Showing papers on "Dielectric published in 1991"

Anelastic and Dielectric Effects in Polymeric Solids

Abstract: Dynamic Mechanical Analysis-Kevin P. Menard 2002-01-01 Although dynamical mechanical analysis or spectroscopy has left the domain of the rheologist and has become a prevalent tool in the analytical laboratory, it is still common to hear, "What is DMA, and what will it tell me?" or "I think I could use a DMA, but I cannot justify its cost." Previously, the novice in the field had to sort through texts on thermal analysis, rheology, and materials science just to find basic information — until now.

(Bi1/2Na1/2)TiO3-BaTiO3 System for Lead-Free Piezoelectric Ceramics

Abstract: One of the (Bi1/2Na1/2)TiO3 (BNT)-based solid solutions, Ba-modified bismuth sodium titanate, (Bi1/2Na1/2)1-xBaxTiO3 (BNBT), is studied for its dielectric and piezoelectric properties as a new group of lead-free piezoelectric ceramics. A rhombohedral (Fα)-tetragonal (Fβ) morphotropic phase boundary (MPB) is shown to exist at x=0.06~0.07 by X-ray data, and dielectric and piezoelectric properties. BNBT ceramics with the MPB composition are superior as piezoelectric ceramics in high-frequency ultrasonic applications or as piezoelectric actuator materials because of a lower free permittivity, e33T/e0, and a high electromechanical coupling factor, kt or k33, along with high mechanical strength.

Nanometer-sized semiconductor clusters: materials synthesis, quantum size effects, and photophysical properties

Abstract: Recent advances in the synthesis of semiconductor clusters open a doorway for the systematic study of size-dependent cluster properties in the condensed phase. This article focuses on the size effect on the optical and photophysical properties. The authors first introduce fundamental concepts and proceed to a discussion of recent progress toward the understanding of the quantum size effect and dielectric confinement effect. They then discuss the current status of materials synthesis and the prospect for making monodisperse clusters of well-defined surfaces.

Donor and acceptor modes in photonic band structure.

Abstract: Three-dimensionally periodic dielectric structures, photonic crystals, possessing a forbidden gap for electromagnetic wave propagation, a photonic band gap, are now known. If the perfect 3D periodicity is broken by a local defect, local electromagnetic modes can occur within the forbidden band gap. Addition of extra dielectric material locally, inside the photonic crystal, produces ``donor'' modes. Conversely, local removal of dielectric material from the crystal produces ``acceptor'' modes. It is now possible to make high-Q electromagnetic cavities of \ensuremath{\sim}1 cubic wavelength, for short wavelengths at which metallic cavities are useless. These new dielectric cavities can cover the range from mm waves to UV wavelengths.

Photonic band structure of two-dimensional systems: The triangular lattice

Abstract: By the use of a position-dependent dielectric constant and the plane-wave method, we have calculated the photonic band structure for electromagnetic waves in a structure consisting of a periodic array of parallel dielectric rods of circular cross section, whose intersections with a perpendicular plane form a triangular lattice. The rods are embedded in a background medium with a different dielectric constant. The electromagnetic waves are assumed to propagate in a plane perpendicular to the rods, and two polarizations of the waves are considered. Absolute gaps in the resulting band structures are found for waves of both polarizations, and the dependence of the widths of these gaps on the ratio of the dielectric constants of the rods and of the background, and on the fraction of the total volume occupied by the rods, is investigated.

Intrinsic dielectric loss in crystals

Abstract: We review the current theory of intrinsic dielectric loss, that is the loss in a perfect crystal due to anharmonic interaction of a.c. electric field with the phonon system of the crystal. Both ordinary dielectrics and displacive ferroelectrics are considered. The theory predicts dependence of the loss on frequency ω and temperature T. This dependence is very sensitive to the symmetry of the crystal. For ordinary dielectrics, the results are presented and tabulated for all 32 symmetry groups, except for non-symmorphic groups. The existing experimental date are analysed and explained on the basis of the theory.

