Voltage Increment Research Articles

Emission Rate Variation and Efficiency Measurement in TiO2Light Emitting Diode

Titanium dioxide light emitting diode was successfully designed and characterised. An approach in developing TiO 2 was based on cylindrically symmetric configuration with shorter computation time. The main goal of the research was to look into the performance of light emitting diode by using titanium dioxide and compare its validity with the standard or common criteria. The circular chip of titanium dioxide with 60 μm diameters was made with a circular active region formed by p and ntype dopants. The drastic reduction of internal quantum efficiency droops almost to zero value even though the current started to increase by 0.002 mA. The efficient operation within the device was observed that it would occur at the lowest current 0.01 mA while the total emission rate shown linearly increased at axis (0.002 mA, 5.6 (1/s)). This light emitting diode based on titanium dioxide also enabled to operate at lower turn-on voltage as low as 0.5 V. As the increment of voltages, the distribution of emission rate became less concentrated towards the top active of p-type layer of the device. The result also compared the two meshes where it was found that the refined mesh was focused around the p-n junction.

ZnSe Light Emitting Diode Quantum Efficiency and Emission Characterization

ZnSe has demonstrated as a potential candidate in realizing advance LED in some appications for current and future works that utilize a cheaper preparation technique. Blue and white LEDs have been shown to spread across compound semiconductors. This II-VI compound semiconductor with a direct and wide band gap is used in the study which focused on a preparation and its characterization. The device is developed using a circular chip of ZnSe but only part of the active region is designed to allow shorter computation time. Analyses of the proposed LED are performed in an environment that allows optical transition and nonradiative recombination mechanisms. Voltage variation from 0 V to 1.5 V is maintained throughout the observation. The curent-voltage plot shows the p-n junction or diode behavior with central emissive layer. The two dimensions surface emission rate obtained indicates that voltage increment causes the emission concentration to become higher near the central pcontact. The LED efficiency is assessed in terms of internal quantum efficiency and emitting rate.

Does QRS Voltage Correction by Body Mass Index Improve the Accuracy of Electrocardiography in Detecting Left Ventricular Hypertrophy and Predicting Cardiovascular Events in a General Population?

The authors assessed the value of body mass index (BMI) correction of two electrocardiographic criteria in improving detection of left ventricular hypertrophy (LVH) and prediction of cardiovascular and all-cause mortality in the Italian study Pressioni Arteriose Monitorate E Loro Associazioni (PAMELA) population. At entry, 1549 patients underwent diagnostic tests, 24-hour ambulatory blood pressure (BP) monitoring, standard electrocardiography, and echocardiography. The BMI-corrected Cornell voltage and Sokolow-Lyon voltage criteria provided better results for detection of echocardiographic LVH as compared with unadjusted electrocardiographic parameters. Cornell voltage index, but not Sokolow-Lyon index, was associated with an increased risk of cardiovascular events (and all-cause mortality). The adjusted risk of cardiovascular events related to one-standard deviation increment of BMI-corrected Cornell voltage was similar to that conferred by the uncorrected criterion in the total population, but outperformed in obese participants. These findings show that correction for BMI may improve the diagnostic accuracy of Cornell voltage index in detecting LVH and prediction of cardiovascular mortality in obese individuals.

Graphene quantum dots decorated electrospun TiO2 nanofibers as an effective photoanode for dye sensitized solar cells

