Dielectric Insulation Materials Research Articles

Mechanics of dielectric polyamide/ SiO 2 nanocomposite coatings for cryogenic service in superconductor systems

Mechanics of dielectric polyamide/ <scp> SiO ₂ </scp> nanocomposite coatings for cryogenic service in superconductor systems

Broadband finite-element impedance computation for parasitic extraction

Parasitic extraction is a powerful tool in the design process of electromechanical devices, specifically as part of workflows that check electromagnetic compatibility. A novel scheme to extract impedances from CAD device models, suitable for a finite element implementation, is derived from Maxwell’s equations in differential form. It provides a foundation for parasitic extraction across a broad frequency range and is able to handle inhomogeneous permittivities and permeabilities, making it more flexible than existing integral equation approaches. The approach allows for the automatic treatment of multi-port models of arbitrary conductor geometry without requiring any significant manual user interaction. This is achieved by computing a connecting source current density that supplies current to the model’s terminals, whatever their location in the model, subsequently using this current density to compute the electric field, and finally calculating the impedance via a scalar potential. A mandatory low-frequency stabilization scheme is outlined, ensuring a stable evaluation of the model at low frequencies as well. Two quasistatic approximations and the special case of perfect electric conductors are treated theoretically. The magnetoquasistatic approximation is validated against an analytical model in a numerical experiment. Moreover, the intrinsic capability of the method to treat inhomogeneous permittivities and permeabilities is demonstrated with a simple capacitor-coil model including dielectric insulation and magnetic core materials. Finally, the method’s practicality is exemplified with a common mode choke model in a comparison of simulated and measured results.

Types and Construction of Power Transformers

Transformers may be classified according to dielectric insulation material as follows: • Oil-filled transformers• Dry type transformers

極低温での氷エレクトレットの脱分極電流特性

We have been studying the characteristics of ice as a dielectric or electrical insulation material at cryogenic temperature. IceXI, ferroelectric ice, exists at cryogenic temperature. It is very difficult to make iceXI. We applied direct-currentvoltage to ordinary ice at 253 K and cooled it to 77 K to obtain a polarized ice similar to iceXI. In this procedure, the protons move towards the cathode side under an electric field. The protons were stopped on the cathode side by cooling to 77 K, resulting in ice polarization. This polarized ice is called “ice electret”. We have previously reported the amount of electrical charge calculated from an integral of the ice electret depolarization current observed. The amount of charge increased as voltage and application time increased. In this paper, the effect of voltage, application time and temperature on depolarization current properties of the ice electret is reported. The depolarization current of the ice electret was examined in detail. Two peaks were observed in the depolarization current. One peak appeared around 270 K. But this peak did not occur in the specimen with a voltage of 140 K applied. The other peak was observed around 130 K in any specimen. The electrical charge calculated from this 130 K peak increased only when a voltage was applied, and did not increase as time and temperature increased when voltage was applied.

Classification of multiple partial discharge sources in dielectric insulation material using Cepstrum analysis–artificial neural network

In high‐voltage equipment insulation, multiple partial discharge (PD) sources may exist at the same time. Therefore, it is important to identify PDs from different PD sources under noisy condition in insulations, with the highest accuracy. Although many studies on classifying different PD types in insulation have been performed, some signal processing methods have not been used in the past for this application. Thus, in this work, Cepstrum analysis on PD signals combined with artificial neural network (ANN) is proposed to classify the PD types from different PD sources simultaneously under noisy condition. Measurement data from different sources of artificial PD signals were recorded from insulation materials. Feature extractions were performed on the recorded signals, including Cepstrum analysis, discrete wavelet transform, discrete Fourier transform, and wavelet packet transform for comparison between the different methods. The features extracted were used to train the ANN. To investigate the classification accuracy under noisy signals, the remaining data were corrupted with artificial noise. The noisy data were classified using the ANN, which had been trained by noise‐free PD signals. It is found that Cepstrum–ANN yields the highest classification accuracy for noisy PD signals than the other methods tested. © 2016 Institute of Electrical Engineers of Japan. Published by John Wiley &amp; Sons, Inc.

