Showing papers on "Dielectric loss published in 1998"

Development of a "laminated waveguide"

Abstract: A waveguide of new structure has been developed for millimeter-wave applications. The dielectric waveguide is constructed with sidewalls consisting of lined via-holes and edges of metallized planes. This structure can be manufactured by lamination techniques, so we refer to the waveguide as a "laminated waveguide". The laminated waveguide can be embedded in a substrate and is able to be wired in three dimensions. The transmission characteristics are evaluated using a glass-ceramic substrate of dielectric constant, /spl epsiv//sub r/=5, and loss, tan /spl delta/=0.0008. Insertion loss per unit length of the guide is estimated to be less than 0.5 dB/cm at 83 GHz. Furthermore, it was confirmed that the laminated waveguide is suitable to feeding lines for a small sized plane array antenna. By electromagnetic simulation, it has been confirmed that fundamental structures, such as bends, branches, power dividers, and interconnections between upper and lower layers can be realized with sufficient performances.

A dielectric resonator for measurements of complex permittivity of low loss dielectric materials as a function of temperature

Abstract: An application of a mode dielectric resonator is described for precise measurements of complex permittivity and the thermal effects on permittivity for isotropic dielectric materials. The Rayleigh-Ritz technique was employed to find a rigorous relationship between permittivity, resonant frequency, and the dimensions of the resonant structure, with relative computational accuracy of less than . The influence of conductor loss and its temperature dependence was taken into account in the dielectric loss tangent evaluation. Complex permittivities of several materials, including cross-linked polystyrene, polytetrafluoroethylene, and alumina, were measured in the temperature range of 300-400 K. Absolute uncertainties of relative permittivity measurements were estimated to be smaller than 0.2%, limited mainly by uncertainty in the sample dimensions. For properly chosen sample dimensions, materials with dielectric loss tangents in the range of to can be measured using the mode dielectric resonator.

The effect of grain and particle size on the microwave properties of barium titanate (BaTiO3)

Abstract: The use of ferroelectric ceramics and thin films in microwave devices requires that they possess frequency-stable, low-loss dielectric properties. At microwave frequencies, ferroelectric polycrystalline ceramic materials typically exhibit a large dielectric relaxation, characterized by a decrease in the relative permittivity (er) and a peak in the dielectric loss (tan δ). Mechanisms attributed to the relaxation phenomenon include piezoelectric resonance of grains and domains, inertia to domain wall movement, and the emission of gigahertz shear waves from ferroelastic domain walls. As a result, the relaxation phenomenon appears to be intimately linked to the domain state of the ferroelectric. The domain state of a ferroelectric is, in part, dependent upon its microstructure. In this study, the microwave dielectric properties of ferroelectric barium titanate were measured as a function of grain and particle size. Polycrystalline ceramic ferroelectric BaTiO3 (having average grain sizes of 14.4, 2.14, and 0.2...

The merging of the dielectric α- and β-relaxations in poly-(methyl methacrylate)

Abstract: Using broad-band dielectric spectroscopy (10−2–109 Hz) the merging of the α- and β-relaxations has been investigated for a polymer, syndiotactic poly(methyl methacrylate) (PMMA), in which the dielectric losses are dominated by a strong β-relaxation. The asymmetrically shaped β-relaxation cannot be described by a Cole–Cole function, not even at low temperatures where the α- and β-relaxations are well separated in frequency. At higher temperatures close to Tg (=404 K), the weak α-relaxation enters our dynamic window and rapidly merges with the β-relaxation. To investigate this merging process we first used a simple addition of two Havriliak–Negami (HN) equations to fit the spectra. The obtained relaxation time for the β-relaxation then displays a kink in its temperature dependence close to Tg. To gain further understanding of the merging, the data were analyzed by means of a regularization method in order to calculate the corresponding distributions of relaxation times directly from the actual measurements ...

Thickness dependence of dielectric loss in SrTiO3 thin films

Abstract: We have measured the dielectric loss in SrTiO3 thin films grown on SrRuO3 electrode layers with thickness ranging from 25 nm to 2.5 μm. The loss depends strongly on the thickness but differently above and below T≈80 K: as the thickness increases, the loss decreases at high temperatures but becomes higher at low temperatures. Our result suggests that, in the high temperature regime, the interfacial dead layer effect dominates while, in the low temperature regime, the losses related to the structural phase transition and quantum fluctuations are important.

