Dielectric Properties of Au/PVA (Cobalt-Doped)/n-Si Photoconductive Diodes

The voltage (V) and frequency (f) dependence of dielectric parameters such as the dielectric constant (ε′), dielectric loss (ε″), dielectric loss tangent (tan δ), real and imaginary parts of electrical modulus (M′ and M″), and alternating-current (AC) electrical conductivity (σ _AC) of Au/PVA (cobalt-doped)/n-Si structures have been investigated by using experimental admittance measurements conducted at room temperature. The values of ε′, ε″, and tan δ were found to be strong functions of voltage and frequency, especially at low frequencies in the positive voltage region. It was observed that the values of ε′ and ε″ increase as the frequency decreases. The M′ values increase with increasing frequency due to increasing dielectric relaxation, while M″ values, in general, remain stable as frequency is changed. The σ _AC values at each bias voltage increase with increasing frequency.     

Automatic measurement of the complex permittivity at millimeter wavelengths

A measuring system including an oversized cavity resonator operating in the TE₀₁ mode for the determination of the complex permittivity ε^′- jε^″ of low-loss liquids at frequencies of about 36 GHz is described. While ε^′ is obtained by wavelength measurements in the filled and the empty resonator, ε^″ is determined from the variation of the Q factor of the filled resonator with the length of the dielectric sample. The Q factors of values of about 2·10⁴ to 10⁵ can be measured automatically by means of a desk calculator which controls the frequency and collects the digitized values of the detector output voltage. By means of the calculator, the Q factors of the resonator are determined by fitting analytical (Lorentzian) resonance curves to the measurement data. ε^″ and the Q factor for zero sample length are calculated according to Göttmann's methods.     

Measurement of Low-Loss Dielectric Materials Using Dielectric Rod Resonator

To obtain the complex permittivity of low-loss dielectric materials at 60 GHz, a measurement method is developed. Using a dielectric rod resonator excited by a dielectric waveguide, effective conductivity of conducting plates for short circuiting the resonator is determined. The complex permittivity of the dielectric rod is determined by the resonant frequency and unloaded quality factor of the TE_0m1-mode resonator. Moreover, the complex permittivity of single crystal sapphire, polycrystalline ceramics, and cordierite has been investigated in virtue of numerical simulation. For all the measured specimens in this study, the proposed method is seen to provide much better accuracy for values.     

Dielectric spectroscopy studies on (PVP + PVA) polyblend film

The thermal behavior of (PVP + PVA) polyblend film have been examined using differential scanning calorimetry and scanning electron microscopy. Capacitance and loss tangent values of polyvinyl pyrrolidone (PVP) + polyvinyl alcohol (PVA) polyblend film were measured in the frequency range 1-100 kHz and temperature range 298-423 K. Dielectric permittivity of real part (ε′) was obtained from capacitance data and dielectric permittivity of imaginary part (ε″) was obtained from real part of dielectric permittivity and loss tangent values. The decrease in dielectric permittivity was observed with increasing frequency and also observed increase in dielectric permittivity with increasing temperature. The complex dielectric constant (ε*) has been described by the electric modulus M* = (1/ε*) = M′ + iM″. The data of M* has been analysed by the stretched exponential decay of the electric field, Φ(t) = exp−(t/τ₀)^β.     

Frequency and gate voltage effects on the dielectric properties of Au/SiO2/n-Si structures

To determine the dielectric constant (ε′), dielectric loss (ε″), loss tangent (tan δ), the ac electrical conductivity (σ_ac) and the electric modulus of Au/SiO₂/n-Si structure, the measurement admittance technique was used. Experimental results show that the values of ε′, ε″, tan δ, σ_ac and the electric modulus show fairly large frequency and gate bias dispersion especially at low frequencies due to the interface charges and polarization. An increase in the values of the ε′ and ε″ were observed with both a decrease in frequency and an increase in frequency. The σ_ac is found to increase with both increasing frequency and voltage. In addition, the experimental dielectrical data have been analyzed considering electric modulus formalism. It can be concluded that the interface charges and interfacial polarization have strong influence on the dielectric properties of metal-insulator-semiconductor (MIS) structures especially at low frequencies and both in depletion and accumulation regions.     