High temperature and low pressure chemical vapor deposition of silicon nitride on AlGaN: Band offsets and passivation studies

In this work, we employed X-ray photoelectron spectroscopy to determine the band offsets and interface Fermi level at the heterojunction formed by stoichiometric silicon nitride deposited on AlxGa1-xN (of varying Al composition “x”) via low pressure chemical vapor deposition. Silicon nitride is found to form a type II staggered band alignment with AlGaN for all Al compositions (0 ≤ x ≤ 1) and present an electron barrier into AlGaN even at higher Al compositions, where Eg(AlGaN) &amp;gt; Eg(Si3N4). Further, no band bending is observed in AlGaN for x ≤ 0.6 and a reduced band bending (by ∼1 eV in comparison to that at free surface) is observed for x &amp;gt; 0.6. The Fermi level in silicon nitride is found to be at 3 eV with respect to its valence band, which is likely due to silicon (≡Si0/−1) dangling bonds. The presence of band bending for x &amp;gt; 0.6 is seen as a likely consequence of Fermi level alignment at Si3N4/AlGaN hetero-interface and not due to interface states. Photoelectron spectroscopy results are corroborated by current-voltage-temperature and capacitance-voltage measurements. A shift in the interface Fermi level (before band bending at equilibrium) from the conduction band in Si3N4/n-GaN to the valence band in Si3N4/p-GaN is observed, which strongly indicates a reduction in mid-gap interface states. Hence, stoichiometric silicon nitride is found to be a feasible passivation and dielectric insulation material for AlGaN at any composition.

Experiment and modeling of void discharges within dielectric insulation material under impulse voltage

The presence of cavity in motor insulation fed by variable speed drive is one of the sources of partial discharge (PD) occurrence, especially under impulse voltage. This is a serious problem as PD can accelerate degradation of the motor insulation. Therefore, it is important to prevent void discharges from occurring in motor insulation under impulse voltage. In this work, the characteristics of void discharges within dielectric insulation material under impulse voltage were investigated through experiment and modeling. The test object consists of a rectangular void within a polyethylene material. The test object was stressed with different peak magnitude, front time and tail time of the applied impulse voltage. The experimental results were reproduced by simulation results from a void discharge model in insulation material. From the model that was developed, a better understanding on physical parameters that influence the characteristics of void discharges within dielectric material under impulse voltage can be attained.

Partial discharges within two spherical voids in an epoxy resin

A void in a dielectric insulation material may exist due to imperfection in the insulation manufacturing or long term stressing. Voids have been identified as one of the common sources of partial discharge (PD) activity within an insulation system, such as in cable insulation and power transformers. Therefore, it is important to study PD phenomenon within void cavities in insulation. In this work, a model of PD activity within two spherical voids in a homogeneous dielectric material has been developed using finite element analysis software to study the parameters affecting PD behaviour. The parameters that have been taken into account are the void surface conductivity, electron generation rate and the inception and extinction fields. Measurements of PD activity within two spherical voids in an epoxy resin under ac sinusoidal applied voltage have also been performed. The simulation results have been compared with the measurement data to validate the model and to identify the parameters affecting PD behaviour. Comparison between measurements of PD activity within single and two voids in a dielectric material have also been made to observe the difference of the results under both conditions.

Dielectric Strength of Laminated Paper and Polymer Materials Under Aging and Tensile Stress at 77 K

Among various factors influencing the service life of electrical equipment, the performance of dielectric insulation materials has an important role. Degradation of insulating materials caused by aging is fatal to insulation breakdown. The dielectric sheets of most conventional and high-temperature superconducting electrical equipment are working at tensile status when lapped on the conductor. Therefore, the study of the dielectric characteristic for insulation materials at aging and tensile status is very important to safely operate electrical equipment. In this paper, a special electrode system was designed to measure the breakdown voltages of polypropylene laminated paper, polyimide, and polytetrafluoroethylene sheets at tensile status both in normal environment and liquid nitrogen. Before the breakdown experiment, the specimens of the three materials all endured the aging process of abrupt temperature change. According to the test results and the Weibull plot analysis, the polyimide presents good dielectric strength at aging and tensile status both in normal environment and in liquid nitrogen.

Polyimide-Silica Hybrid Aerogels with High Mechanical Strength for Thermal Insulation Applications

ABSTRACTHigh performance polyimides have been widely investigated as materials with excellent thermal, mechanical, and electronic properties due to their highly rigid structures. Aspen has developed an approach to prepare polyimide aerogels which have applications as low dielectric constant materials, separation membranes, catalyst supports and insulation materials. In this paper, we will discuss the preparation of polyimide-silica hybrid aerogel materials with good mechanical strengths and low thermal conductivities. The polyimide-silica hybrid aerogels were made by a two-step process and the materials were characterized to determine thermal conductivity and compressive strength. Results show that compressive moduli of the polyimide-silica hybrid aerogels increase dramatically with density (power law relationship). Thermal conductivity of the aerogels is dependent on the aging conditions and density, with the lowest value achieved so far being ~12 mW/m-K at ambient conditions. The relationship between aerogel density and surface area, thermal stability, porosity and morphology of the nanostructure of the polyimide-silica hybrid aerogels are also described in this paper.

