Charge Saturation Research Articles

Analytical non-linear charge control model for InAlAs/InGaAs/InAlAs double heterostructure high electron mobility transistor (DH-HEMT)

An analytical charge control model for sheet carrier density is presented for InAlAs/InGaAs/InAlAs double heterostructure high electron mobility transistor (DH-HEMT). The model uses a polynomial dependence of sheet carrier concentration on position of quasi-Fermi energy level to successfully predict the gradual saturation of charge in the device and is valid from subthreshold region to high conduction region for both the channels. The model has been extended to calculate I d– V d characteristics, transconductance and cut-off frequency of the device.

Development of a packaging material using non‐bleed‐type antistatic ionomer

AbstractGenerally, plastics and plastic films are low in moisture absorption and high in electric insulation. They are inherently vulnerable to static charge build‐up, which can result in a variety of problems. We have developed a functional packaging material to solve these static problems, by using a potassium salt of ethylene ionomer, which is a non‐bleed‐type antistatic agent. Good antistatic performance was shown by evaluating a variety of electric characteristics (e.g. the static decay time, ash test and saturated electrostatic charge and half‐life) and surface resistivity. In addition, antistatic performance was achieved on the mLLDPE (non‐treated) side in a multilayer structure. This means that the use of potassium ionomer on any layers in a multilayer structure provides antistatic performance, leading to the expectation of developing a wide variety and diversity of packaging materials. Copyright © 2004 John Wiley & Sons, Ltd.

Unipolar field charging of particles by electrical discharge: effect of particle shape

In order to control the properties of the pollutant particles (diameter, charge, concentration, aerosol flow rate) to be collected in a coagulation device, a corona charger (negative wire cylinder discharge) has been designed and tested. This paper presents results of di ethyl hexyl sebacat (DEHS) and NaCl particle charging in a corona discharge. The aerosol particles are charged in a high electric field (>10 6 V m −1) so as to check the validity of the field charging law. A special care is taken to characterise accurately the discharge, to calculate, for each experimental condition, the gaseous ion density and electric field in which particles get charged. The first point is that the field charging law fits well with experimental charging data for spherical particles in the intermediate size range (0.44– 1.13 μm ). Nevertheless, for cubic NaCl particles in the same charging conditions (i.e. ion density and transit time), the experimental charge level appears to be greater than predicted by classical field charging law. The only difference between DEHS and NaCl particles seems to be the particle shape, that could lead to an increase of saturation charge in the case of cubic particles, due to local electric field enhancement.

Charging Ability of Pure Hydrocarbons and Lubricating Oils

An experiment using a purpose-built test rig to examine the effect of oil chemistry on the charging ability of various oils revealed that the charge produced depends on two extrinsic properties; the electric field (used to charge the droplet) and the droplet radius. A normalization parameter was developed from these dependencies and used to compare the results from the tests described herein. Four classes of liquids were tested. These were pure hydrocarbon liquids (hexadecane, decane, and squalane), base oils (both mineral and synthetic stocks), formulated oils (mineral base oil with additives), and commercial oils (fully formulated mineral and synthetic oils, available over-the-counter). The charging for both pure hydrocarbons and base oils indicates that the charged species have a low mobility and thus are likely to be large, bulky molecules. For this reason, the charging of the base oils is noticeably time dependent and the charge imparted on the oil did not always reach saturation. The charging (rate) of base oils appears to follow the level of impurities (particularly sulfur). Generally, both pure hydrocarbons and base oils tend to charge more when a positive field is applied. Conductivity values help to explain the measured charge levels. This would be expected as conductivity is related to the ionic species (charge carriers) present. The majority of the formulated and commercial oils tested reached charge saturation for all conditions tested, resulting in a normalized value of around 0.1 pC mm− 1 V− 1 , comparable with a theoretical calculated value. The formulated and commercial oils that did not reach saturation have conductivities comparable with base oils and therefore behave in a fashion similar to the base oils.

A dipole-enhanced approximation for a dielectric mixture

This paper presents a dipole-enhanced approximation to calculate the saturation charge of particles for high-volume fraction particles. An approximate formula for calculating the maximum field strength at the surface of one sphere is derived. It shows the variation of the maximum field strength with the difference in permittivity and the ratio of the particle radius to the distance between particles. The maximum field strengths calculated using this formula are compared with those obtained with the dipole model and the finite-element method, the calculated result shows that the formula is acceptable. A formula for calculating saturation charge of particles is derived, which depends on the volume fraction of particles.