Dielectric relaxation of Ba0.7Sr0.3TiO3 thin films from 1 mHz to 20 GHz

Abstract: The dielectric relaxation of Ba0.7Sr0.3TiO3 thin films was investigated up to K band (20 GHz) using time domain and frequency domain measurements. Our results show that from 1 mHz to 20 GHz, the dielectric relaxation of the complex capacitance of Ba0.7Sr0.3TiO3 thin films can be understood in terms of a power law dependence known as the Curie–von Schweidler law. The small dispersion (less than 7% decrease in capacitance from 1 mHz to 20 GHz) and low loss (loss angle less than 0.006 at 20 GHz) measured in Ba0.7Sr0.3TiO3 thin films indicate that these films are applicable to device application up to at least K band.

Radio absorptive material

Abstract: PROBLEM TO BE SOLVED: To obtain radio-wave absorption in a high-frequency range by wrapping a water absorption material having a large dielectric constant and dielectric loss tangent and absorbing moisture by a water-repellent coating in the high-frequency range. SOLUTION: A water absorption material 1, in which water is absorbed to the water absorption material for absorbing moisture, is wrapped by a coating 2 having water repellency. When the water absorption material having extremely large absorptivity is used at that time, the electrical characteristics of the water absorption material 1 at the time of water absorption can be equalized approximately to water. Consequently, when the thickness of the water absorption material 1 under an absorbing state is set in (d), the electric field E0 of arrival electromagnetic waves vertically projected to a radio absorptive material is attenuated up to an electric field E1 by the water absorption material 1 under the absorbing state. The electric field E1 represents that of arrival electromagnetic waves after passage through the water absorption material 1 under the absorbing state at that time. Accordingly, large radio absorption is obtained in a high-frequency range of 1 GHz or more.

Combinatorial synthesis and high throughput evaluation of ferroelectric/dielectric thin-film libraries for microwave applications

Abstract: A library of 256 differently doped thin films of (BaxSr1−x)TiO3 (where 0.5

Anisotropic complex permittivity measurements of mono-crystalline rutile between 10 and 300 K

Abstract: The dielectric properties of a single crystal rutile (TiO2) resonator have been measured using whispering gallery modes. Q factors and resonant frequencies were measured from 300 to 10 K. Q factors as high as 104, 105, and 107 were obtained at 300, 80, and 10 K, respectively. Using the whispering gallery mode technique we have determined accurately the loss tangent and dielectric constant of monocrystalline rutile and obtained much more sensitive measurements than previously reported. We show that rutile exhibits anisotropy in both the loss tangent and permittivity over the range from 10 to 300 K.

Dielectric and far-infrared spectroscopy of glycerol

Abstract: Broadband dielectric spectroscopy has been performed on supercooled glycerol for temperatures between 184 and 413 K. The measurements cover 18 decades of frequency and extend into the far infrared regime. The timescale of the α-process is observed over 14 decades of frequency as a function of temperature. In the THz range an additional loss peak was observed which is identified as the boson peak known from neutron and light scattering experiments. Between the α and boson peak the loss minimum has been observed as a function of temperature down to the glass temperature. It is very broad and cannot be ascribed to a simple superposition of α and boson peak. The data are compared to the susceptibilities obtained from neutron and light scattering.

Near single crystal-level dielectric loss and nonlinearity in pulsed laser deposited SrTiO3 thin films

Abstract: We present low-frequency dielectric loss and nonlinearity measurements in SrTiO3 thin films grown by pulsed laser deposition on SrRuO3 electrode layers. A low loss tangent in the order of 10−4, close to the level found in SrTiO3 single crystals, was observed. Combined with a large tunability, this resulted in a figure of merit for frequency and phase agile materials that can rival that observed in single crystals. The result is potentially significant for tunable microwave device applications, and it points to stress and interface effects as the possible causes for higher dielectric losses in thin films.

Characterization of thin film microstrip lines on polyimide

Abstract: This paper presents an in depth characterization of thin film microstrip (TFMS) lines fabricated on Dupont PI-2611 polyimide. Measured attenuation and effective dielectric constant is presented for TFMS lines with thicknesses from 2.45-7.4 /spl mu/m and line widths from 5-34.4 /spl mu/m over the frequency range of 1-110 GHz. The attenuation is separated into conductor and dielectric losses to determine the loss tangent of Dupont PI-2611 polyimide over the microwave frequency range. In addition, the measured characteristics are compared to closed form equations for /spl alpha/ and /spl epsiv//sub eff/ from the literature. Based on the comparisons, recommendations for the best closed form design equations for TFMS are made.

