High-speed Switching Devices Research Articles

Effects of SiO2 and TiO2 Nano Fillers in Enhancing the Insulation Breakdown Strength of Epoxy Nano Composite Dielectric under Divergent Electric Fields

The proper mixing of nanoscale fillers in conventional dielectric materials leads to an enhancement in the breakdown strength and voltage endurance. In this study experimental investigations are carried out to compare the breakdown characteristics of epoxy nano-composites with that of a base epoxy resin under the influence of divergent electric fields so as to obtain inferences on its breakdown performances. This would in turn enable providing solutions to acquire more effective electrical insulation systems and explore the prospect of tapping the merits of utilizing the rapid strides made in field of fabrication of nano-dielectrics. The main objective is such studies are to enhance the electrical properties of the epoxy dielectric by employing nano-fillers such as SiO2, TiO2 etc. This research envisages the use of epoxy resin mixed with nano-fillers for ascertaining the ability of the nano-composite to be utilized as a dielectric/ insulator in power apparatus. The epoxy resin is mixed with appropriate proportion of SiO2 and TiO2 and experimentation is carried out under the influence of divergent electric fields. Classical breakdown voltage withstand tests such as AC power frequency, DC voltage, lightning impulse and switching impulse test is carried out on epoxy dielectrics (with and without nano-fillers) and the results are compared. In addition, a non-classical breakdown voltage test (high frequency high voltage) is also devised to analyze and ascertain the breakdown characteristics due to varying frequencies so as to investigate the possibility of utilizing such nano-composites in applications related to high speed switching devices.

Electrical switching dynamics and broadband microwave characteristics of VO2 radio frequency devices

Vanadium dioxide (VO2) is a correlated electron system that features a metal-insulator phase transition (MIT) above room temperature and is of interest in high speed switching devices. Here, we integrate VO2 into two-terminal coplanar waveguides and demonstrate a large resistance modulation of the same magnitude (>103) in both electrically (i.e., by bias voltage, referred to as E-MIT) and thermally (T-MIT) driven transitions. We examine transient switching characteristics of the E-MIT and observe two distinguishable time scales for switching. We find an abrupt jump in conductivity with a rise time of the order of 10 ns followed by an oscillatory damping to steady state on the order of several μs. We characterize the RF power response in the On state and find that high RF input power drives VO2 further into the metallic phase, indicating that electromagnetic radiation-switching of the phase transition may be possible. We measure S-parameter RF properties up to 13.5 GHz. Insertion loss is markedly flat at 2.95 dB across the frequency range in the On state, and sufficient isolation of over 25 dB is observed in the Off state. We are able to simulate the RF response accurately using both lumped element and 3D electromagnetic models. Extrapolation of our results suggests that optimizing device geometry can reduce insertion loss further and maintain broadband flatness up to 40 GHz.

Comprehensive Real-Time Simulation of the Smart Grid

This paper presents a real-time simulation platform for smart grid applications. The developed platform is capable of simulating complex smart grid models with large numbers of high-speed switching devices at real time. Furthermore, an integrated approach is adopted to combine real-time simulations of communication systems and electric power systems together, which provides an effective approach to examine communication and distributed control related issues in smart grids. With the flexibility in representing a wide range of communication network configurations, the developed platform can also be used to evaluate reconfiguration strategies of communication networks in smart grids. A case study is demonstrated based on this platform. Simulation results validate the capability of the platform and also show the importance of the proposed comprehensive approach for the study of smart grids.

기판전압에 따른 나노와이어 Junctionless MuGFET의 전류-전압 특성

In this paper, a current-voltage characteristics of n-channel junctionless and inversion mode(IM) MuGFET, and p-channel junctionless and accumulation mode(AM) MuGFET has been measured and analyzed for the application in high speed and low power switching devices. From the variation of the threshold voltage and the saturation drain current with the substrate bias voltages, their variations in IM devices are larger than junctionless devices for n-channel devices, but their variations in junctioness devices are larger than AM devices for p-channel devices. The variations of transconductance with substrate biases are more significant in p-channel devices than n-channel devices. From the characteristics of subthreshold swing, it was observed that the S value is almost independent on the substrate biases in n-channel devices and p-channel junctionless devices but it is increased with the increase of the substrate biases in p-channel AM devices. For the application in high speed and low power switching devices using the substrate biases, IM device is better than junctionless devices for n-channel devices and junctionless device is better than AM devices for p-channel devices.