In this study, graphene quantum dots (GQDs) are prepared with an average size of ~15nm by a top down approach using carbon nanofibers (CNFs) to improve the photovoltaic performance of DSSCs. The titanium isopropoxide (Ti(OPr)4)/PVP precursor solution is used to get TiO2 NFs by electrospinning technique and then they are decorated with the prepared GQDs. First, the prepared GQDs are confirmed by XRD, Raman, TRPL, DLS, UV–vis, and PL Spectroscopy. The presence of GQDs onto TiO2 NFs is also confirmed by XRD, Raman spectroscopy and EDX studies. The surface morphology and the presence of GQDs onto TiO2 NFs are confirmed by SEM and TEM analysis. The optical properties of GQDs–TiO2 NFs are studied by UV–vis and PL spectroscopy. Finally, the dye sensitized solar cell is fabricated using GQDs decorated TiO2 nanofibers as the photoanode and standard Pt (Dyesol Ltd.) as the counter electrode and 0.5M 1-butyl-3-methylimidazolium iodide, 0.5M LiI, 0.05M I2, 0.5M 4-tertbutylpyridine, in acetonitrile as the electrolyte. A dye-sensitized solar cell (DSSC) with a photoanode based on GQDs–TiO2 NFs exhibited a high energy conversion efficiency of 6.22%, than the DSSC based on pure TiO2 NFs photoelectrode (4.81%), accompanied by an increment in both short-circuit photocurrent density and open-circuit voltage. The overall improvement in PCE is ~29.31% for GQDs decorated TiO2 NFs which is higher than other reported systems. The better photogenerated electron transfer ability, reduced charge recombination, increased dye adsorption, and an effective harvesting of visible light, which together added to an improvement in PCE. The stability test is performed for the DSSCs over a period of 30 days (720h) under one sun soaking, where GQDs decorated TiO2 NFs DSSCs is seen to retain ~99% of its initial normalized efficiency, thereby making it a viable option for practical applications.

High‐voltage compliant microelectrode array drivers for intracortical microstimulation

SummaryWe present in this paper two low‐power high‐impedance microelectrode array drivers (MEDs) dedicated for visual intracortical microstimulation. These output stages of a new microstimulator are highly configurable and able to deliver higher compliance voltage (20 V for anodic and cathodic phases) across microelectrode‐tissue interface impedance compared with previously reported designs. Each MED is featured with a high‐voltage switch‐matrix, 3.3 V/20 V current mirrors, an on‐chip 32‐bit serial‐in parallel‐out shift register, and the new forbidden state logic circuits. Both systems are able to deliver eight bipolar or 16 monopolar stimulation simultaneously. The first MED is able to deliver one stimulation current level and the second one provides four different current amplitudes simultaneously to 16 electrodes. Two microchips have been designed and fabricated using Teledyne DALSA 0.8 µm 5V/ 20v double‐diffused metal‐oxide‐semiconductor field‐effect transistor (Teledyne DALSA Semiconductor, Bromont, Québec, Canada) technology to meet the required high‐voltage compliance. The nominal values of largest supply voltages are ±10 V. The maximum stimulation current per input channel is 400 μA and per output channel through an emulated microelectrode impedance of 100 kΩ is 100 μA. The measured output compliance voltage is 10 V/phase (anodic or cathodic) for the specified supply voltages. Increment of supply voltages to ±13 V allows 220 μA stimulation current per output channel enhancing the output compliance voltage up to 20 V/phase. The measured quiescent power consumptions of the proposed microelectrode array drivers are 316 and 735 μW, respectively. Post‐layout simulation and measurement results of two MEDs and comparison with other designs have been reported in this paper. Copyright © 2015 John Wiley & Sons, Ltd.

The novel preparation method of high-performance thermochromic vanadium dioxide thin films by thermal oxidation of vanadium-stainless steel co-sputtered films

The preparation of high-performance thermochromic vanadium dioxide films and the assurance of its batch-to-batch uniformity is technically difficult since the oxidation number of vanadium ranges from +2 to +5 under various reducing or oxidizing atmospheres at elevated temperatures. In this work, the vanadium dioxide films were fabricated by thermal-oxidation of vanadium and stainless-steel (mainly containing Fe, Cr, Ni) co-sputtered thin films at elevated temperature under air atmosphere. The as-prepared vanadium oxide films were further characterized by four-point probe measurement, ellipsometry, grazing incidence X-ray diffraction (XRD) and X-ray photoelectron spectroscopic (XPS) analysis. Our experiments demonstrated that with the use of an SS target we could efficiently deposit the magnetic atoms (iron and nickel) and nonmagnetic Cr elements into vanadium films in stable plasma conditions. The shift of the main peak of XRD patterns to smaller angles showed that Fe, Cr, and Ni elements were successfully doped into vanadium oxide films. These dopants depressed the vanadium atoms from over-oxidization during the heat treatment. As a result, a noticeable amount of VO2(M) crystalline phase (higher V(+4)/V(+5) ratios) was obtained from the as-prepared films accompanied with the increment of the SS target voltage. Consequently, the formation of V6O13, V3O7, and V2O5 vanadium oxides crystallites was significantly minimized after the thermal-oxidation stage, which gave the as-prepared films outstanding thermochromic-responsive properties. The proposed scheme is proved to be a novel fabrication technique to prepare high-performance thermochromic vanadium dioxide films with the assurance of batch-to-batch uniformity.