Analysis of Plasmonic Waveguides and Gratings Using Implicit Finite-Difference Methods

Various metal-insulator-metal- (MIM-) type plasmonic waveguides and gratings are investigated numerically. Three gratings are treated: one is formed by alternately stacking two kinds of MIM waveguides, another by periodic changes in the dielectric insulator materials of an MIM waveguide, and the other by a periodic variation of the air core width in an MIM waveguide. The dispersion property of each MIM waveguide of which the grating consists is analyzed using the implicit Yee-mesh-based beam-propagation method. It is shown that the third one has a relatively large effective index modulation of the guided mode with a simple grating structure, while maintaining a low propagation loss. Further examination is given to modifications of this grating structure. The transmission characteristics are examined using the frequency-dependent implicit locally one-dimensional FDTD method. We discuss how the modified grating structure affects the bandgap of the transmission characteristics.

Assessments of Low-Temperature Aging Test Method for the Dielectric Materials Immersed in Liquid Nitrogen

Among the various factors influencing the service life of the electric equipment, the performance of dielectric insulation materials has an important role to determine their whole service life. Degradation of insulating materials is fatal to insulation breakdown and finally lead to stop their operations. So the evaluation methods for the degree of degradation and aging for solid, oil and gas insulation have been developed and utilized very effectively to determine their performances. In order to determine the degradation of insulating materials immersed in extremely low temperature media such as liquid nitrogen, the abrupt temperature change from cryogenic to normal room temperature should be considered. But the assessments of low-temperature aging test method for the dielectric materials immersed in liquid nitrogen considering these conditions were not fully reported. Therefore, for the fundamental step to establish the suitable degradation test methods for cryogenic dielectric materials, we focused on the evaluation of aging test methods for dielectric materials exposed to low temperature environments considering thermal shock by cool-down and warm up test, thermal stress test and electric field stress test. In order to verify the effect of various degradation methods on cryogenic dielectric materials, Kraft, Kapton(polyimide) and Nomax type 410 sheets have been prepared and degradation experiments have been conducted. Then dielectric breakdown tests were performed. According to the test results, it was found that thermal shock degradation could be effective factor determining the degradation of cryogenic dielectric materials.

Electrical and reliability characteristics of GaAs MOSHEMTs utilizing high-k IIIB and IVB oxide layers

In this work, the high-k material of gadolinium oxide layer (Gd 2O 3) and zirconium oxide layer (ZrO 2) thin films were fabricated as the gate dielectric insulator materials in GaAs metal–oxide–semiconductor high electron mobility transistors (MOSHEMTs). The dielectric constant of Gd 2O 3 and ZrO 2 oxide layers were estimated to be 10.6 and 7.3 by the MOS-ring capacitor of C– V measurements. In addition, the thermal stability of the devices have been investigated and compared with the high-k material Gd 2O 3 and ZrO 2 thin films for reliability tests. The Gd 2O 3 MOSHEMTs achieved a better thermally stable characteristic duo to its similar lattice structure with GaAs native oxide layer. At high temperature operation, the V BR degradation slope was 1.2 × 10 −3 V/°C and the maximum I ds degradation slope was 1.4 × 10 −2 mA (%)/°C. According to this, the device also showed a good reliability characteristic within 48 h. Based on measurement results, the Gd 2O 3 MOSHEMTs exhibited the best electrical characteristics, including the lowest gate leakage current, the lowest noise spectra density, and the high power performance. Therefore, the Gd 2O 3 MOSHEMTs is suitable for high power amplifier and monolithic microwave integrated circuits (MMICs) applications.

电磁超材料中负磁导率对负介电常数的影响

For further understanding of the interactions between different materials in the electromagnetic metamaterials, the change characteristics of the effective permittivity of wire array embedded in a single negative permeability medium were analyzed theoretically. The interactions between the single negative permittivity and single negative permeability were investigated using both numerical calculation and electromagnetic simulation methods. The strategy of reducing such interactions was also proposed. The simulation results indicate that the wire array embedded directly in the single negative permeability medium exhibits only transmission forbidden band in the whole frequency band. While the wires are cladded with dielectric insulation materials, the above forbidden band turns into transmis

Electric Charge Accumulation in Polar and Non-Polar Polymers under Electron Beam Irradiation

The electric charge accumulation under an electron beam irradiation (40 keV and 60 keV) was measured by using the pressure wave propagation (PWP) method in the dielectric insulation materials, such as polar polymeric films (polycarbonate (PC), polyethylene-naphthalate (PEN), polyimide (PI), and polyethylene-terephthalate (PET)) and non-polar polymeric films (polystyrene (PS), polypropylene (PP), polyethylene (PE) and polytetrafluoroethylene (PTFE)). The PE and PTFE (non-polar polymers) showed the properties of large amount of electric charge accumulation over 50 C/m3 and long saturation time over 80 minutes. The PP and PS (non-polar polymer) showed the properties of middle amount of charge accumulation about 20 C/m3 and middle saturation time about 1 to 20 minutes. The PC, PEN, PI and PET (polar polymers) showed the properties of small amount of charge accumulation about 5 to 20 C/m3 and within short saturation time about 1.0 minutes. This paper summarizes the relationship between the properties of charge accumulation and chemical structural formula, and compares between the electro static potential distribution with negative charged polymer and its chemical structural formula.