Temperature-induced magnetization reversal and ultra-fast magnetic switch at low field in SmFeO3

We have found that SmFeO3, a family of rare-earth orthoferrites, exhibits temperature-induced magnetization reversal below the critical low-temperature along the a-axis of Pbnm symmetry. First-principles calculations demonstrate that this negative magnetization is mainly attributed to the competition between two magnetocrystalline anisotropy terms in the inequivalent magnetic sites of Sm3+ and Fe3+. Interestingly, the room temperature magnetization-field curve further shows an ultra-fast magnetization switch in the low-magnetic field, suggesting a potential applicability to high-speed magnetic switching devices.

Digital Holography Display (2)

This paper describes the extension work from the last Digital Holography Projector System. From the developed works shows that, some unforeseen factors have created the difficulties for the system alignment. Such factors are the DMD frame rate, light source and diffractive zero order. It is really the challenging development works to achieve the virtual 3D model display on the high speed rotation screen. The three most key factors are emphasizing: 1) The display device's frame rate; 2) The light source orientation angle; and 3) The zero order filtering optic.1) This device's is the digital micro mirror, in short is DMD. It is the high speed switching device has developed by the most recent technology. The switching frame rate can go up as high as 291fps. At first, the 8 bits depth file must be digitalized and stored for DMD onboard Ram. The digitalized data are transmitting from the PC USB to DMD onboard Ram. Instead of the data are downloading directly from the PC to DVI or VGA during display, this downloading method cause slower down the display speed, which is the common frame rate of 30Hz. Next, the onboard Ram data then transfer to the DMD mirror's for display, at the 8 bits 291 fps speed. At this frame rate, the display 2D image can almost cover for 10 of out of the 360 0 in 1 revolution.2) This laser light source must be installed such that free for orientated in any arbitrary angle from 220 to 450. Which is normalized to the DMD mirrors and the brief sketch show on figure (a). The purpose of orientated the light source is ensure that multi diffractive order would be reflected straight from the mirrors. (This multi diffractive order is the phenomenon of the digital micro mirror's characteristic). This mean, the reconstruct images would be followed the DMD normalized direction reflected up to fibre conduit. Moreover, this orientated method install of the laser light source is making space for other optical lenses or device driver/controller. Because, all equipments and components can be easy line up and mounted in the compartment.3) This solid 6mm diameter fibre conduit is implemented to transmit the higher diffractive image, it is also the brightest and clearer image as compare to other lower order images. This means many of the lower order and blurred images would be neglected for display and consider as the energy lost.

All-optical switching effect of the excited state proton transfer molecule 2-(2'-hydroxyphenyl) benzothiazole in different polar solvents

An all-optical switching model system comprising a single pulsed pump beam at 355 nm and a cw He-Ne signal beam at 632.8 nm was demonstrated with 2-(2'-hydroxyphenyl) benzothiazole(HBT) in five different polar solvents. The origin of the optical switching effect was discussed, and it was verified that fast excited state intramolecular proton transfer (ESIPT) of HBT and the slow thermal effect of solvent together induced the change of the refractive index of HBT solutions, which lead to the signal beam deflection and dominated the optical switching "off" and "on" states, respectively. The slow thermal effect of solvent results in the "tail" phenomenon of the optical switching recovery, and reducing the signal beam waist radius is a viable means for accelerating the recovery of the optical switching. The results indicated that the HBT molecule could be an excellent candidate for high-speed and high-sensitivity optical switching devices. This work provides a theoretical as well as experimental basis for the production of ultra-fast all-optical switching device.