Tribocharge build-up and decay at a slider-disk interface

As the gap between the head and disk decreases and the sensitivity of recording transducers increases, the head and disk are more likely to come in contact, which may damage the recording transducer during start/stop and flying cases. One important effect associated with the intermittent head-disk contacts is the tribocharge/tribocurrent phenomenon. In this study, tribocharge and tribocurrent generation during a pico-slider/disk interaction were measured by using an electrometer. These triboelectrical properties were compared with friction force and acoustic emission signals. The electrical potential difference between the slider and the disk was caused by mechanical interactions between them. The tribocharge was generated during the slider-disk interaction and its saturation charge level was about 1 V. The tribocharge build-up level was independent of the slider-disk interaction time. However, the tribocharge decayed when there was no interaction between the slider and the disk. The decay of tribocharge was inversely proportional to the square root of time. Tribocurrent generation coincided with tribocharge generation. The tribocurrent was also independent of the slider-disk interaction time. The current level measured in this study may not reach the electrostatic discharge (ESD) damage level, but it can induce the dissociation of lubricant.

Electric Force Microscopy Of Individually Charged Silicon Nanoparticles

ABSTRACTWe report on charge injection experiments performed on single silicon nanoparticles and their analysis by Electric Force Microscopy (EFM). An analytical model is presented, enabling a quantitative determination of the charge state of the semiconductor nanoparticles from EFM signals, for arbitrary tip and nanoparticle shapes.Experimentally, we provide an analysis of the capacitive and charge interactions taking place in EFM of silicon nanoparticles deposited on conductive substrates. We demonstrate that the weak image interactions associated with charged nanoparticles -of dipole-dipole type- can be identified from a spectroscopic EFM analysis.Finally, we address the issue of the charge injection mechanisms. From the hysteretic behaviour of the charge injection spectroscopy, we separate volume versus surface charge effects. We show that charges are mostly injected in the nanoparticle volume, with however some residual injection on the nanoparticle surface. Mechanisms of the charge saturation are discussed.

電子写真における絶縁性トナーヘのイオン荷電及び電子荷電

The electrophotographic image quality depends on the triboelectric charge of insulating toner. However, the control of triboelectric charge is difficult because of the insulating nature of toner. In this study, the controllability of charge on the insulating toner was experimentally investigated by using a corona charging system, an electron charging system (contact type), and an electrostatic induction charging system (non-contact type). The charging systems except the contact type electron charging were able to change the toner. The ion charging system changed the toner polarity to negative from positive. Although the toner was charged to the charge saturation level, the saturated value depended on the initial charge generated by the triboelectric charging. The electrostatic induction charging system was able to charge the toner with a high volume resistivity in the range of electrical insulation.

Density functional theory study of electric potential saturation: planar geometry.

We investigate the possibility of electrostatic potential saturation, which may lead to the phenomenon of effective charge saturation. The system under study is a uniformly charged infinite plane immersed in an arbitrary electrolyte made up of several microspecies. To describe the electric double layer, we use a generic local density functional theory in which the local microionic density profiles are arbitrary functions of the local electrostatic potential. A general necessary and sufficient condition is obtained for saturation, whereby the electrostatic potential created by the plane becomes independent of its bare charge, provided the latter is large enough. As a consequence, for most situations, the following simple and practical sufficient condition follows: if, as the electric potential psi--> infinity, the local theory predicts that the highest valency counterions density diverges as psi(nu) with some nu>1 or faster, then the electrostatic potential will saturate. Otherwise, if the counterion density diverges as psi or slower, or does not diverge as psi--> infinity, the electric potential will not saturate. Using this condition, we investigate the possibility of the saturation phenomenon within the framework of recent theories proposed in the literature to describe electrical double layer beyond the Poisson-Boltzmann description.

Vrla battery rapid charging under stress management

This paper discusses an approach for closed-loop charge control of valve-regulated lead-acid (VRLA) batteries used in telecommunication standby power applications. This is an alternative to conventional preprogrammed, configuration-driven charge control. The developed approach uses the battery's response to the supplied charge to control the recharge process. In this way, only the energy that can be absorbed by the battery in the desired recharge operation is dealt with. Hence, excessive energy that causes battery stress, or lack of energy that slows the charging process is avoided. Two main sources of recharge stress are identified: (a) thermal stress, and (b) charge saturation stress. A charge control algorithm based on thermal management and charge saturation avoidance is suggested. The algorithm utilizes a fuzzy state-of-charge estimation model that derives the state of charge from real-time parameters. This in turn calculates the maximum recharge rate that maintains the battery's thermal rise within permissible limits.

