Voltage Pulse Duration Research Articles

Effect of energetic particles on pulsed magnetron sputtering of hard nanocrystalline MBCN (M = Ti, Zr, Hf) films with high electrical conductivity

Nanocrystalline MBCN (M = Ti, Zr, Hf) films were deposited onto Si substrates using pulsed magnetron co-sputtering of a single B4C-M target (at a fixed 45% fraction of M in the target erosion area) with a repetition frequency of 10 kHz, voltage pulse duration of 85 μs and a fixed target power. The substrate temperature was adjusted to 450 °C during the depositions on the substrates at a floating potential. The total pressure of 95% Ar + 5% N2 gas mixture was 0.5 Pa for TiBCN and ZrBCN, but it had to be increased up to 1.7 Pa for HfBCN to decrease very high compressive stress in the films resulting in their delamination from the substrate. Energy-resolved mass spectroscopy was used to correlate the energy of Ar+ ions bombarding the growing films with high positive voltage overshoots after the negative voltage pulses. Monte-Carlo simulations were carried out to estimate the energy and flux of sputtered M atoms and backscattered Ar atoms at the substrate. It was found that the energy and flux of the backscattered Ar atoms increase significantly with the mass of the M atoms in the target. The MBCN films with 41–46 at.% of M, 25–31 at.% of B, 7–10 at.% of C and 14–22 at.% of N exhibit a high hardness (18–37 GPa), high elastic recovery (69–85%), high H/E⁎ ratio (0.10–0.14) and low electrical resistivity (1.7–2.7 μΩm) at a low internal stress (less than 0.8 GPa).

Voltage-induced switching with long tolerance of voltage-pulse duration in a perpendicularly magnetized free layer

The voltage-induced magnetization switching with the long tolerance of voltage-pulse duration (tp) is theoretically investigated. This method does not require the voltage-pulse to be turned off at around half-period of precessional motion of magnetization, and it can be realized by the energy dissipation through the damping torque. Numerical simulations show that this method is applicable in perpendicularly magnetized free layer at room temperature. The results provide a method for designing a voltage-controlled MRAM which ensures the reliability in writing against the distribution of tp from pulsed power supply and the distribution of precession periods among the MRAM cells.

Beaded Discharges Formed under Pulsed Breakdowns of Air and Nitrogen

The mode of a pulsed discharge in a nonuniform electric field is investigated at which bright plasma bunches with a beaded structure are generated in atmospheric-pressure air. Using an ICCD camera, it is found that, at centimeter gap lengths and a voltage pulse duration of ≈300 ns, the beaded structure can be observed with a probability close to 100% within time intervals from a few nanoseconds to several tens of nanoseconds. The beaded structure can also be observed in the time-integrated photographs of the discharge gap, but with a low probability. It is shown that individual beads arise in the point-to-plane gap after the diffuse stage of the discharge and start from the electrode with a small curvature radius. It is established that the spark channel bridges the gap by passing through the formed beads. The glowing beads are again observed in the final stage of the discharge, when the discharge current and, accordingly, the intensity of spark emission decrease.

Высоковольтные диффузионные диоды с резким восстановлением. II. Теория

Approximate analytical formulas are obtained to evaluate the main characteristics of diffused step recovery diodes (SRD) operating as current interrupters in high-power generators of nanosecond pulses with an inductive energy storage: the unwanted pre-pulse voltage, characterizing resistive losses in SRD, amplitude, duration of front and duration of voltage pulse formed on the resistive load. For comparison, similar formulas for epitaxial SRD, partially obtained for the first time, and partially clarifying the early results, are given.

Modelling of local anodic oxidation of titanium oxide nanostructures formation process

A model for the oxide nanostructures formation by the local anodic oxidation method is presented. Dependences of height, depth, and diameter of titanium oxide nanostructures on the applied voltage pulse duration are obtained, as well as the oxide nanostructures profile for given technological parameters.

Evolution of C-V and I-V characteristics for a commercial 600 V GaN GIT power device under repetitive short-circuit tests

In this article, a repetitive and non-destructive short-circuit aging test is developed to characterize the electrical parameters evolutions of a 600 V GaN Gate Injection Transistor (GIT). The evolutions of C-V and I-V characteristics during the repetitive short-circuit tests with a relatively low bias voltage and long pulse duration are presented and summarized. The capacitance CGD at on-state mode and the gate current at relative high gate voltage show significant degradations before and after test.