Ion behavior and interelectrode breakdown voltage of a drift tube**Supported by Financial Support from the National Major Scientific Instruments and Equipment Development Special Funds (2011YQ030113), National Recruitment Program of Global Experts (NRPGE), the Hundred Talents Program of Sichuan Province (HTPSP) and the Startup Funding of Sichuan University for Setting up the Research Center of Analytical Instrumentation

We experimentally studied ion behavior and interelectrode breakdown voltage. The ion behavior of a drift tube directly influences the detection of ion intensity, and then influences the detection sensitivity of a system. Interelectrode voltage and pressure directly influence the ion behavior. Gas discharge between electrodes influences the adjustments required for interelectrode voltage. The experimental results show: ion intensity increases exponentially with the increment of voltage between drift electrodes; ion intensity decreases exponentially as pressure increases; with the increment of pressure, the breakdown voltage at first decreases, and then increases; ion injection has a significant influence on breakdown voltage, and this influence depends on the pressure and shapes of the electrodes. We explain the results above through assumptions and by mathematical methods.

Semiconductor to metallic transition in bulk accumulated amorphous indium-gallium-zinc-oxide dual gate thin-film transistor

We investigated the effects of top gate voltage (VTG) and temperature (in the range of 25 to 70 oC) on dual-gate (DG) back-channel-etched (BCE) amorphous-indium-gallium-zinc-oxide (a-IGZO) thin film transistors (TFTs) characteristics. The increment of VTG from -20V to +20V, decreases the threshold voltage (VTH) from 19.6V to 3.8V and increases the electron density to 8.8 x 1018cm−3. Temperature dependent field-effect mobility in saturation regime, extracted from bottom gate sweep, show a critical dependency on VTG. At VTG of 20V, the mobility decreases from 19.1 to 15.4 cm2/V ⋅ s with increasing temperature, showing a metallic conduction. On the other hand, at VTG of - 20V, the mobility increases from 6.4 to 7.5cm2/V ⋅ s with increasing temperature. Since the top gate bias controls the position of Fermi level, the temperature dependent mobility shows metallic conduction when the Fermi level is above the conduction band edge, by applying high positive bias to the top gate.

Comparison of Output Current Ripple in Single and Dual Three-Phase Inverters for Electric Vehicle Motor Drives

The standard solution for the traction system in battery powered electric vehicles (EVs) is a two-level (2L) inverter feeding a three-phase motor. A simple and effective way to achieve a three-level (3L) inverter in battery-supplied electric vehicles consists of using two standard three-phase 2L inverters with the open-end winding connection of standard three-phase ac motors. The 3L inverter solution can be usefully adopted in EVs since it combines several benefits such as current ripple reduction, increment of phase motor voltage with limited voltage ratings of the two battery banks, improvement in system reliability, etc. The reduction in current ripple amplitude is particularly relevant since it is a source of electromagnetic interference and audio noise from the inverter-motor power connection cables and from the motor itself. By increasing the inverter switching frequency the ripple amplitude is reduced, but the drive efficiency decreases due to the proportionally increased switching losses. In this paper the peak-to-peak ripple amplitude of the dual-2L inverter is evaluated and compared with the corresponding ripple of the single-2L inverter, considering the same voltage and power motor ratings. The ripple analysis is carried out as a function of the modulation index to cover the whole modulation range of the inverter, and the theoretical results are verified with experimental tests carried out by an inverter-motor drive prototype.

