Showing papers on "Switching time published in 2008"

Low power and high speed bipolar switching with a thin reactive Ti buffer layer in robust HfO2 based RRAM

Abstract: A novel HfO2-based resistive memory with the TiN electrodes is proposed and fully integrated with 0.18 mum CMOS technology. By using a thin Ti layer as the reactive buffer layer into the anodic side of capacitor-like memory cell, excellent memory performances, such as low operation current (down to 25 muA), high on/off resistance ratio (above 1,000), fast switching speed (5 ns), satisfactory switching endurance (>106 cycles), and reliable data retention (10 years extrapolation at 200degC) have been demonstrated in our memory device. Moreover, the benefits of high yield, robust memory performance at high temperature (200degC), excellent scalability, and multi-level operation promise its application in the next generation nonvolatile memory.

Lower-current and fast switching of a perpendicular TMR for high speed and high density spin-transfer-torque MRAM

Abstract: We investigate extremely low programming current and fast switching time of a perpendicular tunnel-magnetoresistance (P-TMR) for spin-transfer torque using a P-TMR cell of 50 nm-diameter. A L10-crystalline ordered alloy is used as a free layer that has excellent thermal stability and a damping constant of about 0.03. The programming current of 49 uA and the switching time of 4 nsec are also demonstrated.

All-optical switching in subwavelength metallic grating structure containing nonlinear optical materials.

Abstract: All-optical switching based on a subwavelength metallic grating structure containing nonlinear optical materials has been proposed and numerically investigated. Metal-dielectric composite material is used in the switching for its larger third-order nonlinear susceptibility (approximately 10(-7)esu) and ultrafast response properties. The calculated dependence of the signal light intensity on the pump light intensity shows a bistable behavior, which results in a significant switch effect. It rests on a surface plasmon's enhanced intensity-dependent change of the effective dielectric constant of Kerr nonlinear media, corresponding to a transition of the far-field transmission from a low- to high-transmission state. The study of this switching structure shows great advantages of smaller size, lower requirement of pump light intensity, and shorter switching time at approximately the picosecond level.

Single molecule electronics: increasing dynamic range and switching speed using cross-conjugated species.

Abstract: Molecular electronics is partly driven by the goal of producing active electronic elements that rival the performance of their solid-state counterparts, but on a much smaller size scale. We investigate what constitutes an ideal switch or molecular device, and how it can be designed, by analyzing transmission plots. The interference features in cross-conjugated molecules provide a large dynamic range in electron transmission probability, opening a new area for addressing electronic functionality in molecules. This large dynamic range is accessible through changes in electron density alone, enabling fast and stable switching. Using cross-conjugated molecules, we show how the width, depth, and energetic location of the interference features can be controlled. In an example of a single molecule transistor, we calculate a change in conductance of 8 orders of magnitude with an applied gate voltage. Using multiple interference features, we propose and calculate the current/voltage behavior of a molecular rectifier with a rectification ratio of >150,000. We calculate a purely electronic negative differential resistance behavior, suggesting that the large dynamic range in electron transmission probability caused by quantum interference could be exploited in future electronic devices.

25ps all-optical switching in oxygen implanted silicon-on-insulator microring resonator

Abstract: We present all-optical switching in oxygen ion implanted silicon microring resonators. Time-dependent signal modulation is achieved by shifting resonance wavelengths of microrings through the plasma dispersion effect via femtosecond photogeneration of electron-hole pairs and subsequent trapping at implantation induced defect states. We observe a switching time of 25 ps at extinction ratio of 9 dB and free carrier lifetime of 15 ps for an implantation dose of 7×1012 cm-2. The influence of implantation dose on the switching speed and additional propagation losses of the silicon waveguide – the latter as a result of implantation induced amorphization – is carefully evaluated and in good agreement with theoretical predictions.

Field-induced nucleation in phase change memory

Abstract: A theory of field-induced crystal nucleation is developed and verified experimentally for the case of switching in nanoglasses of phase change memory. For symmetry-breaking strong electric fields, it predicts needle-shaped crystallites with nucleation barriers lower than that of spherical nuclei and a strong field dependent. We have observed bias dependent switching for times and temperatures far beyond those typically reported and supportive of our predictions, in particular, switching time exponential in voltage and temperature.