Chemical Processing and Microwave Characteristics of (Zr,Sn)TiO4 Microwave Dielectrics

Abstract: Monosized spherical particles of (Zr, Sn)TiO4 with an average diameter of about 0.3 μm were synthesized by the controlled hydrolysis of metal alkoxides. The as-prepared, amorphous, particles were compacted without any sintering aid, crystallized, and then sintered at 1600°C for 3 h into bodies with >96.0% of theoretical density. The dense sintered bodies of (Zr0.80Sn0.20)TiO4 showed good microwave characteristics; ɛr= 40.0, Q= 5000, and τt= 3 ppm/°C at 10 GHz. The dielectric constant was remarkably dependent upon the relative densities of the sintered bodies and the change of the lattice parameters, while Q value was mainly affected by the oxygen deficiency. An increase of the dielectric constant with the substitution of Sn4+ in ZrTiO4 was attributable to the enhancement of ionic polarization with the increase of the c-axis length.

Dielectric properties of agricultural products-measurements and applications

Abstract: The nature of the variation of dielectric properties with frequency, temperature, and product density is discussed. Techniques for measurement of dielectric properties are briefly reviewed, and graphical data on the dielectric properties of grain and soybeans as functions of moisture content, frequency, temperature, and bulk of density are presented. Applications in the electrical measurement of the moisture content and in the dielectric heating of these materials are discussed. >

Force constant and effective mass of 90° domain walls in ferroelectric ceramics

Abstract: Domain wall contributions to the dielectric, piezoelectric, and elastic properties of tetragonal ferroelectric ceramics, as discussed extensively in the past, are calculated. A simple model shows that the motion of 90° domain walls causes a shear deformation and an approximately homogeneous electric field in the grain. The elastic and electric field energies involved allow the calculation of the force constant for the domain wall displacement by external fields. The displacements agree with experimental results. In a moderate electric field the displacement is a small fraction of the lattice cell only. By averaging over the orientational distributions of all grains the contributions of the 90° domain walls to the material properties are calculated for unpolarized and for polarized ceramics and agree with experimental results. The effective mass, which has to be attributed to the domain walls is the mass of the whole grain reduced by the factor S0 (spontaneous deformation), is independent of the domain wid...

Microscopic simulations of macroscopic dielectric constants of solvated proteins

Abstract: Microscopic simulation of solvated proteins are used to evaluate the relationship between the macroscopic field and macroscopic polarization, thus providing the corresponding dielectric constant, e. This parameter is evaluated by two different methods which are first examined and calibrated by calculating the dielectric constant of bulk water. These calculations indicate that the reaction field, which represents the effect of the missing solvent around the given explicit region, must be included in the simulations in order to obtain a reasonable value for e. The corresponding effect is not related to the reduction of the effective interactions between charges in the reference region but to the intrinsic value of e in that region. This means that vacuum calculations of e in proteins might underestimate its actual value. Or in other words, calculations of e in proteins must include the effect of the reaction field or a sufficiently large number of surrounding solvent molecules. Having included the surr...

Charging and flashover induced by surface polarization relaxation process

Abstract: Electric charges trapping into a dielectric medium are described from polarons trapped into sites which are characteristic of the material structure (polaron trap). In terms of susceptibility, that means charges are trapped into sites whose susceptibility is lower than their surrounding environment. The charge trapping produces polarization of the medium. The energy of polarization per embedded charge is estimated to be equal to 5χ (χ being the susceptibility). The surface breakdown of the dielectric is attributed both to charge detrapping and to relaxation of energy of polarization, using the collective many‐body process. The consequences of this interpretation are consistent with experiments on surface breakdown performed with a scanning electron microscope. Furthermore, considerations about the improvement of breakdown voltage for dielectric materials are introduced.

