Simple Nondestructive Method for the Measurement of Complex Permittivity

Novel nitrile-butadiene rubber composites with enhanced thermal conductivity and high dielectric constant

In this paper, carbon black-filled high dielectric constant composites were evaluated as the candidate materials for embedded capacitors. Carbon black was selected as the filler due to its large surface area and its wide range of electrical properties based on its surface chemistry, particle size and aggregate structure. Six different types of carbon blacks were evaluated. With a proper filler loading level and good dispersion, high dielectric constants over 1000 were observed for four out of the six types of carbon. The dispersion of carbon black is critical to obtain high dielectric constant carbon black composites. When the carbon black is well dispersed, the large surface area of tiny carbon black aggregates serve as the electrode surfaces of numerous small capacitors. The capacitor network within the composite can thus give a large capacitance and dielectric constant. For a highly conductive carbon black CBD3, a high dielectric constant over 13,300 (@10 kHz) was achieved, and for a relatively low conductivity carbon black CBC2, a dielectric constant of about 2,300 (@10 kHz) was obtained. A higher conductivity carbon black usually gives a higher dielectric constant; however, its composites are more difficult to process since the composites have a narrower composition window near the percolation threshold due to its high structure and large surface area. The filler loading level required to reach high dielectric constant is much lower than that of ceramic composites, which enable carbon black composites to have good mechanical properties. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) were used to characterize the structure of carbon and their composites, respectively, in order to correlate the structure of carbon blacks and the morphology of their composites with the corresponding material dielectric properties.

A detailed study was carried out to understand the photonic crystal design rules with very high dielectric constant (ε>13), based on plane wave expansion and finite difference time-domain (FDTD) techniques. It is found that the optimal dielectric constant contrast is indeed the one between conventional semiconductors (ε=12-14) and air. Either too high or too low contrast can lead to the reduction of complete photonic bandgap. With very high bulk dielectric constant (ε=20-25), PbSe nanocrystal quantum dots (NQDs) are suitable for air hole based PC structure with large TE gap. On the other hand, NQD backfilled photonic crystals with tunable bandgap is proposed based on the control of packing density of NQDs inside the air holes of photonic crystal structures. Both theoretical and experimental results on the integration process are reported.

The existence of moisture in concrete is a major cause of damage to the concrete structure, so there is an increasing need for nondestructive detection and monitoring of moisture content in concrete. Microwave nondestructive testing (MNDT) techniques have advantages over other NDT methods (such as radiography, ultrasonic, and eddy current) regarding low cost, good penetration in nonmetallic materials, good resolution and requirement of only one face of material for testing. In this paper, microwave open-ended rectangular waveguide was used to measure the electromagnetic properties of Portland cement concrete (PCC) over a frequency range of 7.0 to 13.0 GHz. PCC specimens of six different water cement ratio (w/c) were prepared. PCC dielectric properties were evaluated at different moisture content ranges from saturated to oven dry. The results show reflection coefficients, dielectric constants and loss factors increase with increasing moisture content of PCC. At the same values of moisture content, the reflection coefficients, dielectric constants and loss factors of PCC increase with decreasing w/c ratio. The measured values of reflection coefficients, dielectric constants and loss factors can be used to determine the moisture content of PCC.

High dielectric constant and its dependence on structural strain and grain boundaries (GB) in La0.7Sr0.3MnO3 (LSMO) thin films are reported. X-ray diffraction, magnetization, and magneto-transport measurements of the LSMO films, made by pulsed laser deposition on two different substrates—MgO and SrTiO3 (STO), were compared to co-relate magnetic properties with dielectric properties. At room temperature, in the ferromagnetic phase of LSMO, a high dielectric constant (6 × 104) was observed up to 100 kHz frequency for the films on MgO, with polycrystalline properties and more high-angle GB related defects, while for the films on STO, with single-crystalline properties but strained unit cells, high dielectric constant (≈104) was observed until 1 MHz frequency. Also, a large dielectric relaxation time with significant broadening from the Debye single-dielectric relaxation model has been observed in samples with higher GB defects. Impedance spectroscopy further shows that large dielectric constant of the single-crystalline, strained LSMO film is intrinsic in nature while that in the polycrystalline films are mainly extrinsic due to higher amount of GBs. The presence of high dielectric constant value until high frequency range rules out the possibility of “apparent giant dielectric constant” arising from the sample-electrode interface. Coexistence of ferromagnetism and high dielectric constant can be very useful for different microelectronic applications.