Temperature dependent dielectric studies of Ni/n-GaP Schottky diodes by capacitance and conductance measurements

The dielectric properties of Ni/n-GaP Schottky diode were investigated in the temperature range 140–300 K by capacitance–voltage (C–V) and conductance–voltage (G/ω–V) measurements. The effect of temperature on series resistance (R_s) and interface state density (N_ss) were investigated. The dependency of dielectric constant (ε′), dielectric loss (ε′′), loss tangent (tan δ), ac conductivity (σ_ac), real (M′) and imaginary (M′′) parts of the electric modulus over temperature were evaluated and analyzed at 1 MHz frequency. The temperature dependent characteristics of ε′ and ε′′ reveal the contribution of various polarization effects, which increases with temperature. The Arrhenius plot of σ_ac shows two activation energies revealing the presence of two distinct trap states in the chosen temperature range. Moreover, the capacitance–frequency (C–f) measurement over 1 kHz to 1 MHz was carried out to study the effect of localized interface states.     

An asymmetric multilayer pendry lens

The optical-band subwavelength imaging by a multilayer Pendry lens consisting of alternating layers of a metal with the permittivity ε _m < 0 and a dielectric with the permittivity ε _d = ?ε _m is considered. In the earlier papers by Pendry and Ramakrishna, it is shown that, in a nonideal case, i.e., for |ε _d | = |ε _m | ≠ 1, the image can be obtained only with the use of an asymmetric scheme, when the image is formed in a medium with a permittivity equal to ε _d , the source being located in vacuum. However, in this case, the image quality is impaired (the image spectrum is narrowed). This phenomenon is explained in this study.     

Determination of electrodynamical parameters of dielectric pipe-shaped materials using millimeter wave cavity

Employment ofE _0np modes of cylindrical cavity resonator for measurement of electrodynamical parameters of dielectric pipe-shaped materials in millimeter wavelength band is suggested. Dielectric permittivity ? and conductivity σ of a sample can be found by measuring the frequency shift and theQ-factor change of the resonator. Method of “mode basis” is used for the calculation of sample permittivity ? and conductivity σ. Measurements were carried out at 8mm wavelength and related calculations have demonstrated use and possibilities of the method in studying the dielectric properties of samples of cylindrical and other forms.     

Quasioptical measurement of ferrite material parameters at terahertz frequencies by a new method: Faraday angle resonance

A new method for measuring the dielectric constant? _r and the saturation magnetizationM _S of ferrites in the terahertz frequency region is introduced in theory and experiment. The method, which bases on a resonance effect of the Faraday angle, gives an estimation of the loss factor tan δ, too. The derivation of the effect is based on a simple 4-port model of the ferrite disc which is axially premagnetized. Using the scattering matrix from the 4-port model the resonance effect is described and the extraction of the material parameters of some special data from the measurement record is explained. The measurement setup at 290 GHz is described and records of the ferrite Trans Tech TT 1–105 are evaluated, including an error calculation. Data for the hard ferrite Philips Ferroxdure FXD 330 are given, too. Using error minimizing algorithms which fit the material parameters to the measurement data a further increase in accuracy can be achieved.     

Electromagnetic characterization of ceramic material produced with natural zeolite

The aim of this study is to investigate the electromagnetic characterization of ceramic panel produced with natural zeolite via considering the frequency-dependent transmission (T), reflection (R) and absorption (A) coefficients. For this purpose, first of all, frequency-dependent complex dielectric values(dielectric permittivity and tangent loss) of material are measured via LCR meter and complex dielectric values used in three dimensional(3D) electromagnetic simulation tool. Then, Debye parameters such as static permittivity(ε_s), optic permittivity(ε_∞) and relaxation time(τ) are derived by using genetic algorithms. Finally, to validate the simulation results, T, R and A coefficients obtained from simulations are compared with frequency-dependent T, R and A values calculated by using the transmission-line equation.     

Permittivity of modified polyimide layers on LTCC

In this work, the permittivity of a tailored compound material was investigated consisting of a polyimide matrix in which hollow glass microspheres with a mean diameter of 30 μm are implemented as filler material. Choosing this approach the dielectric constant compared to that of the pure polyimide material is further decreased due to the enclosed air targeted to improve the high-frequency performance of patch antennas operated in the GHz range. Furthermore, the thickness of one single layer can be increased substantially from a maximum of about 10 μm for pure polyimide films to values above 80 μm by simply adding this type of filler material to the liquid polyimide precursor so that cavities in LTCC (low temperature co-fired ceramics) substrates can be filled more reliable. Two different variations of this compound material with filler to polymer ratios of 1:7.5 and 1:10 are realized. Basically, the film thickness depends on the spin coating speed and the microsphere content, respectively. The high initial surface roughness can be decreased to an average value of about 3 μm by applying additional layers of pure polyimide on top enabling thin film technology. The dielectric constant of the complete substrate comprising the LTCC and the compound material is measured using a ring resonator in microstrip configuration. From the resonances occurring in the transmission S-parameter |S₂₁| spectrum between 1 and 10 GHz, the relative dielectric constant can be determined. Using 820 μm thick LTCC substrates the permittivity can be reduced from originally ε_r = 7.8-6.6. By applying numerical calculations, a reduced permittivity of the pure polymer film from ε_r = 3.3 to about 2.9 can be determined when adding the glass microspheres.     