Charge storage in a nitride‐oxide‐silicon medium by scanning capacitance microscopy

Abstract: In this paper we describe a variant of the scanning capacitance microscope (SCaM) which is based on the atomic force microscope. Our SCaM involves a cantilever beam that is used to press a conducting tip against a conducting substrate coated with a dielectric film. A capacitance sensor is then used to measure the tip‐sample capacitance as a function of lateral position. The deflection of the cantilever can also be used to measure independently the surface topography. This microscope can be used to measure electrical properties of dielectric films and their underlying substrates. We have applied this microscope to the study of the nitride‐oxide‐silicon (NOS) system. This system has been studied extensively because of its ability to store information by trapping charge in the silicon nitride. Commercial semiconductor nonvolatile memories have been designed using this NOS technology. We have used the SCaM tip to apply a localized bias to the NOS sample, causing charge to tunnel through the oxide layer and to...

Dielectric studies of the soft mode and Goldstone mode in ferroelectric liquid crystals

Abstract: Different contributions to the dielectric permittivity in ferroelectric liquid crystals are discussed, with emphasis on the soft mode and the Goldstone mode and their location in the dielectric spectrum. Experimentally, the complex dielectric permittivity has been studied as a function of temperature and frequency in the range 5 Hz - 13 MHz for three different ferroelectric liquid crystal materials. The main problems encountered in dielectric measurements at low and high frequency are discussed in some detail. The soft mode dielectric behaviour has been studied as a function of temperature, frequency and bias electric field. The applicability of the Curie-Weiss law for the soft mode dielectric contribution in the A* phase was analyzed. In the C* phase the temperature dependence of the dielectric contribution of the Goldstone mode has been measured. By applying a bias electric field, we have been able to study the soft mode dielectric behaviour also deep into the C* phase. In the A* and C* phases ...

Guided optical waves in planar heterostructures with negative dielectric constant.

Abstract: A detailed study of guided optical modes in planar heterostructures involving one or two media with negative dielectric constant is presented. The existence and the form of the solutions with respect to geometrical and physical parameters are derived. The cases of a metal between two dielectrics and a metal-dielectric-metal heterostructure are treated successively.

Ferroelectric thin films for electronic applications

Abstract: This is a review paper on the history of ferroelectric thin films, current practices in their fabrication, characteristics of interest which relate to their use, and the application of these films to memory and electrooptic devices.

High-power radiator

Abstract: In a UV high-power radiator, the electrodes (6', 6") consist of wires embedded in a glass dielectric (3). The dielectric is arranged spaced between two UV-transparent sheets (1, 2). The discharge spaces (8, 9) are filled with a filler gas emitting radiation under discharge conditions. The surface discharges (10) form on the dielectric surface in each case between two adjacent electrode wires (6', 6"). A high-power radiator constructed in this manner is characterized by simple and economical construction and high UV yield.

Electric polarization in crystals and its response to thermal and elastic perturbations

Abstract: The basic properties of electric polarization response in crystalline dielectrics are theoretically analysed. Spontaneous polarization, pyroelectricity, piezoelectricity, flexoelectricity (polarization response to strain gradient) and thermopolarization effect (polarization response to temperature gradient) are discussed on the basis of a unified approach. Special attention is paid to the problem of the adequate theoretical definition of these phenomena. The effect of the sample termination on the polarization response is considered in detail.

Generation of excimer emission in dielectric barrier discharges

Abstract: Dielectric barrier discharges (silent discharges) are used to excite a large number of excimers radiating in the VUV, UV or visible spectral range. The excited species include rare-gas dimers, halogen dimers as well as rare-gas halogen excimers and mercury halogen excimers. In many cases narrow-band UV radiation of typically 1–17 nm halfwidth and remarkable efficiency (1–10%) could be generated. Thus, dielectric barrier discharges provide a simple, versatile arrangement to study the basic reaction kinetics of excimer formation and also bear a substantial potential for large-scale industrial UV processes.