The anionic polymerization of styrene by phenyllithium was studied in various solvents The order of the decreasing molecular weights obtained depending on the solvent, was: tetrahydrofuran » toluene > benzene > petroleum ether > diethyl ether. The molecular weight, due to absence of termination, is governed by the ratio of the rate propagation to the rate of initiation (Rp/Ri). Both these rates are influenced by the dielectric constant and the solvating power of the solvent for the phenyllithium and for the growing end, solvation of the growing end being greater due to the resonance of the propagating styryl anions. This leads to the fact that on passing from petroleum ether (low dielectric constant) to tetrahydrofuran (relatively high dielectric constant and high solvating power), Rp increases much more than Ri, leading to higher molecular weight. The polymerization of styrene in mixtures of petroleum ether and tetrahydrofuran was studied by the addition of increasing amounts of tetrahydrofuran while keeping the catalyst and monomer concentrations constant. Initially (up to 2 vol.‐% tetrahydrofuran) there was a sharp decrease in molecular weight due to a greater dissociation of the phenyllithium, with a corresponding increase in Ri. On further addition of tetrahydrofuran (up to about 25 vol.‐%), the molecular weight increased and approached the order of that obtained in petroleum ether. This is due to a greater increase in Rp over Ri due to greater solvation of the propagating end. At this relatively high tetrahydrofuran concentration we have maximum solvation both of the catalyst and of the growing end. With further addition of tetrahydrofuran there is a linear dependence of the molecular weight both on the concentration of the tetrahydrofuran and on the dielectric constant of the system. Ether gave the lowest molecular weights, in spite of its relatively high dielectric constant, due to greater dissociation of the catalyst associates (C6H5Li)x leading to an increased efficiency of the catalyst (greater Ri). Toluene and benzene led to higher molecular weights than petroleum ether, although the dielectric constants are of approximately the same order, due to the homogeneous nature of the polymerization in these solvents as compared with the heterogeneous polymerization in petroleum ether. The molecular weight increased with decrease in temperature in various solvents due to the increase in the dielectric constant and the lowering in Ri

