite powders was performed at room temperature. It is shown that this powder which is composed of crystalline NiFe₂O₄ monophase, exhibited M_s = 54 (emu/g) at magnetic field of 2 (kOe).     

Dependence of the properties of compositionally graded Pb(Zr,Ti)O3 ferroelectric films of the bottom electrode

Compositionally graded Pb(Zr_,Ti)O₃ thin films were prepared on the Pt(1 1 1)/Ti/SiO₂/Si, LNO/Si(1 0 0) and LNO/Pt(1 1 1)/Ti/SiO₂/Si substrates by a modified sol–gel method and rapid heat-treatment. The composition depth profile of a typical up-graded film was determined using a combination of auger electron spectroscopy and Ar-ion etching. The crystallographic orientation and the microstructure of the resulting graded PZT thin films on the different substrates were characterized by XRD. The dielectric and ferroelectric properties of the graded PZT films were discussed. The graded PZT films on LNO/Pt/Ti/SiO₂/Si and LNO/Si(1 0 0) substrates have larger dielectric constant and remnant polarizations compared to that grown on Pt/Ti/SiO₂/Si substrates.     

High tunability in (1 1 0)-oriented BaZr0.2Ti0.8O3 (BTZ) lead-free thin films fabricated by pulsed laser deposition

Using a pulsed laser deposition method the BaZr_0.2Ti_0.8 O₃ (BTZ) lead–free thin films with a thickness of ~250 nm were grown on FTO, ITO and Pt–Si substrates, respectively. The analysis results of microstructural, dielectric properties and leakage current reveal that the thin films deposited on Pt–Si substrates are oriented growth along the (1 1 0) direction and exhibit the optimal performance characteristics. Calculations of figure of merit (FoM) and dielectric tunability display a maximum value of ~42.8 and ~68.5% at E = 400 kV/cm at room temperature, respectively. The excellent tunable properties, high dielectric constant (~635@ 100 kHz) and low leakage current density of (9.3 × 10^–8 A/cm² at 400 kV/cm) make the (1 1 0)–oriented BaZr_0.2Ti_0.8 O₃ thin film to be an attractive material for applications of tunable devices.     

Dielectric properties of Fe-doped Ba0.65Sr0.35TiO3 thin films fabricated by the sol–gel method

Fe-doped Ba_0.65Sr_0.35TiO₃ (BST) thin films have been fabricated on Pt/Ti/SiO₂/Si substrate using the sol–gel method. The structural and surface morphology, dielectric, and leakage current properties of undoped and 1 mol% and 2 mol% Fe-doped BST thin films have been studied in detail. The results demonstrate that the Fe-doped BST films exhibit improved dielectric loss, tunability, and leakage current characteristics as compared to the undoped BST thin films. The improved figure of merit (FOM) of Fe-doped BST thin film suggests a strong potential for utilization in microwave tunable devices.     

Microwave dielectric properties of multi-ions Ba(Zn,Ta)O3-based perovskite ceramics

In this study, Ba(Zn_1/3Ta_2/3)O₃-based complex perovskite compounds, including Ba(Zn_1/3Ta_2/3)O₃, Ba(Zn_1/3Ta_1/3Nb_1/3)O₃, Ba(Zn_1/6Co_1/6Ta_2/9Nb_2/9Sb_2/9)O₃, and Ba_1/2Sr_1/2(Zn_1/6Co_1/6Ta_2/9Nb_2/9Sb_2/9)O₃, were prepared and characterized. There was no second phase formation shown in the XRD patterns. Though it has been suggested that substitutions of multiple ions over A-site or B-site of the Ba(Zn_1/3Ta_2/3)O₃ ceramics may not be beneficial to their microwave dielectric properties, the Ba(Zn_1/6Co_1/6Ta_2/9Nb_2/9Sb_2/9)O₃ and Ba_1/2Sr_1/2(Zn_1/6Co_1/6Ta_2/9Nb_2/9Sb_2/9)O₃ ceramics in this study were found to perform in a fairly acceptable manner. The Ba(Zn_1/6Co_1/6Ta_2/9Nb_2/9Sb_2/9)O₃ ceramic (sintered at 1575 °C for 6 h) and the Ba_1/2Sr_1/2(Zn_1/6Co_1/6Ta_2/9Nb_2/9Sb_2/9)O₃ ceramic (sintered at 1550 °C for 6 h) reported the following characteristics after annealing at 1400 °C for 10 h: 24.9 and 27.0 for dielectric constants (?_r), 83,000 and 32,100 GHz for quality factors (Q × f) values and −12.8 and −22.6 ppm/°C for temperature coefficients of resonance frequency (τ_f).     

