Electrothermal Properties Research Articles

Investigation on Self-Heating Effect in Carbon Nanotube Field-Effect Transistors

Electrothermal modeling of single-walled carbon nanotube (SWCNT) field-effect transistor (FET) is performed in this paper, with special attention focused on its self-heating effect. The method of finite difference is implemented for solving a 1-D heat conduction equation in the semiconducting channel self-consistently, and its nonuniform temperature distribution is evaluated for 20-, 32-, and 45-nm technology nodes, respectively. The numerical results are presented to show the self-heating effect on the I -V characteristics, signal delay, and cutoff frequency of the carbon nanotube FET (CNTFET). It is further demonstrated that the maximum temperature rise, as well as the performance degradation of the CNTFET, is quite lower than that of the silicon-based FET counterpart. All these advantages are contributed by the excellent electrothermal properties of the SWCNTs, and they have great potential for the development of active devices with low power dissipation and good reliability at high-operating temperature.

Aspects of the Electrocaloric Behavior of Ferroelectric Thin Films: A Review of the Predictions of the Landau-Ginzburg Theory

A thermodynamic model is used to investigate the electrocaloric response of thin film perovskite ferroelectrics under the influence of differing electrical, thermal and mechanical boundary conditions including bias and driving field, temperature, lateral clamping and misfit strain. A comparison of the electrothermal properties of ferroelectric solid solutions comprised of BaTiO3, PbTiO3 and/or SrTiO3 illustrates the influence of composition on electrocaloric properties. Computations made for (001) textured polycrystalline BaTiO3 films on IC-friendly substrates quantify the effects of thermal stresses. The combined results provide insights concerning how the deposition temperature, substrate material and composition can be adjusted to obtain desired electrocaloric response.

Three-Dimensional Numerical Simulation of the Joule Heating of Various Shapes of Armatures in Railguns

This paper reports the results of 3-D numerical simulations of the Joule heating of armatures and rails in railguns. Armatures of various shapes with homogeneous and orthotropic electrical conductivity, homogeneous rails, and rails with a resistive coating are considered. It is shown that the maximum current density is reached at the perimeter of the rail-armature interface. The current-density value and, hence, the armature-heating dynamics are significantly affected by the armature shape and the electrothermal properties of the armature and rail materials, as well as by the acceleration dynamics, which, in turn, is determined by the total current value in the electromagnetic launcher and the total mass of the projectile. The ultimate projectile velocities are obtained when the Joule heating of the rails and armature by electric current during the shot does not tend to increase the temperature at any point of the railgun above its melting point. By controlling the structure and properties of rail materials, it is possible to reach ultimate (in terms of heating conditions) velocities much higher than those with homogeneous materials.

An Investigation of Electrothermal Characteristics on Low-Temperature Polycrystalline-Silicon Thin-Film Transistors

In this paper, theoretical and experimental analyses have been performed to explore the electrothermal characteristics in low-temperature polycrystalline-silicon thin-film transistors (LTPS TFTs). A theoretical simulation reveals that electrothermal effects strongly influence the performance of LTPS TFTs, particularly under high-current conditions. Measurements show that, under extremely high currents, LTPS devices demonstrate an open-circuit behavior, while the behavior of devices based on single-crystalline silicon films using an SOI CMOS process results in a short-circuit model. In summary, both the simulation and measurements indicate that grain boundaries will degrade the electrothermal properties of the LTPS thin film and suppress reliability in TFT design.

Electrothermal properties of perovskite ferroelectric films

The electrothermal properties of the perovskite oxides barium titanate (BTO), lead titanate (PTO), and strontium titanate (STO) are computed near the temperatures of their ferroelectric and/or ferroelastic phase transitions. The computations are performed using a modified 2-4-6 Ginzburg–Landau–Devonshire polynomial as functions of applied electric field and temperature for mechanically free monodomain crystals and for epitaxial thin films subject to perfect lateral clamping. For BTO and PTO, which display weak first-order ferroelectric phase transitions at their Curie points, the application of a bias field exceeding the electrical critical point reduces the dependence of the electrocaloric (EC) response on temperature and automatically reduces its magnitude. Under conditions of perfect lateral clamping, the weak first-order phase change is transformed into second-order phase change. In this instance the electrical critical point is coincident with the Curie temperature and a lower bias field is required to produce a comparable reduction in temperature sensitivity. Comparison of the electrothermal behaviors of BTO and PTO with that computed for STO near the temperature of the second-order ferroelastic phase transition provides insight concerning the EC properties of ferroelectric solid solution systems wherein the Curie temperature and the first-order character of the paraelectric to ferroelectric transition both may change subject to a change in composition. The results illustrate how electrical and mechanical boundary conditions can be adjusted, in conjunction with composition, in altering the EC properties of ferroelectric materials selected for use in a particular temperature range.