In the semiconductor industry, increasing density requirements continue to motivate the production of microelectronic devices that function reproducibly at ever-smaller dimensions (a trend known as Moore’s law). The need for insulating films with nanometer-scale thickness that show good compatibility with semiconductor technology is a critical issue for future device development. As the film thickness scales down to 10 nm, conventional SiO2 gate dielectrics show a poorly insulating character with high leakage currents of 10– 10 A cm due to quantum tunneling, thereby causing large energy consumption and deteriorated device reliability. Continued device scaling will therefore require substitution of SiO2 with high-dielectric-constant (high-j) metal oxide gate dielectrics that afford high capacitance without reliance on film thickness, thus allowing for efficient charge injection and also reducing tunneling leakage currents. Here, we show that 2D titania (Ti0.87O2) nanosheets function as a high-j nanomaterial. We have successfully fabricated high-j nanofilms by forming multilayer assemblies of titania nanosheets via a layer-by-layer approach through solution-based processes at room temperature. The use of an atomically flat (001) SrRuO3 (SRO) epitaxial film as the bottom electrode enables the fabrication of atomically uniform, highly dense, and void-free nanofilms that retain the superior electrical properties of the titania nanosheets. These films exhibit a reduced leakage current density (10–10 A cm) with a high relative dielectric constant of ∼ 125, even for thicknesses as low as 10 nm. These results, as well as the facile molecular-scale assembly of the nanostructures, suggest that titania nanosheets are attractive candidates for use in nanocomponent insulating high-j dielectric films. In the area of high-j dielectrics, there is currently an intense research effort focused on the synthesis and device integration of various oxide materials. Current candidates are placed into two categories according to the j value: simple metal oxides with j= ∼ 10–20, such as Ta2O5, HfO2 and ZrO2, and materials with j> 100, such as rutile-type TiO2 [7] and (Ba,Sr)TiO3 (BST). [8] In addition to intrinsic properties such as a high dielectric constant and good insulating properties, high-j gate oxides have to fulfill a number of other requirements for device integration: i) they must be chemically stable in contact with the bottom electrodes (Si and/or metals), ii) for optimal performance, they should have an atomically defined interface with the bottom electrodes, without a low-j interfacial layer, and iii) they should have a simple metal oxide system and be accessible through a low temperature ( 600 °C), which often causes both a reduction in the polarizability due to non-stoichiometry, as well as degradation of the bottom electrode. Thus, the development of new high-j oxides fulfilling these requirements represents a critical challenge for materials science. In searching for alternative materials, we have focused on titania (Ti0.87O2) nanosheets, [4] a new class of nanomaterials that represent a modification of nanometer-sized titanium oxide prepared by delaminating layered titanates into their molecular single sheets (Fig. 1a). Compared with rutile and other high-j oxides, titania nanosheets have some unique features: i) they are completely 2D nanomaterials, with a thickness of 0.7 nm, and ii) due to their colloidal and negatively charged character, they can be self-assembled layer-by-layer via a solution-based process to construct ultrathin films. Therefore, the use of titania nanosheets as building blocks for high-j films could provide a potential route to the room-temperature manufacture of high-j devices, eliminating the degradation of the bottom electrode during the annealing process. Here, we report the performance of high-j nanofilms fabricated from titania nanosheets by a solution-based layer-by-layer approach. Multilayer films of large-sized titania nanosheets (with an average lateral size of 30 lm) have been fabricated by an electrostatic self-assembly technique, using poly(diallyldimethylammonium) (PDDA) as a counter polycation. As the bottom electrode, we use an atomically flat conducting SRO substrate, consisting of a 50 nm thick (001)-oriented epitaxial SRO layer on a (001) SrTiO3 single crystal. The as-deC O M M U N IC A IO N S

The possibility of using microstrip reflector microwave resonators in solving problems of resonant gas-sensor telemetry on layered dielectric substrates with gas-sensitive sputtering was investigated. It is noted that the use of chemically active sputtering, for example, on the basis of zeolites having a high selective gas adsorbent kinetics in terms of speed, makes it possible to create radiosensor materials capable of changing the dielectric constant in the process of absorbing gases, as well as of sublimated vapors of solid and liquid phases of various compounds. As an alternative approach in the field of dosimetric gas monitoring, a modification of radiosensor applications based on microwave sensors is proposed, which allows using microwave solutions based on microstrip microwave resonators with active gas-sensitive sorption zeolite sputtering on a dielectric substrate to conduct gas analysis in real time. The radio-wave principle of the microstrip gas sensor analyzer was formulated. An electrodynamic model of a microstrip gas sensor analyzer in the Altair Feko environment was developed. An experiment was planned, and gas-sensor telemetry tests of ammonia vapors dissolved in water were carried out. It was established that the amount of sorbed water and ammonia in the zeolite unambiguously conforms both to the absolute value of the reflection coefficient at resonance and to the resonant frequency itself. Using the example of recording hydrogen nitride vapors it was shown that the reflection coefficient and frequency shift in the resonator, which depend on the concentration of the adsorbed gas, correspond to the saturation characteristics of the gas sensor and make it possible to repeatedly measure small concentrations of a gas that can be absorbed by zeolite at a temperature corresponding to the condition of rapid evaporation of controlled gas from the active dielectric layer, which guarantees desorption of the sensor. It was established that in order to increase the speed of the gas sensor response it is advisable to create a microstrip resonator for the resonance region of 8...10 GHz and to use a microstrip sensor substrate material with a high dielectric constant. This is due to the fact that the transition to the upper microwave frequencies will allow reducing the size of the topology of the microstrip resonator and reducing the effective area of the zeolite deposition, and, consequently, increasing the adsorption rate of the gas-sensitive layer of the active dielectric.