Local Anodic Oxidation of Thin GeO Films and Formation of Nanostructures Based on Them

The process of local anodic oxidation of thin GeO films has been studied using an atomic force microscope. The electron-probe microanalysis showed that oxidized areas of a GeO film were germanium dioxide. The effect of the voltage pulse duration applied to the probe–substrate system and the atmospheric humidity on the height of the oxide structures has been studied. The kinetics of the local anodic oxidation (LAO) in a semi-contact mode obeys the Cabrera–Mott model for large times. The initial growth rate of the oxide (R0) significantly increases and the time of starting the oxidation (t0) decreases as the atmospheric humidity increases by 20%, which is related to an increase in the concentration of oxygen-containing ions at the surface of the oxidized GeO film. It was shown that nanostructures in thin GeO layers can be formed by the LAO method.

A High‐Speed and Low‐Power Multistate Memory Based on Multiferroic Tunnel Junctions

AbstractFerroic‐order‐based devices are emerging as alternatives to high density, high switching speed, and low‐power memories. Here, multi‐nonvolatile resistive states with a switching speed of 6 ns and a write current density of about 3 × 103 A cm−2 are demonstrated in crossbar‐structured memories based on all‐oxide La0.7Sr0.3MnO3/BaTiO3/La0.7Sr0.3MnO3 multiferroic tunnel junctions. The tunneling resistive switching as a function of voltage pulse duration time, associated with the ferroelectric domain reversal dynamics, is ruled by the Kolmogorov–Avrami–Ishibashi switching model with a Lorentzian distribution of characteristic switching time. It is found that the characteristic resistance switching time decreases with increasing voltage pulse amplitude following Merz's law and the estimated write speed can be less than 6 ns at a relatively higher voltage. These findings highlight the potential application of multiferroic devices in high speed, low power, and high‐density memories.

Comparison Study of Spatiotemporally Resolved Emissions of Nanosecond Pulsed Microplasma Jets

A single needle-electrode helium microplasma jet powered by 5- or 164-ns 8-kV pulses at 500 Hz is investigated to elucidate the impact of nanosecond pulse rising rate and pulse duration on emission behaviors of plasmas. For the 5-ns pulsed plasma, the energy per pulse was measured to be 83 $\mu \text{J}$ , and it is 1.3 times of the 164-ns pulsed plasma. Time-integrated, spatially resolved emissions revealed that the shorter pulsed plasma generated higher production of excited $N_{2}^{+}$ (by a factor of 1.3) but less excited $N_{2}$ , He, O, and OH productions. In addition, all of these species maintained their maximal emissions near the needle nozzle, implying the importance of direct electron impact on generation of these excited species. Temporally resolved emissions showed that comparable or more excited species were produced by the 5-ns pulsed plasma for the first 100 ns, and the additional productions of excited species by the longer pulsed plasma occurred during the failing phase of the 164-ns voltage pulse. These findings suggested that rising and falling rates (≥ 1011 V/s) of a voltage pulse may not only play important roles in energy deposition during the plasma initiation but also influence the plasma chemistry that is associated with the production of excited species. The voltage pulse duration became important for the streamer development and charge transfer, which critically contributed to the total production of the reactive plasma species.

Preparation of nickel-containing conductive amorphous carbon films by magnetron sputtering with negative high-voltage pulsed substrate bias