A Simple Capacitor Voltage Balancing Method with a Fundamental Sorting Frequency for Modular Multilevel Converters

A Fundamental Frequency Sorting Algorithm (FFSA) is proposed in this paper to balance the voltages of floating dc capacitors for Modular Multilevel Converters (MMCs). The main idea is to change the sequences of the CPS-PWM carriers according to the capacitor voltage increments during the previous fundamental period. Excessive frequent sorting is avoided and many calculating resources are saved for the controller. As a result, more sub-modules can be dealt with. Furthermore, it does not need to measure the arm currents. Therefore, the communication between the controllers can be simplified and the number of current sensors can be reduced. Moreover, the proposed balancing method guarantees that all of the switching frequencies of the sub-modules are equal to each other. This is quite beneficial for the thermal design of the sub-modules and the lifetime of the power switches. Simulation and experimental results acquired from a 9-level prototype verify the viability of the proposed balancing method.

50 nm AlxOy ReRAM program 31% energy, 1.6× endurance, and 3.6× speed improvement by advanced cell condition adaptive verify-reset

Two verify-reset schemes are proposed to improve the program energy, endurance and speed of 50nm AlxOy ReRAM cells. Both of the proposed schemes improve the verify-reset program by adapting the program voltage and pulse width to the variation of ReRAM cell filament status during the verify-reset. In this paper, first, the reset resistance and cell endurance are compared using different reset voltages and reset pulse widths. Then, two proposed verify-reset schemes are introduced independently. The first proposed scheme controlled reset voltage (Vreset) increment demonstrates 32% program energy reduction and 6.7× program speed increase. In this scheme, the reset voltage stress is increased from −1.5V to −1.65V, only when the reset-tries fail continuously during verify-reset (hard-to-reset). The second proposed scheme set-before-reset applies the set pulse during verify-reset, to convert the filament from a hard-to-reset state to an easy-to-reset state. With this approach, 31% program energy reduction, 1.6× program endurance and 3.6× program speed increase can be obtained simultaneously.

ZnO nanorod arrays pre-coated with DCJTB dye for inverted type hybrid solar cells incorporating P3HT donor

This paper reports the utilization of a fluorescent dye, 4-(dicyanomethylene)-2-tert-butyl-6-(1,1,7,7-tetra-methyljulolidyl-9-enyl)-4H-pyran (DCJTB) as the surface modifier of ZnO nanorods for inverted type hybrid solar cell application. The DCJTB solution with concentrations of 10 and 15 mM was spin-coated onto the ZnO nanorod arrays grown on the fluorine-doped tin oxide glass substrate pre-coated with ZnO seed layer. The poly(3-hexylthiophene-2,5-diyl) (P3HT) as electron donor was then spin-coated onto ZnO nanorod arrays, followed by the deposition of silver as anode using magnetron sputtering technique. A large portion of pre-coated DCJTB has been redissolved and washed out in the subsequent P3HT spin coating process. Nevertheless, the increase in hydrophobicity of ZnO nanorod arrays pre-coated with DCJTB leads to improved interfacial compatibility between ZnO nanorods and P3HT. As a result, the enhanced exciton dissociation efficiency at the ZnO nanorods/P3HT interfaces results in the increment of short circuit current density and open circuit voltage. In addition, DCJTB residue covering the FTO exposed area could reduce the hole leakage current from P3HT to FTO, hence resulting in higher open circuit voltage. The device with the optimum DCJTB pre-coating concentration of 10 mM exhibited almost two times increase in power conversion efficiency as compared to that of pristine device.

Hysteresis loop and cross-talk of organic memristive devices

Similarly to inorganic memristors, the organic memristive devices reveal a variation of the hysteresis loop upon the frequency of the applied bias voltage. The on/off ratio of the conductivity increases from 4 to 1000 times for the variation of time delay (equilibration after the application of the voltage increment) from 5 to 60s. Being implemented in multi-element electrical circuits memristive devices provide a cross-talk, leading to an equilibration trend of the conductivity values. This effect is mainly related to the formation of stable signal pathways.

