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1.
As integrated circuits have become more and more complex and with smaller and smaller feature sizes several limitations have become apparent. One of these is the need for low-k dielectric materials as insulating layers. Recent work has reported promising materials for such insulators that include some fluorinated polymers. These dielectric materials were further improved by introducing porosity into the polymer films. One of the key factors in the dielectric constant of a material is its density. As the polarization of the material is related to the number of bonds, the dielectric constant will scale with the density. In this paper a series of molecular modeling calculations were conducted on various fluorine substituted polymers in order to predict their densities. A surprising result of these calculations was the prediction that some of the polymers would have densities less than 1 g/cm3. One of these polymers was synthesized and the density determined. The calculated density was in extremely good agreement with the experimental density. This paper will present the details of the molecular modeling technique as well as the synthesis and characterization of one of the polymers of interest. 相似文献
2.
The introduction of very sensitive detectors and the use of phase modulation has enabled interferometric spectroscopy to be extended downwards in frequency until the spectral coverage overlaps that provided by microwave dielectric methods. The radiometric precision available has been steadily improved by taking advantage of both instrumental and computational advances and the accuracy which can now be attained is comparable to that of dielectric or mid-infrared methods. Both the real and the imaginary components of the complex dielectric constant (or the complex refractive index) can now be obtained for moderately transparent materials over the millimetre and submillimetre bands for a wide range of specimen temperature, and reflectance methods have been developed for the study of heavily absorbing specimens. The far infrared band is particularly appropriate for the study of high polymers. With these instrumental innovations considerable advances may be expected in the understanding of molecular motion in these materials. 相似文献
3.
This paper reports the measured values of dielectric permittivity ε′ and dielectric loss ε″ of ethylene glycol, diethylene glycol and poly(ethylene glycol)s of average molecular weight 200, 300, 400 and 600 g mol−1 in the pure liquid state. The measurements have been carried out in the frequency range 200 MHz to 20 GHz at four different temperatures of 25, 35, 45 and 55 °C. The complex plane plots (ε″ versus ε′) of these molecules are Cole–Cole arcs. The static dielectric constant ε0, high‐frequency limiting dielectric constant ε∞, average relaxation time τ0 and distribution parameter α have been determined from these plots. The value of the Kirkwood correlation factor g and the dielectric rate free energy of activation ΔF have also been evaluated. The dependence of relaxation time on molecular size and viscosity has been discussed. A comparison has also been made with the dielectric behaviour of these molecules in dilute solutions of non‐polar solvents, which were carried out earlier in this laboratory. The influences of intermolecular hydrogen bonding and molecular chain coiling on the dielectric relaxation of these molecules have been recognized. © 2000 Society of Chemical Industry 相似文献
4.
—It has been shown that quenched Pb(Sc1/2Ta1/2)O3 (PST) disordered ceramics and crystals show diffuse dispersive dielectric properties, while well annealed ordered materials exhibit normal sharp first order transition. The pyroelectric depolarization measurements taken using a Hewlett Packard Model 4140B picoammeter/DC Source under computer controlled heating cycle also have shown different behaviors between disordered and ordered materials.
In this work pyroelectric measurements by Chynoweth method under DC bias up to 1.8 KV/mm within a temperature range of 70°C around the temperature of maximum dielectric constant have been studied. A very significant enhancement of the pyroelectric signal under DC bias is observed in thermally quenched disordered samples. The largest enhancement of the signal appears at temperatures some degrees below the temperature of maximum dielectric constant.
The existence of microdomains in disordered materials is believed to be responsible for this new extrinsic component of reversible pyroelectricity.
The large reversible pyroelectric effect is a promising phenomenon for developing new pyroelectric devices. 相似文献
In this work pyroelectric measurements by Chynoweth method under DC bias up to 1.8 KV/mm within a temperature range of 70°C around the temperature of maximum dielectric constant have been studied. A very significant enhancement of the pyroelectric signal under DC bias is observed in thermally quenched disordered samples. The largest enhancement of the signal appears at temperatures some degrees below the temperature of maximum dielectric constant.
The existence of microdomains in disordered materials is believed to be responsible for this new extrinsic component of reversible pyroelectricity.
The large reversible pyroelectric effect is a promising phenomenon for developing new pyroelectric devices. 相似文献
5.
