Frequency Of AC Signal Research Articles

Performance of the Au/MgO/Ni photovoltaic devices

A 100μm thick MgO film is used to design a metal semiconductor metal device. The device is characterized by means of current voltage characteristics in the dark and under various light energies in the photon energy range of 3.70–2.15eV. A photovoltaic effect presented by an open circuit voltage of 0.12–0.47V, short circuit current density of 3.9–10.5μA/cm2, quantum efficiency of 0.662–0.052, and responsivity of 0.179–0.024A/W under photoexcitation optical power of 2.2–28.2μW is observed. The device was also tested as a UV optical communication component. The test revealed a wide range of tunability and sensitivity for microwave resonant frequencies of 0.5 and 2.9GHz. The differential resistance of the device exhibited different values at each applied ac signal frequency. When the frequency is fixed, the illuminated to the dark current ratio remained constant for all signal powers in the range of 0.00–20.0dBm.

The Research and Application Based on Removable High-Precision DC Weak Current Sensor

sensor used in DC ground fault detection system according to measurement method can be divided into low frequency AC signal detecting and DC signal detecting of leakage current . It greatly affect the accuracy of the earth fault signal because of the existence of capacitance in the detecting of low frequency AC signal and it doesnt have online measurement DC current sensor in the market when we want to measure load leakage current. Caliper DC ammeter cant meet the requirements in DC system ground fault diction in terms of resolution, accuracy, range, on-line installation and on-line measurement.

미세유체칩내 electrode의 opening window형태에 따른 유전전기영동력 특성 규명

Dielectrophoresis(DEP) is useful in manipulation and separation of micro-sized particles including biological samples such as bacteria, blood cells, and cancer cells in a micro-fluidic device. Especially, those separation and manipulation techniques using DEP in combination of micro fabrication technique have been researched more and more. Recently, it is revealed that a window structure of insulating layer in microfluidic DEP chip is key role in trap of micro-particles around the window structure. However, the trap phenomenon-driven by DEP force gradient did not fully understand and is still illusive. In this study, we characterize the trap mechanism and efficiency with different shapes of window in a microfluidic DEP chip. To do this characterization, we fabricated 4 different windows shapes such as rhombus, circle, squares, and hexagon inside a micro-fluidic chip, and performed micro-sized particles manipulation experiments as varying the frequency and voltage of AC signal. Moreover, the numerical simulation with the same parameters that were used in the experiment was also performed in order to compare the simulation results and the experimental results. Those comparison shows that both results are closely matched. This study may be helpful in design and development of microfluidic DEP chip for trapping micro-scaled biological particle.

Fabrication of Al/MgO/C and C/MgO/InSe/C tunneling barriers for tunable negative resistance and negative capacitance applications

Abstract In this work, the design and characterization of magnesium oxide based tunneling diodes which are produced on Al and InSe films as rectifying substrates are investigated. It was found that when Al thin films are used, the device exhibit tunneling diode behavior of sharp valley at 0.15 V and peak to valley current ratio (PVCR) of 11.4. In addition, the capacitance spectra of the Al/MgO/C device show a resonance peak of negative capacitance (NC) values at 44.7 MHz. The capacitance and resistance–voltage characteristics handled at an ac signal frequency of 100 MHz reflected a build in voltage ( V bi ) of 1.29 V and a negative resistance (NR) effect above 2.05 V. This device quality factor ( Q )–voltage response is ~10 4 . When the Al substrate is replaced by InSe thin film, the tunneling diode valley appeared at 1.1 V. In addition, the PVCR, NR range, NC resonance peak, Q and V bi are found to be 135, 0.94–2.24 and 39.0 MHz, ~10 5 and 1.34 V, respectively. Due to the wide differential negative resistance and capacitance voltage ranges and due to the response of the C/MgO/InSe/C device at 1.0 GHz, these devices appear to be suitable for applications as frequency mixers, amplifiers, and monostable–bistable circuit elements (MOBILE).

Heating strategies for Li-ion batteries operated from subzero temperatures

Electric vehicles (EVs) suffer from significant driving range loss in subzero temperature environments due to reduced energy and power capability of Li-ion batteries as well as severe battery degradation due to Li plating. Preheating batteries to room temperature is an essential function of an effective battery management system. The present study employs an electrochemical–thermal coupled model to simulate, for the first time, the process of heating Li-ion batteries from subzero temperatures. Three heating strategies are proposed and compared using battery power, namely self-internal heating, convective heating and mutual pulse heating, as well as one strategy (AC heating) using external power. Their advantages and disadvantages are discussed in terms of capacity loss, heating time, system durability, and cost. For heating using battery power, model predictions reveal that Li-ion batteries can be heated from −20°C to 20°C at the expense of only 5% battery capacity loss using mutual pulse heating with high-efficiency dc–dc converter, implying considerable potential for improved driving range of EVs in cold weather conditions. Moreover, the heating time can be reduced to within 2min by increasing cell output power using convective heating and mutual pulse heating. For external power heating, high frequency AC signal with large amplitude is a preferred choice, offering both high heating power and improved battery cycle life.