Nickel-containing amorphous carbon (a-C-Ni) films were deposited by magnetron sputtering of graphite and nickel. Graphite magnetron sputtering power was 1500 W. Nickel magnetron sputtering power changed from 0 W to 1000 W, allowing control of the Ni concentration in the films from 0 to 58 at.%. Growth rates of a-C-Ni films were 1.4–2.5 μm/h. High-voltage negative pulsed bias voltage of ‐3 kV amplitude, frequency of 1 kHz, and pulse duration of 50–250 μs was applied to a substrate. The chemical composition of the films was determined using Auger electron spectroscopy. The surface morphology was observed by atomic force microscopy (AFM). The film structure was characterized by Raman spectroscopy and X-ray diffractometry (XRD). The resistivity of the films was measured by a four-point probe method. Film properties that are changed by the added metal, such as structure, electrical resistivity, and hardness, were evaluated and compared with those of pure a-C films as well as with literature values for a-C-Ni films. It is shown that the resistivity of a-C films depends on the duration of the bias voltage pulses and varies from 3.4 to 7.6·10−2 Ohm·cm at pulse duration 50 and 250 μs, respectively. In the case of Ni doping, the a-C-Ni film resistivity can be reduced to 6.7·10−4 Ohm·cm. Where Ni is included in the film in the form of Ni3C carbide, which has hexagonal (hcp) modification, the crystallite size averages 12 nm. The film has a columnar structure and carbon is also present as a graphite-like interlayer 3 nm thick between the Ni3C crystallites. At sputtering power of 600 W of nickel magnetron, a-C-Ni film with resistivity of 5.3·10−3 Ohm·cm is obtained, which can be used as a barrier layer in thermoelements based on bismuth telluride.

Исследование процесса локального анодного окисления тонких пленок GeO и создание наноструктур на их основе

AbstractThe process of local anodic oxidation of thin GeO films has been studied using an atomic force microscope. The electron-probe microanalysis showed that oxidized areas of a GeO film were germanium dioxide. The effect of the voltage pulse duration applied to the probe–substrate system and the atmospheric humidity on the height of the oxide structures has been studied. The kinetics of the local anodic oxidation (LAO) in a semi-contact mode obeys the Cabrera–Mott model for large times. The initial growth rate of the oxide ( R _0) significantly increases and the time of starting the oxidation ( t _0) decreases as the atmospheric humidity increases by 20%, which is related to an increase in the concentration of oxygen-containing ions at the surface of the oxidized GeO film. It was shown that nanostructures in thin GeO layers can be formed by the LAO method.

The Discharge Channel Formation and the Mechanism of Material Removal During Electrical Discharge Micromachining by Nanosecond Pulses

The conditions of improvement of the electrical discharge machining (EDM) by means of rational choice of the voltage pulse duration are considered. The shorter and smaller power voltage pulses (including, nanosecond pulses) are proposed to use. Streamer and heat mechanisms of the formation of the discharge channel in dielectric medium are considered. It is proved that in the small interelectrode gaps (1÷5μm) the streamer mechanism of the initial formation of the discharge channel is most likely. Two periods of the formation of the discharge channel: without the conduction current and with passing the conduction current are considered.The conditions of the formation of the erosional craters at using nanosecond voltage pulses are considered. It is shown that under these conditions the diameter of the discharge channel significantly reduces, the crater depth increases and their diameter decreases.The estimation of the effectiveness of EDM on the basis of the fracture kinetics of materials is made. The estimates of the fracture activation energy for various metals are presented. These estimates are in good agreement with a specific energy consumption with a fixed amount of dispersion.It is shown that the effect of hydrodynamics on the mechanism of material removal at EDM with using nanosecond voltage pulses substantially weakens. The recommendations for the improvement of EDM with the use of nanosecond voltage pulses are presented.

Synthesis of Nanosecond Ultrawideband Radiation Pulses

The synthesis of electromagnetic pulses with an extended spectrum by summing pulses of different duration in free space has been studied. The radiation spectrum has been estimated analytically for a 4-element array of combined antennas excited by bipolar voltage pulses of duration 0.5, 1, 2, and 3 ns. It has been shown experimentally that radiation with a spectral width of more than three octaves can be produced using a 2×2 array of combined antennas excited by bipolar pulses of duration 2 and 3 ns.

Generation of runaway electrons beams during the breakdown of high-pressure gases

Generation of run-away electrons in SF6, CO2, argon and nitrogen at high and super high pressures is studied. Super-short avalanches electron beams (SAEB) was obtained and measured with a collector at pressures up to 0.3, 0.7, 1.0 and 1.2 MPa in SF6, CO2, argon and nitrogen, respectively. The SAEB duration was shown to be ∼60 ps (FWHM) and gas composition has only minor effect on the duration. It was found that in a gap of 4 mm in SF6, CO2, argon and nitrogen at pressure up to 0.3, 0.7, 1.0 и 1.2 MPa the voltage pulse duration (FWHM) and amplitude increase with pressure.