A comparative experimental investigation of deep-hole micro-EDM drilling capability for cemented carbide (WC-Co) against austenitic stainless steel (SUS 304)

Microelectro-discharge machining (micro-EDM) has become a widely accepted non-traditional material removal process for machining difficult-to-cut but conductive materials effectively and economically. The present study aims to investigate the feasibility of machining deep microholes in two difficult-to-cut materials: cemented carbide (WC-Co) and austenitic stainless steel (SUS 304) using the micro-EDM drilling. The effect of discharge energy and electro-thermal material properties on the performance of the two work materials during the micro-EDM drilling has also been investigated. The micro-EDM drilling performance of two materials has been assessed based on the quality and accuracy of the produced microholes, machining stability, material removal rate (MRR), and electrode wear ratio. The results show that deep-hole micro-EDM drilling is technically more feasible in WC-Co as it offers microholes with smooth and burr-free surfaces at the rim in addition to improved circularity and lower overcut than those provided by SUS 304. Moreover, WC-Co exhibits better machinability during the deep-hole micro-EDM drilling, providing relatively higher MRR and stable machining.

Electrothermal-Chemical Ignition Research on 120-mm Gun in Korea

Electrothermal-chemical (ETC) propulsion with the control of a combustion process yet requires large electrical energies for an appreciable effect. Referring to the changed tendency of focusing ETC researches on the early ignition phase, the Agency for Defense Development (ADD), Korea, has been studying an electrothermal ignition for a 120-mm gun using a capillary plasma injector. Under the condition of a limited capillary geometry, design efforts with various liner materials have been done to achieve robust capillary discharges capable of transferring energies around 100 kJ. Electrical properties were estimated with the help of plasma theories and compared with experimental results. Experiments using a closed vessel and a gun-chamber simulator have been done to investigate the burning behaviors and the early phase of an electrothermal ignition, respectively. The closed vessel was designed for both a plasma and a conventional ignition. The burning rates could be obtained up to 70 MPa. The gun-chamber simulator was designed in the shape of the chamber of a 120-mm gun except for an acrylic chamber wall withstanding up to 30 MPa. Through prior tests using the closed vessel and the gun-chamber simulator, appropriate electrical energies and propellant have been selected. Firings of the full-scale 120-mm gun have been done using JA2 propellant. Electrical pulses of 1-2.5-ms duration in the energy from 20 to 120 kJ were applied. Aside from ignition capability, the results showed a possibility of a control on the peak pressure. Currently, ADD, Korea, continues the research to enhance the efficiency of the plasma injector, to compact the pulse forming network, and to investigate the electrothermal ignition properties of LOVA propellant.

Calculation of magnetic fields and currents in axisymmetric systems of inductively coupled moving conductors

An algorithm for calculating magnetic fields and currents in axisymmetric systems of inductively coupled moving and stationary conductors is developed using a hybrid method which combines the finite and boundary element methods. The finite element method is used to approximate the unsteady diffusion equation for the θ-component of the magnetic vector potential in the conductors, and the boundary-element method is employed to eliminate the space around the conductors. The proposed method takes into account the connections of the conductors with each other or with external energy sources by means of ideal electrical circuits with lumped parameters R, L, and C. An effective method is developed to take into account the external circuits by an appropriate modification of the mass matrix and the source vector of the obtained system of ordinary differential equations. Examples of using the method to calculate the fields of single- and multi-turn solenoids, magnetic flux concentrators, and induction accelerators with various methods of delivering external electromagnetic energy are considered. The high computational efficiency of the method is shown, in particular, for the case of constant electrothermal properties and sizes of the conductors.

Electrothermal properties of regenerable carbon contained porous ceramic fiber media

Electrically regenerable carbon contained porous ceramic fiber media have been prepared for adsorption/regeneration system. The effect of carbon coating methods on the electrothermal properties of the media was studied by investigating electrical resistivity, and adsorption and electrothermal desorption behavior of gaseous adsorbates. At the similar levels of carbon content, the electrical resistivity of the media produced from mixtures of ceramic fiber and phenolic resin powder was almost one order of magnitude lower than the value of those produced by infiltration of liquid phenolic resin into porous ceramic body. In situ thermal desorption and adsorption experiments show that the adsorption abilities of the media apparently depended on the Brunauer-Emmett-Teller surface area of carbon.