Wall material effects in stationary plasma thrusters. II. Near-wall and in-wall conductivity

Simulations and experimental characterizations of a stationary plasma thruster are compared for four different wall materials to investigate near-wall conductivity (dielectric materials) and in-wall conductivity (conducting materials) in such a discharge. Using a one-dimensional transient fluid model that takes into account a possible electron temperature anisotropy, it is shown that electron-wall backscattering plays a crucial role by maintaining a relatively high electron temperature along the magnetic field lines which in turn drives large electron currents toward the walls. The large differences in discharge current observed experimentally for the dielectric materials are qualitatively recovered, confirming that near-wall conductivity results from the combined effects of secondary electron emission and electron backscattering. A clear correlation is found between the appearance of space charge saturation at the walls and a jump of the discharge current observed in experiments when varying the discharge voltage or the magnetic field. The anomalously high values of discharge current observed experimentally with graphite are also correctly recovered in simulations, which highlight a plasma short-circuiting effect resulting from in-wall currents.

Design and performance of tunnel collector HBTs for microwave power amplifiers

AlGaAs/GaAs/GaAs and GaInP/GaAs/GaAs n-p-n heterojunction bipolar transistors (HBTs) are now in widespread use in microwave power amplifiers. In this paper, improved HBT structures are presented to address issues currently problematic for these devices: high offset and knee voltages and saturation charge storage. Reduced HBT offset and knee voltages (V/sub CE,os/ and V/sub k/) are important to improve the power amplifier efficiency. Reduced saturation charge storage is desirable to increase gain under conditions when the transistor saturates (such as in over-driven Class AB amplifiers and switching mode amplifiers). It is shown in this paper that HBT structures using a 100-/spl Aring/-thick layer of GaInP between the GaAs base, and collector layers are effective in reducing V/sub CE,os/ to 30 mV and V/sub k/ measured at a collector current density of 2/spl times/10/sup 4/ A/cm/sup 2/ to 0.3 V (while for conventional HBTs V/sub CE,os/=0.2 V and V/sub k/=0.5 V are typical). A five-fold reduction in saturation charge storage is simultaneously obtained.

Charging of one or several cylindrical particles by monopolar ions in electric fields

In many electrostatic processes (precipitation of dust, separation of granular mixtures, spraying of powders) insulating particles are subjected to unipolar charging in the presence of other bodies. The present paper addresses this problem from both a computational and an experimental point of view, with the aim to extend an original numerical method of unipolar charge computation to the case of two or more particles, relatively close to each other. The charge acquired by cylinders of various dielectric constants was evaluated with a computer program based on the boundary element method of field analysis. The experimental setup simulated the charging conditions of millimeter-size calibrated cylinders of polyvinyl chloride in a roll-type electrostatic separator, the unipolar space charge being generated by a wire-type electrode. The experimental results, which were in good agreement with the theoretical predictions, put forward that the relative spacing between the particles changes the value of the saturation charge, an effect, which is stronger for particles of higher dielectric constant. These facts should be taken into account in the design of any electrostatic technology based on the corona charging of granular matter.

Low Voltage Operation of PZT Ferroelectric Film deposited by Liquid Source MOCVD

ABSTRACTThin Pb(Zr, Ti)O3 films were grown on a 8-inch Ir(111)/SiO2/Si substrate by a liquid-source MOCVD system. These films showed dependency of ferroelectric properties on several deposition parameters. PZT single phase was obtained at a substrate temperature of 620°C. The film showed (111) preferred orientation and the Pt/Pb1.16(Zr0.45, Ti0.55)Ox(115nm)/Ir capacitors had excellent ferroelectric properties. The switching charge (Qsw) value (at 2V), saturation voltage (V90) and leakage current density (at 1.5V) were 47.4uC/cm2, 1.7V and 7.5E-8A/cm2 respectively. The capacitor made by using an IrOx top electrode had excellent fatigue-free property.

Effective charge saturation in colloidal suspensions

Because micro-ions accumulate around highly charged colloidal particles in electrolyte solutions, the relevant parameter to compute their interactions is not the bare charge, but an effective (or renormalized) quantity, whose value is sensitive to the geometry of the colloid, the temperature or the presence of added-salt. This nonlinear screening effect is a central feature in the field of colloidal suspensions or polyelectrolyte solutions. We propose a simple method to predict effective charges of highly charged macro-ions, that is reliable for monovalent electrolytes (and counterions) in the colloidal limit (large size compared to both screening length and Bjerrum length). Taking reference to the non linear Poisson–Boltzmann theory, the method is successfully tested against the geometry of the macro-ions, the possible confinement in a Wigner–Seitz cell, and the presence of added salt. Moreover, our results are corroborated by various experimental measures reported in the literature. This approach provides a useful route to incorporate the nonlinear effects of charge renormalization within a linear theory for systems where electrostatic interactions play an important role.