High-Reliability Miniature RF-MEMS Switched Capacitors

Abstract: This paper presents a radical departure from the standard RF microelectromechanical systems (MEMS) devices and introduces novel miniature MEMS switched capacitors for RF to millimeter-wave applications, which are around 150 times smaller in lateral dimensions than standard MEMS designs. The measured capacitance of a single device (l,w,t of 20, 9.5, 0.37 mum), suspended 0.25 mum above the pull-down electrode, is 3.9 and 11.7-12.1 iF (Cr = 3.0-3.1) in the up- and down-state positions, respectively. The measured capacitance ratio of a 4 X 4 array fabricated on quartz substrates and in a coplanar waveguide (CPW) configuration is 3.0 with an electrical Q > 90 at 20 GHz. The miniature MEMS spring constant is very high, and is much less sensitive to residual stress or temperature variations than standard MEMS devices. Dielectric charging simulations show that these devices can withstand a charge density 6.25 times higher than the standard MEMS devices. The mechanical resonant frequency for a gold device is 2.6 MHz and results in a switching time of 200 ns under a 32-V actuation voltage. Preliminary reliability tests at 13 GHz using bipolar actuation (plusmn30 V) and hot power switching have been performed on five 4 times 4 devices at 100 mW for 20 billion cycles, and at 500 mW for 5 billion cycles with no failures. A 4 times 4 array has also been used in the design of a tunable CPW resonator at 19.3 GHz with a 21% tuning range and 1.6-dB insertion loss. The authors believe that miniature MEMS devices will be very useful in the future for high-reliability MEMS and reconfigurable networks.

Voltage polarity dependent low-power and high-speed resistance switching in CoO resistance random access memory with Ta electrode

Abstract: Structural and resistance switching properties were investigated in the CoO resistance random access memory (RRAM) with the Ta electrode. The intermediate layer consisting of Co and Ta oxides was confirmed at the interface by the transmission electron microscopy and electron energy loss spectroscopy. The great affinity with oxygen in Ta together with a high resistivity of the Ta oxide improves the operational performance of RRAM. The controllability of the resistance after forming and the low-current operation property were substantially improved by using the load resistor connected in series with CoO RRAM with the Ta electrode. The reset current less than 0.2 mA and the switching speed faster than 20 ns were demonstrated.

Tunnel field-effect transistor with gated tunnel barrier

Abstract: A tunnel field effect transistor (TFET) is disclosed. In one aspect, the transistor comprises a gate that does not align with a drain, and only overlap with the source extending at least up to the interface of the source-channel region and optionally overlaps with part of the channel. Due to the shorter gate, the total gate capacitance is reduced, which is directly reflected in an improved switching speed of the device. In addition to the advantage of an improved switching speed, the transistor also has a processing advantage (no alignment of the gate with the drain is necessary), as well as a performance improvement (the ambipolar behavior of the TFET is reduced).

Optimal Design of Resonant Gate Driver for Buck Converter Based on a New Analytical Loss Model

Abstract: In this paper, the advantages of a new resonant driver are verified thoroughly by the analytical analysis, simulation and experimental results. A new accurate analytical loss model of the power metal oxide semiconductor field effect transistor driven by a current-source resonant gate driver is developed. Closed-formed analytical equations are derived to investigate the switching characteristics due to the parasitic inductance. The modeling and simulation results prove that compared to a voltage driver, a current-source resonant driver significantly reduces the propagation impact of the common source inductance during the switching transition at high (>1 MHz) switching frequency, which leads to a significant reduction of the switching transition time and the switching loss. Based on the proposed loss model, a general method to optimize the new resonant driver is proposed and employed in the development of a 12 V synchronous buck voltage regulator (VR) prototype at 1 MHz switching frequency. The level-shift circuit and digital implementation of complex programmable logic device (CPLD) are also presented. The analytical modeling matches the simulation results and experimental results well. Through the optimal design, a significant efficiency improvement is achieved. At 1.5 V output, the resonant driver improves the VR efficiency from 82.7% using a conventional driver to 86.6% at 20 A, and from 76.9% using a conventional driver to 83.6% at 30 A. More importantly, compared with other state of the art VR approaches, the new resonant driver is promising from the standpoints of both performance and cost-effectiveness.

Carrier Diffusion and Recombination in Photonic Crystal Nanocavity Optical Switches

Abstract: Carrier dynamics in silicon photonic crystal (PhC) nanocavities are studied numerically. The results agree well with previous experimental demonstrations. It is shown that the presence of carrier diffusion makes fast switching possible, which is an advantage of nanocavity switches over other types of larger carrier based nonlinear optical switches. In particular, diffusion is effective in PhC nanocavity switches, which makes the switching recovery time even faster than that of silicon waveguide-based optical switches. In addition, calculations suggest that the thermo-optic effect can be reduced if the carriers are extracted within a few 100 ps by introducing a p-i-n structure.