On the triggering mechanism for the metal–insulator transition in thin film VO2 devices: electric field versus thermal effects

Vanadium dioxide (VO2) has been shown to undergo an abrupt electronic phase transition near 70 °C from a semiconductor to a metal, with an increase in dc conductivity of over three orders of magnitude, making it an interesting candidate for advanced electronics as well as fundamental research in understanding correlated electron systems. Recent experiments suggest that this transition can be manifested independent of a structural phase transition in the system, and that it can be triggered by the application of an electric field across the VO2 thin film. Several experiments that have studied this behavior, however, also involve a heating of the VO2 channel by leakage currents, raising doubts about the underlying mechanism behind the transition. To address the important question of thermal effects due to the applied field, we report the results of electro-thermal simulations on a number of experimentally realized device geometries, showing the extent of heating caused by the leakage current in the “off” state of the VO2 device. The simulations suggest that in a majority of the cases considered, Joule heating is insufficient to trigger the transition by itself, resulting in a typical temperature rise of less than 10 K. However, the heating following a field-induced transition often also induces the structural transition. Nevertheless, for certain devices, we identify the possibility of maintaining the field-induced high conductivity phase without causing the structural phase transition: an important requirement for the prospect of making high-speed switching devices based on VO2 thin film structures. Such electronically driven transitions may also lead to novel device functionalities including ultra-fast sensors or gated switches incorporating ferroelectrics.

Development of Gate Drive Circuit for Next-Generation Ultra High-Speed Switching Devices

This paper describes a gate drive circuit which is capable to drive an ultra high-speed switching device and to suppress a high-frequency noise caused by its high-dV/dt rate of 104-V/μs order. SiC (Silicone Carbide) based power semiconductor devices are very promising as next generation ultra high-speed switching devices. However, one of their application problems is how to drive them with less high-frequency noise without sacrificing their ultra high-speed operation capability. The paper proposes a new gate drive circuit specialized for such devices, which charges and discharges the input capacitance of the device by using an impulse voltage generated by inductors. This ultra high-speed switching operation causes the high-frequency common-mode noise current in the gate drive circuit, which penetrates an isolated power-supply transformer due to the parasitic capacitance between the primary and the secondary windings. In order to overcome this secondary problem, a toroidal multi-core transformer is also proposed in the paper to reduce the parasitic capacitance drastically. By applying the former technique, the turn-on time and the turn-off time of the power device were shortened by 50% and by 20%, compared with a conventional push-pull gate drive circuit, respectively. In addition, the latter technique allows suppressing the peak common-mode noise current down to 25%, compared with a case of using a conventional standard utility power-supply transformer.

Imaging small-amplitude magnetization dynamics in a longitudinally magnetized microwire

We have used time-resolved scanning Kerr microscopy to study spin waves in a magnetic microwire subjected to a bias magnetic field applied parallel to its long axis. The spin-wave spectra obtained from different points near one end of the wire reveal several normal modes. We found that modes of a higher frequency occupied regions located further from the end of the wire. This was interpreted in terms of the confinement of the spin-wave modes by a nonuniform demagnetizing field. Furthermore, at a particular distance from the end of the wire, two or more modes occupying different regions along the width of the wire were observed. This was interpreted in terms of the confinement of the spin-wave modes due to an asymmetric variation in the local angle between the static magnetization and the effective direction of the wave vector of the confined modes. Images of the dynamic magnetization that are acquired at fixed pump-probe time delays revealed stripes lying perpendicular to the long axis of the wire and, hence, to the applied magnetic field. We interpret the stripe pattern in terms of a collective mode of the quasiperiodic system of ripple domains existing within the polycrystalline sample. Our results give an additional insight into the connection between the nonuniform static magnetic state in small magnetic elements and their precessional dynamics, which is fundamentally important for the design of future high-speed switching and spin-wave logic devices of magnonics.

All-Optical Comb Switch for Multiwavelength Message Routing in Silicon Photonic Networks

Simultaneous all-optical switching of 20 continuous-wave wavelength channels is achieved in a microring resonator-based silicon broadband 12 comb switch. Moreover, single-channel power penalty measurements are performed during active operation of the switch at both the through and the drop output ports. A statistical characterization of the drop-port insertion losses and extinction ratios of both ports shows broad spectral uniformity, and bit-error-rate measurements during passive operation indicate a negligible increase in signal degradation as the number of wavelength channels exiting the drop port are scaled from one to 16, with peak powers of 6 dBm per channel. A high-speed broadband switching device, such as the one described here, is a crucial element for the deployment of interconnection networks based on silicon photonic integrated circuits.