Electrothermal Properties of Porous Ceramic Fiber Media Containing Carbon Materials

Electrically regenerable porous ceramic fiber media containing nanoporous carbon from 2.5% to 19.2% have been prepared for adsorption/regeneration system. An experimental apparatus was built for in situ measurement of the sample weight during adsorption and electrothermal desorption of gaseous adsorbates. Adsorption and electrothermal desorption behavior of gaseous adsorbates on carbon contained porous ceramic fiber media was explained by physical and electrothermal properties of these materials measured in this work. In situ thermal desorption and adsorption experiments showthat a considerable amount of water vapor is adsorbed on the carbon contained media exposed to ambient air.

Electrothermal Properties of Porous Ceramic Fiber Media Containing Carbon Materials

Electrically regenerable porous ceramic fiber media containing nanoporous carbon from 2.5% to 19.2% have been prepared for adsorption/regeneration system. An experimental apparatus was built for in situ measurement of the sample weight during adsorption and electrothermal desorption of gaseous adsorbates. Adsorption and electrothermal desorption behavior of gaseous adsorbates on carbon contained porous ceramic fiber media was explained by physical and electrothermal properties of these materials measured in this work. In situ thermal desorption and adsorption experiments show that a considerable amount of water vapor is adsorbed on the carbon contained media exposed to ambient air.

Deformation adjustment of concrete beams laminated with carbon fiber mats

A carbon fiber mat is a sheet composed of intercrossing short carbon fibers, which has more stable and lower electrical resistivity compared with dispersed short carbon fiber mixed in cement. Thereby carbon fiber mats can be used in cement and then make cement structures exhibit obvious electro-thermal effect. In this paper, Electro-thermal properties of carbon fiber mats and an elementary strengthening experiments against deformation of carbon fiber mat cement laminated beams were researched. Firstly, electro-thermal properties of carbon fiber mats were studied. Secondly, carbon fiber mat laminated beams are designed and experiments were conducted to get temperature and deformation responses driven by the electro–thermal effects of the carbon fiber mat cement laminated beams. Finally, some experiments of deformation adjustment were done according to the above experimental results. The results show that deformation of concrete beams upon loads can be reduced even removed, and the beams can be strengthened against deformation.

Ultimate kinematic characteristics of composite solids

This paper considers the ultimate (under heating conditions) kinematic characteristics of composite solid bodies accelerated by a unsteady-state magnetic-field pressure. The accelerated sheet comprises two layers: a layer of a composite material consisting of a mixture of two materials with different electrothermal properties, and a homogeneous material layer. Variation of the electrical properties of the composite layer with the coordinate is achieved by changing the volume concentration of its constituent materials. For an exponential magnetic field rise, an analytical solution is obtained for the problem of finding the optimum variation in the volume concentration of the composite constituents to attain a maximum increase in the ultimate velocity of the sheet. Numerical simulation showed that the optimum structure of the sheet calculated using analytical relations is nearly optimal for different pulse shapes of the accelerated magnetic fields. The possibility of considerably increasing the ultimate velocity through the use of composite layers compared to the ultimate velocities for the homogeneous materials constituting the composite is shown analytically and numerically. For an Fe-Cu-Cu sheet, this increase can reach a factor of two to three.

Ultimate kinematic characteristics of composite solids accelerated by a magnetic field

The present paper considers the ultimate (under heating conditions) kinematic characteristics of composite solid bodies accelerated by unsteady magnetic‐field pressure. The accelerated sheet comprises two layers: a layer of a composite material consisting of a mixture of two materials with different electrothermal properties and a homogeneous material layer. The electrical properties of the composite layer with the coordinate are varied along the coordinate by changing the volume concentration of its constituent materials. For an exponential magnetic field rise, an analytical solution is obtained for the problem of determining the optimum distribution of the volume concentration of the composite constituents for which there is a maximum increase in the ultimate velocity of the sheet. Numerical simulation showed that the distribution of the volume concentration obtained from analytical relations is also nearly optimal for pulse shapes of the accelerating magnetic field different from exponential ones. The possibility of considerably increasing the ultimate velocity through the use of composite layers compared to the ultimate velocities for the homogeneous materials constituting the composite is shown analytically and numerically.

Thermopolychromism and electrothermal properties of ferric acetylacetonate and its resonating structures

Abstract Ferric acetylacetonate Fe(ac. ac)3 was prepared by the reaction of ferric chloride with acetylacetone in ethanolic solution. Vergin and various samples preheated at 170, 220 and 330°C were carefully obtained. X-ray diffraction, IR absorption spectra, scanning electron microscopy and differential thermal analysis (DTA) were done for all samples. The temperature dependence of the electrical and dielectric properties of selective batches of Fe(ac. ac) phases and intermediates were evaluated. The results obtained are discussed on the basis of induced lattice imperfections which may lead to phase change and change in the degree of crystallinity, polythermochromism is established herein for the first time.

