Intentionally inserted oxygen depleted (Ba/sub 0.5/Sr/sub 0.5/)TiO/sub 3/ layers as a model of DC-electrical degradation

The relative dielectric constant versus voltage (/spl epsiv//sub r/-V) characteristics and the current density versus electric field (J-E) characteristics of (Ba/sub 0.5/Sr/sub 0.5/)TiO/sub 3/ films, which have intentionally inserted oxygen depleted layers near the bottom electrodes, were investigated as a model of dc-electrical degradation phenomena. Our investigation demonstrated that the intentionally inserted oxygen depleted layer is the cause of the tunneling conduction.     

Effect of puffer volume and operating force on dielectric recovery performance in thermal puffer-type gas circuit breaker

In order to investigate the influence of puffer volume V/sub P/ and operating force to dielectric performance of GCB at current interruption, we calculated the prospective dielectric withstand voltage V/sub W/ between arcing contacts. The withstand voltage was calculated by the electric field strength appeared on arcing contacts and the allowable electric field strength E/sub W//sup */ of hot gas due to thermal puffer action. We could clarify that large initial puffer volume V/sub P/ can increase withstand voltage V/sub W/ at current breaking point and also that an optimum point exists in operating force F. For example, it was found that in case of the operating force of 1000 kgf, the puffer volume V/sub P/ of 1.2 liter would be best choice in the interrupting condition of i=50 kA and arcing time of 1.35 cycle.     

Electron mobility in dense argon gas at several temperatures

The mobility /spl mu/ of excess electrons in dense Argon gas was measured as a function of the applied electric field E and of the gas density N at several temperatures in the range 142.6 < T < 200 K, encompassing the critical temperature T/sub c/ = 150.86 K We report here measurements up to N /spl ap/ 7 nm/sup -3/, close to the critical density, N/sub c/ /spl ap/ 8.1 nm/sup -3/. At all temperatures, and up to moderately high densities, the density-normalized mobility /spl mu/N shows the usual electric field dependence in a gas with a Ramsauer-Townsend minimum due to the mainly attractive electron-atom interaction. /spl mu/N is constant and field independent for small E, shows a maximum for a reduced field E/N /spl ap/ 4 mTd, and then decreases rapidly with the field. The zero field density-normalized mobility /spl mu//sub 0/N, for all T > T/sub c/, shows the well known anomalous positive density effect, i.e., /spl mu//sub 0/N increases with increasing N. Below T,, however, /spl mu//sub 0/N does not show the expected effect, but features a broad maximum. This appears to be a crossover behavior between the positive density effect shown for T > T, and the small negative effect previously observed for T /spl ap/ 90 K However, the data at all temperatures confirm the interpretation of the anomalous density effect as being essentially due by the density-dependent quantum shift of the electron ground state kinetic energy in a disordered medium as a result of multiple scattering (MS) processes, although other MS processes influence the experimental outcome.     

A finite-element analysis of the electrostatic force on a uniformlycharged dielectric sphere resting on a dielectric-coated electrode in adetaching electric field

In the electrophotographic process, charged toner particles are transferred from one surface to another with an electric field. To enable electric field transfer of toner, the externally applied field strength must be greater than a threshold value, so that the Coulomb force can overcome the toner adhesion force at the supporting surface. In this paper, the threshold field strength to detach a charged dielectric particle is determined efficiently by using the Galerkin finite-element method to simultaneously solve the Laplace equation for the field distribution and an overall constraint equation for the force balance. This computational method also enables calculation of the electrostatic adhesion force and is applicable to various particle-electrode configurations. For illustrative purposes, however, we consider the axisymmetric problem of electric field detachment of a dielectric sphere with uniform surface charge resting on a planar dielectric-coated electrode. The analysis is particularly focused on the dependence of the electrostatic force upon the dielectric overcoating thickness and spacing between parallel plate electrodes. The electrostatic force on a uniformly charged particle in contact with a surface is found to be influenced significantly by the thickness of dielectric overcoating and the spacing between electrodes when either becomes less than five times the particle radius     

Electrical insulation characteristics of cold dielectric high temperature superconducting cable

