Voltage-dependent Characteristics Research Articles

On frequency and voltage dependent physical characteristics and interface states characterization of the metal semiconductor (MS) structures with (Ti:DLC) interlayer

In this present study, the electrical parameters of Al/p-Si (MS) structures with (Ti-doped DLC) interfacial layer were investigated between 1 kHz and 4 MHz utilizing impedance-spectroscopy method. The (Ti:DLC) interlayer grown by electrochemical deposition method and its structural characterization was performed by SEM, EDX, and XPS methods. The XPS results show that the chemical-structure of the interlayer has 15.53% Ti, 50.18% O, 18.15% C, 4.14% Si, 10.24% N after annealing. The concentration of acceptor-atoms (NA), Fermi-energy (EF), depletion-layer thickness (Wd), maximum electric-field (Em), and barrier-height (ΦB(C–V)) values were calculated from the C−2-V plots as 4.78 × 1015cm−3, 0.20eV, 3.28x10−5cm, 2.40 × 104 V/cm, 0.594eV at 20 kHz and 4.96 × 1015cm−3, 0.199eV, 4.14x10−5cm, 3.14 × 104 V/cm, 0.849eV at 4 MHz, respectively. The surface-states (Nss) and their life-time (τ) were obtained from conductance-method as 0.77 × 1013/(eVcm2) and 1.40x10−3s at 0.05V and 1.57 × 1013/(eVcm2) and 1.74x10−5s at 1.00 V, respectively.

Key role for Kv11.1 (ether-a-go-go related gene) channels in rat bladder contractility.

In addition, to their established role in cardiac myocytes and neurons, ion channels encoded by ether-a-go-go-related genes (ERG1-3 or kcnh2,3 and 6) (kcnh2) are functionally relevant in phasic smooth muscle. The aim of the study was to determine the expression and functional impact of ERG expression products in rat urinary bladder smooth muscle using quantitative polymerase chain reaction, immunocytochemistry, whole-cell patch-clamp and isometric tension recording. kcnh2 was expressed in rat bladder, whereas kcnh6 and kcnh3 expression were negligible. Immunofluorescence for the kcnh2 expression product Kv11.1 was detected in the membrane of isolated smooth muscle cells. Potassium currents with voltage-dependent characteristics consistent with Kv11.1 channels and sensitive to the specific blocker E4031 (1μM) were recorded from isolated detrusor smooth muscles. Disabling Kv11.1 activity with specific blockers (E4031 and dofetilide, 0.2-20 μM) augmented spontaneous contractions to a greater extent than BKCa channel blockers, enhanced carbachol-driven activity, increased nerve stimulation-mediated contractions, and impaired β-adrenoceptor-mediated inhibitory responses. These data establish for the first time that Kv11.1 channels are key determinants of contractility in rat detrusor smooth muscle.

Implementation of high-performance and high-yield nanoscale hafnium zirconium oxide based ferroelectric tunnel junction devices on 300 mm wafer platform