In situ monitoring technique and apparatus for chemical/mechanical planarization endpoint detection

Abstract: This invention provides an in situ monitoring technique and apparatus for chemical/mechanical planarization end point detection in the process of fabricating semiconductor or optical devices. Fabrication of semiconductor or optical devices often requires smooth planar surfaces, either on the surface of a wafer being processed or at some intermediate stage e.g. a surface of an interleaved layer. The detection in the present invention is accomplished by means of capacitively measuring the thickness of a dielectric layer on a conductive substrate. The measurement involves the dielectric layer, a flat electrode structure and a liquid interfacing the article and the electrode structure. Polishing slurry acts as the interfacing liquid. The electrode structure includes a measuring electrode, an insulator surrounding the measuring electrode, a guard electrode and another insulator surrounding the guard electrode. In the measurement a drive voltage is supplied to the measuring electrode, and in a bootstrap arrangement to a surrounding guard electrode, thereby measuring the capacitance of the dielectric layer of interest without interferring effect from shunt leakage resistance. The process and apparatus are useful not only for measuring the thickness of dielectric layers on conductive substrates in situ, during planarizing polishing, but also for measuring the dielectric thickness on substrates in other processes, e.g. measuring the dielectric layer thickness prior to or after an etching process.

Modeling ferroelectric capacitor switching with asymmetric nonperiodic input signals and arbitrary initial conditions

Abstract: The switching behavior of ferroelectric capacitors experiencing arbitrary time‐dependent electric fields and arbitrary initial conditions is investigated both theoretically and experimentally. A general approach for modeling incomplete dipole switching in ferroelectric capacitors is used to derive equations describing the electrical behavior of a simple characterization circuit with arbitrary initial conditions and arbitrary time‐dependent applied voltages. The equations include four experimentally determined parameters: the remanent and spontaneous polarizations, the coercive field, and the ferroelectric dielectric constant. Once these model parameters are determined from a single high‐frequency sinusoidal hysteresis loop, model predictions are made with no adjustable parameters. The circuit behavior for both sinusoidal and trapezoidal input signals is computed, including asymmetric and nonperiodic signals as well as several different initial conditions. The accuracy of the model predictions is quantitatively verified with experimental data. The approach is also utilized to model the switching behavior of a ferroelectric capacitor containing a sheet of space charge. It is found that hysteresis loop distortions resulting from ionizing radiation resemble those caused by a sheet of space charge. This quantitative modeling capability facilitates the optimization of the design of ferroelectric memory circuits by minimizing the amount of required electrical testing and characterization. It can also be used to facilitate the identification and understanding of degradation mechanisms occurring in ferroelectric thin films.

Photonic bound states in periodic dielectric materials

Abstract: It is demonstrated that lattice imperfections in a periodic array of dielectric material can give rise to fully localized electromagnetic states. Calculations are performed by using a plane-wave expansion to solve Maxwell's equations. The frequency of these localized states is tunable by varying the size of the defect. Potential device applications in the microwave and millimeter wave regime are proposed.

Electrostatic particle-particle interactions in electrorheological fluids

Abstract: A model for the particle‐particle interaction in a chain of spherical particles in an electrorheological (ER) fluid is developed based on an expansion of the potential which satisfies the Laplace equation. The electric‐field distribution and force‐distance relationship between particles are calculated as a function of Kp/Kf (the dielectric constant of the sphere relative to that of the medium) and particle‐particle spacing using this model. The calculations predict electric‐field concentrations of about an order of magnitude near particle contacts. This gives a force between particles that is approximately an order of magnitude higher than predicted by the classical point‐dipole approximation, and is in reasonable agreement with that measured experimentally. Subtle effects of the carrier fluid on the interaction force and an explanation for the non‐Ohmic behavior of ER fluids are deduced in terms of its dielectric constant and dielectric strength.

Area array connector

Abstract: An area array connector (32,42,50) for electrically interconnecting two electronic devices is disclosed. The connector (32,42,50) includes a plurality of contact elements (10) having parallel cantilevered contact fingers (18) extending obliquely outwardly from a plate (20) for one embodiment, a laminate (32) is formed by securing the contact elements (10) to a dielectric (26) having windows (28) through which the fingers (18) extend. The laminate (32) can then be fixed to a device such as a circuit board (40) to form another form of a connector (42) and further, the dielectric (26) can be removed to form yet another form of connector (50).