Temperature dependent transport and dielectric properties of cadmium titanate nanofiber mats

We investigate electrical and dielectric properties of cadmium titanate (CdTiO3) nanofiber mats prepared by electrospinning. The nanofibers were polycrystalline having diameter ∼50 nm-200 nm, average length ∼100 μm and crystallite size ∼25 nm. Alternating current impedance measurements were carried out from 318 K – 498 K. The frequency of ac signal was varied from 2 – 105 Hz. The complex impedance plots revealed two depressed semicircular arcs indicating the bulk and interface contribution to overall electrical behavior of nanofiber mats. The bulk resistance was found to increase with decrease in temperature exhibiting typical semiconductor like behavior. The modulus analysis shows the non-Debye type conductivity relaxation in nanofiber mats. The ac conductivity spectrum obeyed the Jonscher power law. Analysis of frequency dependent ac conductivity revealed presence of the correlated barrier hopping (CBH) in nanofiber mats over the entire temperature range.

Multi-dimensional admittance spectroscopy

We introduce the concept of multi-dimensional admittance spectroscopy capable of characterizing thin-film diode structures in both the (standard) transversal and lateral directions. This extends the capabilities of standard admittance spectroscopy based on the model of leaky capacitor with area defined by the metal contacts. In our approach, the ac signal spreads in the lateral directions far beyond the contact area. The spreading range defines the area of the effective capacitor determining the measured capacitance and conductance. It depends on the ac signal frequency, dc bias, and various structure parameters. A phenomenological description of these dependencies here is verified numerically using our original software to model the distributed admittance via finite element circuits. We analyze the case of photovoltaic devices and show how the multi-dimensional admittance spectroscopy is sensitive to lateral nonuniformity of the system, particularly to the presence of shunts and weak diodes and their location. In addition, the proposed characterization provides information about the system lump parameters, such as sheet resistance, shunt resistance, and open circuit voltage.

Frequency dependence of potentials of minimum capacitance for electrodes of copper subgroup metals in alkali halide melts

The electrochemical impedance technique was use to obtain the potentials of the minimum capacitance of Cu, Ag, and Au electrodes in chlorides, bromides, and iodides of sodium, potassium, and cesium. Their dependence on the nature of the metal and electrolyte, temperature and ac signal frequency is studied. It is shown that the potential of the minimum capacitance tends at a decrease in the frequency to the zero charge potential measured under similar conditions. An assumption is ventured that the cause of this may be specific adsorption of halide ions on the electrode in the form of negatively charged dihalide complexes. It is found that in the systems where two minimums are observed, a decrease in the spacing between the cathodic and anodic minimums correlates with an increase in the strength of the metal-adsorbate bond.

Observation of peripheral charge induced low frequency capacitance-voltage behaviour in metal-oxide-semiconductor capacitors on Si and GaAs substrates

We report on experimental observations of room temperature low frequency capacitance-voltage (CV) behaviour in metal oxide semiconductor (MOS) capacitors incorporating high dielectric constant (high-k) gate oxides, measured at ac signal frequencies (2 kHz to 1 MHz), where a low frequency response is not typically expected for Si or GaAs MOS devices. An analysis of the inversion regions of the CV characteristics as a function of area and ac signal frequency for both n and p doped Si and GaAs substrates indicates that the source of the low frequency CV response is an inversion of the semiconductor/high-k interface in the peripheral regions outside the area defined by the metal gate electrode, which is caused by charge in the high-k oxide and/or residual charge on the high-k oxide surface. This effect is reported for MOS capacitors incorporating either MgO or GdSiOx as the high-k layers on Si and also for Al2O3 layers on GaAs(111B). In the case of NiSi/MgO/Si structures, a low frequency CV response is observed on the p-type devices, but is absent in the n-type devices, consistent with positive charge (>8 × 1010 cm−2) on the MgO oxide surface. In the case of the TiN/GdSiOx/Si structures, the peripheral inversion effect is observed for n-type devices, in this case confirmed by the absence of such effects on the p-type devices. Finally, for the case of Au/Ni/Al2O3/GaAs(111B) structures, a low-frequency CV response is observed for n-type devices only, indicating that negative charge (>3 × 1012 cm−2) on the surface or in the bulk of the oxide is responsible for the peripheral inversion effect.