Electromechanical and electrothermal behaviours of carbon whisker reinforced elastomer composites

The electromechanical and electrothermal properties of conducting carbon whisker reinforced thermoplastic elastomer (TPE) composites were investigated. The carbon whiskers were derived by a catalytic chemical vapour Deposition (CCVD) process and the TPE was a styrene-ethylene-butylene-styrene (S-EB-S) block copolymer. The electrical resistivity (ϱ) of the composites can be varied either by uniaxial deformation (101–108 Ω cm) or by temperature (101–105 Ω cm). The temperature-resistivity studies indicated that the resistivity of these composites was influenced by the glass transition temperature (Tg) of the TPE. The ϱ versus 1/T curves exhibited two distinct regimes each with a different negative slope which intersected at the Tg of the elastomer. This was correlated to the Tgof the EB segments in the S-EB-S block copolymer (∼ -50°C) by the dynamic mechanical thermal analysis. Further, uniaxial deformation studies at room temperature (20 °C) demonstrated that the resistivity increased exponentially with the deformation. Processing technique considerations and electron micrographs of the morphology of the composites indicated the formation of polymeric film on the carbon whiskers. Thus, the electrical conduction between carbon whiskers in these highly loaded (33 and 52 vol % fraction) composites occurred through the elastomeric film by electron tunnelling. This is explained on the basis of Mott's electron hopping theory, for conduction through several carbon-polymer-carbon (C-P-C) junctions. Further studies by scanning electron microscopy, dielectric thermal analysis and voltage-current characteristics confirmed this observation. Mechanical and electrical properties of the composites indicated that CCVD carbon whiskers can be used to improve the strength and electrical conductivity of TPEs. The change in resistivity (up to five orders of magnitude) of the composites with respect to the deformation or temperature can find use in electromechanical and electrothermal device applications.

Further investigations on the electrothermal properties of yttria-doped gallia ceramics

Numerous polycrystalline ceramic specimens of yttria-doped gallia, have been prepared in the solid state, have been studied by powder X-ray diffraction IR and UV spectroscopy. The electrical conductivities (D.C.) measured for various yttria contents and at various temperatures up to 150°C, and the bulk and true density, and the percentage porosity of the test samples are compared. Correlations of the results obtained have been determined. Some evidence of compound formation could be traced if prior firing had been carried out at 1350 °C, this was not the case when firing was carried out at 800°C. Doping gallia with yttria results in a decreased conductivity and an unaltered mode of conduction.

Composites for improved armature performance

The use of advanced composites to improve the performance of a railgun armature is considered. The authors discuss the theoretical basis for material selection, review the materials options, and describe the composite of choice. It is shown that composite armatures can be developed that have a mass that is 15% or less of the total mass launched by a railgun. The composite with the best performance as an armature is beryllium-lithium. The toxicity of beryllium makes beryllium-lithium an expensive material to produce and use. It is concluded that aluminum-lithium armatures can be fabricated at a reasonable cost to demonstrate the potential of tailoring the electrothermal properties of metal armature materials.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Electric, galvanomagnetic and electrothermal properties of vacuum-evaporated antimony films

The electrical resistivity, temperature coefficient of resistivity, Hall constant and thermoelectric power of antimony films were measured in situ. Measurements of the Hall mobility and the thermoelectric power indicated that holes were the majority carriers in these films. The values of the fundamental parameters describing the electron transport processes were derived. The effect of grain boundary scattering was studied critically.

The solubility of hydrogen in transition metals and their alloys

The micro-electro-mechanical system (MEMS)-based field effect transistor (FET) sensor for hydrogen detection was fabricated by modifying the gate electrode with boron nitride nanotubes (BNNTs) decorated Pd-ternary alloy (Pd63·2Ni34·3Co2.5) as a hydrogen sensing layer Electro-thermal properties of the micro-heater embedded under sensor membrane were analyzed by a finite element method (FEM) simulation. The structural and morphological properties of the gate electrode were studied by Raman spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and field emission scanning electron microscopy (FESEM). A variation in gate potential is observed due to the H2 atmosphere that leads to the variation in the depletion region, therefore, changing the current in the channel (BNNTs decorated Pd-ternary alloy). The BNNTs-decorated Pd ternary alloy displayed high sensing response, fast response and recovery time for H2 gas, low power consumption, long-term stability, and wide detection range from 1 to 5000 ppm H2. The drain current of the H2 FET sensor varied significantly at hydrogen gas exposure and increased with H2 concentration. As proposed H2 FET sensor can be utilized to the H2 leak detection system for safe applications.