Dielectric and Mechanical Losses in (Ba,Sr)TiO3 Systems

In the application of tuneable microwave devices of ferroelectric (BaSr)TiO₃ systems the two critical parameters needed for optimal device performance are high tunability and low dielectric loss. The dielectric loss of the materials is strongly dependent on microstructure. This paper is concerned with an investigation of the variation in the dielectric and mechanical losses in Ba _x Sr_{1 – x} TiO₃ systems (x = 0.5, 0.6, 0.7 and 1.0) with microstructure (grain sizes from 1 m to 50 m). The magnitude of the loss peak and sharpness of the anomaly in the dielectric constant/elastic modulus observed for the phase transitions in Ba _x Sr_{1 – x} TiO₃, depend not only on the composition and but also on the grain size. A relaxation peak has been observed in large grain material, which is indication of interactions between different configurations of domain walls and the diffusion of oxygen vacancies in the domains.     

Synthesis, Microstructure and Electrical Properties of Hydrothermally Prepared Ferroelectric BaTiO3 Thin Films

Thin films of polycrystalline, tetragonal BaTiO₃ on oxidized Ti metal substrates were synthesized at 240°C under hydrothermal conditions. Microstructure and electrical properties of the films generated over a four week period of synthesis formed the focus of this study. The films displayed a smooth and shiny surface with a relatively dense structure and no observable cracks. Film thickness reached 0.5 m after two weeks of synthesis and thereafter remained constant. Diameters of the grains on the film surface were in the range of 12 m. It is proposed that initial formation of the BaTiO₃ film occurs by reaction of Ba²⁺ with solubilized titanium oxide on the Ti metal surface followed at later stages by an in-situ growth via reaction of TiO_x with Ba²⁺ diffusing through the BaTiO₃ film. X-ray diffraction and Raman spectroscopy indicated that the BaTiO₃ films are tetragonal, and the films exhibited typical ferroelectric hysteresis loops at room temperature. However, no evidence of the dielectric anomaly (Curie transition) between 30 and 200°C was observed. Dielectric constant of the films at 1 kHz at room temperature was between 400–500. Both dielectric constant and tan exhibited low dispersion as a function of frequency at temperatures below 150°C, and the dispersion increased with temperature.     

Coplanar Waveguide Using Ferroelectric Thin Oxide Film: Dielectric Constant

Coplanar waveguide (CPW) transmission lines were fabricated on thin ferroelectric Ba_{1 – x}Sr_xTiO₃ films for tunable microwave applications. The growth of the ferroelectric oxide films was accomplished by a pulsed laser deposition with a partial oxygen background. Microwave properties of the CPW phase shifter were measured using a HP 8510C vector network analyzer from 0.045–20 GHz with –40–40 V of dc bias. A large phase shift angle of 120 at 10 GHz was observed from the CPW (gap = 4m, length = 3 mm) with a 40 V of dc bias change. The dielectric constant of the thin ferroelectric film was extracted from the dimension of the CPW (gap, width, length) and the measured S-parameter by a modified conformal mapping. However, the dielectric constant of the ferroelectric thin film exhibits a gap dependency; dielectric constant (990–830) decreases with increasing gap size (4–19 m, respectively). By adjusting the filling factors of the film, a constant dielectric constant of BST film is found to be 810 ± 5.     

Microwave Dielectric Properties of Ferroelectric BaTiO3 Thin Film

The dielectric properties of c-axis epitaxial BaTiO₃ thin film on LaAlO₃ are investigated at frequencies of 0.5–30 GHz. For the measurements, interdigital capacitors with the Au/Ti electrode configurations of five fingers pairs that are 15 m wide and spaced 2 m apart are prepared by photolithography and lift-off patterning. Finger length varies from 20 to 80 m. The capacitance of epitaxial BaTiO₃ films exhibited no frequency dependence up to 10 GHz with the exception of slightly upward tendency of capacitance in BaTiO₃ film with a finger length of 80 m due to the self resonant frequency at 20 GHz. The Q-factors of the capacitors, defined as Q = 1/CR, are decreased up to 10 GHz with increased frequency. At 10 GHz, the BaTiO₃ film has a tunability [defined as k(V) = [C(0)–C(V)]C(0)] of 1.5% at 15 V, a loss tangent of 0.2 at room temperature. The small tunability can be interpreted as a result of in-plane compressive stress of BaTiO₃ film exhibiting large dielectric anisotropy. For the improvement of tunability and dielectric loss in the interdigital BaTiO₃ capacitor, the tetragonality (c/a) of epitaxial BaTiO₃ film and design of interdigital capacitor should be modified.     