In this work, hafnium zirconium oxide (HZO)-based 100 × 100 nm2 ferroelectric tunnel junction (FTJ) devices were implemented on a 300 mm wafer platform, using a baseline 65 nm CMOS process technology. FTJs consisting of TiN/HZO/TiN were integrated in between metal 1 (M1) and via 1 (V1) layers. Cross-sectional transmission electron microscopy and energy dispersive x-ray spectroscopy analysis confirmed the targeted thickness and composition of the FTJ film stack, while grazing incidence, in-plane x-ray diffraction analysis demonstrated the presence of orthorhombic phase Pca21 responsible for ferroelectric polarization observed in HZO films. Current measurement, as a function of voltage for both up- and down-polarization states, yielded a tunneling electroresistance (TER) ratio of 2.28. The device TER ratio and endurance behavior were further optimized by insertion of thin Al2O3 tunnel barrier layer between the bottom electrode (TiN) and ferroelectric switching layer (HZO) by tuning the band offset between HZO and TiN, facilitating on-state tunneling conduction and creating an additional barrier layer in off-state current conduction path. Investigation of current transport mechanism showed that the current in these FTJ devices is dominated by direct tunneling at low electric field (E < 0.4 MV/cm) and by Fowler–Nordheim (F–N) tunneling at high electric field (E > 0.4 MV/cm). The modified FTJ device stack (TiN/Al2O3/HZO/TiN) demonstrated an enhanced TER ratio of ∼5 (2.2× improvement) and endurance up to 106 switching cycles. Write voltage and pulse width dependent trade-off characteristics between TER ratio and maximum endurance cycles (Nc) were established that enabled optimal balance of FTJ switching metrics. The FTJ memory cells also showed multi-level-cell characteristics, i.e., 2 bits/cell storage capability. Based on full 300 mm wafer statistics, a switching yield of >80% was achieved for fabricated FTJ devices demonstrating robustness of fabrication and programming approach used for FTJ performance optimization. The realization of CMOS-compatible nanoscale FTJ devices on 300 mm wafer platform demonstrates the promising potential of high-volume large-scale industrial implementation of FTJ devices for various nonvolatile memory applications.

Protein and DNA Yield Current Enhancements, Slow Translocations, and an Enhanced Signal-to-Noise Ratio under a Salt Imbalance.

Nanopores are a promising single-molecule sensing device class that captures molecular-level information through resistive or conductive pulse sensing (RPS and CPS). The latter has not been routinely utilized in the nanopore field despite the benefits it could provide, specifically in detecting subpopulations of a molecule. A systematic study was conducted here to study the CPS-based molecular discrimination and its voltage-dependent characteristics. CPS was observed when the cation movement along both electrical and chemical gradients was favored, which led to an ∼3× improvement in SNR (i.e., signal-to-noise ratio) and an ∼8× increase in translocation time. Interestingly, a reversal of the salt gradient reinstates the more conventional resistive pulses and may help elucidate RPS-CPS transitions. The asymmetric salt conditions greatly enhanced the discrimination of DNA configurations including linear, partially folded, and completely folded DNA states, which could help detect subpopulations in other molecular systems. These findings were then utilized for the detection of a Cas9 mutant, Cas9d10a─a protein with broad utilities in genetic engineering and immunology─bound to DNA target strands and the unbound Cas9d10a + sgRNA complexes, also showing significantly longer event durations (>1 ms) than typically observed for proteins.

Nonlinear Dielectric Properties of the Stator and Transformer Insulation Systems

Composite insulation systems usually exhibit nonlinear phenomena, such as voltage-dependent dielectric response and high-order current harmonics. In this article, a high-voltage system capable of performing both dielectric frequency response (DFR) and polarization/depolarization current (PDC) measurements up to 20 kV is devised. The nonlinear properties of the motor stator and power transformer insulation systems are studied. Experimental results show that the voltage-dependent effect becomes significant as the voltage magnitude approaches the nominal and frequency decreases. The third current harmonic component is found to be dominant over the other components and has a strong correlation with the decrease in the dissipation factor. By taking both the fundamental and third-harmonic components into account, more consistent voltage-dependent characteristics are revealed. These features are important indications of insulation defects that are often neglected in field diagnostic testings. The investigation of the nonlinear properties helps to enhance the condition diagnosis reliability.

A scheme for enabling the ultimate speed of threshold switching in phase change memory devices

Phase change materials exhibit threshold switching (TS) that establishes electrical conduction through amorphous material followed by Joule heating leading to its crystallization (set). However, achieving picosecond TS is one of the key challenges for realizing non-volatile memory operations closer to the speed of computing. Here, we present a trajectory map for enabling picosecond TS on the basis of exhaustive experimental results of voltage-dependent transient characteristics of Ge2Sb2Te5 phase-change memory (PCM) devices. We demonstrate strikingly faster switching, revealing an extraordinarily low delay time of less than 50 ps for an over-voltage equal to twice the threshold voltage. Moreover, a constant device current during the delay time validates the electronic nature of TS. This trajectory map will be useful for designing PCM device with SRAM-like speed.