On the Dynamic Response of Electrostatic MEMS Switches

Abstract: The undamped dynamic response of electrostatic MEMS switches that are driven by a step-function voltage is investigated. A systematic analysis using energy methods is presented. An analytic expression for switching time is derived and this expression may be used as a design rule for electrostatic switches. The analytic predictions are validated experimentally using test structures with parallel-plates actuators. It is shown that the analysis is also applicable for switches with more general geometry.

Thermal fluctuation effects on spin torque induced switching: Mean and variations

Abstract: Thermal fluctuation effects on mean and variation of spin torque induced magnetic element switching are analyzed. Asymptotic forms of the switching time distribution from the stochastic Landau–Lifshitz–Gilbert equation, and numerical solutions of the first and second moments of switching time from the corresponding Fokker–Planck equation, are used to characterize switching time and switching current density for the whole time range, from the second thermal reversal region to the nanosecond dynamic reversal region. It is shown that as time scales become shorter, switching time distributions become narrower, whereas switching current distributions may become broader. This paper provides a physical understanding of these different scaling behaviors.

Inherent Stochasticity of Superconductor-Resistor Switching Behavior in Nanowires

Abstract: We study the stochastic dynamics of superconductive-resistive switching in hysteretic current-biased superconducting nanowires undergoing phase-slip fluctuations. We evaluate the mean switching time using the master-equation formalism, and hence obtain the distribution of switching currents. We find that as the temperature is reduced this distribution initially broadens; only at lower temperatures does it show the narrowing with cooling naively expected for phase slips that are thermally activated. We also find that although several phase-slip events are generally necessary to induce switching, there is an experimentally accessible regime of temperatures and currents for which just one single phase-slip event is sufficient to induce switching, via the local heating it causes.

Bistability and Switching Properties of Semiconductor Ring Lasers With External Optical Injection

Abstract: We investigate both analytically and numerically the switching, locking and stability properties of a bistable semiconductor ring laser subject to an external optical injection. Minimum optical power required for the injected signal at certain frequency to switch the lasing direction of a bistable semiconductor ring laser from its initially lasing direction to initially nonlasing direction is determined. Locking to the injected signal and stability of the switched laser are investigated to give an area of reliable switching operation. Correspondingly, numerical simulation has been carried out to find successful switching and stable locking region with variable injection power and frequency, and is compared with the analytical results. The region obtained from simulation coincides well with the intersection of switching, locking and stable locking regions. The relation between switching speed and parameters of injected source is also studied numerically.

New Protection Circuit for High-Speed Switching and Start-Up of a Practical Matrix Converter

Abstract: The matrix converter (MC) presents a promising topology that needs to overcome certain barriers (protection systems, durability, the development of converters for real applications, etc.) in order to gain a foothold in the market. Taking into consideration that the great majority of efforts are being oriented toward control algorithms and modulation, this paper focuses on MC hardware. In order to improve the switching speed of the MC and thus obtain signals with less harmonic distortion, several different insulated-gate bipolar transistor (IGBT) excitation circuits are being studied. Here, the appropriate topology is selected for the MC, and a recommended configuration is selected, which reduces the excursion range of the drivers, optimizes the switching speed of the IGBTs, and presents high immunity to common-mode voltages in the drivers. Inadequate driver control can lead to the destruction of the MC due to its low ride-through capability. Moreover, this converter is especially sensitive during start-up, as, at that moment, there are high overcurrents and overvoltages. With the aim of finding a solution for starting up the MC, a circuit is presented (separate from the control software), which ensures correct sequencing of supplies, thus avoiding a short circuit between input phases. Moreover, it detects overcurrent, connection/disconnection, and converter supply faults. Faults cause the circuit to protect the MC by switching off all the IGBT drivers without latency. All this operability is guaranteed even when the supply falls below the threshold specified by the manufacturers for the correct operation of the circuits. All these features are demonstrated with experimental results. Lastly, an analysis is made of the interaction that takes place during the start-up of the MC between the input filter, clamp circuit, and the converter. A variation of the clamp circuit and start-up strategy is presented, which minimizes the overcurrents that circulate through the converter. For all these reasons, it can be said that the techniques described in this paper substantially improve the MC start-up cycle, representing a step forward toward the development of reliable MCs for real applications.