《Journal of the European Ceramic Society》2007,27(8-9):2823-2826
A dielectric resonator technique has been developed for measurements of conductivity and surface resistance of thin metal films deposited on a dielectric substrate. This technique allows for measurements of films having surface resistances that are smaller than 5 Ω without requiring the need to perform measurements of the substrate thickness. The uncertainty of the surface resistance measurements is about 2–3% for both thin films and bulk materials. The accuracy of the conductivity measurements of the thin films is similar to the accuracy of the measurements of their thickness. Several samples have been measured having thicknesses that range from 66 nm to 50 μm. 相似文献
6.
L. M. Smith A. J. Clifford C. L. Hamblin R. K. Creveling 《Journal of the American Oil Chemists' Society》1986,63(8):1017-1023
This study evaluated some of the changes that occur in shortenings used for commercial deep-fat frying in fast-service restaurants. Foods cooked in partially hydrogenated soybean oil were battered chicken parts and french fries. Sixty-five samples of fresh and used shortenings were collected from nine restaurants on three occasions over a three-month period. Frying periods varied from 0 to 300 hr, and most samples were taken just before the used fat was discarded. For fresh shortenings, percentages of polar materials, free fatty acids (FFA), materials not eluted by gas chromatography, and fatty acid profiles differed only slightly. For used samples, there were marked variations in these analyses and in increases of dielectric constant measurements. Frying times were highly correlated with increases in dielectric constant, polar materials and FFA. The greatest change in fatty acid profiles occurred intrans-C18 monoenes which decreased from over 40% to as low as 13%. Due to lipid exchange with chicken fat, both oleic and linoleic acids increased in the shortenings with hours of use, whereas stearic acid decreased. There were high correlations, among increases in dielectric constant, percentages of polar materials and FFA, demonstrating that each of these methods could predict degradation of the shortening. However, the increase in dielectric constant, as measured by a Foodoil Sensor (FOS), was the most convenient for quality control in restaurant situations. In most cases, used shortening was discarded before 100 hr of frying time; and only a few of these samples had FOS readings near 4.0, FFA over 1.00%, or percentages of polar materials over 27%. These values have been suggested as discard criteria. However, a number of samples used between 100 and 300 hr exceeded these limits. There is a need to specify suitable limits, related to quality and health factors, to determine at what point a cooking fat should be discarded. 相似文献
7.
微波介质陶瓷及器件研究进展 总被引:47,自引:9,他引:47
现代移动通信、无线局域网、全球卫星定位系统等技术的革新,对以微波介质陶瓷为基础的微波电路器件提出了更高的要求,各种微型化、高频化、片式化、模块化的新型微波介质陶瓷器件及相关介质陶瓷得到迅速发展。综述了近几年在高介电常数、高频、低温烧结微波介质陶瓷方面的进展,对不同材料体系的离子取代、离子置换、低熔点烧结助剂对微波介质陶瓷结构、介电性能的影响进行了分析讨论。概述了介质谐振型、叠层型、功能模块型微波介质陶瓷器件的研究和生产情况,重点论述了与低温共烧技术相关的介质陶瓷、器件及模块的进展,探讨了材料特性、微波器件结构与微波特性之间的关系,并指出了今后微波介质陶瓷及器件的发展方向。 相似文献
8.
《Ceramics International》2020,46(17):26829-26840
Open-cell ceramic foams are promising materials in the field of microwave heating. They can be manufactured from susceptor materials and can, therefore, be used as selective heating elements. In this study, the complex permittivities of ceramic foam materials, including silicon-infiltrated silicon carbide (SiSiC), pressureless sintered silicon carbide (SSiC), silicate-bonded silicon carbide (SBSiC), and cordierite were determined. The dielectric properties of the foams were determined by the cavity perturbation technique using a TE104 WR340 waveguide resonator at 2.45 GHz. Samples were preheated in a tubular furnace, enabling temperature-dependent permittivity measurements up to 200 °C. The effective dielectric constant and effective loss factor were found to depend on the porosity and material composition of the foam. The SiSiC material had a higher effective dielectric constant than the SSiC and SBSiC ceramics. The effective dielectric constant of the foams showed a trend of gradual increase with increasing temperature. Some selected dielectric mixing relations were then applied to describe the effective permittivity of the foams and compare them with predictions from finite element simulations performed using the CST Studio Suite. The foam morphologies and simple block inclusions were used in the simulations. 相似文献
9.
