Absolute Voltage Research Articles

Voltage Cycling Induced Losses in Electrochemically Active Surface Area and in H2/Air-Performance of PEM Fuel Cells

The influence of voltage cycling profiles on the degradation of MEAs (membrane electrode assemblies) for PEM (proton exchange membrane) fuel cells was investigated using MEAs with carbon supported catalysts. The loss of electrochemically active surface area (ECSA) of the cathode electrodes significantly increased with the upper potential limit. The ECSA loss was correlated with the performance decrease for hydrogen/air polarization curves, revealing purely kinetic losses at low and additional mass-transport related voltage losses at high platinum surface area normalized current densities (≡specific current densities). The absolute voltage losses only depended on the specific current density, independent of the extent of ECSA loss and the geometric current density.

A novel approach for fuel cell parameter estimation using simple Genetic Algorithm

A new problem formulation for effective identification of fuel cell parameters is proposed. The proposed formulation is solved by applying Genetic Algorithm optimization technique. The algorithm steps are coded in MATLAB and the objective function is solved for PEM fuel cell. In order to estimate the performance of the proposed formulation; extensive simulations are performed with both the proposed and conventional objective functions and the results obtained are compared. Further, a comprehensive evaluation based on objective function value, convergence speed and absolute voltage error value is also made to prove the superiority of the proposed formulation over the conventional curve fitting approach.

Influences of ICP etching damages on the electronic properties of metal field plate 4H-SiC Schottky diodes**Project supported by the Suzhou Research Fund (No. BY2011129) and the State Grid Corporation of China Research Fund (No. 525500140003).

Inductively coupled plasma (ICP) etching of 4H-SiC using SF6/O2 gas mixture was studied systematically and the effect of etching was examined by metal field plate SiC Schottky diodes (SBDs). It was found that the etch rate as well as SiC surface morphology were related with ICP power, RF power, pressure, the flow of SF6 and O2. Etching damages (the cone-in-pits and pits) generated at high chuck self-bias were observed, and they were thought to be caused by SiC defects. The degradation of both the reverse and forward I–V performances of SiC SBDs was ascribed to the cone-in-pits and pits. Moreover, the absolute value of forward current is even less than the reverse counterpart in the absolute value voltage range of 0–50 V for SiC SBDs with etching damages.

Two-Photon Lifetime Imaging of Voltage Indicating Proteins as a Probe of Absolute Membrane Voltage

Genetically encoded voltage indicators (GEVIs) can report cellular electrophysiology with high resolution in space and time. Two-photon (2P) fluorescence has been explored as a means to image voltage in tissue. Here, we used the 2P electronic excited-state lifetime to probe absolute membrane voltage in a manner that is insensitive to the protein expression level, illumination intensity, or photon detection efficiency. First, we tested several GEVIs for 2P brightness, response speed, and voltage sensitivity. ASAP1 and a previously described citrine-Arch electrochromic Förster resonance energy transfer sensor (dubbed CAESR) showed the best characteristics. We then characterized the voltage-dependent lifetime of ASAP1, CAESR, and ArcLight under voltage-clamp conditions. ASAP1 and CAESR showed voltage-dependent lifetimes, whereas ArcLight did not. These results establish 2P fluorescence lifetime imaging as a viable means of measuring absolute membrane voltage. We discuss the prospects and improvements necessary for applications in tissue.

Research of Magnetic Characteristics of the Split-Drain MAGFET Based on Nano-Polysilicon TFTs

The split-drain magnetic field effect transistor (MAGFET) based on nanopolysilicon thin film transistor (TFT) is fabricated on <100> high resistivity silicon substrates by (complementary metal oxide semiconductor) CMOS technology in this paper. It contains source (S), drain1 (D1), drain2 (D2) and gate (G), and adopts nanopolysilicon thin films and nanopolysilicon/high resistivity silicon heterojunction interfaces as the magnetic field sensing layers. The influence of the channel size and shapes on the transistor, are studied to further improve its magnetic sensitivity. When the ratio of channel length and width (L/W) of MAGFET is 80 μm/160 μm, VDS=5.0 V, the MAGFET with convex channel has higher magnetic sensitivity than the rectangle and concave, the absolute current magnetic sensitivity SI and the absolute voltage magnetic sensitivity SV of the proposed sensor reach the maximum values, and are 0.021 mA/T and 55 mV/T, respectively.