Nano-clip based composites with a low percolation threshold and high dielectric constant

Synthesis and characterization of PTFE/(NaxLi1-x)0.5Nd0.5TiO3 composites with high dielectric constant and high temperature stability for microwave substrate applications

The results of various experiments performed to characterize electromagnetic properties of typical building materials at BRAN (Broadband Radio Access Networks) and MVDS (Multipoint Video Distribution System) bands are presented and compared. Transmission and reflection coefficients were measured as functions of the angle of incidence, using a wideband sounder based on the swept frequency technique. A high precision angular positioning system was built and used in co-ordination with the measurement equipment. The dielectric constants (er) were estimated by comparing values predicted with a multiple successive internal reflection model and measured transmission and reflection coefficients. It has been found that the variation of the dielectric constant value with the frequency does not necessarily follow the same trend for different materials. For example, the measured er for plasterboard presents an increment with frequency (2.02 at 5.8 GHz, 2.5 at 41.5 GHz – measured by the authors –, 2.58 at 59.5 GHz, and 2.81 at 60.2 GHz – given by literature –), while the values for glass follow a wandering pattern (6.06 at 5.8 GHz, 5–10 at 10 GHz, 3.41 at 41.5 GHz, 7.51 at 57.6 GHz, and 5.29 at 60.2 GHz). Moreover, the measured er for a brick wall at 5.8 GHz (3.58) shows differences with values reported at 2 GHz (4.44).

The composition of the lithium cation (Li(+)) solvation shell in mixed linear and cyclic carbonate-based electrolytes has been re-examined using Born-Oppenheimer molecular dynamics (BOMD) as a function of salt concentration and cluster calculations with ethylene carbonate:dimethyl carbonate (EC:DMC)-LiPF6 as a model system. A coordination preference for EC over DMC to a Li(+) was found at low salt concentrations, while a slightly higher preference for DMC over EC was found at high salt concentrations. Analysis of the relative binding energies of the (EC)n(DMC)m-Li(+) and (EC)n(DMC)m-LiPF6 solvates in the gas-phase and for an implicit solvent (as a function of the solvent dielectric constant) indicated that the DMC-containing Li(+) solvates were stabilized relative to (EC4)-Li(+) and (EC)3-LiPF6 by immersing them in the implicit solvent. Such stabilization was more pronounced in the implicit solvents with a high dielectric constant. Results from previous Raman and IR experiments were reanalyzed and reconciled by correcting them for changes of the Raman activities, IR intensities and band shifts for the solvents which occur upon Li(+) coordination. After these correction factors were applied to the results of BOMD simulations, the composition of the Li(+) solvation shell from the BOMD simulations was found to agree well with the solvation numbers extracted from Raman experiments. Finally, the mechanism of the Li(+) diffusion in the dilute (EC:DMC)LiPF6 mixed solvent electrolyte was studied using the BOMD simulations.