High-power nano- and picosecond optoelectronic switches based on high-voltage silicon structures with p–n junctions: I. Physics of the switching process

Numerical simulation of switching process of high-voltage silicon photodiodes, phototransistors and photothyristors those triggered-on homogeneously over the area by picosecond laser pulses, has been performed for the first time. The analysis of results allowed to obtain "empirical" relationship between key parameters of switches (energy of control pulses, a radiation absorption coefficient, the area of structures) and parameters those characterizing the switching process in a circuit with the resistive load. For some of these relationship the approximate analytical formulas which seem to be quite adequate to the simulation results has been deduced. It is noted that distinctions between switching processes in structures of the three different types become apparent only at long duration of voltage pulses at a final stage when the blocking capability of photodiodes and phototransistors is recovered.

Optical emission spectroscopy during the deposition of zirconium dioxide films by controlled reactive high-power impulse magnetron sputtering

Time-resolved optical emission spectroscopy was performed near the sputtered Zr target and in a plasma bulk during a controlled high-rate reactive high-power impulse magnetron sputtering of stoichiometric ZrO2 films in argon-oxygen gas mixtures at the argon pressure of 2 Pa. The repetition frequency was 500 Hz at the deposition-averaged target power density of 52 W cm−2 with a peak target power density of 1100 W cm−2. The voltage pulse duration was 200 μs. From the time evolutions of the excited-state populations for the chosen atoms (Zr, Ar, and O) and ions (Zr+, Zr2+, Ar+, and O+), and of the excitation temperature during a voltage pulse, the trends in a time evolution of the local ground-state densities of these atoms and ions during the voltage pulse were derived. Near the target, a decrease in the ground-state densities of Ar and O atoms, caused by a gas rarefaction and intense electron-impact ionization, was observed in the first half of the voltage pulse. Simultaneous, very effective electron-impact ionization of sputtered Zr atoms was proved. A composition of particle fluxes onto the substrate during a film deposition was found almost independent of the instantaneous oscillating oxygen partial pressure.

Enhanced Temporal Resolution with Ion Channel-Functionalized Sensors Using a Conductance-Based Measurement Protocol.

The binding of a target analyte to an ion channel (IC), which is readily detected electrochemically in a label-free manner with single-molecule selectivity and specificity, has generated widespread interest in using natural and engineered ICs as transducers in biosensing platforms. To date, the majority of developments in IC-functionalized sensing have focused on IC selectivity or sensitivity or development of suitable membrane environments and aperture geometries. Comparatively little work has addressed analytical performance criteria, particularly criteria required for temporal measurements of dynamic processes. We report a measurement protocol suitable for rapid, time-resolved monitoring (≤30 ms) of IC-modulated membrane conductance. Key features of this protocol include the reduction of membrane area and the use of small voltage steps (10 mV) and short duration voltage pulses (10 ms), which have the net effect of reducing the capacitive charging and decreasing the time required to achieve steady state currents. Application of a conductance protocol employing three sequential, 10 ms voltage steps (-10 mV, -20 mV, -30 mV) in an alternating, pyramid-like arrangement enabled sampling of membrane conductance every 30 ms. Using this protocol, dynamic IC measurements on black lipid membranes (BLMs) functionalized with gramicidin A were conducted using a fast perfusion system. BLM conductance decreased by 76 ± 7.5% within 30 ms of switching from solutions containing 0 to 1 M Ca2+, which demonstrates the feasibility of using this approach to monitor rapid, dynamic chemical processes. Rapid conductance measurements will be broadly applicable to IC-based sensors that undergo analyte-specific gating.

Screening somatic cell nuclear transfer parameters for generation of transgenic cloned cattle with intragenomic integration of additional gene copies that encode bovine adipocyte-type fatty acid-binding protein (A-FABP).