Dielectric Properties of Bi4−x La x Ti3O12 (0 ≤ x ≤ 2) Ceramics

The dielectric properties of the Bi_4–x La _x Ti₃O₁₂ (0 x 2) ceramics were characterized and discussed together with the P-E relation (polarization vs. electric field). With increasing x, the P-E relation changed from normal ferroelectric hysteresis loops to pure linear relation, which indicated that La³⁺ substitution for Bi³⁺ in Bi₄Ti₃O₁₂ induced a phase transition from ferroelectric to paraelectric state at ambient temperature. Low loss dielectric ceramics with temperature stable dielectric constant were obtained for x > 1.2 in Bi_4–x La _x Ti₃O₁₂ at 1 MHz. And the loss increased in all the compositions when the ceramics were measured at microwave frequencies.     

Monolayer-Mediated Patterning of Integrated Electroceramics

Integrated electroceramic thin-film devices on semiconducting or insulating substrate materials offer a wide variety of attractive attributes, including high capacitance density, nonvolatile memory, sensor/actuator ability, and other unique electrical, electromechanical, magnetic and optical functions. Thus the ability to pattern such electroceramic thin films is a critical technology for future device realization. Patterned oxide thin-film devices are typically formed by uniform film deposition followed by somewhat complicated post-deposition ion-beam or chemical etching in a controlled environment i.e., a subtractive method. We review here an upset technology, a different way of patterning, by an additive approach, which allows for the selective deposition of electroceramic thin layers without such post-deposition etching. In this method, substrate surfaces are selectively functionalized with hydrophobic self-assembled monolayers to modify the adhesion of subsequently deposited solution-derived electroceramics. The selective functionalization is achieved through microcontact printing (-CP) of self-assembled monolayers of the chemical octadecyltrichlorosilane on substrates of current technical interest. Subsequent sol-gel deposition of ceramic oxides on these functionalized substrates, followed by lift-off from the monolayer, yields high quality, patterned oxide thin layers only on the unfunctionalized regions. A variety of micron-scale dielectric oxide devices have been fabricated by this method, with lateral resolution as fine as 0.5 m. In this paper, we review the monolayer patterning and electrical behavior of several patterned electroceramic thin films, including Pb(Zr,Ti)O₃ [PZT], LiNbO₃, and Ta₂O₅. A multilevel example is also given which combines selective MOCVD deposition of metal electrodes and sol-gel patterned PZT for Pt//PZT//Pt//Si(100) ferroelectric memory cells.     

Dielectric relaxation in paraelectric phase of Ba(Ti,Sn)O3 ceramics

Study on dielectric relaxation of various ferroelectric perovskites in their paraelectric phase had been reported recently. A common accepted idea is oxygen vacancy should be responsible for the observed nonferroelectric dielectric relaxation. The present authors had observed low-frequency dielectric relaxations in the paraelectric phase of Ba(Ti,Sn)O₃ ceramics. In the temperature range of 100 to 450 °C, peaks of loss tangent shift to higher temperature for higher frequency. The results of redox treatment excluded the possibility of defect polarization of oxygen vacancy. It is argued that hopping of localized hole contribute to the dielectric relaxation and to the electronic conducting characteristics.     

Structure,Ferroelectric, Dielectric and Energy Storage Studies of Ba0.70Ca0.30TiO3, Ba(Zr0.20Ti0.80)O3 Ceramic Capacitors

Ba_0.70Ca_0.30TiO₃-(BCT),Ba(Zr_0.2Ti_0.8)O₃-(BZT) ceramics were fabricated by conventional mixed oxide route to develop inorganic dielectric materials suitable for use as an insulator with high dielectric constant and low energy loss for capacitor applications. The structural phase transition, ferroelectric, dielectric and energy storage properties of BCT, BZT ceramic capacitors were investigated. Room temperature X-ray diffraction (XRD) patterns revealed prominent peaks corresponding to tetragonal perovskite crystal structure for both BCT, BZT solid solutions. Slim ferroelectric hysteresis (P-E) loops were observed for BCT, BZT solid solutions. Temperature dependent dielectric property measurements of BCT, BZT solid solutions have shown a high dielectric constant and low dielectric loss. Room temperature (300K) breakdown field strength and energy densities were obtained from the integral area of P-E loops. For the BCT ceramics, the largest recoverable energy (unreleased energy) density is 1.41 J/cm³ with dielectric breakdown strength as high as 150 kV/cm. For the BZT ceramics, the largest recoverable energy (unreleased energy) density is 0.71 J/cm³ with dielectric breakdown strength as high as 150 kV/cm. Bulk BCT, BZT ceramics have shown interesting energy densities; these might be the strong candidate materials for capacitor applications.     