Design and Characterization of High-Voltage 4H-SiC p-IGBTs

Abstract: High-voltage p-channel 4H-SiC insulated gate bipolar transistors (IGBTs) have been fabricated and characterized. The devices have a forward voltage drop of 7.2 V at 100 A/cm2 and a -16 V gate bias at 25degC, corresponding to a specific on-resistance of 72 mOmega ldr cm2 and a differential on-resistance of 26 mmOmega ldr cm2. Hole mobility of 12 cm2/V ldr s in the inversion channel with a threshold voltage of -6 V was achieved by optimizing the n+ well doping profile and gate oxidation process. A novel current enhancement layer was adopted to reduce the JFET resistance and enhance conductivity modulation by improving hole current spreading and suppressing the electron current conduction through the top n-p-n transistor. Inductive switching results have shown that the p-IGBT exhibited a turn-off time of ~1 mus and a turn-off energy loss of 12 m J at 4-kV dc-link voltage and 6-A load current at 25degC. The turn-off trajectory from the measured inductive load switching waveforms and numerical simulations shows that the p-IGBT had a near-square reverse bias safe operating area. Numerical simulations have been conducted to achieve an improved tradeoff between forward voltage drop and switching off energy by investigating the effects of drift layer lifetime and p-buffer layer parameters. The advantages of SiC p-IGBTs, such as the potential of very low ON-state resistance, slightly positive temperature coefficient, high switching speed, small switching losses, and large safe operating area, make them suitable and attractive for high-power high-frequency applications.

Resonant spin-transfer-driven switching of magnetic devices assisted by microwave current pulses

Abstract: The torque generated by the transfer of spin angular momentum from a spin-polarized current to a nanoscale ferromagnet can switch the orientation of the nanomagnet much more efficiently than a current-generated magnetic field and is therefore in development for use in next-generation magnetic random access memory (MRAM). Up to now, experiments have focused on spin-torque switching driven by simple square-wave current pulses. Here we present measurements showing that spin transfer from a microwave-frequency current pulse can produce a resonant excitation of a nanomagnet and improved switching characteristics in combination with a square current pulse. With the assistance of a microwave-frequency pulse, the switching time is reduced and achieves a narrower distribution than when driven by a square current pulse alone, and this can permit significant reductions in the integrated power required for switching. Resonantly excited switching may also enable alternative, more compact MRAM circuit architectures.

5kV/200ns Pulsed Power Switch based on a SiC-JFET Super Cascode

Abstract: In many pulse power applications there is a trend to modulators based on semiconductor technology. For these modulators high voltage and high current semiconductor switches are required in order to achieve a high pulsed power. Therefore, often high power IGBT modules or IGCT devices are used. Since these devices are based on bipolar technology the switching speed is limited and the switching losses are higher. In contrast to bipolar devices unipolar ones (e.g. SiC JFETs) basically offer a better switching performance. Moreover, these devices enable high blocking voltages in case large bandgap materials as SiC are used. At the moment SiC JFET devices with a blocking voltage of 1.5 kV per JFET are available. Alternatively, the operating voltage could be increased by connecting N JFETs and a low voltage MOSFET in series resulting in a Super Cascode switch with a blocking voltage N-times higher than the blocking voltage of a single JFET. In order to evaluate the achievable switching speed of the Super Cascode and its applicability in solid state modulators, the performance of such a SiC switch is examined in this paper. Furthermore, the performance of the Super Cascode is compared with 4.5 kV IGBTs made by Powerex, which are mounted in a special low inductive housing for minimising the rise and fall times.

Switched Controllability via Bumpless Transfer Input and Constrained Switching

Abstract: In this note, we investigate the controllability of linear hybrid systems via bumpless transfer input and constrained switching. By bumpless transfer input, we mean that the control input signals are as close as possible at switching times. By constrained switching, we mean that the switching index sequence is cyclic and the switching time sequence is possibly with pre-assigned duration intervals. While the problem is well motivated in several practical situations, it is also theoretically interesting. A complete criterion for controllability is presented, and a computational procedure is developed for finding a switching signal and a control input to achieve the controllability.

Optical switching based on high-speed phased array optical beam steering

Abstract: We present a high-speed optical switching scheme based on phased array optical beam steering, and analyze the trade-off between the switch power efficiency, signal-to-noise-ratio, number of output channels, and switching speed. For the proof of concept, a two-channel optical switch has been fabricated, using a high-speed GaAs∕AlGaAs multiple quantum well phase modulator. We demonstrate a beam deflection angle of 100mrad at the fastest ever reported speed of 18GHz, consuming 1.8mW. A signal-to-noise ratio of 8dB is measured at each output channel. The relatively low signal-to-noise ratio can be further improved by increasing the number of phased arrays.