Analysis of improved characteristics of pentacene thin-film transistor with an embedded copper oxide layer

Organic thin-film transistor (OTFT) based on pentacene semiconductor with an embedded copper oxide (CuO) thin layer is investigated. With the 3 nm-thick CuO layer embedded in the pentacene semiconductor, the drain current of the OTFT increases more than 3 times compared with that of pentacene organic field-effect transistor without CuO layer, and the absolute threshold voltage reduces from -21 V to -7.9 V. The hole mobility and current on/off ratio are much improved. It is interpreted by the mechanism based on the analysis of the interface charge transfer between pentacene layer and CuO layer. Results of X-ray photoelectron reveal electron transfer from pentacene to high work function CuO and the formation of charge transfer (CT) complexes based on electron transfer near the contact of CuO and pentacene. The CT complexes between pentacene layer and CuO layer could reduce the exponential density of state near the band edge of pentacene and the pentacene bulk hole trap density, and enhance the pentacene bulk hole carriers injection, which leads to the improvement of the field-effect mobility of OTFT with CuO layer. Electrons are transfered from the highest occupied molecular orbital of pentacene to the thin CuO layer which can generate holes in pentacene. The generated hole has the same effect as that with applying negative gate voltage which influences the threshold voltage. The drain current of the device increases and the threshold voltage shifts from -21 V to -7.9 V. Therefore, the thin CuO layer that is directly embedded in the organic semiconductor layer, serves as the hole-injection layer, which is responsible for reducing the contact barrier of OTFT with CuO layer.

FPGA-based voltage and current dual drive system for high frame rate electrical impedance tomography.

Electrical impedance tomography (EIT) is used to image the electrical property distribution of a tissue under test. An EIT system comprises complex hardware and software modules, which are typically designed for a specific application. Upgrading these modules is a time-consuming process, and requires rigorous testing to ensure proper functioning of new modules with the existing ones. To this end, we developed a modular and reconfigurable data acquisition (DAQ) system using National Instruments' (NI) hardware and software modules, which offer inherent compatibility over generations of hardware and software revisions. The system can be configured to use up to 32-channels. This EIT system can be used to interchangeably apply current or voltage signal, and measure the tissue response in a semi-parallel fashion. A novel signal averaging algorithm, and 512-point fast Fourier transform (FFT) computation block was implemented on the FPGA. FFT output bins were classified as signal or noise. Signal bins constitute a tissue's response to a pure or mixed tone signal. Signal bins' data can be used for traditional applications, as well as synchronous frequency-difference imaging. Noise bins were used to compute noise power on the FPGA. Noise power represents a metric of signal quality, and can be used to ensure proper tissue-electrode contact. Allocation of these computationally expensive tasks to the FPGA reduced the required bandwidth between PC, and the FPGA for high frame rate EIT. In 16-channel configuration, with a signal-averaging factor of 8, the DAQ frame rate at 100 kHz exceeded 110 frames s (-1), and signal-to-noise ratio exceeded 90 dB across the spectrum. Reciprocity error was found to be for frequencies up to 1 MHz. Static imaging experiments were performed on a high-conductivity inclusion placed in a saline filled tank; the inclusion was clearly localized in the reconstructions obtained for both absolute current and voltage mode data.

Features of schematic and physical and topological design of analog integrated comparators

In practice, devices, which form either voltage with opposite polarity at the output at almost equal absolute values or voltage with the same polarity are the most widely used. The first option is typical for using as a comparison circuit of operational amplifier (OP), and the second – in using specialized integrated circuits. In the second case, the output voltages of the comparator are consistent in magnitude and polarity with the signals, used in digital technology. Based on the above, we can say that the input signal of the comparator is of the analog nature, and output – digital. Consequently, comparators often act as elements of communication between analog and digital devices, i.e. act as analog-digital converters (ADC). Due to the fact that both analog and digital signals are used in modern telecommunication systems, we have both analog and digital comparators, respectively. Digital comparator differs from analog in that it is designed to compare two numbers that are given in the form of binary codes.