Ferroelectric Properties of (Bi, Sm)4Ti3O12 (BST) Thin Films Fabricated by a Metalorganic Solution Deposition Method

Ferroelectric properties of samarium substituted Bi₄Ti₃O₁₂ films, Bi_3.15Sm_0.85Ti₃O₁₂ (BST), were evaluated for use as lead-free thin film ferroelectrics for FeRAM applications. The BST films were fabricated on the Pt/Ti/SiO₂/Si(100) substrates by a metalorganic solution deposition method. The measured XRD patterns revealed that the BST films showed only a Bi₄Ti₃O₁₂-type phase with a random orientation. The BST film capacitors showed excellent ferroelectric properties. For the film capacitor annealed at 700C, 2P_r of 64.2 C/cm² and 2E_c of 101.7 kV/cm at applied electric field of 150 kV/cm were observed. The capacitor did not show any significant fatigue up to 1.5 × 10⁸ read/write switching cycles at a frequency of 1 MHz, which suggests that the samarium should be considered for a promising lanthanide elements to make a good thin ferroelectric film for memory applications.     

DFT studies of electronic structure and dielectric properties in layered perovskite $$\hbox {LaSrAlO}_{4}$$

The structural, electronic, dielectric and optical properties of tetragonal \(\hbox {LaSrAlO}_{4}\) are studied in detail using density functional theory calculations. The energy band structures and density of states are predicted by generalized gradient approximation (GGA) and local density approximation (LDA) respectively. The fundamental band gaps of \(\hbox {LaSrAlO}_{4}\) are all indirect by GGA (2.860 eV) and LDA (2.863 eV) calculations. The complex dielectric function was calculated. There are two peaks in the real part \(\varepsilon _{1}(\omega )\) and three peaks in the imaginary part \(\varepsilon _{2}(\omega )\). The optical spectra are assigned to the interband transition from O valence to La and Sr conduction bands in the low energy region. In addition, the electron energy-loss spectrum, optical conductivity, reflectivity spectrum, and refractive index, are given to support the potential applications for microwave dielectric ceramics.     

Multilayer Ceramic Capacitors with Thin (Ba,Sr)TiO3 Layers by MOCVD

Barium strontium titanate ((Ba,Sr)TiO₃; BST) thin films were prepared on platinum-coated MgO substrates at 650°C by metalorganic chemical vapor deposition (MOCVD). Perovskite single phased BST thin films were obtained. Dielectric constant at 1 kHz–100 mV was 1000. Multilayer ceramic capacitor with twelve BST dielectric layers of 0.26 m thick was formed on the MgO substrate. Capacitance and dissipation factor (tan) at 1 kHz–100 mV were 32 nF and 1.5% respectively. Capacitance per unit volume of 33 F/mm³ provided 10 to 20 times larger volumetric efficiency than the conventional multilayer ceramic capacitors. Temperature coefficient of capacitance was –4000 ppm/°C. The leakage current at 1 V was 2.3×10^-9 A that yielded an acceptable CR product of 12.8 M-F. MOCVD was proposed as one of the promising manufacturing technologies for multilayer ceramic capacitors of high performance with sub-micron thick dielectric layers.     

Electronic Conductivity and Dielectric Properties of Nanocrystalline CeO2 Films

The growth of dielectric layers on silicon substrates has attracted a great deal of recent interest given their potential applicability in the fabrication of high quality silicon-on-insulator (SOI) structures, high density capacitor devices, and stable buffer layers between silicon and other materials. In this study, nanocrystalline CeO₂ films were deposited on n-type (100) silicon substrates using pulsed laser deposition (PLD) to form a gate dielectric for a Pt/n-Si/CeO₂/Pt MOS device. XRD, AFM and FESEM measurements were used to characterize the crystal structure and grain size of the CeO₂ films. The electrical properties of the device structure were examined by capacitance-voltage (C-V) and impedance spectroscopy measurements. The CeO₂ films exhibited an activated conductivity, characterized by an activation energy E_a = 0.45 eV. An estimated room temperature electron mobility _e of 2.8 × 10^{– 7} cm²/Vs leads to a corresponding electron concentration n of 5.5 × 10¹⁷ cm^{– 3}. In contrast to conventional MOS capacitors, we find an additional capacitive contribution under strong accumulation conditions as a result of space charge effects inside the CeO₂ thin film.     

