Dielectric properties of ZnNb2 O 6 -TiO 2 mixture thin films

ZnNb₂O₆-TiO₂ mixture thin films with multilayer structures were fabricated via a sol-gel spin coating process. TiO₂ layers were deposited on the pre-crystallized ZnNb₂O₆ layers in order to suppress the formation of the ixiolite phase which always forms in the bulk system. The phase constitution of the thin films, confirmed by X-ray diffraction (XRD), could be controlled by the annealing temperatures, which, in turn, influenced the dielectric properties of the thin films. TiO₂ layers crystallized as the anatase phase and then transformed to the rutile phase at temperatures higher than 725^∘C. Dielectric constants of the mixture thin films, measured at 1 MHz with an MIM (metal-insulator-metal) structure, increased from 27 to 41 with dielectric losses below 0.005 as the annealing temperature increased from 700^∘C to 900^∘C. The increase in the dielectric constants was understood to originate from the increasing amounts of the rutile phase. Temperature coefficients of capacitance (TCC) were also measured between 25^∘C and 125^∘C, which showed a decreasing manner from positive values to negative values with increasing annealing temperatures. When annealed at 850^∘C, the TCC of the thin films could be tuned to be approximately 0 ppm/^oC with dielectric constant and dielectric loss of 36 and 0.002, respectively.     

Effects of Oxide Additives Coating on Microstructure and Dielectric Properties of BaTiO3

Effects of mixing methods (mechanical mixing, chemical coating) on microstructure and dielectric properties of Ho, Mg and Mn doped BaTiO₃ have been studied. BaTiO₃ particles coated with Ho, Mn and Mg were prepared by a homogeneous precipitation method using urea, and then silica was coated by the sol-gel technique. The adsorption of additives on the BaTiO₃ surface was confirmed. Temperature characteristics of capacitance were satisfied by mechanical mixing and chemical coating techniques, both of which yield different sintering and microstructure behaviors. Pyrochlore phase (Ho₂Ti₂O₇) was observed on the mechanically mixed sample, whereas none of pyrochlore phase was observed at the coated sample after thermal etching. Those different behaviors caused by the degree of homogeneous distribution of the additives in BaTiO₃ matrix were confirmed by EDS analysis.     

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.     

Dielectric behavior of Bi2/3Cu3Ti4O12 ceramic and thick films

The paper reports on synthesis, sintering and microstructure of Bi_2/3Cu₃Ti₄O₁₂, a lead-free, high-permittivity material with internal barrier layer capacitor behavior. Complex impedance and capacitance of the ceramic and thick films were studied as a function of frequency (10 Hz–2 MHz) and temperature (−170 to 400°C). Dc electrical conductivity of the samples was measured in the temperature range 20–400°C. Broad and high maxima of dielectric permittivity versus temperature plots were observed reaching 60,000 for ceramic and 5,000 for thick films. The maxima decrease and shift to higher temperatures with increasing frequency. Two arcs ascribed to grains and grain boundaries were found in the plots of imaginary part versus real part of impedance. Analysis of the impedance spectra indicates that Bi_2/3Cu₃Ti₄O₁₂ ceramic could be regarded as electrically heterogeneous system composed of semiconducting grains and less conducting grain boundaries. The developed thick film capacitors with dielectric layers based on Bi_2/3Cu₃Ti₄O₁₂ exhibit dense microstructure, good cooperation with Ag electrodes, high permittivity up to 5,000 and relatively low temperature coefficient of capacitance in the temperature range 100–300°C. Broad maxima in the dielectric permittivity versus temperature curves may be attributed to Maxwell–Wagner relaxation.     