Effects of the emission charge saturation in photocathodes under nonuniform illumination

Photoemission from a semiconductor having a negative electron affinity under nonuniform illumination is investigated theoretically for stationary and pulsed excitation regimes. The maximum emission current is shown to grow exponentially with increasing ratio of the negative electron affinity Δ0 to a characteristic tunneling energy E0, and the excitation intensity Iopt corresponding to the maximum current has been determined. Excitation nonuniformity results in a weakening of the dependence of the emission current on illumination intensity near the current maximum. The quantum efficiency recovery time measured in a two-pulse excitation mode depends weakly on the illumination intensity and on its nonuniformity over the illuminated spot and is close to the relaxation time of low photovoltages.

Triboelectrification of houseflies ( Musca domestica L.) walking on synthetic dielectric surfaces

Houseflies ( Musca domestica L.) have been found to accumulate significant electrostatic charges when walking on uncharged dielectric surfaces. The number of steps taken was found to determine the amount of charge transferred whereas time, on its own, did not play a significant role. After walking only a short distance, typically 30 cm, flies reached saturation charge. The level of this varied according to the position of the surface in the triboelectric series relative to the fly. The rate of charging (pC/footstep) was directly proportional to the difference between the fly's charge and its saturation charge, hence the initial rate of charging for an uncharged fly was directly proportional to the saturation charge. A model has been fitted to the relationship between distance travelled (and hence the number of steps taken) with charge. The reciprocal charge left on the surface has been visualised using photocopier toner.

Determination of ice precipitation rates and thunderstorm anvil ice contents from satellite observations of lightning

The continuous satisfactory functioning of satellite-borne devices for the detection of global lightning offers the opportunity to explore relationships between lightning frequency f and other thundercloud parameters, notably, in this paper, the precipitating and non-precipitating contents and fluxes of ice. Simple calculations predict that the lightning frequency f is proportional to the product of the downward flux of solid precipitation through the body of the thundercloud and the upward flux of ice crystals into its anvil. This prediction is reinforced by computations performed using the multiple lightning model of Baker et al. [Q. J. R. Meteorol. Soc. 121 (1995) 1525; Atmos. Res. 51 (1999) 221]. Calculations indicate that the separation of charge and associated field development in thunderclouds are not significantly limited by charge saturation of the interacting hydrometeors: and that the mutual interactions of graupel pellets in the charging zones of thunderstorms can significantly enhance electric field development, culminating in lightning. An examination of data from the satellite-borne Lightning Imaging Sensor (LIS) and TRMM Microwave Imager (TMI) suggests that thunderstorms with the highest frequency of total lightning also possess the most pronounced microwave scattering signatures at 37 and 85 GHz. A total of 292 individual thunderstorms were examined, and a log-linear relationship was shown to exist (one for each frequency) between the number of optical lightning pulses produced by each storm and the corresponding microwave brightness temperatures. These relationships are consistent throughout the seasons in a variety of regimes (12 sites encompassing five continents, as well as oceanic measurements), suggesting that global relationships may be found to exist between lightning activity and cloud ice content.

Influence of Ga flux on the growth and electron transport properties of AlGaN/GaN heterostructures grown by plasma-assisted molecular beam epitaxy

The growth and electrical properties of the Al 0.15Ga 0.85N/GaN two-dimensional electron gas (2DEG) were studied for a range of III/V ratios during growth. All films were grown by RF-plasma assisted molecular beam epitaxy. Al 0.15Ga 0.85N growth in the Ga-rich regime has a surface structure that is controlled by the Ga flux, ranging from morphologies indicative of statistical roughening effects to step-flow growth. The 2DEG sheet carrier concentration was insensitive to Ga flux—this is because the saturated 2DEG charge is approximately equal to the fixed polarization charge at the AlGaN/GaN interface. By increasing the Ga flux during growth, the measured low temperature 2DEG mobility was found to increase, reaching a maximum just before Ga droplets began to form on the surface. In the Ga droplet growth regime, the mobility decreased and was insensitive to further increase in Ga flux. The highest quality surface structure and maximum mobility were realized for structures grown with Ga fluxes just below those necessary to form droplets.

Two-step model for contact charge accumulation

In contact electrification of metal against insulator, multiple contacts, not a single contact, are always needed for reaching the charge saturation level. Many experiments have been done to find out the reason for this. The results are the same: multiple contacts are needed for reaching the saturation level. Two-step model is proposed as a tentative explanation of charge accumulation. Charge transfer involves two steps: contact of the two surfaces and their separation. Separation plays a major role. In this two-step process, interface states are formed when contact is established. They are then populated with electrons from one or both sides. During separation, before the interface states are eliminated, all electrons from these interface states are transferred to either the metal or the insulator. Should more or fewer electrons be transferred to the insulator, it will thus gain or lose some electrons. This two-step cycle is repeated to transfer charge into polymer until the equilibrium is established.