Temperature dependent electrical and dielectric properties of a metal/Dy2O3/n-GaAs (MOS) structure

This paper describes the structural properties, electrical and dielectric characteristics of thin Dy₂O₃ layer deposited on the n-GaAs substrate by electron beam deposition under ultra vacuum. Structural and morphological characterizations are investigated by atomic force microscopy (AFM) and X-ray diffraction measurements (XRD). The XRD shows that the elaborated Dy₂O₃ oxide has a cubic structure. The electrical and dielectric properties of Co/Au/Dy₂O₃/n-GaAs structure were studied in the temperature range of 80–500 K. The conductance and capacitance measurements were performed as a function of bias voltage and frequency. The dielectric constant (ε′), dielectric loss (ε″) and dielectric loss tangent (tanδ) of the structure are obtained from capacitance–voltage (C–V) and conductance–voltage (G/ω–V) measurements. These parameters are found to be strong functions of temperature and bias voltage. A strong negative capacitance (NC) phenomenon has been observed in C–V; hence ε′–V plots for each temperature value take negative values. The following behavior of the C and ε′ in the forward bias region has been explained with the minority-carrier injection and relaxation theory. From DC conductance study, electronic conduction is found to be dominated by thermally activated hopping at high temperature. Activation energy is deduced from the variation of conductance with temperature. The interface state density (N_ss) of the structure is of the order 1.13×10¹³ eV⁻¹ cm⁻².     

New Measuring Apparatus for Complex Permittivity at Millimeter-Wave Frequencies

A dielectric rod resonator excited by a nonradiative dielectric waveguide is used for measuring complex permittivity of low loss dielectric materials. The complex permittivties of single crystal sapphire, polycrystalline Ba (Mg_1/2 W_1/2) O₃ and Mg₂ Al₄ Si₅ O₁₈ (cordierite) have been obtained at 60 and 77 GHz by the new apparatus. The first time the measurement results of complex permittivity of brain grey and white matters from 15 to 50GHz utilizing a two-port microstrip test fixture is presented. S-parameters of Test fixture are simulated employing the finite-element method. A new spectrometer for the precision measurement of dielectric permittivity and loss tangent, which is capable of providing high resolution data for the first time over an extended W-band (68-118 GHz) frequency for specimens with a large range of absorption values, including highly absorbing specimens that otherwise would not be possible.     

Influence of Geometric Parameters and Permittivity of Stripline Filters on Resonator Coupling Coefficients

It has been proved that electromagnetic coupling coefficients K of resonators in stripline filters with homogeneous dielectric depend only on geometric parameters of the filter designs and are independent of relative permittivity ε_r (if the dielectric is two-layer, coefficients K depend only on geometric parameters of the filter designs and ratio ε_r2/ε_r1). It has been shown that the revealed earlier influence of permittivity ε_r and the operating frequency on K is only a consequence of the influence of the length of stripline resonators on K: the lesser is the length, the larger is coefficient K. It has been found that these propositions enable consideration of frequency characteristics of the same design of the bandpass filter in different frequency bands by changing εr and performing slight changes in outermost resonators. The results of computer simulation of the transfer of frequency characteristics of a stripline bandpass filter from 3 GHz to 6 and 12 GHz with retaining the fractional bandwidth and selectivity are presented.     

Dielectric properties in Au/SnO2/n-Si (MOS) structures irradiated under Co-γ rays

The metal-oxide-semiconductor (MOS) structures with insulator layer thickness range of 55-430 Å were stressed with a bias of 0 V during ⁶⁰Co-γ ray source irradiation with the dose rate of 2.12 kGy/h and the total dose range was 0-5×10⁵ Gy. The real part of dielectric constant ε′, dielectric loss ε″, dielectric loss tangent tanδ and the dc conductivity σ_dc were determined from against frequency, applied voltage, dose rate and thickness of insulator layer at room temperature for Au/SnO₂/n-Si (MOS) structures from C-V capacitance and G-V conductance measurements in depletion and weak inversion before and after irradiation. The dielectric properties of MOS structures have been found to be strongly influenced by the presence of dominant radiation-induced defects. The frequency, applied voltage, dose rate and thickness dependence of ε′, ε″, tanδ and σ_dc are studied in the frequency (500 Hz-10 MHz), applied voltage (−10 to 10 V), dose rate (0-500 kGy) and thickness of insulator layer (55-430 Å) range, respectively. In general, dielectric constant ε′, dielectric loss ε″ and dielectric loss tangent are found to decrease with increasing the frequency while σ_dc is increased. Experimental results shows that the interfacial polarization can be more easily occurred at the lower frequency and/or with the number of density of interface states between Si/SnO₂ interfaces, consequently, contribute to the improvement of dielectric properties of Au/SnO₂/n-Si (MOS) structures.     