For the optimization of electrical insulation design for high temperature superconducting (HTS) cable, evaluation of electrical insulation characteristics especially for butt gap of LN/sub 2/ impregnated cold dielectric (CD) which consists of the wrapped tape insulation impregnated with LN/sub 2/ plays an important role. This paper presents partial discharge (PD) inception and breakdown characteristics in LN/sub 2/ impregnated butt gap model which modeled a weak point of the wrapped tape insulation impregnated with LN/sub 2/ and cable model with short length with polypropylene laminated paper (PPLP/sup /spl reg//), Nomex/sup /spl reg// paper and cellulose paper. PD current pulse was found to have a steep rise time of /spl sim/ ns and amplitude of /spl sim/ tens /spl mu/A at PD inception voltage region. Little dependency of breakdown stress on the insulating material is found. PD inception stress is almost independent of insulation thickness of 1 to 3 mm. The requirement insulation thickness for 66 kV class HTS cable is estimated to be /spl sim/ 5 mm under PD-free condition from viewpoint of long-term reliability.     

Multipole Corrections to Dielectrophoretic Force

Calculation of the dielectrophoretic (DEP) force on a neutral dielectric partide in a nonuniform electric field is simplified by using the effective dipole method. Once the instantaneous effective dipole moment peff(t) has been correctly identified using Gauss's law, then the expression (peff(t)?)E0(t) is used to determine the force on the particle. Recent work has demonstrated that the effective dipole method produces a result consistent with integration of the Maxwell stress tensor. In the present paper, the issues concerning identification of peff(t) are aired, and an alternate derivation of the DEP force on a conducting dielectric sphere immersed in a conducting dielectric fluid is offered. Then the effective dipole theory is generalized to account for higher order (multipole) contributions. This new effective multipole theory is restricted to spherical particles in a cylindrically symmetric cusped electric field, but the analysis leads to straightforward computation of the quadrupolar correction factor for the DEP force. A quantitative example is provided.     

Switching of capacitive currents and the correlation of restrike and pre-ignition behavior

The new IEC 62271-100 requires an extensive proof of the capability of capacitive switching for a breaker under test. For vacuum circuit breakers, dielectric properties are mainly determined by the condition and topology of the contact surfaces, which are modified by in-rush currents as well as load-breaking currents and other effects. A synthetic single-phase test device has been erected in order to simulate three-phase network conditions and to collect more data on the statistical properties of the relevant processes. The distribution of pre-ignition field strengths is evaluated for different contact strokes and surface conditions, when discharging a capacitor through the closing interrupter. On the other side, the probability of restrikes for a given switching condition defined by full contact gap d/sub 0/ and peak recovery voltage U/sub re//spl circ/ is measured and compared with the cumulative probability of pre-ignition just at the field strength E=U/sub re//spl circ//d/sub 0/. A correlation between pre-ignition and restrike probabilities suggests a breakdown mechanism being field-emission dominated. In addition a rather strong conditioning effect has been observed at smaller contact gaps smoothening the contact surfaces.     

Charging characteristics and electric field distribution on alumina as affected by triple junctions in vacuum

This paper describes the dependence of the charging characteristics on the electric field distribution on the alumina (Al/sub 2/O/sub 3/) surface as affected by the triple junction in vacuum. For HV electrical insulation design of vacuum interrupter, surface flashover in vacuum is very important problem to be solved. Attention should be paid to the fact that the insulation characteristics on the dielectric surface are strongly influenced by field emission of electrons from the triple junction and the accumulated charges on the dielectric surface. In order to clarify the charging mechanism, we measured the charging characteristics for various types of triple junctions. In particular, we focused on the influence of the electric field distribution along the solid dielectrics and near the cathode triple junction (CTJ) on the charging characteristics. The results confirmed that the electric field distribution strongly affected the 2-dimensional (2D) distribution of the surface charge on the dielectric sample. Consequently, it was found that positive charging was generated on alumina, when the incident angle of the electric line of force on the alumina surface became >60/spl deg/.     