Study of the Electrical Properties of Pb(Mg,Ni)1/3Nb2/3O3-PbTiO3 System Across the Morphotropic Phase Boundary

Phase transitional behavior and electrical properties of (1 – x)Pb(Mg,Ni)_1/3Nb_2/3O₃-xPbTiO₃ ceramics (PMNN-PT with Mg/Ni = 1:1, x = 0.20–0.40) across the morphotropic phase boundary (MPB) were examined. X-ray diffraction and dielectric measurement reveal that two phases, pseudocubic and tetragonal phases, coexist in the composition range x = 0.30–0.36. The maximum d ₃₃ (about 570 pC/N) was observed at the composition x = 0.32–0.34. Dielectric and ferroelectric properties exhibit abnormal high near the MPB. An unusual peak shoulder occurred in the dielectric measurement upon thermal cycling for poled samples. This phenomenon was considered to be associated with the macro to micro domain transition and depolarization.     

Synthesis of Sr0.5Ba0.5Nb2O6 by Coprecipitation Method—Dielectric and Microstructural Characteristics

Sr_0.5Ba_0.5Nb₂O₆ (SBN50) has been synthesized by coprecipitation method using Sr(NO₃)₂, Ba(NO₃)₂ and Nb-oxalate as precursors and ammonium hydroxide as precipitant. Calcination at 1150C resulted in pure SBN50 phase (XRD) and nano powder with size varying between 100–250 nm (TEM). The average grain size (SEM) in the sintered pellets ranged from 2.5 to 5 m as the sintering temperature varied from 1250 to 1350C. The maximum sintered density was observed to be 93% of _th. The plot of dielectric constant vs. temperature clearly showed a shift of dielectric maxima (_max) with frequency, indicating the relaxor nature of SBN50. The room temperature dielectric constant (_RT > 2300) observed for all these samples is higher compared to the earlier reported values (_RT 1500). The T_c (for 1 KHz) varied from 47–60C depending on the sintering conditions. The hystersis loops were recorded at various temperatures. The maximum saturation polarization for the unpoled pellets was found to be 2.3 C/cm² when sintered at 1350C. The improvement in dielectric and ferroelectric behavior is attributed to the enhanced homogeneity attained by the coprecipitation synthesis route used in the present study. Correlations between microstructure (sintering conditions) and dielectric behavior is explored.     

Fabrication of PZT Composite Thick Films for High Frequency Membrane Resonators

High frequency, thickness mode resonators were fabricated using a 7 m PZT thick film which was produced using a modified composite ceramic sol-gel process. Initial studies dealt with the integration of the PZT thick film onto the substrate. Two different diffusion barrier layers were tested, titanium oxide and zirconium oxide, in conjunction with the use of 2 types of silicon substrate (differing in the etch stop layer employed, either silicon nitride or silicon oxide). Zirconium oxide gave good results in conjunction with silicon oxide. Using these conditions, devices were produced and the acoustic properties measured for different electrode sizes ranging from 45*45 to 250*250 m². The best electrode size, which maximised the acoustic response and minimised the insertion loss, was found to have an area of 110*110 m². This device showed a resonant frequency of about 200 MHz, an effective electro-mechanical coupling coefficient of 0.29 and a Q factor of 22.     

Crystal Growth and Dielectric Properties of New Ferroelectric Barium Titanate: BaTi2O5

Single crystals of the ferroelectric BaTi₂O₅ and BaTiO₃ were prepared from a solution of 33-mol% BaO and 67-mol% TiO₂ by a rapid cooling method. The dielectric constant () and dielectric loss tangent (tan) were measured in a wide temperature range of 10–860 K and in a frequency range of 0.1–3,000 kHz. The along the b-axis of the BaTi₂O₅ crystal, prepared in air, shows a sharp dielectric anomaly reaching 30,000 at the ferroelectric Curie temperature of T_C = 752 K. By contrast, the crystal prepared in a reducing atmosphere shows a diffuse phase transition near T_C = 703 K. The values of and tan are compared between these three crystals consisting of two kinds of BaTi₂O₅ and one BaTiO₃.     