In this work, a metal-ferroelectric-semiconductor (MFS) type capacitorwas fabricated and admittance measurements were held in a wide frequency rangeof 1 kHz-5 MHz at room temperature for the investigation of frequency andvoltage dependence of complex dielectric constant, complex electric modulus andelectrical conductivity of the MFScapacitor. Bismuth titanate (Bi4Ti3O12) with high dielectric constant was used asinterfacial ferroelectric material and the structure of MFS capacitor wasobtained as Au/Bi4Ti3O12/n-Si. Experimentalresults showed that dielectric, modulus and conductivity parameters are strongfunctions of frequency and voltage especially in depletion and accumulationregions due to the existence of surface states (Nss), seriesresistance (Rs), interfacial polarization and interfacial layer. Itwas found that Rs of the structure and interfacial ferroelectriclayer are efective in accumulation region whereas surface states (Nss)and interfacial polarization are efective indepletion region. Also the changes in dielectric, modulus and conductivityparameters become considerably high particularly at low frequencies due to highvalues of Rs and Nss. The observed anomalous peak in voltage dependent plots ofcapacitance and dielectric constant was atributed to the particular densitydistribution of Nss, Rs and minority carrier injection.Moreover, the value of conductivityat low and intermediate frequencies is almost independent of frequency thus lowfrequency data was used to extract d.c. conductivity. This work showed that the use of high-dielectric Bi4Ti3O12as ferroelectric interfacial layer in a MFS capacitor is preferable due to highvalues of its dielectric constant compared with traditional insulator layermaterials such as SiO2 and SnO2. Therefore, a MFScapacitor with Bi4Ti3O12 interfacial layer canstore more energy thanks to its high dielectric constant.

Electric field tunable ferroelectric materials have attracted extensive attention in recent years due to their potential applications for tunable microwave device such as tunable filters, phased array antennas, delay lines and phase shifters (Maiti et al. 2007a; Rao et al. 1999; Romanofsky et al. 2000; Varadan et al 1992.; Zhi et al. 2002). Ba1-xSrxTiO3 and BaZrxTi1−xO3 have received the most attention due to their intrinsic high dielectric tunability. However, the high inherent materials loss and high dielectric constant has restricted its application in tunable microwave device. Various methods have been investigated to lower the dielectric constant and loss tangent of pure ferroelectrics. Forming ferroelectric-dielectric composite is an efficient method to reduce material dielectric constant, loss tangent and maintain tunability at a sufficiently high level. For binary ferroelectric-dielectric composite (such as BST+MgO) (Chang & Sengupta 2002; Sengupta & Sengupta 1999), with the increase of dielectrics content, the dielectric constant and tunability of composites decrease. In order to decrease the dielectric constant of binary composite, it is necessary to increase the content of linear dielectric, and the tunability will decrease inevitably due to ferroelectric dilution. Replacing one dielectric by the combination of dielectrics with different dielectric constants and forming ternary ferroelectric-dielectric composite can decrease the dielectric constant of composite and maintain or even increase the tunability. This is beneficial for tunable application. The Ba0.6Sr0.4TiO3-Mg2SiO4-MgO and BaZr0.2Ti0.8O3-Mg2SiO4-MgO composites exhibited relatively high tunability in combination with reduced dielectric permittivity and reduced loss tangent (He et al. 2010, 2011). With the increase of Mg2SiO4 content and the decrease of MgO content in Ba0.6Sr0.4TiO3-Mg2SiO4-MgO composite, the dielectric constant decrease and the tunability remain almost unchanged. For BaZr0.2Ti0.8O3-Mg2SiO4-MgO composite, an anomalous relation between dielectric constant and tunability was observed: with the increase of Mg2SiO4 content (>30 wt%), the dielectric constant of composite decreases and the tunability increases. The anomalous increased tunability can be attributed to redistribution of the electric field. Ba1-xSrxTiO3-Mg2TiO4-MgO can also form ferroelectric (Ba1-xSrxTiO3)-dielectric (Mg2TiO4-MgO) ternary composite and the dielectric constant can be decreased. With the increase of Mg2TiO4 content and the decrease of MgO content, the tunability of Ba1-xSrxTiO3Mg2TiO4-MgO composite increase. The multiple-phase composites might complicate method to effectively deposit films, particularly if the dielectrics and ferroelectric are not compatible for simultaneous deposition or simultaneous adhesion with a substrate or with

Is superparelectric 2-dimensional Sn2P2S6 having a “higher dielectric constant” desirable for more real Na+ pseudocapacitance?