Sensitivity Analysis for Voltage Stability Considering Voltage Dependent Characteristics of Loads and DGs

The sensitivity analysis becomes particularly critical for voltage stability analysis due to the fluctuation in power outputs of renewable energy resources. Besides, impacts of different load modeling and the operation mode of Distributed Generations (DGs) are not addressed in the well-known sensitivity analysis methods. Therefore, this work presents a new sensitivity analysis approach to find the relation between the Voltage Stability Margin (VSM) and the control variables of power systems, considering the voltage dependent characteristics of loads and DGs. The sensitivity analysis is performed on VSM, defined from equivalent nodal analysis, via its differential equation. To include the voltage dependent characteristics, loads are modeled as polynomial function (ZIP model) and DGs are considered to be operated with constant current and constant power modes. Based on this analysis, the sensitivity of VSM can be directly obtained by taking the derivatives of nodal voltages with respect to control variables. The validity of the developed approach is demonstrated on the IEEE 118 bus system.

Dronedarone blockage of the tumor-related Kv10.1 channel: a comparison with amiodarone.

Kv10.1 (Eag1, or KCNH1) is a human potassium-selective channel associated with tumor development. In this work, we study the interaction of the drug dronedarone with Kv10.1. Dronedarone presents two chemical modifications aimed to lessen side effects produced by its parent molecule, the antiarrhythmic amiodarone. Hence, our observations are discussed within the framework of a previously reported interaction of amiodarone with Kv10.1. Additionally, we show new data regarding the interaction of amiodarone with the channels. We found that, unexpectedly, the effect of dronedarone on Kv10.1 differs both quantitatively and qualitatively to that of amiodarone. Among other observations, we found that dronedarone seems to be an open-pore blocker, in contrast to the reported behavior of amiodarone, which seems to inhibit from both open and closed states. Additionally, herein we provide evidence showing that, in spite of their chemical similarity, these molecules inhibit the K+ conductance by binding to non-overlapping, independent (non-allosterically related) sites. Also, we show that, while amiodarone inhibits the Cole-Moore shift, dronedarone is unable to inhibit this voltage-dependent characteristic of Kv10.1.

Exploring ultrafast threshold switching in In3SbTe2 phase change memory devices

Phase change memory (PCM) offers remarkable features such as high-speed and non-volatility for universal memory. Yet, simultaneously achieving better thermal stability and fast switching remains a key challenge. Thus, exploring novel materials with improved characteristics is of utmost importance. We report here, a unique property-portfolio of high thermal stability and picosecond threshold switching characteristics in In3SbTe2 (IST) PCM devices. Our experimental findings reveal an improved thermal stability of amorphous IST compared to most other phase change materials. Furthermore, voltage dependent threshold switching and current-voltage characteristics corroborate an extremely fast, yet low electric field threshold switching operation within an exceptionally small delay time of less than 50 picoseconds. The combination of low electric field and high speed switching with improved thermal stability of IST makes the material attractive for next-generation high-speed, non-volatile memory applications.

Probing the pseudocapacitance and energy-storage performance of RuO2 facets from first principles

The energy density of ruthenia (${\mathrm{RuO}}_{2}$) pseudocapacitor electrodes is critically dependent on their surface structure. To understand this dependence, we simulate the electrochemical response of ${\mathrm{RuO}}_{2}$(110), ${\mathrm{RuO}}_{2}$(100), and ${\mathrm{RuO}}_{2}$(101) in aqueous environments using a self-consistent continuum solvation (SCCS) model of the solid-liquid interface. The insertion of protons into the ${\mathrm{RuO}}_{2}$(110) sublayer is found to profoundly affect the voltage-dependent characteristics of the system, leading to a sharp transition from a battery-type to capacitor-type response. The calculated charge-voltage properties for ${\mathrm{RuO}}_{2}$(101) are in qualitative agreement with experiment, albeit with a pseudocapacitance that is significantly underestimated. In contrast, the ${\mathrm{RuO}}_{2}$(100) facet is correctly predicted to be pseudocapacitive over a wide voltage window, with a calculated pseudocapacitance in close agreement with experimental voltammetry. These results establish the SCCS model as a reliable approach to predict and optimize the facet-dependent pseudocapacitance of polycrystalline systems.