A drain avalanche hot carrier lifetime model for n- and p-channel MOSFETs

A simple and physical drain avalanche hot carrier lifetime model has been proposed. The model is based on a mechanism of interface trap generation caused by recombination of hot electrons and hot holes. The lifetime is modeled as /spl tau/(I/sub d//W)/sup 2//spl prop/(I/sub sub//I/sub d/)/sup -m/. The formula is different from the conventional /spl tau/I/sub d//W-I/sub sub//I/sub d/ model in that the exponent of I/sub d//W is 2, which results from the assumed mechanism of the two-carrier recombination. It is shown that the mechanism gives a physical basis of the empirical /spl tau/-I/sub sub//W model for NMOSFETs. The proposed model has been validated experimentally both for NMOSFETs and for PMOSFETs. Model parameters extracted from experimental data show that carrier critical energies for creating damage are lower than the interface potential barriers. It is supposed that oxide band edge tailing enables low-energy carriers to create the damage. The channel hot electron condition becomes the worst case in short channel NMOSFETs, because gate voltage dependence of the maximum channel electric field decreases.     

Analysis of Electrostatic Adhesion and Detachment of a Nonuniformly Charged Particle on a Conducting Plane

This paper presents the analysis of electrostatic adhesion and detachment of a charged, dielectric particle resting on a conducting plane. We have studied the effects of particle dielectric constant and the nonuniform charge distribution on the force acting on the particle. Charge on the particle surface is assumed to be smoothly varied and (a) concentrated at the bottom pole or (b) concentrated at the top and bottom poles. The analysis utilizes the method of multipole images to obtain accurate values of the electric field, and determines the electrostatic force from the stress on particle surface. Compared with the force on a uniformly charged particle having the same total charge amount, the analytical results show that the force is significantly enhanced by both kinds of nonuniform charge distribution treated in this work, and is particularly strong when charge is highly concentrated at the bottom pole. It is found that electric field in a limited range must be applied in order to detach the particle from the conducting plane. The electric field necessary for detachment depends strongly on the dielectric constant and the distribution of charge on the particle. The detachment becomes difficult for a particle with charged distributed at the bottom pole, and may be hardly possible if the dielectric constant is too high.     

Optimization of high-voltage self-blast interrupters by gas flow and electric field computations

Self-blast interrupters have the advantage of operating with low mechanical energy as they build up the pressure of the arc extinguishing gas flow from the thermal energy of the arc. This creates a higher pressure, but also a higher gas temperature than in interrupters with mechanical compression. Detailed flow field and electric field computations are necessary to achieve under such conditions the energy removal and dielectric recovery in view of an increase in breaking capacity and voltage rating. In particular, the optimization of the electric field/gas density distribution E//spl rho/ is a tool to improve the short-circuit and capacitive current breaking performance.     

Electric field modeling and field formation mechanism in HVDC SF/sub 6/ gas insulated systems

This paper reports on the electric field behavior in HVDC SF/sub 6/ gas insulated systems. In the field model definitions, the SF/sub 6//epoxy interfaces are assumed as thin slightly conducting layers with non-zero thickness. The boundary conditions involving surface-reduced parameters of these layers are adopted. This allows avoidance of problems of calculation regarding the proximity of interfaces between subdomains. The boundary-value problem describing capacitive-resistive time-varying electric field is formulated. On this basis, the transient HVDC electric field model and time domain-calculating algorithm are constructed. The model accounts simultaneously for both the surface layer properties and bulk conduction parameters of the bounding dielectrics, while surface conductivity may be specified as a non-linear or an arbitrary function. The method employs direct integration of a continuity equation in the time domain with the calculation of an electrostatic field approximation at each integration step. The basic features and applicability of the method are discussed. The model has been applied for analysis of HVDC electric field formation mechanism in SF/sub 6//epoxy insulation. It is demonstrated that charge accumulation phenomena cannot be described by a single time-stable mechanism. Some directions regarding further development of the field model and calculating algorithm are suggested.     