On the frequency dependent negative dielectric constant behavior in Al/Co-doped (PVC+TCNQ)/p-Si structures

The dielectric properties, electric modulus and ac electrical conductivity (σac) of Al / Co -doped (PVC+TCNQ)/p- Si structures have been investigated in the wide frequency and voltage range of 0.5 kHz–3 MHz and (-4 V)–(9 V), respectively, using the capacitance-voltage (C–V) and conductance-voltage (G/ω–V) measurements at room temperature. The real and imaginary parts of dielectric constant (ε′, ε″), loss tangent ( tan δ), σac and the real and imaginary parts of electric modulus (M′, M″) were found strongly function of frequency and applied voltage especially at low frequencies. The ε′–V plot shows an anomalous peak in the forward bias region due to the series resistance (Rs), surface states (Nss) and interfacial layer (PVC+TCNQ) effects for each frequency and then it goes to negative values known as negative dielectric constant (NDC) at low frequencies (f ≤ 70 kHz). Such observation of NDC is important result because it implies that an increment of bias voltage produces a decrease in the charge on the electrodes. The amount of negativity ε′ value increases with decreasing frequency and this decrement in the NDC corresponds to the increment in the ε″.

Distribution Network Loss Minimization via Simultaneous Distributed Generation Coordination with Network Reconfiguration

The power loss is one of the constraints to achieve a more reliable and economic distribution system. The installation of distributed generation (DG) in the existing problem is one of the available solutions; however, the random use of DGs will actually worsen the problem. Moreover, the network reconfiguration is another approach for losses reduction. This method works by controlling the tie and sectionalizes switches to change the topology of the distribution network. Nevertheless, this process must maintain the system in radial network due to protection scheme. Hence, a suitable technique is needed to tackle the DG coordination (DG output and DG location) and network reconfiguration problems. This paper presents a new hybrid optimization technique based on Artificial Bee Colony and Artificial Immune System algorithm to determine the optimal DG coordination with network reconfiguration for multiple DG simultaneously. The effectiveness of the proposed method is demonstrated on a 33-bus distribution test system and validated with various test cases. The results prove that the approach to determine DG coordination with network reconfiguration simultaneously reduces the power losses by 95.10 % from the initial power losses. Furthermore, the proposed method gives a better percentage of minimum voltage increment and improvement of stability index, which is 9.14 % and 0.0428, respectively.

An investigation on the photoelectrochemical properties of dye-sensitized solar cells based on graphene–TiO2 composite photoanodes

The graphene–TiO2 nanocomposite has been prepared by mixing graphene oxide (GO) and tetra-n-butyl titanate (TBT) followed by the facile hydrothermal process when the reduction of GO to reduced graphene oxide (RGO) and the hydrolysis of TBT to TiO2 happen. Characterization of the graphene–TiO2 nanostructures is investigated in detail by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and Raman spectroscopy. A dye-sensitized solar cell (DSSC) based on graphene–TiO2 composite photoelectrode exhibits a high energy conversion efficiency of 4.28%, compared with a DSSC based on pure TiO2 photoelectrode (3.11%), accompanied by an increment in both short-circuit photocurrent density and open-circuit voltage. The significant enhancement in performance of DSSC is investigated through intensity-modulated photovoltage spectroscopy, intensity-modulated photocurrent spectroscopy, and electrochemical impedance spectroscopy. It is found that the incorporation of two-dimensional graphene nanosheets in the TiO2 electrodes is the key factor leading to the improved photogenerated electron transfer ability and reduced charge recombination.

High Performance Process Variations Aware Technique for Sub-threshold 8T-SRAM Cell

The demand of low power high density integrated circuits is increasing in modern battery operated portable systems. Sub-threshold region of MOS transistors is the most desirable region for energy efficient circuit design. The operating ultra-low power supply voltage is the key design constraint with accurate output performance in sub-threshold region. Degrading of the performance metrics in Static random access memory (SRAM) cell with process variation effects are of major concern in sub-threshold region. In this paper, a bootstrapped driver circuit and a bootstrapped driver dynamic body biasing technique is proposed to assist write operation which improves the write-ability of sub-threshold 8T-SRAM cell under process variations. The bootstrapped driver circuit minimizes the write delay of SRAM cell. The bootstrapped driver dynamic body bias increases the output voltage levels by boosting factor therefore increasing in switching threshold voltage of MOS devices during hold and read operation of SRAM latch. The increment in threshold voltage improves the static noise margin and minimizing the process variation effects. Monte-Carlo simulation results with 3 $$\sigma $$ ? Gaussian distributions show the improvements in write delay by 11.25 %, read SNM by 12.20 % and write SNM by 12.57 % in 8T-SRAM cell under process variations at 32 nm bulk CMOS process technology node.