Ultraviolet photoconduction in tungsten disulphide based Schottky heterostructure photodetector

A proposed Ag/WS2/SiO2/p-Si/Ag Schottky heterostructure photodetector is tested for its photoconduction behaviour under ultraviolet (UV) illumination using a light emitting diode (LED) at 380 nm. This is done at various illumination powers as well as different direct current (DC) bias voltages. A simple and feasible drop casting method and heating process allows good adhesion of tungsten disulphide (WS2) onto a silicon dioxide/p-silicon (SiO2/p-Si) substrate forming a Schottky contact. In order to enhance photoconduction, iron (Fe) powder is introduced to build contacts between WS2 and the substrate. Field emission scanning electron microscope (FESEM) analysis, energy dispersive x-ray (EDX) spectroscopy and x-ray diffraction (XRD) results confirm the formation of the WS2 thin film. Raman spectrum peaks at 357 cm−1 (E12g) and 417 cm−1 (A1g) confirm the presence of WS2 while peaks 214, 223, 274 and 292 cm−1 and a small broad shoulder at 694 cm−1 confirm the presence of iron (III) oxide (Fe2O3). Furthermore, profound D and G bands at 1370 and 1585 cm−1 respectively indicate defected carbon (C) structures in the WS2 thin film. Excellent photoconduction of UV LED 380 nm light source showed power and DC bias voltage dependent characteristics. Wide variations in rise and fall time justifies that the device can be operated at selected bias voltages and frequency modulations.

Modeling of Residential EV Loads Applicable to Power Sytem Long-term Voltage Stability Analysis

With the increasing concern over the environmental and energy problems, electric vehicles (EVs) develop rapidly. This paper proposes a deterministic modeling methodology of electric vehicle loads. The modelling of one single EV load is conducted from the dc and the ac side separately, in which the time-varying and voltage dependent load characteristics are considered. The daily loads of aggregate EVs are modelled based on the electricity tariff structure and the initial state of charge distribution. Four types of private EVs are taken as the example to confirm the effectiveness of the proposed methodology. The impact of EV loads on power system voltage stability is analysed. The model developed by the proposed methodology provides accurate EV load characteristics with proper model complexity and it is suitable for long-term large scale power system numerical simulation.

A Physics-Based Compact Model for Transition-Metal Dichalcogenides Transistors With the Band-Tail Effect

Due to structural disorder effects, variable range hopping (VRH) transport via band-tail states has been widely observed in the transition-metal dichalcogenide field-effect transistor (TMD FET). However, this significant mechanism has not been incorporated into existing compact models. In this letter, a continuous physics-based compact model considering VRH in TMD FET is developed. Key parameters are extracted by calibration to experimental molybdenum disulfide FET. The voltage dependent carrier density and temperature dependent current characteristics are physically predicted by utilizing the general percolation theory and generalized Einstein relation. Our model is validated by the good agreement between the simulation and experimental results. Furthermore, the relationship between the disorder effects and circuit-level performances are presented. This letter is significant for material engineering and device optimization of TMD FET.