Thermal-stability improvement of a sulfur-passivated InGaP/InGaAs/GaAs HFET

The temperature-dependent characteristics of an InGaP/InGaAs/GaAs heterostructure field-effect transistor (HFET), using the (NH/sub 4/)/sub 2/S/sub x/ solution to form the InGaP surface passivation, are studied and demonstrated. The sulfur-passivated device shows significantly improved dc and RF performances over a wide temperature range (300-510 K). With a 1/spl times/100-/spl mu/m/sup 2/ gate-dimension HFET by (NH/sub 4/)/sub 2/S/sub x/ treatment, the considerably improved thermal stability over dc performances including lower temperature variation coefficients on the turn-on voltage (-1.23 mV/K), the gate-drain breakdown voltage (-0.05 mV/K), the gate leakage current (1.04 /spl mu/A/mm/spl middot/K), the threshold voltage (-1.139 mV/K), and the drain-saturation-current operating regimes (-3.11/spl times/10/sup -4//K) are obtained as the temperature is increased from 300 to 510 K. In addition, for RF characteristics, the sulfur-passivated device also shows a low degradation rate on drain-saturation-current operating regimes (-3.29/spl times/10/sup -4//K) as the temperature is increased from 300 to 400 K. These advantages provide the promise for high-speed high-frequency high-temperature electronics applications.     

Dielectric relaxation in piezo-, pyro- and ferroelectric polyamide 11

Ferroelectric polyamide 11 films were prepared by melt-quenching, cold-drawing and electrical poling. Their ferroelectricity was studied by means of dielectric-hysteresis measurements. A remnant polarisation of up to 35 mC/m/sup 2/ and a coercive field of 75 MV/m were obtained. The piezoelectric d/sub 33/ coefficient and the pyroelectric coefficient of the films are reduced by annealing just below the melting region, but remain at about 3 pC/N and 8 /spl mu/C/(m/sup 2/K), respectively, during further heat treatment. Differential scanning calorimetry (DSC), dielectric relaxation spectroscopy (DRS) and thermally stimulated depolarisation (TSD) were applied for investigating the conformational changes induced by melt-quenching, cold-drawing and annealing. The results indicate that the cold-drawn film mainly consists of a rigid amorphous phase which exhibits considerably lower conductivity, no glass transition and consequently no dielectric /spl alpha/ relaxation. Instead, an /spl alpha//sub r/ relaxation is found, which is related to chain motions in regions of the rigid amorphous phase where the amide-group dipoles are not perfectly ordered. Annealing removes imperfectly ordered structures, but does not affect the ferroelectric polarisation. Therefore, it may be concluded that essentially the /spl alpha//sub r/ relaxation causes the thermally nonstable part of the piezo- and pyroelectricity in polyamide 11.     

Electrical breakdown triggered by a free conducting spherical particle in saturated liquid He I and He II under uniform dc field

This paper is concerned with the pre-breakdown phenomena and the breakdown voltage characteristics, in the presence of a free moving conducting spherical particle, of saturated normal liquid helium (He I) and saturated superfluid liquid helium (He II) under uniform dc field. Experiments show that the particle lifts off around the theoretical value of the lift-off electric field, and the particle oscillates between the electrodes at higher applied voltages. In that case, the microdischarge appears just before the charged particle collides with the oppositely charged electrode, and the bubble is generated at the moment of every collision of the particle with the electrode. It is confirmed theoretically as well as experimentally that the maximum bubble radius in He II is nearly proportional to the E/sub in//sup 1/3/, which is the released energy from the particle for the bubble generation. The insulation environment before the electrical breakdown suddenly changes at the /spl lambda/-point since the bubble behavior in He I and He II greatly differs. In the characteristics of the breakdown voltage vs. liquid pressure, a clear discontinuity appears at the /spl lambda/-point. Furthermore, the breakdown voltage in the parallel plane gap contaminated by a particle is lower than that in the rod-plane gap without a particle. It is found that the breakdown voltage characteristics are closely related to the trigger effect of the microdischarge and the bubble generation.     

Atmospheric pressure of nitrogen plasmas in a ferroelectric packed bed barrier discharge reactor. Part I. Modeling

Numerical modelling of ferroelectric packed bed nonthermal plasma reactor has been conducted to predict plasma parameters in a pure nitrogen environment. Simplified time averaged one-dimensional physical model based on Poisson's equation for electric field and transport equation for electrons was developed. The mean electron energy was obtained by a swarm relationship from calculated electric field profiles and plasma neutral conditions. For chemical model, N/sup +/, N/sub 2//sup +/, N/sub 3//sup +/, N/sub 4//sup +/, N/sup */, N/sub 2//sup */ and electron were considered where N/sup */ and N/sub 2//sup */ are the total excited atoms and molecules, respectively. The results show that all the plasma parameters increase with increasing applied AC voltage and pellet dielectric constant. The numerical results also show that the dominant ion is N/sub 4//sup +/ and the metastable molecule density is much higher than radical and the electron densities at atmospheric gas pressure.     