Annealing Effects on Structural and Dielectric Properties of Tunable BZT Thin Films

Ba(Zr, Ti)O₃ thin films have attracted great attention in recent years for their potential use in DRAMs and MCMs due to their high dielectric constant and relatively low leakage current. However, their tunable dielectric properties were rarely investigated and the corresponding potential for tunable microwave applications was seldom reported. In this paper, we present the tunable dielectric behavior of BZT thin films deposited by RF magnetron sputtering from a Ba(Zr_0.3Ti_0.7)O₃ ceramic target on MgO single crystal substrates. The composition, thickness and crystallinity of the thin films were analyzed by Rutherford backscattering (RBS), scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. The dielectric constant and loss tangent were measured as a function of electric field (0–7 kV/mm) and temperature (–140 to +160°C) at frequencies up to 1 MHz, using interdigital capacitors (IDC) with Au electrodes on thin films. By optimizing the preparation process, a tunability {defined as = [ (0) – (E_max)]/ (0)} of 76% at E_max = 7 kV/mm and a low loss tangent of 0.0078 can be achieved. In addition, the influence of annealing temperature on the dielectric properties of the thin films is also discussed.     

SrLnAlO4 (Ln=Nd and Sm) Microwave Dielectric Ceramics

SrLnAlO₄ (Ln=Nd and Sm) ceramics with K₂NiF₄ structure were prepared by a solid state reaction approach, and their microwave dielectric characteristics were evaluated together with the microstructures. The single phase dense SrNdAlO₄ and SrSmAlO₄ ceramics were obtained by sintering at 1450–1475°C and 1475–1500°C, respectively, and the good microwave dielectric characteristics were achieved: (1) = 17.8, Q · f = 25,700 GHz, _f = –9 ppm/°C for SrNdAlO₄; and (2) = 18.8, Q · f = 54,880 GHz, _f = 2 ppm/°C for SrSmAlO₄ dense ceramics. The Qf value significantly increased with increasing sintering temperature.     

Quantitative Measurement of Dielectric Properties Using Scanning Nonlinear Dielectric Microscopy with Electro-Conductive Cantilever

A quantitative measurement method of the linear and nonlinear dielectric constant using cantilever-type scanning nonlinear dielectric microscopy (SNDM) is reported. Using this method, we succeed in quantitatively measuring the linear dielectric constant distribution of TiO 2 -Bi 2 Ti 4 O 11 ceramics and nonlinear dielectric constant of LiTaO 3 single crystal.     

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.     

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.     

The Dielectric Properties for Yttrium Doped SBT Thin Films Prepared by Sol-Gel Method

In this work, Sr_0.5Ba_0.5Ti_1-zY_zO₃ (SBT) thin films were prepared on a Pt/SiO₂/Si substrate by sol-gel process. The microstructures of SBT thin films were examined by IR, XRD and TEM. The influences of Y on the microstructure and dielectric properties of Sr_0.5Ba_0.5Ti_1-zY_zO₃ thin films were studied. It is found that tetragonal perovskite crystal grains existed in SBT thin films. Increasing Y doping has a clear effect on the grain size of SBT. It is found that the proper Y doping content decreases dielectric loss for SBT thin films.     

Co-Modification of Ba5NdTi3Ta7O30 Dielectric Ceramics by Substitution and Introducing Secondary Phase

Co-modification of Ba₅NdTi₃Ta₇O₃₀ dielectrics ceramics was investigated through Pb substitution for Ba and introducing Bi₄Ti₃O₁₂ secondary phase. The dielectric constant increased from 150 to 283, the temperature coefficient of the dielectric constant decreased from –2500 ppm/°C to –1279 ppm/°C, and the dielectric loss decreased to 0.0007 at 1 MHz. Meanwhile, the bi-phase ceramics were investigated to achieve temperature stable ceramics with high dielectric constant and low dielectric loss. As the composition x varied from 0.4 to 0.7 for (1 – x)(Ba_0.8Pb_0.2)₅NdTi₃Ta₇O₃₀/xBi₄Ti₃O₁₂, the temperature coefficient of the dielectric constant changed from negative to zero to positive.     