Comprehensive Study of GaAs MOSFETs Using Gadolinium Oxide and Praseodymium Oxide Layers

The high-dielectric-constant (high-) gadolinium oxide layer and praseodymium oxide layer are demonstrated as gate dielectric insulator materials in GaAs metal-oxide-semiconductor field-effect transistors (MOSFETs) using in situ high oxygen flow rate electron-beam deposition technology. The dielectric constants of the and layers developed in this study were 9.2 and 9.8, respectively. The Schottky gate turn-on voltages of GaAs MOSFETs with and insulators were 2.23 and , respectively, representing an improvement on the conventional p-type high electron mobility transistors . Moreover, the MOSFETs had a higher thermal stability and thermal linearity than the MOSFET (temperature range ) due to its high binding energy, as revealed by X-ray photoelectron spectroscopy.

Low-dielectric, nanoporous polyimide films prepared from PEO–POSS nanoparticles

Dielectric insulator materials that have low dielectric constants ( k<2.5) are required as inter-level dielectrics to replace silicon dioxide (SiO 2) in future semiconductor devices. In this paper, we describe a novel method for preparing nanoporous polyimide films through the use of a hybrid PEO–POSS template. We generated these nanoporous foams are generated by blending polyimide as the major phase with a minor phase consisting of the thermally labile PEO–POSS nanoparticles. The labile PEO–POSS nanoparticles would undergoes oxidative thermolysis to releases small molecules as byproducts that diffuse out of the matrix to leave voids into the polymer matrix. We achieved significant reductions in dielectric constant (from k=3.25 to 2.25) for the porous PI hybrid films, which had pore sizes in the range of 10–40 nm.

High dielectric insulation coating for time domain reflectometry soil moisture sensor

Insulation coating is often applied to time domain reflectometry (TDR) soil moisture sensors to reduce the conduction loss of energy. However, because of low dielectric constants of common plastic insulation materials, sensitivity is reduced, and the measurements are strongly dependent on coating thickness. Analytical studies clearly showed that these unwanted features could be mitigated if a high dielectric material is used for coating. An epoxy‐ceramic nanocomposite was selected as a high dielectric insulation material because of its high dielectric constant and high adhesion. Experimental work using this composite indicated that the material has the potential to be used as a high dielectric coating for TDR soil moisture probes. On the basis of the results of these analytical and experimental studies a framework for designing an improved epoxy‐ceramic composite for coating TDR soil moisture sensors is suggested.

The Modeling and Calculation of One Transistor Memory Devices

Metal/Ferroelectrics/Metal/Insulator/Si (MFMIS) and Metal/Ferroelectrics/ Insulator/Si (MFIS) one-transistor devices are being proposed for non-volatile memory applications. In order to determine the basic theory of one-transistor memory devices, we use equivalent circuits to model and calculate the basic properties of one-transistor memory devices. The capacitance of MFMIS and MFIS capacitors, memory windows, operation voltages, threshold voltages, and both switching and retention properties of one-transistor memory devices have also been calculated. According to the modeling and calculation, the ferroelectric materials with lower dielectric constant (ϵ), low polarization (PR), appropriate coercive field and square hysteresis loop are required for one-transistor memory devices and low voltage applications. High dielectric constant insulator materials may improve the performance of one-transistor memory devices. In addition, the effects of depolarization fields, leakage current, and defect density on the switching and retention properties of one-transistor memory devices are also calculated. Based on the modeling and calculation, the retention problem dealing with depolarization fields and leakage current is a big challenge for one-transistor memory devices.

Closed-Cell Mesostructured Porous Silica Films Templated by PS-b-PEO Without Additional Microporosity

AbstractMesostructured silica/diblock films with a 3D arrangement of spherical domains (bcc) were prepared through evaporation-induced self-assembly (EISA) using polystyrene-blockpoly( ethylene oxide) diblock copolymers as structure-directing agents and TEOS (Si(OCH2CH3)4) and/or MTES (Si(OCH2CH3)3CH3) as silica precursors. A detailed small angle x-ray scattering (SAXS) analysis of the calcined mesoporous films showed that, in contrast to recently reported studies, no additional microporosity due to the PEO was observed, indicating that the PEO block formed a layer at the interface between the PS domain and the silica matrix and thus contributed to the mesopore volume. These mesostructured porous silica films are believed to be the first in respect of isolated spheres with a 3D array distributed in a silica matrix without additional microporosity and with MTES as silica precursor. Such closed-cell mesostructured porous materials with high porosity and controllable hydrophobicity can be excellent candidates for low dielectric (K) insulator materials.