Optical and electrical characterization of creeping discharges over solid/liquid interfaces under lightning impulse voltage

This paper deals with the experimental characterization of discharges propagating over solid insulators immersed in mineral oil, under impulse voltages using a point-plane electrode arrangement. It's shown that the nature and the thickness of the solid insulator significantly influence the characteristics of creepage discharge and especially the final length L/sub f/ and the density of branches /spl rho/. For a given thickness, L/sub f/ increases quasi-linearly with the voltage; it decreases when the thickness increases. So /spl rho/ increases with the dielectric constant of the solid insulator; it also increases when the thickness is reduced. This indicates the important role of the capacitive effect in the propagation mechanism. The main discharge is followed by a secondary one of opposite sign to that of the main discharge.     

Influence of copper vapor contamination on dielectric properties of hot air at 300-3500 K in atmospheric pressure

The influence of copper vapor contamination on the dielectric properties of hot air at atmospheric pressure was numerically predicted in heavy particle temperature range 300-3500 K. Dielectric properties of hot gases are very important for effective design of switching devices and other applications. Copper vapor is known to be injected from the electrodes into the hot gas during arc interruption in a circuit breaker, which may substantially affect the dielectric strength of the hot gas. Analysis of equilibrium composition for a hot air contaminated with copper vapor and computations of Boltzmann equation made it possible to study the dielectric properties of interest. The result indicates that 1.0% copper vapor contamination remarkably increases the effective ionization coefficient /spl alpha/~ and thereby decreases the critical electric field (E/N)/sub cr/ drastically. This arises from a much lower ionization potential of the copper atom.     

Electrical characterization of benzocyclobutene polymers for electric micromachines

An approach using interdigitated capacitors for electrical characterization of CYCLOTENE, a spin-on low-k benzocyclobutene (BCB)-based polymer is introduced and the effect of moisture uptake is investigated. The dielectric constant of CYCLOTENE is extracted from capacitance measurements with a systematic error less than 0.1%, giving an average value of 2.49 with a standard deviation of 1.5%. The dielectric constant increases by 1.2% after a humidity stress of 85% RH at 85/spl deg/C. The I-V characteristics of CYCLOTENE show a dependency of breakdown strength and leakage current on the geometrical dimensions of the device under test. A breakdown strength of 225V//spl mu/m and 320 V//spl mu/m for 2-/spl mu/m and 3-/spl mu/m finger spacing, respectively, and a leakage current of a few to tens of pA are measured. The I-V characteristics degrade drastically after the humidity stress, showing a breakdown strength of 100 V//spl mu/m and 180 V//spl mu/m for 2-/spl mu/m and 3-/spl mu/m finger spacing, respectively, and a maximum increase in the leakage current as large as one order of magnitude. The maximum performance and long-term reliability of an electric micromachine are adversely affected by the degradation of the breakdown voltage and the leakage current after moisture absorption. It is expected, however, that the electrical efficiency is improved using BCB-based polymers with negligible dependency on moisture absorption.     

Atmospheric pressure of nitrogen plasmas in a ferroelectric packed-bed barrier discharge reactor. Part II. Spectroscopic measurements of excited nitrogen molecule density and its vibrational temperature

For pt.I see ibid.(vol.11 no.3 p.481-90, 2004). In order to validate a nonthermal plasma model using nitrogen in a ferroelectric packed-bed reactor, the number density of the excited nitrogen molecules has been investigated by spectroscopic measurements. Experiments were conducted at applied voltages from 0 to 20 kV, 60 Hz and gas flow rates from 1 to 5 L/min in pure nitrogen gas. The results show that the number density for excited N/sub 2/ molecules increases with increasing applied voltage and dielectric constant and agrees qualitatively with the numerical modeling results at lower applied voltage. The vibrational temperature of the C/sup 3//spl Pi//sub u/ (v') state of N/sub 2/ has been calculated from the light intensity emitted by the 2nd positive band. The vibrational temperature decreases with increasing gas flow rate and no significant effects of the applied voltage and dielectric constant were observed.