Dielectric response analysis of a conducting polymer dominated by the hopping charge transport

Abstract: The d.c. conductivity and the electric a.c. response from 100 Hz up to 40 MHz of poly(3n-decylpyrrole) were measured in the 80-330 K interval to characterize the charge transport behaviour of the system. The d.c. conductivity well fitted the variable range hopping model, and the loss factor, after having deducted the d.c. contribution, showed a relaxation peak when the conductivity versus frequency started to rise. The strength of this relaxation increased with temperature and became too large to be related to a dipolar relaxation; moreover, the temperature dependence of the loss peak frequency and d.c. conductivity coincided. The observed relaxation was attributed to the hopping charge transport, as further confirmed by the temperature behaviour of the relaxation strength and by the frequency dependence of the exponents of the power law which locally approximate the conductivity behaviour. As the activation energy of the d.c. conductivity differed from the frequency of the loss peak, the theoretical prediction concerning the selfsimilarity of the a.c. conductivity was roughly verified.

Microwave losses in incipient ferroelectrics as functions of the temperature and the biasing field

Abstract: The dielectric constant of ferroelectric materials can be controlled by an applied electric field. That is promising for applications using the microwave technique. The widespread use of ferroelectric materials at microwaves is retarded by a considerable high dielectric loss by the materials at high frequencies. The goal of this article is to model the essential mechanisms of losses in incipient ferroelectrics at microwave frequencies. The following materials are studied: strontium titanate (SrTiO3) and potassium tantalate (KTaO3). The following loss mechanisms are considered: fundamental loss determined by multiphonon scattering of the soft ferroelectric mode and transformation of microwave electric field oscillations into acoustic oscillations due to residual ferroelectric polarization.

RF measurement technique for characterizing thin dielectric films

Abstract: We have developed a novel technique for measuring the dielectric constant and loss tangent of a thin film dielectric material up to 5 GHz. The dielectric film needs to be deposited on a metal layer and capped with a metal electrode layer. The bottom metal layer does not have to be very conductive, as long as its sheet resistance is uniform and known. Only one step lithography on the top metal layer is required. No dc electrical contact to the bottom metal layer is necessary. The measurement is taken with a Vector Network Analyzer and a coplanar-wave-guide miniature wafer probe.

Improved low frequency and microwave dielectric response in strontium titanate thin films grown by pulsed laser ablation

Abstract: We have grown epitaxial strontium titanate films on lanthanum aluminate substrates at a range of oxygen pressures and substrate temperatures. The complex dielectric function was measured as a function of temperature and electric field bias using a microwave ring resonator and a flip-chip technique. The films having the highest dielectric constant were grown with an oxygen pressure of 600 mTorr and showed large grains in the plane of the film. The small-signal dielectric constant of these films could be changed by a factor of 4 by applying an electric field. The films with the highest dielectric constant showed increased losses, but an improved figure of merit for application to tunable circuits.

Dynamical structure of oligo(ethylene glycol)s-water solutions studied by time domain reflectometry

Abstract: Dielectric relaxation measurements on water solutions of ethylene glycol 200 and 400, (degree of polymerization N=4 and 9) in entire concentration region were carried out using a time domain reflectometry at 25 °C in the frequency range from 300 MHz to 20 GHz. For all the samples, only one dielectric loss peak was observed in this frequency range. Plots of the relaxation strength and logarithm of the relaxation time calculated from apparent peak frequency of dielectric loss curves against monomer unit molar fraction of ethylene glycol X give straight lines in the region of 0

Growth and field dependent dielectric properties of epitaxial Na0.5K0.5NbO3 thin films

Abstract: Na0.5K0.5NbO3 thin films have been grown on LaAlO3(001) substrates using rf magnetron sputtering from a Na and K enriched target. X-ray diffraction showed that the films are epitaxial with mosaic broadening as narrow as 0.044°. Interdigital Au finger electrodes were photolithographically defined on the film surfaces. The dielectric properties of these interdigital capacitors were measured at 1 MHz from room temperature down to 50 K. The capacitor showed 35% tunability at room temperature and a loss tangent of 0.007 without dc bias applied. The loss decreased further with increasing dc bias. For lower temperatures, the capacitance exhibited a broad maximum at ∼200 K, which is possibly linked to a phase transformation of the Na0.5K0.5NbO3 film.