Microstructure and ferroelectric properties of sol–gel graded PZT (40/52/60) and (60/52/40) thin films

Graded Pb(Zr_x,Ti_1−x)O₃ films with Zr compositions varied across the thickness direction were deposited on Pt/Ti/SiO₂/Si substrate using a conventional spin-coating method. The up- and down-graded PZT films exhibited the perovskite polycrystalline structure. Microstructure investigations of the films showed a dense texture and successive layers of different compositions. The relative permittivities of the up- and down-graded PZT films measured at 1 kHz and room temperature were 1846 and 1019, respectively. Good dielectric and ferroelectric properties as well as the low-temperature processing suggested that the compositionally graded PZT films were promising for memory device applications.     

The influence of sintering aids for Nd(Mg0.5Ti0.5)O3 microwave dielectric ceramics properties

The influence of various sintering aids on the microwave dielectric properties and the structure of Nd(Mg_0.5Ti_0.5)O₃ ceramics were investigated systematically. B₂O₃, Bi₂O₃, and V₂O₅ were selected as liquid-phase sintering aids to lower the sintering temperature. The sintered Nd(Mg_0.5Ti_0.5)O₃ ceramics are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and microwave dielectric properties. The sintering temperature of Nd(Mg_0.5Ti_0.5)O₃ microwave dielectric ceramics is generally high, about 1500 °C. However, the sintering temperature was significantly lowered about 175 °C from 1500 °C to 1325 °C by incorporating in 10 mol% B₂O₃ and revealed the optimum microwave dielectric properties of dielectric constant (_r) value of 26.2, a quality factor (Q × f) value of 61,307 (at 9.63 GHz), and τ_f value of −45.5 ppm/°C. NdVO₄ secondary phase was observed at 10 mol% V₂O₅ addition in the sintering temperature range of 1300–1325 °C, which led the degradation in microwave dielectric properties. The microwave dielectric properties as well as grain sizes, grain morphology, and bulk density were greatly dependent on sintering temperature and various sintering aids. In this study, it is found that Nd(Mg_0.5Ti_0.5)O₃ incorporated with 10 mol% B₂O₃ with lower sintering temperature and excellent dielectric microwave properties may be suggested for application in microwave communication devices. The use of liquid-phase sintering, the liquid formed during firing normally remains as a grain boundary phase on cooling. This grain boundary phase can cause a deterioration of the microwave properties. Therefore, the selection of a suitable sintering aid is extremely important.     

Enhanced dielectric loss of Mg doped Ba0.7Sr0.3TiO3 ceramics

The effect of MgO doping on the structural, microstructural and dielectric properties of Ba_0.7Sr_0.3TiO₃ (BST) ceramic from the point of view of its application in microwave tunable devices has been studied. All the samples crystallize into perovskite structure. There is significant reduction in the value of loss factor with the increase in Mg-level, the dielectric constant and tunability are also reduced with the increase in Mg-level. Interestingly, the Fig. of merit of the material is found to be enhanced with increase of Mg-doping. The observed dielectric properties are explained on the basis of defect chemistry involved when Mg is doped in Ba_0.7Sr_0.3TiO₃ ceramics. The effect of dc field on the dielectric constant and the dielectric breakdown strength of the paraelectric phase Mg doped BST ceramic samples are also studied.     

Low temperature synthesis of MgxAl2(1−x)Ti(1+x)O5 films by sol–gel processing

Aluminium titanate films thicker than 0.5 μm have been synthesized by sol–gel methods. The films have been deposited via repetitive dip-coating on silicon wafers and their thermal stability has been tested as a function of the annealing time and temperature. The sol–gel approach has allowed the formation of the aluminium titanate phase at temperatures (700 °C) much lower than those necessary for solid-state reactions (1450 °C). Magnesium oxide has been used to improve the thermal stability of the films at high temperatures. The behavior of samples prepared with two different Mg content, i.e. Mg_0.2Al_1.6Ti_0.8O₅ and Mg_0.6Al_0.8Ti_1.6O₅, has been studied. The films have proven to be stable at 1150 °C, for up to 90 h. X-ray photoelectron spectroscopy has shown that after firing at 500 °C the surface chemical composition of the films is in accordance with the nominal one, whilst at higher annealing temperatures some differences, attributed to diffusion effects, have been observed.     