Investigation of the electrical parameters of Ag/p-TlGaSeS/C Schottky contacts

Abstract p-type TlGaSeS single crystal was used to fabricate a Schottky device. Silver and carbon metals were used as the Ohmic and Schottky contacts, respectively. The device which displayed wide RF band at 13.200 and narrow band at 62.517 kHz with Q value of 1.4 and of 6.3 × 104, respectively, is characterized by means of current (I)–voltage (V), capacitance (C)–voltage characteristics as well as capacitance–frequency (f) characteristics. The device series resistance, ideality factor and barrier height are determined from the I–V curve as 35.8 MΩ, 1.2 and 0.74 eV, respectively. The apparent acceptor density and the build in voltage of the device increased with increasing ac signal frequency. The high Q value, observed at 62.517 kHz, indicated a much lower rate of energy loss relative to the stored energy of the device. The energy loss (Q−1) is much less than 0.001% of the stored value. The device was tested and found to remain at the same mode of resonance for several hours. It never switched or ceased unless it was tuned off.

Dynamical and passive characteristics of the Ag/TlGaSeS/Ag RF resonators

AbstractAg contacts on the surface of the TlGaSeS single crystals are observed to exhibit Schottky characteristics. The ideality factor of the Ag/ TlGaSeS/Ag device decreased from 5.2 to 1.3 by the reduction of series resistance effect on the I‐V characteristics. Cheung's model analysis revealed a series resistance and barrier height of 40.6 KΩ and 0.32 V, respectively. The device was run on the passive mode by injection with an alternating ac signal of variable frequency in the frequency range of 0‐120 MHz and recoding the device capacitance. Several resonance‐antiresonance positions in the range of 27‐350 KHz were observed. The tangent loss factor of the passive device was observed to decrease with increasing frequency. It exhibited a very low loss value of the order of 10−5 at 120 MHz. Such property is a characteristic of high performance tunable device being suitable as processor clock controller.

(Invited) Can Metal/Al2O3/In0.53Ga0.47As/InP MOSCAP Properties Translate to Metal/Al2O3/In0.53Ga0.47As/InP MOSFET Characteristics

In this paper we present the electrical characteristics of Metal/Al2O3/In0.53Ga0.47As/InP MOS capacitor (MOSCAP) structures formed using a relatively straightforward capacitor process flow and for MOSCAPs which experience the full process flow of an In0.53Ga0.47As n channel MOSFET. From analysis of the capacitance-voltage response over a range of ac signal frequencies fixed oxide charge densities and interface state concentrations are determined for the MOSCAP structures and the impact of forming gas annealing on oxide and interface state densities is presented. The MOSCAP results are compared to the properties of fully processed metal/Al2O3/In0.53Ga0.47As/InP n channel MOSFETs, and the results indicate that the findings from the MOSCAPS do translate to the measured InGaAs MOSFET characteristics.

Design of the ultra low-power synchronizer using ADCL buffer for adiabatic logic

The adiabatic dynamic CMOS logic (ADCL) has been studied to reduce the power dissipation in conventional CMOS logic. The clock signal of logic circuits should be synchronized with the AC power source to maintain adiabatic charging/discharging with low power for the ADCL. In this paper, an ultra low-power synchronizer using ADCL buffer is proposed. The ADCL buffer has been designed using features of automatic synchronization between AC signal and output of gate stage. Power consumptions of the proposed ADCL synchronizer are found to be 99.4nW at best case and 109.8nW at worst case, when AC signal and clock frequencies are 110MHz and 10MHz, respectively.

Effect of conductivity and frequency on detection of heterogeneities in solid/liquid interfaces using local electrochemical impedance: Theoretical and experimental study

This short communication demonstrates, by solving the Laplace equation with proper boundary conditions (BC) using finite element method (FEM), that it is not possible to establish a correlation between what happens in the electrolyte near an active boundary and what really occurs at the actual boundary if adequate ranges of electrolyte conductivity and input AC signal frequency are not selected, especially when inhomogeneities approximated by Neumann BC are present. Experimental evidence obtained by local electrochemical impedance mapping (LEIM) supports the theoretical results.

Capacitance of a polycrystalline silver electrode in Na, K, and Cs bromide melts

The differential capacitance of the polycrystalline silver-NaBr, KBr, or CsBr salt melt interface is measured. At high and medium ac signal frequencies, the potential dependence of the capacitance of all salts represents a parabolic curve with one minimum. At frequencies of several or several tens of hertzs, an additional minimum appears in the anode potential region; it decreases to zero with increasing temperature. The temperature and frequency dependences of the cathode and anode minima are analyzed.