Structural implications of hERG K+ channel block by a high-affinity minimally structured blocker

Cardiac potassium channels encoded by human ether-à-go-go–related gene (hERG) are major targets for structurally diverse drugs associated with acquired long QT syndrome. This study characterized hERG channel inhibition by a minimally structured high-affinity hERG inhibitor, Cavalli-2, composed of three phenyl groups linked by polymethylene spacers around a central amino group, chosen to probe the spatial arrangement of side chain groups in the high-affinity drug-binding site of the hERG pore. hERG current (IhERG) recorded at physiological temperature from HEK293 cells was inhibited with an IC50 of 35.6 nm with time and voltage dependence characteristic of blockade contingent upon channel gating. Potency of Cavalli-2 action was markedly reduced for attenuated inactivation mutants located near (S620T; 54-fold) and remote from (N588K; 15-fold) the channel pore. The S6 Y652A and F656A mutations decreased inhibitory potency 17- and 75-fold, respectively, whereas T623A and S624A at the base of the selectivity filter also decreased potency (16- and 7-fold, respectively). The S5 helix F557L mutation decreased potency 10-fold, and both F557L and Y652A mutations eliminated voltage dependence of inhibition. Computational docking using the recent cryo-EM structure of an open channel hERG construct could only partially recapitulate experimental data, and the high dependence of Cavalli-2 block on Phe-656 is not readily explainable in that structure. A small clockwise rotation of the inner (S6) helix of the hERG pore from its configuration in the cryo-EM structure may be required to optimize Phe-656 side chain orientations compatible with high-affinity block.

A Modulation Compensation Scheme to Reduce Input Current Distortion in GaN-Based High Switching Frequency Three-Phase Three-Level Vienna-Type Rectifiers

Wide bandgap semiconductors are gradually being adopted in high power-density high efficiency applications, providing faster switching and lower loss, and at the same time imposing new challenges in control and hardware design. In this paper, a gallium nitride-based Vienna-type rectifier with SiC diodes is proposed to serve as the power factor correction stage in a high-density battery charger system targeting for aircraft applications with 800 Hz ac system and 600 V level dc link, where power quality is required according to DO160E standard. To meet the current harmonic requirement, PWM voltage distortion during the turn-off transient, is studied as the main harmonics contributor. The distortion mechanism caused by different junction capacitances of the switching devices is presented. A mitigation scheme considering the nonlinear voltage-dependent characteristics of these capacitances is proposed and then simplified from a pulse-based turn-off compensation method to a general modulation scheme. Simulation and experimental results with a 450 kHz Vienna-type rectifier demonstrate the performance of the proposed approach, showing a THD reduction from 10% to 3% with a relatively low-speed controller.

Nonlinear analysis of vanadium- and titanium-based contacts to Al-rich n-AlGaN

In this work, we report on voltage dependent contact characteristics of Al-rich n-AlGaN due to the presence of a Schottky barrier at the metal–AlGaN interface. Current–voltage characteristics appear to be linear at low voltages, but a clear nonlinearity is evident at high voltages. Unlike Ga-rich n-AlGaN where V-based contact marginally outperforms the Ti-based contact, V-based contact to Al-rich n-AlGaN outperforms the Ti-based contact by ∼2 orders of magnitude for all voltage ranges. The improved performance of V-based contacts is likely due to a lower Schottky barrier and partly due to ease of formation of a low barrier V–AlGaN interface.

A weak electric field-assisted ultrafast electrical switching dynamics in In3SbTe2 phase-change memory devices

Prefixing a weak electric field (incubation) might enhance the crystallization speed via pre-structural ordering and thereby achieving faster programming of phase change memory (PCM) devices. We employed a weak electric field, equivalent to a constant small voltage (that is incubation voltage, Vi of 0.3 V) to the applied voltage pulse, VA (main pulse) for a systematic understanding of voltage-dependent rapid threshold switching characteristics and crystallization (set) process of In3SbTe2 (IST) PCM devices. Our experimental results on incubation-assisted switching elucidate strikingly one order faster threshold switching, with an extremely small delay time, td of 300 ps, as compared with no incubation voltage (Vi = 0 V) for the same VA. Also, the voltage dependent characteristics of incubation-assisted switching dynamics confirm that the initiation of threshold switching occurs at a lower voltage of 0.82 times of VA. Furthermore, we demonstrate an incubation assisted ultrafast set process of IST device for a low VA of 1.7 V (∼18 % lesser compared to without incubation) within a short pulse-width of 1.5 ns (full width half maximum, FWHM). These findings of ultrafast switching, yet low power set process would immensely be helpful towards designing high speed PCM devices with low power operation.