Thickness dependent growth and ferroelectric/dielectric properties of phase-pure 0.65Pb(Mg1/3Nb2/3)O3-0.35PbTiO3 thin film derived from a modified sol-gel process

Annealing parameter and thickness are two significant factors affecting microstructure and electrical performance of sol-gel derived 0.65Pb(Mg_1/3Nb_2/3)O₃?0.35PbTiO₃ (0.65PMN-0.35PT) thin film. In this paper, various durations are firstly selected for the investigations on annealing parameter of 0.65PMN-0.35PT thin film. Enhanced insulating and ferroelectric properties can be obtained for the film annealed for 1 min due to its phase-pure and homogeneous perovskite structure. Based on this, a series of 0.65PMN-0.35PT thin films with various thicknesses by modifying deposition layer are synthesized annealed for 1 min and the effects of thickness on crystalline, insulating, ferroelectric and dielectric properties are characterized. It reveals that thickness-dependent behavior can be noticed for 0.65PMN-0.35PT thin film with the results that the 8-layered film possesses a relative large remanent polarization (P_r) of 23.34 μC/cm², and reduced leakage current density of 10^?9 A/cm² with low dissipation factor (tanδ) of 0.03 can be achieved for the 14-layered film.     

Effect of Bi2O3 additives on sintering and microwave dielectric behavior of La(Mg0.5Ti0.5)O3 ceramics

Bi₂O₃ was selected as liquid phase sintering aid to lower the sintering temperature of La(Mg_0.5Ti_0.5)O₃ ceramics. The sintering temperature of La(Mg_0.5Ti_0.5)O₃ ceramics is generally high, about 1600 °C. However, the sintering temperature was significantly lowered about 275 °C from 1600 °C to 1325 °C by incorporating in 15 mol% Bi₂O₃ and revealed the optimum microwave dielectric properties of dielectric constant (?_r) value of 40.1, a quality factor (Q × f) value of 60,231 GHz, and the temperature coefficient (τ_f) value of 70.1 ppm/°C. During all addition ranges, the relative dielectric constants (?_r) were different and ranged from 32.0 to 41.9, the quality factors (Q × f) were distributed in the range of 928–60,231 GHz, and the temperature coefficient (τ_f) varies from 0.3 ppm/°C to 70.3 ppm/°C. Noticeably, a nearly zero τ_f can be found for doping 5 mol% Bi₂O₃ sintering at 1325 °C. It implies that nearly zero τ_f can be achieved by appropriately adjusting the amount of Bi₂O₃ additions and sintering temperature for La(Mg_0.5Ti_0.5)O₃ ceramics.     

Electrical conductivity of sol–gel derived yttria-stabilized zirconia

A 3 mol% Y₂O₃ zirconia stabilized powder has been synthesized by destabilization of an aqueous zirconia sol prepared by the alkoxide hydrolysis method. The powder calcined at 500°C is ultrafine with tetragonal crystallites of about 8 nm, slightly agglomerated and with a narrow pore size distribution having an average pore size of 5.2 nm. Zirconia ceramics with density higher than 92%TD and grain size on the order of 100 nm have been obtained by uniaxial pressing at 500 MPa and vacuum sintering at 1000°C. Electrical conductivity of sintered samples, evaluated by complex impedance spectroscopy measurements, indicated that the zirconia stabilized with 3 mol% Y₂O₃ can potentially be used as an oxygen semipermeable dense membrane, but only at a relatively high temperature.     

Dielectric and ferroelectric properties of Ba(ZrxTi1−x)O3 ceramics

It is known that Curie temperature of barium titanate system can be altered by the substitution of dopants into either A- or B-site. Dopants could pinch transition temperature, lower Curie temperature, and raise the rhombohedral–orthorhombic and orthorhombic–tetragonal phase transition close to room temperature. This isovalent substitution could improve the ferroelectric properties of the BaTiO₃-based system. In this study, barium zirconate titanate Ba(Zr_xTi_1−x)O₃ (BZT; x = 0, 0.02, 0.05 and 0.08) ceramics were prepared by conventionally mixed-oxide method. The ferroelectric properties of BZT ceramics were investigated. Increasing Zr content in the BaTiO₃-based compositions caused a decrease in Curie temperature (T_c). At T_c, the highest relative permittivity of BZT with an addition of 0.08 mol% of Zr was 12,780. The BZT specimens with the additions of 0.05 mol% and 0.08 mol% of Zr presented the remanent polarization at 25 μC/cm² and 30 μC/cm², respectively.