The High Frequency Properties and Crystallization of PbTiO3 Glass-Ceramics by Sol-Gel Process

PbTiO₃ glass-ceramics were produced by a sol-gel process. DTA and X-ray diffraction analysis provided information about the structural transformations and crystallization temperature. The range of crystallization temperature of PbTiO₃ is larger than that of PbTiO₃ glass-ceramics. By increasing the glass composition, the crystallization temperature was increased. The phase transformation of PbTiO₃ from the cubic to the tetragonal phase depends on the crystal size caused by the different heat treatment temperatures. The dielectric measurements in high frequency range (> 10⁷Hz) exhibited evidence of a relaxation phenomena near 850 MHz. With increasing glass composition, the position of the relaxation frequency was increased. The temperature dependence of the dielectric constant of PbTiO₃ and PbTiO₃ glass-ceramics has an obvious discrepancy. The dielectric constant of PbTiO₃ glass-ceramics shows the characteristic dispersion at the Curie point. It indicated that the glass ceramic sample has a stronger tendency for a diffuse phase transition.     

Effect of Temperature on the Elastic and Anelastic Behaviour of Magneto-Ferroelectric Composites Ba0.8Pb0.2TiO3 + Ni0.93Co0.02Mn0.05Fe1.95O4-δ in the Ferroelectric Rich Region

Composites with composition xBa_0.8Pb_0.2TiO₃+ (1 –x) Ni_0.93Co_0.02Mn_0.05Fe_1.95O_4- in which x varies as 1.0, 0.9, 0.7 and 0.5 in molar percent have been prepared by the conventional ceramic double sintering process. The presence of the two phases has been confirmed by X-ray diffraction. These composites were prepared for their use as magnetoferrolectric devices. Variation of longitudinal modulus (L) and internal friction loss (Q ^–1) of these samples with temperature at 142 kHz has been studied in the wide temperature range 300 to 630 K. The elastic behaviour (L) showed a break at the ferroelectric Curie temperature (498 K) in the case of pure ferroelectric material (Ba_0.8Pb_0.2TiO₃). This break shifted to lower temperature side as the ferrite component increases in the composite. The temperature variation of internal friction loss (Q ^–1) showed a corresponding stress induced relaxation peak at the ferroelectric-non-ferroelectric phase transition. This behaviour is explained in the light of structural phase transition.     

Characterization of Piezoelectric Shear Mode Inkjet Actuator

ABSTRACT

Impedance analysis was used to characterize the properties of Piezoelectric Shear Mode Inkjet Actuators. Ceramic actuators poled parallel to the channel walls exhibit good performance. Applying high voltage the actuators can be depolarized at high temperature or even re-poled perpendicular to the channel walls. This limits the drive pulse and the bias voltage below the coercive voltage. The leakage current also has been studied with various conditions. For the ferroelectric ceramic materials, the Schottky barrier also can be measured at definite voltage and temperature ranges, the corresponding Barrier for the Al/PZT contact is 0.98 eV. A pronounced low-temperature dielectric relaxation process was observed between 100–150 K; the relaxation rate fellows the Arrhenius law, the fitted activation energy is 0.194 eV. The resonance frequency increases as decreasing the temperature because of increasing for the stiffness coefficient at low temperature.     

Ferroelectric lead iron-chromium-nickel niobate films

Abstract

The fabrication of ferroelectric films of modified lead iron niobate by a multiple magnetron sputtering technique with a subsequent rapid thermal annealing at 800°C for 5 seconds is reported. Since the magnetic properties of pure iron preclude its use in magnetron sputtering, a non-magnetic stainless steel was used as one of the target materials resulting in a ferroelectric of composition Pb[(Fe_0.7Cr_0.2Ni_0.1)_0.5Nb_0.5]O₃. The reaction sequence involved in the formation of the ferroelectric perovskite phase has been identified. The films exhibit unsaturated ferroelectric hysteresis loops with a remanent polarization of 15 μC/cm² and a coercive field of 100 kV/cm. The room temperature dielectric constant and dielectric loss at 1 kHz were 640 and 0.1, respectively. The dielectric constant showed a dielectric anomaly as a function of temperature in the form of a broad maximum around 90°C confirming the ferro-para electric phase transition. The films were highly insulating with a room temperature conductivity of ≈1 X^?12 Ω^?1 cm^?1, and an activation energy of 0.8 eV.