Lanthanides Report Calcium Sensor in the Vestibule of Ryanodine Receptor

Ca2+ regulates ryanodine receptor’s (RyR) activity through an activating and an inhibiting Ca2+-binding site located on the cytoplasmic side of the RyR channel. Their altered sensitivity plays an important role in the pathology of malignant hyperthermia and heart failure. We used lanthanide ions (Ln3+) as probes to investigate the Ca2+ sensors of RyR, because they specifically bind to Ca2+-binding proteins and they are impermeable to the channel. Eu3+’s and Sm3+’s action was tested on single RyR1 channels reconstituted into planar lipid bilayers. When the activating binding site was saturated by 50 μM Ca2+, Ln3+ potently inhibited RyR’s open probability (Kd Eu3+ = 167 ± 5 nM and Kd Sm3+ = 63 ± 3 nM), but in nominally 0 [Ca2+], low [Eu3+] activated the channel. These results suggest that Ln3+ acts as an agonist of both Ca2+-binding sites. More importantly, the voltage-dependent characteristics of Ln3+’s action led to the conclusion that the activating Ca2+ binding site is located within the electrical field of the channel (in the vestibule). This idea was tested by applying the pore blocker toxin maurocalcine on the cytoplasmic side of RyR. These experiments showed that RyR lost reactivity to changing cytosolic [Ca2+] from 50 μM to 100 nM when the toxin occupied the vestibule. These results suggest that maurocalcine mechanically prevented Ca2+ from dissociating from its binding site and support our vestibular Ca2+ sensor-model further.

Ferroelectric polarization and resistive switching characteristics of ion beam assisted sputter deposited BaTiO3 thin films

In this work, 150nm thick polycrystalline BaTiO3 (BTO) films were deposited on Pt/TiO2/SiO2/Si substrate by ion beam assisted sputter deposition technique. The bias voltage dependent resistive switching (RS) and ferroelectric polarization characteristics of Au/BTO/Pt devices are investigated. The devices display the stable bipolar RS characteristics without an initial electroforming process. Fittings to current–voltage (I–V) curves suggest that low and high resistance states are governed, respectively, by filamentary model and trap controlled space charge limited conduction mechanism, where the oxygen vacancies act as traps. Presence of oxygen vacancies is evidenced from the photoluminescence spectrum. The devices also display P–V loops with remnant polarization (Pr) of 5.7μC/cm2 and a coercive electric field (Ec) of 173.0kV/cm. The coupling between the ferroelectric polarization and RS effect in BTO films is demonstrated.

Voltage instability detection based on the concept of short circuit capacity

Summary This paper proposes an online detection method for power system voltage instability, which considers the internal impedances of generators and the voltage-dependent and recovery characteristics of the electric loads. First, a novel voltage stability analysis method based on the concept of short circuit capacity (SCC) is established. Based on it, a SCC-based voltage stability index (VSI) is defined as the ratio of the SCC supplied by the combined generation-transmission system and the SCC required by load bus to maintain voltage stability. Then, for the calculation of SCC-based VSI, a two-step equivalent method of power system is presented to obtain the SCC supplied by the system side, in which the generator is modeled as a time-varying internal voltage behind constant internal impedance. Meanwhile, a modification method of load power is proposed to deal with the voltage-dependent characteristics and the restoration dynamics of system loads. As a result, the SCC required by loads can be precisely calculated. At last, the 5-bus system and the New England 39-bus system are used to validate the effectiveness of the proposed voltage instability detection method. Copyright © 2015 John Wiley & Sons, Ltd.