Dielectric properties of nanocrystalline TiO2 prepared using spark plasma sintering

Ultra fine rutile powders (below 50 nm) were prepared via the sol-gel process and bulk type TiO₂ specimens were fabricated using spark plasma sintering (SPS). The TiO₂ specimen sintered at a low temperature (720^∘C) exhibited a highly relative density (97%) and a nano-sized grain structure (200 nm). Dielectric properties of spark plasma sintered TiO₂ specimens including dielectric constants (k) and losses (tan δ) were measured. The TiO₂ specimen, obtained by SPS, showed a high dielectric constant (∼780) and a low tan δ (∼0.005), and a relaxation behavior at 1 MHz. After the subsequent annealing process of the TiO₂ specimen in O₂ flow, the dielectric constants remarkably decreased (k = 100s). These dielectric properties of nanocrystalline TiO₂ specimens prepared by SPS were discussed in terms of space charges produced by the reduction of Ti⁴⁺ ions and crystallographic orientations of grains.     

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.     

Dielectric and mechanical properties of hot-pressed SiCN/Si3N4composites

A series of high temperature radar wave-absorbing materials, SiCN/Si₃N₄ceramics, were prepared by hot-pressing. The nanometer SiCN powder, used as an absorber in the SiCN/Si₃N₄ceramic, was synthesized through laser pyrolysis of ((CH₃)₃Si)₂NH) and NH₃. The dielectric and mechanical properties of the prepared ceramics were investigated. XRD and SAED were conducted to study the growth of crystals in the ceramics. The results showed that the transformation of Si₃N₄from α to β was inhibited. The growth of the rod-like β -Si₃N₄grains in SiCN/Si₃N₄ceramics was retarded during hot-pressing process due to the existence of the nanometer SiCN particles. The relative density and the strength of the composites both decreased with the increase of the SiCN content in the composites. The dielectric properties of the ceramics prepared at different temperatures were very different. For the samples sintered at 1600^∘C and 1700^∘C, both the real and imaginary parts of the complex permittivity of them increased as the content of SCN powder in the sample obviously. For the sample with same concentration of SCN, the real and imaginary parts of them varied with the sintering temperature. SAED pattern revealed that structure of the SiCN in SiCN/Si₃N₄sintered at 1800^∘C tended to crystallize fully. Its real, imaginary parts and dissipation factor were much lower than those sintered at 1600^∘C and 1700^∘C greatly. Supported by national natural science foundation of China (No. 50572090)     

温度和电压对变压器矿物绝缘油频域介电特性的影响

本文中作者以传统变压器矿物绝缘油为研究对象,研究了不同温度和电压下绝缘油频域介电谱的变化,并通过电路参数模型分析了温度和电压对绝缘油频域介电特性的影响。     

Effects of structural characteristics on microwave dielectric properties of (1−x)CaWO4 –xLaNbO4 ceramics

Dependences of microwave dielectric properties on the structural characteristics of (1−x)CaWO₄–xLaNbO₄ ceramics were investigated as a function of LaNbO₄ content (0.0 ≤ x ≤ 0.5). A single phase with tetragonal scheelite structure was obtained up to x = 0.35, and then the mixture phases with scheelite and fergusonite structure were detected. With the increase of LaNbO₄, the deviation of the observed dielectric polarizabilities calculated by the Clausius-Mosotti equation from the theoretical values calculated by the additivity rule of dielectric polarizability, was decreased due to the decrease of oxygen bond valence in ABO₄ scheelite structure. Dielectric constant (K) and temperature coefficient of resonant frequency (TCF) were increased with LaNbO₄ content due to the decrease of oxygen bond valence. Q ⋅ fvalue was dependent on the atomic packing fraction of unit cell as well as the grain size. Typically, K = 13.3, Qf = 50,000 GHz and TCF = −8.7 ppm/^oC were obtained for the specimens with 0.3 mol of LaNbO₄ sintered at 1150^oC for 3 h.     