MOPSO-based optimal fuzzy logic control strategy for standalone hybrid diesel-wave energy conversion system

The paper proposes a Multi-Objective Particle Swarm Optimization (MOPSO)-based Fuzzy Logic Control Proportional-Integral-Derivative (MOPSO-FLC-PID) controller for stand-alone hybrid Diesel- variable speedWave Energy Conversion System (WECS).The optimal control performance can be achieved by tuning scaling factors of the FLC and gain parameters with Multi-ObjectiveParticle Swarm Optimization (MOPSO) algorithm in order to improve system dynamic performance especially when nonlinearity,uncertainty and complexity of the hybrid Diesel-WECS are involved. Number of objective functions is defined to measurethe performance of the proposed controllers such as minimize the transient DC and AC voltage and current ripples, minimizethe DC and AC voltage and current Total Harmonic Distortion (THD), minimize the absolute total control steady state errordeviations, minimize the RMS absolute voltage deviations at the DC and AC load collection buses, ensure minimal losses aswell as wave energy optimal power utilization. Since some of these objective functions are conflicting, MOPSO is used to finda Pareto front from which a desired optimal operating state can be chosen. For the purpose of comparing the improvementobtained in the system dynamic performance with the application of the MOPSO-FLC-PID procedure to tune the scaling factorsof the FLC and the PID controller gains, these results are compared with those obtained using traditional Ziegler-Nichols PIDapproach, PID type fuzzy logic controller designed with Single-Objective Particle Swarm Optimization (SOPSO-FLC-PID),traditional PID type controller optimized with SOPSO-PID and traditional PID type controller optimized with MOPSO-PID.A complete simulation model is developed for such stand-alone hybrid Diesel-WECS under variable speed operation usingMATLAB Simulink environment. Simulation results show that the proposed design approaches are efficient to find the optimalscaling factors and PID gains of the controllers and therefore improves the transient performance of the hybrid Diesel-WECSover a wide range of operating conditions, sudden load change and three-phase short circuit fault.

Transistor application of alkyl-substituted picene.

Field-effect transistors (FETs) were fabricated with a thin film of 3,10-ditetradecylpicene, picene-(C14H29)2, formed using either a thermal deposition or a deposition from solution (solution process). All FETs showed p-channel normally-off characteristics. The field-effect mobility, μ, in a picene-(C14H29)2 thin-film FET with PbZr0.52Ti0.48O3 (PZT) gate dielectric reached ~21 cm2 V−1 s−1, which is the highest μ value recorded for organic thin-film FETs; the average μ value (<μ>) evaluated from twelve FET devices was 14(4) cm2 V−1 s−1. The <μ> values for picene-(C14H29)2 thin-film FETs with other gate dielectrics such as SiO2, Ta2O5, ZrO2 and HfO2 were greater than 5 cm2 V−1 s−1, and the lowest absolute threshold voltage, |Vth|, (5.2 V) was recorded with a PZT gate dielectric; the average |Vth| for PZT gate dielectric is 7(1) V. The solution-processed picene-(C14H29)2 FET was also fabricated with an SiO2 gate dielectric, yielding μ = 3.4 × 10−2 cm2 V−1 s−1. These results verify the effectiveness of picene-(C14H29)2 for electronics applications.

Band-Edge Steepness Obtained From Esaki/Backward Diode Current–Voltage Characteristics

While science has good knowledge of semiconductor bandgaps, there is not much information regarding the steepness of the band edges. We find that a plot of absolute conductance, I/V versus voltage V , in an Esaki diode or a backward diode will reveal a best limit for the band tails, defined by the tunneling joint density of states of the two band edges. This joint density of states will give information about the prospective subthreshold swing voltage that could be expected in a tunneling field-effect transistor. To date, published current-voltage characteristics indicate that the joint band-tail density of states is not steep enough to achieve <;60 mV/decade. Heavy doping inhomogeneity, among other inhomogeneities, results in a gradual density of states extending into the bandgap. The steepest measured tunnel diodes have a tunneling joint density of states >90 mV/decade.

A Molecular Voltmeter Based on Fluorescence Dynamics

In this issue, Hou et al. (1) introduce an elegant method for measuring the absolute voltage across a cell membrane with an accuracy of 10 mV. Their study presents an incisive approach to voltage imaging in which the voltage value is encoded in the temporal dynamics of fluorescence rather than in the raw fluorescence intensity. Together with an engineered microbial rhodopsin with properties amenable to the approach, the method provides a genetically encoded optical read-out independent of the reporter’s expression level and insensitive to variations in common experimental parameters. Their work presents a conceptually new avenue toward developing probes for membrane voltage useful for myriad systems from bacteria to mammalian tissue.