Liquid-crystal varactors with fast switching times for microwave applications

Abstract: A varactor using liquid crystal (LC) as tunable dielectric is presented. The two devices described feature LC layer thicknesses of 5 and 1 µm, respectively. A more advanced fabrication scheme is used, which incorporates the use of fused silica as the LC enclosing substrate. The devices exhibit tunabilities of at least 18% and quality factors of at least 40 at 1 GHz. The switching times toff are as low as 4 ms.

Pulsed laser triggered high speed microfluidic switch

Abstract: We report a high-speed microfluidic switch capable of achieving a switching time of 10 μs. The switching mechanism is realized by exciting dynamic vapor bubbles with focused laser pulses in a microfluidic polydimethylsiloxane (PDMS) channel. The bubble expansion deforms the elastic PDMS channel wall and squeezes the adjacent sample channel to control its fluid and particle flows as captured by the time-resolved imaging system. A switching of polystyrene microspheres in a Y-shaped channel has also been demonstrated. This ultrafast laser triggered switching mechanism has the potential to advance the sorting speed of state-of-the-art microscale fluorescence activated cell sorting devices.

Enhancement of switching speed by laser-induced clustering of nanoparticles in magnetic fluids

Abstract: The switching speed of magnetic fluids was investigated by using laser light of different power densities as well as incandescent light. It was found that the switching speed exhibited a strong dependence on incident power density and there existed an optimum value at which the fastest switching operation was achieved. In addition, it was revealed that the clustering of magnetic nanoparticles, which became resolved at large power densities, resulted in a rapid agglomeration of nanoparticles when a magnetic field was applied. It is suggested that the optical trapping force of the laser beam is responsible for the formation of clusters.

Simplified Voltage-Sag Filler for Line-Interactive Uninterruptible Power Supplies

Abstract: There are three types of static uninterruptible power supplies (UPSs): passive standby, line interactive, and double conversion. The last one protects the load against all types of line disturbances, but it is the most expensive and the one with the lowest efficiency. On the other hand, passive-standby and line-interactive UPSs have higher efficiency and lower cost, but they show an important drawback: a switching time from normal to stored-energy mode. As a consequence, there is a notch in the UPS output voltage during this switching time. In a previous paper, the authors proposed a method for filling these voltage notches with a sinusoidal waveform generated by a switch-mode converter. In this one, a simplified notch filler is proposed. It consists of two capacitors, one charged with positive voltage and the other with negative voltage. If the fault occurs in the positive period, the positive-charged capacitor is connected to the load. This connection is then modulated in order to obtain a sinusoidal waveform at the load. In the negative period, the other capacitor is used in the same way.

Maximally Confined High-Speed Second-Order Silicon Microdisk Switches

Abstract: We demonstrate the first high-speed second-order silicon microdisk bandpass switch. The switch, constructed of a pair of 3?m radii active microdisks possesses ~40GHz flat-top passbands, a 4.2THz free-spectral-range, and a 2.4ns switching time.

A 2-Bit Ka-Band RF MEMS Frequency Tunable Slot Antenna

Abstract: A 2-bit Ka-band RF MEMS frequency tunable slot antenna is disclosed. It is demonstrated on a fused silica wafer using a micro-fabrication process requiring six masks. The return loss and gain for each of the four states are measured using a probe station based setup for on-wafer antenna measurements. The antenna has a measured tunable bandwidth of 6.8 GHz. The average measured gain is 1.74 dBi, and the average measured cross-polarization is -9.22 dBi. The extracted switching time is 5.19 mus for a drive voltage of 45 V.

Apparatus and method for control of a thermostat

Abstract: A thermostat is provided that includes a temperature sensor for sensing ambient temperature, and a switching device that is configured to apply electrical power to a heating element when the switching device is activated The thermostat further includes a processor that is configured to periodically determine for a finite switching time period a temperature delta value indicative of the difference between the sensed temperature and a desired set point temperature The processor is further configured to calculate a duty cycle ratio of the switch activation time relative to the total switching time period The calculated duty cycle ratio for determining the switch activation time is determined as a function of the temperature delta value, a duty cycle offset and a heat dissipation offset The duty cycle offset and the heat dissipation offset are based on an average of a predetermined number of prior duty cycle ratios

PLZT Waveguide Devices for High Speed Switching and Filtering

Abstract: High-speed optical switches were developed in electro-optic (Pb,La)(Zr,Ti)O3 (PLZT) waveguides. A 1×2 optical path switch showed <;2.5 ns switching time. An 8×1 wavelength selective switch based on a tunable AWG showed 15 ns switching time.