Light scattering from random rough dielectric surfaces

Abstract: A theoretical and numerical study is made of the scattering of light and other electromagnetic waves from rough surfaces separating vacuum from a dielectric. The extinction theorem, both above and below the surface, is used to obtain the boundary values of the field and its normal derivative. Then we calculate the angular distribution of the ensemble average of intensity of the reflected and transmitted fields. The scattering equations are solved numerically by generating one-dimensional surface profiles through a Monte Carlo method. The effect of roughness σ and correlation distance T on the aforementioned angular distribution, as well as on the reflectance, is analyzed. Enhanced backscattering and new transmission effects are observed, also depending on the permittivity. The ratio σ/T is large in all cases studied, and thus no analytical approximation, such as the Kirchhoff approximation (KA) and small perturbation methods, could a priori be expected to hold. We find, however, that the range of validity of the KA can be much broader than that previously found in perfect conductors.

Coplanar waveguide excitation of dielectric resonator antennas

Abstract: The circuit and radiation properties of a cylindrical dielectric resonator antenna excited by a coplanar waveguide feed are investigated. The coupling between the feed and the radiator was measured as a function of the position, dielectric constant, and height of the cylinder. The radiation patterns and resonant frequencies were also measured. These measured results are found to be in good agreement with theoretical calculations. >

Structures of water and primary alcohol studied by microwave dielectric analyses

Abstract: By the use of the time domain reflectometry method dielectric measurements were carried out first on methanol mixtures with ethanol and 1‐propanol, and second, water mixtures with methanol, ethanol and 1‐propanol in the frequency range 10 MHz–20 GHz. The first mixtures show a Debye relaxation and logarithm of the relaxation time is given by a linear function of the mole fraction of methanol. These mixtures have the same chainlike cluster of pure alcohol. The second mixtures show the same trend of the relaxation time in a region 0≤xw 0.83 and that the cluster must be cyclic, consisting of six molecules.

Selective plating method for forming integral via and wiring layers

Abstract: In a multi-level wiring structure wires and vias are formed by an isotropic deposition of a conductive material, such as copper, on a dielectric base, such as a polyimide. In a preferred embodiment of the invention copper is electroplated to a thin seed conducting layer deposited on the surface of the dielectric base in which via openings have been formed. Openings in a resist formed on the surface of the dielectric base over the seed layer forms a pattern defining the wiring and via conductor features. Electroplated copper fills the via openings and wire pattern openings in the resist isotropically so that the upper surfaces of the wiring and vias are co-planar when the plating step is complete. In adding subsequent wiring levels, the resist is removed and the via conductor and wiring pattern covered with another dielectric layer which both encapsulates the conductors of the previous layer and serves as the base for the next level which is formed in the same manner as the previous level.

Geometric and dielectric characterization of porous media.

Abstract: This paper introduces local porosity distributions and local percolation probabilities as well-defined and experimentally observable geometric characteristics of general porous media. Based on these concepts the dielectric response is analyzed using the effective-medium approximation and percolation scaling theory. The theoretical origin of static and dynamic scaling laws for the dielectric response including Archie's law in the low-porosity limit are elucidated. The zero-frequency real dielectric constant is found to diverge as \ensuremath{\epsilon}\ensuremath{'}(0)\ensuremath{\propto}(1-\ensuremath{\varphi}${)}^{\mathrm{\ensuremath{-}}\mathrm{m}\ensuremath{'}}$ in the high-porosity limit, where \ensuremath{\varphi} denotes the porosity and m\ensuremath{'} is analogous to the cementation exponent. Model calculations are presented for the interplay between geometric characteristics and the frequency-dependent dielectric response. Three purely geometric mechanisms are identified, each of which can give rise to a large dielectric enhancement.

Scaling of the α relaxation in low-molecular-weight glass-forming liquids and polymers

Abstract: By measuring the complex dielectric susceptibility over 15 decades in frequency we compare the \ensuremath{\alpha} relaxation in low-molecular-weight glass-forming liquids and polymers. To describe the scaling behavior of the \ensuremath{\alpha} relaxation, a minimal set of four parameters is necessary, the mean relaxation time, the dielectric strength, and two shape parameters, describing the low- and high-frequency wings of the relaxation function, in pronounced contrast to a recently published scaling function.