Preparation of c-Axis Oriented La2CuO4Thin Films on the Si Substrate by Pulsed Laser Deposition

The parent materials of the first high-TC cuprate, La2CuO4 (LCO) are known to be correlated with Mott insulators that become metallic and superconducting upon doping with charge carriers. 1 A large number of researches have been performed on bulk samples in the LCO-based materials due to their simple chemical composition and crystal structures as well as the rich physical properties. 2 The transition from the Mott-Hubbard insulating state to the metallic state is called the metal insulator transition (MIT), 3 and is a topic of great current interest. As an important application of the MIT, a high-speed Mott switching device using an abrupt current jump was predicted for a transistor. 4 LCO is known to have three different structures, 5 T-phase (K2NiF4-type) containing edge-shared CuO6 octahedra arranged in a planar array, T’-phase (Nd2CuO4-type) in which the apical oxygen in the T-phase is shifted away from the Cu atoms, and S-phase (Sr2CuO3) which has isolated CuO3 chains running along the a-axis of the orthorhombic structure. Transitions among T, T’ and S phases were found in the annealing process of bulk LCO. These are quasi-two-dimensional materials which consist of layers of copper-oxide planes separated. It seems that most of the properties are determined by electrons moving within CuO2 planes. The preparation of the thin film 6 is a key point to develop the devices such as thermal switching, thermochromatic coatings, non-volatile memory etc. applying MIT properties of LCO. High quality thin film of LCO is required for a variety of fundamental studies. The electrical and transport properties of LCO-based thin films are highly sensitive to the degree of c-axis orientation in the film growth and induced strain due to lattice mismatch with the substrate. A large number of substrates have been used to obtain highly oriented LCO thin films with good electrical properties such as NdGaO3, LaALO3, SrTiO3, and SrLaAlO3 substrates with a small lattice mismatch. 7 However, these cannot be used in the development of the MIT devices as common substrates because it is too difficult and expensive for the preparation of their single crystalline structure. LCO thin film is required to be grown with c-axis orientation on the surface of common substrates such as SiO2 acting as a gate oxide for fabrication of MIT devices. In the present work, we report the first preparation of caxis oriented LCO thin films on Si substrate, which is largely lattice-mismatched with LCO, by pulsed laser deposition (PLD) following in-situ post-annealing in oxygen ambient. PLD technique is a well-known deposition technique providing stoichiometric transfer of target materials via congruent evaporation for a wide range of materials including metals, alloys and oxide films.

All-optical switching and nonlinear optical properties of HBT in ethanol solution

This paper demonstrates an all-optical switching model system comprising a single pulsed pump beam at 355 nm and a CW He–Ne signal beam at 632.8 nm with 2-(2'-hydroxyphenyl)benzothiazole (HBT) in ethanol solution. The origins of the optical switching effect were discussed. By the study of nonlinear optical properties for HBT in ethanol solvent, this paper verified that the excited-state intramolecular proton transfer (ESIPT) effect of HBT and the thermal effect of solvent worked on quite different time scales and together induced the change of the refractive index of HBT solution, leading to the signal beam deflection. The results indicated that the HBT molecule could be an excellent candidate for high-speed and high-sensitive optical switching devices.

Novel Current-Source Multi-Level Inverter Driven by Single Gate Drive Power Supply

This paper proposes a novel current-source multi-level inverter, which is based on a current-source half bridge topology. Multi-level inverters are effective to reduce harmonic distortion of the output voltage and the output current. However, the multi-level inverters require many gate drive power supplies to drive switching devices. The gate drive circuits using a bootstrap circuit and a pulse transformer can reduce the number of the gate drive power supplies, but a pulse width of the output PWM waveform is limited. Furthermore, high-speed power switching devices are indispensable to compose a high-frequency power converter but various problems of high frequency noise arise due to high dv/dt rate, especially in high-side switching devices.The proposed current-source multi-level inverter is composed with a common emitter topology of all switching devices. Therefore, it is possible to operate with a single power supply of gate drive circuit, which allows stabilizing a potential level of all the drive circuits.In this paper, effectiveness of the proposed circuit is verified with experimental results.