Somatic cell nuclear transfer (SCNT) is frequently used to produce transgenic cloned livestock, but it is still associated with low success rates. To our knowledge, we are the first to report successful production of transgenic cattle that overexpress bovine adipocyte-type fatty acid binding proteins (A-FABPs) with the aid of SCNT. Intragenomic integration of additional A-FABP gene copies has been found to be positively correlated with the intramuscular fat content in different farm livestock species. First, we optimized the cloning parameters to produce bovine embryos integrated with A-FABP by SCNT, such as applied voltage field strength and pulse duration for electrofusion, morphology and size of donor cells, and number of donor cells passages. Then, bovine fibroblast cells from Qinchuan cattle were transfected with A-FABP and used as donor cells for SCNT. Hybrids of Simmental and Luxi local cattle were selected as the recipient females for A-FABP transgenic SCNT-derived embryos. The results showed that a field strength of 2.5kV/cm with two 10-μs duration electrical pulses was ideal for electrofusion, and 4-6th generation circular smooth type donor cells with diameters of 15-25μm were optimal for producing transgenic bovine embryos by SCNT, and resulted in higher fusion (80%), cleavage (73%), and blastocyst (27%) rates. In addition, we obtained two transgenic cloned calves that expressed additional bovine A-FABP gene copies, as detected by PCR-amplified cDNA sequencing. We proposed a set of optimal protocols to produce transgenic SCNT-derived cattle with intragenomic integration of ectopic A-FABP-inherited exon sequences.

Microstructure of hard and optically transparent HfO2 films prepared by high-power impulse magnetron sputtering with a pulsed oxygen flow control

Reactive high-power impulse magnetron sputtering was used to deposit HfO2 films on Si substrates using a voltage pulse duration, t1, from 100 to 200μs and an deposition-averaged target power density, <Sd>, from 7.2 to 54Wcm−2. The effects of these processing parameters on the microstructure and properties of the films were studied by atomic force microscopy, nano-indentation, X-ray diffraction, electron diffraction and high-resolution transmission electron microscopy. Four HfO2 films were prepared with (1) t1=100μs, <Sd>=7.2Wcm−2 (T100S7), (2) t1=200μs, <Sd>=7.3Wcm−2 (T200S7), (3) t1=200μs, <Sd>=18Wcm−2 (T200S18) and (4) t1=200μs, <Sd>=54Wcm−2 (T200S54). All films were found to be composed of an interlayer next to the Si interface followed by a nano-columnar structure layer. The interlayer structure of the films was found to contain a population of lower density nanoscale regions. A reduction in <Sd> in films T200S54, T200S18, T200S7 and T100S7 caused an increase in the interlayer thickness and a decrease in the width of the nano-columnar structures from ~46nm to ~21nm. This microstructural change was accompanied by a concomitant change of the grain boundary structure from tight and interlocking in films T200S54 and T200S18, to rough and thicker (~1nm) boundaries in films T200S7 and T100S7. Films prepared with larger t1=200μs have a monoclinic HfO2 structure and that with smaller t1=100μs exhibits a mixture of monoclinic and orthorhombic HfO2. A high hardness of 17.0–17.6GPa was shown for films with a monoclinic HfO2 structure. The films exhibited a refractive index of 2.02–2.11 and an extinction coefficient between 0.1×10−3 and 1×10−3 (both at a wavelength of 550nm). High refractive index was achieved for films T200S54 and T200S18 owing to the presence of a dense microstructure with sharp and interlocking grain boundaries.

Scanning thermal probe microscope method for the determination of thermal diffusivity of nanocomposite thin films.

A commercial scanning thermal microscope has been upgraded to facilitate its use in estimating the radial thermal diffusivity of thin films close to room temperature. The modified setup includes a microcontroller driven microhotplate coupled with a Bluetooth module for wireless control. The microcontroller board (Arduino Leonardo) is used to generate a bias of suitable voltage amplitude and pulse duration which is applied across the microhotplate contact pads. A corresponding heat pulse from the Pt heating element (1 mm(2)) embedded within the microhotplate is delivered to the lower surface of the thin film (25 mm(2)) deposited over it. The large difference in the dimensions of the heating source and the thin film surface causes heat to flow radially outwards on the top surface of the latter. The decay of this radial heat wave as it flows outwards is recorded by the scanning thermal microscope in terms of temperature-time (T-t) profiles at varying positions around the central heating zone. A fitting procedure is suggested to extract the thermal diffusivity value from the array of T-t profiles. The efficacy of the above setup has been established by evaluating the thermal diffusivities of Bi2Te3 and Bi2Te3:Si thin film samples. Further, with only minor alterations in design the capabilities of the above setup can be extended to estimate the axial thermal diffusivity and specific heat of thin films, as a function of temperature.