J. L. Hedrick K. R. Carter H. J. Cha C. J. Hawker R. A. DiPietro J. W. Labadie R. D. Miller T. P. Russell M. I. Sanchez W. Volksen D. Y. Yoon David Mecerreyes R. Jerome James E. McGrath 《Reactive and Functional Polymers》1996,30(1-3):43-53
Foamed polyimides have been developed in order to obtain thin film dielectric layers with very low dielectric constants for use in microelectronic devices. In these systems the pore sizes are in the nanometer range, thus, the term ‘nanofoam’. The polyimide foams are prepared from block copolymers consisting of thermally stable and thermally labile blocks, the latter being the dispersed phase. Foam formation is effected by thermolysis of the thermally labile block, leaving pores of the size and shape corresponding to the initial copolymer morphology. Nanofoams prepared from a number of polyimides as matrix materials were investigated as well as from a number of thermally labile polymers. The foams were characterized by a variety of experiments including TEM, SAXS, WAXD, DMTA, density measurements, refractive index measurements and dielectric constant measurements. Thin film foams, with high thermal stability and low dielectric constants approaching 2.0, can be prepared using the copolymer/nanofoam approach. 相似文献
10.
Ecofriendly materials are becoming a need of the day. We have severe setback when there is lot of use of agro wastes in plastics. To reduce pure plastic use in agriculture, this study has been made to find some remedial measure. In the process, we sought the effect of addition of rice husk (RH) in polyvinylchloride (PVC) on the dielectric properties at different frequency and temperature has been studied. Measurements have been performed in the frequency range from 1 to 10 kHz and temperature range of 32–80°C. The experimental results show that dielectric constant (ε′) increases with the addition of RH in PVC. Dielectric constant (ε′) decreases with increasing frequency, which indicates that the major contribution to the polarization comes from orientation polarization. Dielectric constant (ε′) increases with increasing temperature due to greater freedom of movement of dipoles within PVC at higher temperatures. A theoretical model for dielectric constant with temperature and frequency dependent is proposed. Experimental results are in good agreement with the proposed theoretical model. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012 相似文献
11.
《应用陶瓷进展》2013,112(2):93-99
AbstractIt has been appreciated for some years now that the dielectric properties of a material need to be considered if microwave processing is to progress from an empirical basis. The present paper describes the evaluation of materials for use in a pilot plant scale hybrid kiln. Previous kilns at Staffordshire University using microwaves as the only source of energy operated at 2·45 GHz but a new pilot plant scale hybrid kiln for operation at 896 MHz with 75 kW of microwave power is under development with improved, more complex, insulation and firing arrangements. For this reason a range of new refractory and insulation materials has been assessed, e.g. support tubes for heating elements and previously used products and materials measured at only 2·45 GHz have been remeasured at 911 MHz. The results of dielectric property measurements are presented for a range of refractory materials together with an assessment of their likely interactions with the microwave environment. 相似文献
12.
Complete relaxation map of polypropylene: radiation-induced modification as dielectric probe 总被引:1,自引:1,他引:0
E. Suljovrujic 《Polymer Bulletin》2012,68(7):2033-2047
The molecular relaxation behaviour of isotactic polypropylene (iPP) exposed to gamma radiation in air to various absorbed
doses (up to 700 kGy) has been investigated by dielectric loss (tan d { \tan }\;\delta ) analysis; the polar (mainly carbonyl and hydroperoxide) groups that were introduced by radiation-induced oxidation were
considered as tracer groups. All relaxation zones (α, β, γ and δ in the order of decreasing temperature), between 25 K and
melting temperature, were studied in the frequency range from 1 kHz to 1 MHz. The changes observed in the dielectric relaxation
spectra were related to the modifications in the structural and morphological parameters attributed to exposure of the iPP
samples to radiation. Wide-angle X-ray diffraction was used to investigate radiation-induced changes in the crystalline structure
and degree of crystallinity, since the α relaxation is connected with this phase. Infrared spectroscopy and gel measurements
were used to determine the changes in the oxidative degradation and the degree of network formation, respectively. Conclusions
derived using different methods were compared. This study reveals high dielectric and/or relaxation sensitivity of iPP to
gamma radiation. Disappearance of the low-temperature dielectric (γ and δ) relaxations together with large changes in intensity,
position and activation energy of the dielectric α relaxation are observed with gamma irradiation and are mainly connected
with oxidative degradation in iPP structure. 相似文献
13.