Analysis of high frequency properties of multilayer structures for multichip modules

The microwave surface resistance and reactance of YBa₂Cu₃O₇ multilayers for MCMs have been studied as a function of thickness and relative permittivity of dielectric layers at 500 MHz and 10 GHz propagation frequency. Additionally, frequency properties of a YBCO/CeO₂/SrTiO₃/YBCO/LaAlO₃ multilayer have been analyzed and results compared with measurement results. Performed simulations have shown that a dielectric layer of high relative permittivity, necessary for good isolation between superconducting ground planes and power planes in the multichip modules, has negligible influence on the effective surface resistance and reactance up to 0.5 μm dielectric thickness.     

Development of Measurement and Extraction Technique of Complex Permittivity Using Transmission Parameter <Emphasis Type="Italic">S</Emphasis><Subscript>21</Subscript> for Millimeter Wave Frequencies

This study provides an overview of measured S-parameters and its processing to extract the dielectric properties of materials such as Teflon, PMMA, and PVC which are preferred for materials characterization process. In addition, a correction model is presented for transmission parameter (S ₂₁) to obtain the dielectric constant with high accuracy. A non-destructive and non-contact free space measurement method has been used to measure S-parameters of thin samples in the low THz frequency range. S-parameters are measured in free space by vector network analyzer supported with two frequency extenders. Additionally, the parabolic mirrors are used to collimate the generated beam in wide frequency range. Furthermore, a standard filter process is performed to remove the undesired ripples in signal using singular spectrum analyzer before the implementation of extraction process. Newton-Raphson extraction technique is used to extract the material complex permittivity as a function of the frequency in Y-band (325–500 GHz).     

Low-Cost Dielectric Reflective Surface for Low-Level Backscattered Diffuse Reflections

This article presents the design of non-subwavelength, non-resonant, and non-absorptive dielectric surface that creates a low-level backward diffuse reflections under illumination of a far-field plane wave at millimeter wave regime. Thus, radar cross section reduction of a solid metallic object can be achieved. The dielectric surface is consist of unit cells of only two different electric permittivity (ε _r1?=?6.14 and ε _r2?=?3.49) distributed across the surface aperture to achieve low-level backscattered diffuse reflections. The unit cells used are having non-subwavelength size (0.53λ_80GHz) which ensures an easier fabrication of the presented surface using low cost simple PCB technology, in particular at high frequencies. RCS reduction of more than 10 dBsm is achieved from 70 to 87 GHz (BW?≈?21.65 %) using the presented dielectric surface of optimized permittivity distribution. The RCS reduction capabilities of the presented surface are studied theoretically under both normal and oblique incidences and then fabricated and verified experimentally by reflectivity measurements.     

Preparation and Study of Bismuth Rare-Earth Tungstate Composite Screen-Printed Thick Films

In this paper, we report the microstructural and dielectric properties of bismuth rare-earth tungstate composite screen-printed thick films (BiGd_1?X Nd _X WO₆, BiGd_1?X Y _X WO₆, and BiY_1?X Nd _X WO₆). The crystal structure of BiREWO₆ (RE = Gd, Nd, and Y) can be associated with the Bi₂WO₆ perovskite structure. It was observed that the crystalline structure was attributed to a monoclinic phase with space group A12/m1. BiYWO₆ and BiY_0.5Gd_0.5WO₆ films showed characteristics of the dielectric relaxation phenomenon. The thick films exhibited moderate dielectric permittivity (ε _r′) values from 10 to 42. The results showed that the obtained ε _r′ values for films can be useful for capacitor applications and certainly for microelectronics and microwave devices (mobile phones, for example), where miniaturization of devices is crucial.     

The improved resonator method for measuring the complex permittivity of materials

An improved resonator method for determination of the complex permittivity of materials in a reflective resonator is presented. The method is specific in the following. In the obtained relationship, imaginary part ε₂ of the permittivity of an investigated material is determined using the variation of the resonance frequency and coupling coefficient of the resonator observed when a specimen is introduced, which increases the measurement accuracy. The method is approbated in the investigations of high-resistance silicon specimens.