The Reliability of LTPS-TFTs Alternately Stressed in OFF Region

The reliability of n-channel low temperature poly-Si thin film transistors (LTPS TFTs), which are dynamically stressed in OFF region with drain zero biased and source grounded, is investigated. Rectangular pulses with different parameters such as rising time, falling time or frequency are imposed to the gate electrode to examine the degradation. It is observed that the degradation depends strongly on the rising time and frequency of ac signal. As the gate voltage switches in the rising period, the accumulated holes should be swept out and flow into source or drain terminals, owing to the floating body structure of TFTs. Therefore, there is high electric field at the rising period of transient stress, which enhances the degradation. A degradation model is proposed to explain the degradation mechanism of LTPS TFTs on the basis of the flowing direction of the sampling current Id, and demonstrated by two electrical measuring items, saturation forward & reverse Id-Vg transfer curves and C-V curves.

Electrohydrodynamic‐mediated dielectrophoretic separation and transport based on asymmetric electrode pairs

This paper presents a system for continuous separation and transport of micron and submicron particles in fluidic environment based on dielectrophoretic fractionation in concert with AC electrothermal (AC ET)-induced fluidic pumping action. In this system, high frequency AC signals are used to energize asymmetric electrode pairs. AC ET-driven fluidic pumping is utilized as an alternative to the commonly used external pressure-driven fluid flow. Distinct collection sites for negative-dielectrophoretic and positive-dielectrophoretic particle populations are identified. The coupling effects of dielectrophoretic force and viscous drag from AC ET fluid flow on particle motions are investigated theoretically and numerically. We demonstrate that these two forces can be efficiently coupled to achieve continuous separation and transport of particle mixture in a fluidic medium when the dielectric properties of the particles and the fluidic environment are different. The combination of dielectrophoretic separation and AC ET pumping function provides a promising approach to further miniaturize and integrate these mechanisms into lab-on-chip devices.

Magnetoimpedance, magnetoresistance, and magnetic properties of nanometric CMR manganites

The effects of nanometric grain size (ϕ=14–28nm) modulation on the behavior of magnetoimpedance (MI), magnetoresistance, and magnetic properties of chemically synthesized a series of single-phase soft ferromagnetic nanocrystalline colossal magnetoresistance La0.7Sr0.3MnO3 (LSMO) manganites at room temperature have been reported. From the frequency and magnetic filed dependent MI measurement it is found that the MI percent increases with the increase in nanometric grain size (ϕ) for this series of samples. This behavior has been explained in the light of classical electrodynamics, which relates this effect with the dependency of skin depth on external magnetic field and applied ac signal frequency. Room temperature low field magnetoresistance (LFMR) study of this series of LSMO nanoparticles has also been carried out for comparison.

AC Conductance of DNA molecule at low temperature

Using nonequilibrium Green's function technique, we have investigated the ac conductance of poly(C)-poly(G) DNA molecule at low temperature. Our results indicate that thermal fluctuations of DNA hopping energy will play a profound role for the ac conductance. It smoothes out the conductance curves at high ac signal frequency while does not suppress it substantially. The dependences of the ac conductance on the density of states in the contacts, ac signal frequency and temperature are also investigated.

Effect of nanometric grain size on room temperature magnetoimpedance, magnetoresistance, and magnetic properties of La0.7Sr0.3MnO3 nanoparticles

In this paper we have investigated the effect of nanometric grain size modulation on the behavior of magnetoimpedance (MI), magnetoresistance, and magnetic properties of a series of single-phase nanocrystalline colossal magnetoresistance La0.7Sr0.3MnO3 (LSMO) manganites all synthesized through chemical route “pyrophoric reaction process.” MI measurements were carried out at room temperature (T=300K) in the ac signal frequency (f) range of 40kHz-110MHz and in dc magnetic field (H) range of −2.5kOe<H<+2.5kOe, respectively. The experimental results show that MI% increases with the increase in nanometric grain size (ϕ) for this series of samples. This behavior can be explained in the light of classical electrodynamics, which relates this effect with the dependency of skin depth on external magnetic field and applied ac signal frequency. Interestingly, MI of about 92% was obtained for the 28nm LSMO sample at a frequency (f) of 10MHz and at H=2.5kOe. The same sample also showed a maximum MI sensitivity of about 1%/Oe near 60Oe dc magnetic field at f=10MHz. Magnetization measurements were carried out in the applied magnetic field range of −5kOe<H<+5kOe and the experimental results reveal that spontaneous magnetization decreases with decrease in particle size. These nanometric LSMO samples also showed a paramagnetic-ferromagnetic transition near TC=360K. For comparison, we have also presented room temperature low-field magnetoresistance (LFMR) study of this series of LSMO nanoparticles. This study reveals that within this particle size range, 14–28nm, LFMR decreases with decrease in particle size, which in fact mimics the variation of MI with particle size.