Different types of chelated polymer complexes have been synthesized to obtain improved electrical properties. Compact discs from powders of the chelated polymers were prepared and heated in a specially designed holder. Electrical conductivity and dielectric constant of Cu(II) and Ni(II): N-salicylidene polymethacrylic acid hydrazide samples were measured at a fixed frequency (1600 Hz) throughout the temperature range 25-150°C. The AC conductivity as well as dielectric measurements showed maxima at 85°C. The water molecules which were trapped in the polymer matrix are believed to play the main role in conduction and dielectric behaviour of the polymeric material. From the AC conductance and dielectric constant measurements, the dielectric losses of these polymeric materials were calculated as a function of temperature. 相似文献
14.
Kazuki Kanehara Shingo Urata Sou Yasuhara Takaaki Tsurumi Takuya Hoshina 《Journal of the American Ceramic Society》2023,106(9):5341-5350
Oxide glasses are dielectric materials with potential applications in high-frequency communications; hence, their dielectric properties in the gigahertz to terahertz frequency range should be investigated. In this study, the dielectric properties of silica glass and five single alkali silicate glasses were measured at 0.5–10 THz using terahertz time-domain spectroscopy and far-infrared spectroscopic ellipsometry. At 0.5–10 THz, the silica glass exhibited low dielectric dispersion with a low dielectric constant and loss. By contrast, the alkali silicate glasses exhibited high dielectric dispersion, and the dielectric constant and loss were higher than those of the silica glass. The shape of the dielectric dispersion profile depended on the alkali-metal ions; it was broader for lighter ions such as Li ions and sharper for heavier ions such as Cs ions. The peak dielectric loss shifted toward a lower frequency as the weight of the alkali-metal ions in the alkali-silicate glass increased. To understand the dielectric dispersion, the complex permittivity was calculated using molecular dynamics simulations. The theoretical results qualitatively agreed with the experimental data. Ion dynamics analysis revealed that alkali-metal ions vibrate and migrate under an applied electric field, which affects the dielectric constant and loss of alkali-silicate glasses at gigahertz to terahertz frequencies. To fabricate filter devices at low temperatures, alkali metals should be added to silicate glass; therefore, a minimum amount of light alkali metals should be used to minimize the dielectric loss of the glass materials while maintaining productivity. 相似文献
15.
F.F. Nazem 《Carbon》1982,20(4):345-354
The rheological behavior of molten mesophase pitch has become a subject of major scientific curiosity as well as of technological importance. With the exception of a few recent studies, the early experimental techniques were not entirely adequate for precise rheological characterization of such a complex fluid as molten mesophase pitch. A reasonably extensive literature, therefore, does not seem to exist on mesophase pitch rheology. The factors which could contribute to the difficulties of accurately measuring the apparent viscosity of carbonaceous anisotropic materials are discussed herein. A Couette-flow instrument has been modified for measuring the apparent viscosity of mesophase pitch, circumventing most of the experimental difficulties. The reliability of this apparatus has been tested by cross checking the apparent viscosity measurements with the values measured from two other rheometers, Instron Capillary and Seiscor/Han, for a number of fluids. Changes in rheological properties that occur during the transformation of a commercial pitch into a totally anisotropic pitch have now been studied by an improved technique on the modified Couette apparatus. The rheology of two mesophase pitches, made from model compounds, have also been investigated for comparison. 相似文献
16.
《Ceramics International》2016,42(8):9591-9598
Nickel-zinc ferrite nanoparticles with suitable chemical modifications by Mn or Co substitutions for Zn as two systems (namely, Ni–Zn–Mn and Ni–Zn–Co) were synthesized by sol-gel autocombustion method. X-ray diffraction measurements on the synthesized nanoparticles confirm that the samples attain single phase cubic spinel structures only. The powders were then used to obtain pellets in desired dimensions by employing usual ceramic procedure for carrying out measurements of resistivity and dielectric properties. The variations of dc resistivity as a function of composition and temperature, and the corresponding variation of activation energies for both the systems are presented and discussed. Also, the results of dielectric constant as a function of substituent concentration, dielectric dispersion and dielectric loss tangent are discussed. Effect of Mn/Co substitutions in Ni–Zn ferrites and possible mechanisms responsible for variations in resistivity and dielectric properties of both the ferrite systems have been evolved independently. Also, comparison of the trends between the dielectric constant and the resistivity with substituents’ concentration and their inter-relation with conduction mechanisms has been thoroughly analyzed for both the ferrite systems. 相似文献
17.