Dielectric Characteristics and Tunability of Barium Stannate Titanate Ceramics

Ba(Ti_{1 –x} Sn _x )O₃ solid solutions were prepared by a solid state reaction method, and their dielectric and tunable characteristics were investigated together with the microstructures and diffused phase transition behaviors. The dielectric relaxation behaviors were observed and became stronger with increasing x.The obvious field dependence of the present system was observed with high dielectric constant and low loss at relatively lower DC electric field. The excellent tunable dielectric characteristics were achieved for x= 0.15 at room temperature: tunability 56%, tan 0.003 at 10 kHz under 7.6 kV/cm, indicating that it is a promising candidate for electric-field tunable dielectrics working at room temperature.     

Effects of Substrate and Annealing Temperatures on the Characteristics of SrBi4Ti4O15 Thin Films

In this study, radio frequency (RF) sputtering was used as the method and the layer-structured bismuth compound of SrBi₄Ti₄O₁₅ + 4 wt% Bi₂O₃ ferroelectric ceramic was used as the target to deposit the SrBi₄Ti₄O₁₅ (SBT) thin films. The addition of excess Bi₂O₃ content in the target ceramic was used to compensate the vaporization of Bi₂O₃ during the sintering and deposition processes. SBT ferroelectric thin films were deposited on Pt/Ti/SiO₂/Si under optimal RF magnetron sputtering parameters with different substrate temperatures for 2 h. After that the SBT thin films were post-heated using rapid temperature annealing (RTA) method. The dielectric and electrical characteristics of the SBT thin films were measured using metal-ferroelectric-metal (MFM) structure. From the physical and electrical measurements of X-ray diffraction pattern, scanning electronic microscope (SEM), I-V curve, and C-V curve, we had found that the substrate temperature and RTA-treated temperature had large influences on the morphology, the crystalline structure, the leakage current density, and the dielectric constant of the SBT thin films.     

Effect of B2O3 and CuO on the sintering temperature and microwave dielectric properties of the BaTi4O9 ceramics

The effect of B₂O₃ and CuO on the sintering temperature and microwave dielectric properties of BaTi₄O₉ ceramics was investigated. The BaTi₄O₉ ceramics were able to be sintered at 975^∘C when B₂O₃ was added. This decrease in the sintering temperature of the BaTi₄O₉ ceramics upon the addition of B₂O₃ is attributed to the formation of BaB₂O₄ second phase whose melting temperature is around 900^∘C. The B₂O₃ added BaTi₄O₉ ceramics alone were not sintered below 975^∘C, but were sintered at 875^∘C when CuO was added. The formation of BaCu(B₂O₅) second phase could be responsible for the decrease in the sintering temperature of the CuO and B₂O₃ added BaTi₄O₉ ceramics. The BaTi₄O₉ ceramics containing 2.0 mol% B₂O₃ and 5.0 mol% CuO sintered at 900^∘C for 2 h have good microwave dielectric properties of ε_r = 36.3, Q× f = 30,500 GHz and τ_f = 28.1 ppm/^∘C     

Dielectric Properties of Homoepitaxial SrTiO3SrTiO3SrTiO3 Thin Films Grown in the Step-Flow Mode

We have deposited SrTiO₃ thin films on Nb-doped SrTiO₃ substrates by pulsed laser deposition at temperatures of up to 1400°C. Reflection high energy electron diffraction was used to monitor the film growth mode at various temperatures and it was shown that growth proceeded in the step-flow mode at above 900°C. Capacitors were formed by evaporating platinum pads on the film surface and gold pads on the substrate. Films grown in the step-flow mode showed consistently higher dielectric constants below 200 K than films grown in the layer-by-layer mode. Films with the highest dielectric constant () were obtained using a stoichiometric ablation target at an oxygen pressure of 10SrTiO₃ ^–6SrTiO₃ Torr.