Raman study of electric-field-induced first-order metal-insulator transition in VO2-based devices

An abrupt first-order metal-insulator transition (MIT) as a current jump has been observed by applying a dc electric field to Mott insulator VO2-based two-terminal devices. The size of the jumps was measured to be asymmetrical depending on the direction of the applied voltage due to heating effects. The structure of VO2 is investigated by micro-Raman scattering experiments. An analysis of the Raman-active Ag modes at 195 and 222cm−1, explained by pairing and tilting of V cations, and 622cm−1, shows that the modes below a low compliance (restricted) current do not change when the MIT occurs, whereas a structural phase transition above the low compliance current is found to occur secondarily, due to heating effects in the device induced by the MIT. The MIT has applications in the development of high-speed and high-gain switching devices.

Modelling and Minimizing of high Frequency Leakage Currents in Adjustable Speed Drives

Today, adjustable speed drives (ASDs) manufacturers use high-speed switching devices such as the insulated gate bipolar transistors (IGBTs) to achieve higher efficiency, low weight, and small size. However, the advent of fast power devices has produced several unexpected problems, such as premature deterioration of ball bearing and high levels of electromagnetic emissions, caused by flowing of parasitic capacitive currents known as common mode (CM) currents. In order to evaluate these leakage currents, a suitable model of the ASD is obtained by identification of the high-frequency spreading paths. The authors first carry out simulations using the proposed model and compare the results with experimental one. They then propose two methods of reduction of the CM currents in the ASD system.

Modelling and Minimizing of High Frequency Leakage Currents in Adjustable Speed Drives

Today, adjustable speed drives (ASDs) manufacturers use high-speed switching devices such as the insulated gate bipolar transistors (IGBTs) to achieve higher efficiency, low weight, and small size. However, the advent of fast power devices has produced several unexpected problems, such as premature deterioration of ball bearing and high levels of electromagnetic einissions, caused by flowing of parasitic capacitive currents known as common mode (CM) currents. In order to evaluate these leakage currents, a suitable model of the ASD is obtained by identification of the high-frequency spreading paths. The authors first carry out simulations using the proposed model and compare the results with experimental one. They then propose two methods of reduction of the CM currents in the ASD system.

Optimal area control of AC railway systems via PWM traction drives

The latest generation of AC-fed traction drives, employing high-speed switching devices, is able to control the reactive power drawn by each locomotive or train from the overhead line. If the conditions at each train could be fed back to a central control point, it would be possible for a centrally located controller to calculate optimal values for the reactive power in each drive and to send these commands back to the individual equipments. A scheme is proposed whereby the AC power flows are analysed in real time and the results used to optimise some particular system objective via control of the PWM equipments as mobile reactive power compensators. The system voltage profile can be improved and the overall power factor at the feeder substation made nearer to unity. Computational verification is presented with results obtained from a multi-train simulator with the power network optimisation operating in several test case scenarios. The test results are compared with those obtained without compensation and with classical trackside Var compensation methods. The scheme is shown to give the best improvement where an existing fleet of diode or thyristor equipments is partially replaced with PWM front-end equipments. From these results, the potential for PWM locomotives to improve overall system performance is clearly confirmed.

Temperature-dependent delay time in GaAs high-power high-speed photoconductive switching devices

Temperature-dependent delay time between the beginning of optical illumination and the onset of switching in the transient response of semi-insulating GaAs high-power, high-speed photoconductive switching devices is studied in this letter. The temperature-dependent electroabsorption caused by absorption edge shifting due to bandgap narrowing is found to be responsible for the experimentally observed temperature-dependence in delay time. Our analysis shows delay time has little dependence on temperature when photon energy is larger than band gap, but depends strongly on temperature when photon energy is smaller than band gap and the applied electric field is low.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Delay time in GaAs high-power high-speed photoconductive switching devices

The delay time between the beginning of optical illumination and the onset of switching in the transient response of semi-insulating GaAs high-power high-speed photoconductive switching devices is discussed. The field- and laser-energy-dependent optical absorption coefficient is used to explain the experimentally observed open-state-field, and laser-energy-dependent delay time. Calculations are shown to agree with the experimental results.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>