Long-lasting UV-induced physical and/or physico-chemical modifications of nano-structured TiO2 (anatase) films are highlighted in this work by electrochemical methods. These changes occurring in TiO2 film upon UV exposure are analysed through electrochemical impedance spectroscopy (EIS) measurements. Interfacial capacity measurements show significant and long-lasting modifications of the semiconducting and dielectric properties of TiO2 due to UV exposure. Furthermore, UV exposure significantly modifies the energetic distribution of surface states in the gap of TiO2. Based on Mott-Schottky analysis, the relative dielectric constant is found to increase (from 440 to 870) after UV exposure. An explanation for such an effect is that UV exposure enables hydrogen insertion into the nano-columnar TiO2 film and thereby increases the dielectric constant of the film. 相似文献
18.
Scott L. Swartz C. A. Randall A. S. Bhalla 《Journal of the American Ceramic Society》1989,72(4):637-641
The low-temperature dielectric and pyroelectric properties of pyrochlore Cd2 Nb2 O7 ceramics have been investigated over the temperature range from 10 to 300 K. Dielectric data confirmed that two ferroelectric transitions occurred in the Cd2 Nb2 O7 ceramics at temperatures near 80 and 192 K. The higher-temperature ferroelectric transition is complex, with evidence for three separate transitions occurring within a narrow temperature range. The temperature and frequency dependencies of the dielectric constant were consistent with both second-order (diffuse) and improper ferroelectric (ferroelastic) effects. Pyroelectric data also confirmed the multiple-transition behavior, with anomalies in the pyroelectric coefficient at temperatures corresponding to the onset of the diffuse ferroelectric transition and the ferroelastic effect. Dielectric loss data (analyzed by both Arrhenius and Cole-Cole formalisms) indicated the presence of three separate relaxation-type dielectric loss mechanisms in this temperature range. Unambiguous explanations for the observed dielectric and pyroelectric phenomena could not be made, but domain effects are believed to be responsible for at least part of the complex nature of the ferroelectric transitions in this material. 相似文献
19.
Martin Wijaya Hermanto Guangwen HeMartin Tjahjono Pui Shan ChowReginald B.H. Tan Marc Garland 《Chemical Engineering Research and Design》2011,89(12):2613-2619
Metastable zone width, which can be approximated as the gap between the loci of cloud and clear points is an important control parameter for successful operations of solution crystallization processes. This study attempts to improve the accuracy of cloud point determination in paracetamol-ethanol solution using dielectric constant measurements and a special calibration technique. A suitable calibration model based on logarithm-polynomial expansion is developed using adjusted R2 and Akaike Information Criterion as model selection guides. The model, which decouples the effects of temperature and solute concentration on solution dielectric constant, is utilized to transform the dielectric constant profile into a solute concentration profile. The results show that the cloud points determined from the solute concentration profile are more accurate than those determined directly from the dielectric constant profile. The former are shown to be in good agreement with those obtained from the turbidity measurements, which are used as benchmarks in this study. Consequently, a more accurate metastable zone width could also be obtained using this calibration technique. 相似文献
20.
《Journal of the European Ceramic Society》2006,26(13):2785-2792
The electrical properties of B-site donor and acceptor doped Aurivillius phase Bi3NbTiO9-based ceramics have been investigated. The effect of donor and acceptor doping on the dielectric constant, coercive field, dc conductivity and piezoelectric constant are presented. The band gap of Bi3NbTiO9 (BNTO) is about 3.4 ± 0.2 eV, determined from high-temperature dc conductivity measurements. All of the ceramics are ferroelectrics with high Curie points (∼900 °C). In acceptor doped ceramics, a low-temperature peak in the dielectric loss tangent is explained in terms of a Debye-type relaxation that results from an oxygen ion-jump mechanism. The activation energy for the relaxation is calculated as 0.93 ± 0.05 eV. The reduction of the piezoelectric constant below 500 °C is produced by depolarization, which is produced by the switching of thermally unstable non-180° domain walls. 相似文献