Combinatorial synthesis and evaluation of epitaxial ferroelectric device libraries

Abstract: Combinatorial libraries of parallel-plate capacitors, consisting of Pt and La0.5Sr0.5CoO3 electrodes and a doped BaxSr1−xTiO3 dielectric layer, have been fabricated and analyzed to systematically study the effects of dopants on device performance. Epitaxial heterostructure libraries with sharp interfaces were generated from amorphous layers on LaAlO3 substrates. Two hundred and forty different host/dopant combinations were synthesized on a 1/2 in. by 1/2 in. substrate, with 23 capacitors for each combination. Addition of 1.5 mol % W was found to increase the figure of merit (e/Ileak) 220-fold and reduce the high-frequency (MHz and GHz) loss tangent by fourfold.

Dielectric study in nanocrystalline Bi4Ti3O12 prepared by chemical coprecipitation

Abstract: Bi4Ti3O12 nanoparticles were synthesized by chemical coprecipitation and crystallized in the perovskite structure after calcining at 520 °C. The dielectric properties were measured in bulk nanocrystalline compacts with different grain sizes. It was found that there were three peaks in the curves of the dielectric response as a function of temperature. The first peak shifts to higher temperature with decreasing grain size, which is considered to originate from the polarization of the ions in the conductive (Bi2O2)2+ layers across the potential barrier of the weak conductive perovskitelike layers. The second peak, contributed by the polarization of the defect dipoles on the grain surfaces, especially Bii.–Vo″ dipoles, decreases gradually in intensity and finally disappears with increasing grain size. The last one, corresponding to a ferroelectric phase transition temperature, increases at first with decreasing grain size from 56 to 25 nm, then decreases with further decreasing grain size, and the mechanism ...

Nonlinear behavior of thin film SrTiO3 capacitors at microwave frequencies

Abstract: The voltage-dependent dielectric constant (e) of SrTiO3 (STO) thin films is the basis for developing cryogenic capacitors for tunable microwave applications. In this study, the effect of microwave signal level on nonlinear response at 1.7–1.9 GHz was examined by measuring the level of the third order intermodulation distortion (IMD) signal relative to the input signal level. Small signal dielectric properties such as capacitance, tuning, and loss (tan δ) were also measured at 1 MHz, 3 GHz, and 10 GHz, at temperatures from 4.2 to 300 K. Planar capacitors were comprised of highly (100)-oriented, 1 μm thick STO films deposited via magnetron sputtering onto CeO2-buffered (11_02)-oriented sapphire substrates, with 10 μm gaps between the electrodes. Deviations from the anticipated cubic dependence of the third order IMD product on incident power, for incident power ranges from −10 to 22 dBm, were attributed to conductivity nonlinearity. At incident power levels of 22 dBm and with no dc bias applied to the capac...

Electrical characteristics of metal-dielectric-metal and metal-dielectric-semiconductor structures based on electron beam evaporated Y2O3, Ta2O5 and Al2O3 thin film

Abstract: This work examines the electrical properties of metal-dielectric-semiconductor (Au/Ti–D–pSi) and metal-dielectric-metal (Au/Ti–D–Pt/Ti–pSi) capacitors which incorporate as dielectrics Y2O3, Al2O3 and Ta2O5 films evaporated by an electron beam at room temperature. The emphasis of the results is twofold: the first is the high quality of the investigated films as evidenced by the small measured values of loss factor, flatband voltages, and surface states density as well as the low dispersion of the relative dielectric constants. The second is an analytical procedure for discrimination of current flow mechanisms, under different regimes of applied voltage. A detailed study of the power exponent parameter α=d(Log I)/d(Log V) was found to be superior to conventional graphical representation of I–V data. The dominant mechanisms of charge transport through the metal-dielectric-metal structures was found to be the Schottky emission for Y2O3 and Al2O3 at low electrical fields. For structures with Y2O3 and Ta2O5 fil...

Moisture–absorption, dielectric relaxation, and thermal conductivity studies of polymer composites

Abstract: In the search for new packaging materials for the electrical/electronics industry, three types of polymer composites have been studied. Silicone/boron nitride powders, polyurethane/alumina powders, and polyurethane/carbon fibers have all been synthesized to study the moisture–absorption kinetics, thermal conductivities, and the dielectric loss spectra under various levels of humidity. The water uptake data indicate that water molecules are absorbed not only by the polymer matrix, but also by the interfaces introduced by the fillers. For all materials, the dielectric relaxation spectroscopy shows the presence of a peak in the 175–200 K range, which is largely due to absorbed water. The silicone/boron nitride samples absorbed the least amount of moisture. Incorporating this result with the thermal conductivity data of the three types of polymer composites, it is concluded that silicone polymers embedded with boron nitride can best serve as the coating for the electronic devices that require heat dissipation and moisture resistance, in addition to electrical insulation. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 2259–2265, 1998

Frequency-dependent propagation characteristics of coplanar waveguide electrode on 100 GHz Ti:LiNbO3 optical modulator

Abstract: The microwave propagation characteristics of a coplanar waveguide electrode in the frequency range 45 MHz – 110 GHz were studied in order to evaluate the factors which limit the performance of a high-speed ridged Ti:LiNbO3 optical modulator. Since the effective microwave index is constant in the higher frequency range, neither structure nor material dispersions of the modulator are observed. In addition to the conductor loss, the dielectric loss also increases above 20 GHz. The dielectric loss is shown to originate not only in the LiNbO3 substrate, but also in the silicon oxide buffer layer.