Role of Ultrathin Metal Fluoride Layer in Organic Photovoltaic Cells: Mechanism of Efficiency and Lifetime Enhancement

Although rapid progress has been made recently in bulk heterojunction organic solar cells, systematic studies on an ultrathin interfacial layer at the electron extraction contact have not been conducted in detail, which is important to improve both the device efficiency and the lifetime. We find that an ultrathin BaF2 layer at the electron extraction contact strongly influences the open-circuit voltage (Voc ) as the nanomorphology evolves with increasing BaF2 thickness. A vacuum-deposited ultrathin BaF2 layer grows by island growth, so BaF2 layers with a nominal thickness less than that of single-coverage layer (≈3 nm) partially cover the polymeric photoactive layer. As the nominal thickness of the BaF2 layer increased to that of a single-coverage layer, the Voc and power conversion efficiency (PCE) of the organic photovoltaic cells (OPVs) increased but the short-circuit current remained almost constant. The fill factor and the PCE decreased abruptly as the thickness of the BaF2 layer exceeded that of a single-coverage layer, which was ascribed to the insulating nature of BaF2 . We find the major cause of the increased Voc observed in these devices is the lowered work function of the cathode caused by the reaction and release of Ba from thin BaF2 films upon deposition of Al. The OPV device with the BaF2 layer showed a slightly improved maximum PCE (4.0 %) and a greatly (approximately nine times) increased device half-life under continuous simulated solar irradiation at 100 mW cm(-2) as compared with the OPV without an interfacial layer (PCE=2.1 %). We found that the photodegradation of the photoactive layer was not a major cause of the OPV degradation. The hugely improved lifetime with cathode interface modification suggests a significant role of the cathode interfacial layer that can help to prolong device lifetimes.

Prediction of Neutron Yield of IR-IECF Facility in High Voltages Using Artificial Neural Network

Artificial neural network (ANN) is applied to predict the number of produced neutrons from IR-IECF device in wide discharge current and voltage ranges. Experimentally, discharge current from 20 to 100 mA had been tuned by deuterium gas pressure and cathode voltage had been changed from −20 to −82 kV (maximum voltage of the used supply). The maximum neutron production rate (NPR) of 1.46 × 107 n/s had occurred when the voltage was −82 kV and the discharge current was 48 mA. The back-propagation algorithm is used for training of the proposed multilayer perceptron (MLP) neural network structure. The obtained results show that the proposed ANN model has achieved good agreement with the experimental data. Results show that NPR of 1.855 × 108 n/s can be achieved in voltage and current of 125 kV and 45 mA, respectively. This prediction shows 52% increment in maximum voltage of power supply. Also, the optimum discharge current can increase 1270% NPR.

An RF energy harvester system using UHF micropower CMOS rectifier based on a diode connected CMOS transistor.

This paper presents a new type diode connected MOS transistor to improve CMOS conventional rectifier's performance in RF energy harvester systems for wireless sensor networks in which the circuits are designed in 0.18 μm TSMC CMOS technology. The proposed diode connected MOS transistor uses a new bulk connection which leads to reduction in the threshold voltage and leakage current; therefore, it contributes to increment of the rectifier's output voltage, output current, and efficiency when it is well important in the conventional CMOS rectifiers. The design technique for the rectifiers is explained and a matching network has been proposed to increase the sensitivity of the proposed rectifier. Five-stage rectifier with a matching network is proposed based on the optimization. The simulation results shows 18.2% improvement in the efficiency of the rectifier circuit and increase in sensitivity of RF energy harvester circuit. All circuits are designed in 0.18 μm TSMC CMOS technology.