Dielectric Behavior of (1-x)LaAlO3–xSrTiO3 Solid Solution System at Microwave Frequencies

Abstract: The (1-x)LaAlO3–xSrTiO3 solid solution system with the perovskite structure was synthesized and its dielectric behavior was investigated. The lattice parameter of (1-x)LaAlO3–xSrTiO3 increases with increasing the fraction of SrTiO3 in the system. 0.45LaAlO3–0.55SrTiO3 shows a dielectric constant e of 34, a temperature coefficient of resonant frequency τf of -8 ppmK-1 and a dielectric loss Q of 6900, which satisfy the suggested requirements for applications to mobile communications devices. The annihilation of the ferroelectric mode of SrTiO3 corresponds to the drastic decrease of e and τf of SrTiO3 to those of 0.25LaAlO3–0.75SrTiO3.

Improved SrTiO3 multilayers for microwave application: Growth and properties

Abstract: Au/SrTiO3 (STO), Au/YBa2Cu3O7−x (YBCO)/STO, Au/STO/CeO2/STO, and Au/STO/MgO/STO multilayer structures on LaAlO3 substrates have been fabricated Their properties are investigated at 1 MHz and at microwave frequencies (40 MHz–40 GHz) as a function of applied voltage, and in the temperature range between 20 and 300 K The STO thin films showed comparatively high values of dielectric constant (up to 1800 at 50 K) with low measured film losses, tan δ<0005, (limit of the measurement setup), at 20 GHz and 20 K, indicating their applicability for microwave devices The dielectric constant is shown to be independent of frequency to at least 40 GHz, while the losses exhibit no or weak frequency dependence Relaxation of the STO film in oxygen atmosphere before deposition of YBCO is shown to reduce interactions between the YBCO and STO films After an “ex situ” high-temperature (900 °C) treatment in flowing oxygen a reduction of the STO dielectric constant as well as tan δ has been observed Using cerium dioxide a

Dielectric properties of Bi doped SrTiO3 ceramics in the temperature range 500–800 K

Abstract: The (Sr1−1.5xBix)TiO3 (0.0133⩽x⩽0.133) ceramic system reveals several sets of dielectric permittivity peaks in different temperature ranges. Dielectric permittivity and dielectric loss peaks were detected in the temperature range 500–800 K and in the present article the dielectric polarization behavior is presented and discussed. The activation energy of the dielectric relaxation is in the range of 0.99–1.12 eV. It is suggested that the permittivity peaks are related to the movement of oxygen ions or oxygen vacancies.

Observation of dipole complexes in PbWO4:La3+ single crystals

Abstract: The frequency dependence of dielectric loss factor (tan δ) in undoped and La-doped PbWO4 crystals has been investigated over a frequency range from 10 Hz to 10 MHz and a temperature range from 40 to 370 °C. A typical dielectric relaxation phenomenon in PbWO4:La3+ has been observed. Experimental results indicate that there exist intrinsic mobile defects in pure PbWO4 crystals and lead vacancies are the predominant mobile defects. In La-doped PbWO4 crystals, La3+ ions may be located at the Pb2+ sites and combine with lead vacancies to form the dipole complexes [2(LaPb3+)•−VPb″], which may be the origin of the dielectric relaxation phenomenon in PbWO4:La3+ crystals.

Dielectric response measurements in time and frequency domain on high voltage insulation with different response

Abstract: Diagnostic measurements of dielectric materials can be performed either in time-domain or frequency-domain. If the dielectric material can be described as a linear system the acquired information in the two domains are in theory equivalent. In time-domain charging/discharging currents and recovery voltage are used and in frequency-domain capacitance and loss factor are measured as a function of frequency. These methods are today used as diagnostic methods for example for high voltage cables, transformers and rotating machines. The purpose of this paper is to discuss the relation between time-domain and frequency domain and how well the different existing measurement methods can characterise a dielectric material depending on the material's response.