Temporal Dynamics of Microbial Rhodopsin Fluorescence Reports Absolute Membrane Voltage

Plasma membrane voltage is a fundamentally important property of a living cell; its value is tightly coupled to membrane transport, the dynamics of transmembrane proteins, and to intercellular communication. Accurate measurement of the membrane voltage could elucidate subtle changes in cellular physiology, but existing genetically encoded fluorescent voltage reporters are better at reporting relative changes than absolute numbers. We developed an Archaerhodopsin-based fluorescent voltage sensor whose time-domain response to a stepwise change in illumination encodes the absolute membrane voltage. We validated this sensor in human embryonic kidney cells. Measurements were robust to variation in imaging parameters and in gene expression levels, and reported voltage with an absolute accuracy of 10 mV. With further improvements in membrane trafficking and signal amplitude, time-domain encoding of absolute voltage could be applied to investigate many important and previously intractable bioelectric phenomena.

2-in-1 red-/green-/blue sensitive a-SiC:H/a-Si:H/a-SiGeC:H thin film photo detector with an integrated optical filter

This paper presents an inventive unipolar amorphous silicon (a-Si:H) two terminal two color photo sensor, featuring two functional modes of operation. The sensor structure is green sensitive at −8.5V and reaches a sensitivity maximum of 130mA/W. At lower absolute bias voltage values the spectral response at 550nm is suppressed by an internal optical filter. The filter structure consists of an a-Si:H/a-SiGeC:H absorber interface, generating an interior trapping area with high defect densities. The combination of an internal band gap barrier and an area with high defect states causes localized charge recombination. The interface deteriorates transport properties locally to suppress green sensitivity while the detectors blue and red efficiencies exceed. The maximum suppression of the 530nm response is 32.5mA/W at −5.5V bias voltage. Additionally, we observe a shift of both two color sensitivity maxima. The peak at lower wavelength shifts from 350nm to 480nm. In consequence, the device is even able to detect signals in the near ultraviolet spectrum. The second peak shifts from 590nm to 640nm. At −8.5V the filter is deactivated and the maximum detector response is located at 530nm. In reverse biased conditions the device's dynamic range remains constantly high and reaches values of 90dB at 1000lx white-light illumination. The interior 85nm a-Si:H layer reduces the dark current density to 10−8A/cm2 at −8V. Possible sensor applications may exist in fields of medical diagnostics, fluorescence and spectrophotometrical measurements, chemical analysis or in colorimetric and hyperspectral imagery.

Back Cover: Quantitative evaluation method for electroluminescence images of a‐Si:H thin‐film solar modules (Phys. Status Solidi RRL 9/2013)

Electroluminescence (EL), i.e. the emission of light under a forward voltage bias, is the reciprocal process of the standard operation mode of a solar cell. For this study, Tran et al. used a charged coupled device (CCD) Si-CCD camera and an InGaAs camera, which are sensitive to light absorbed in the infrared spectral range, to detect the electroluminescent emission from hydrogenated amorphous silicon (a-Si:H) thin-film solar modules. In their Letter on pp. 627–630, the authors demonstrate a method to extract the absolute local junction voltage of a-Si:H modules from electroluminescence images due to the relation between the local junction voltage and the local EL emission. Thereby, a radiative ideality factor nr for the electroluminescence emission with nr >1 is derived which depends on the samples and the spectral sensitivity of the camera system used in the experiment.

Quantitative evaluation method for electroluminescence images of a‐Si:H thin‐film solar modules

AbstractThis work presents a method for extracting the absolute local junction voltage of a‐Si:H thin‐film solar cells and modules from electroluminescence (EL) images. It is shown that the electroluminescent emission of a‐Si:H devices follows a diode law with a radiative ideality factor nr larger than one. We introduce an evaluation method that allows us to determine the absolute local junction voltage in cases of nr &gt; 1, while existing approaches rely on the assumption of nr = 1. Furthermore, we find that the experimentally determined values of nr vary from sample to sample. It is also explained why the derived radiative ideality factor is influenced by the spectral sensitivity of the camera system used in the experiment. (© 2013 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Fabrication of single crystal field-effect transistors with phenacene-type molecules and their excellent transistor characteristics

Single crystal field-effect transistors (FETs) using [6]phenacene and [7]phenacene show p-channel FET characteristics. Field-effect mobilities, μs, as high as 5.6×10−1cm2V−1s−1 in a [6]phenacene single crystal FET with an SiO2 gate dielectric and 2.3cm2V−1s−1 in a [7]phenacene single crystal FET were recorded. In these FETs, 7,7,8,8-tetracyanoquinodimethane (TCNQ) was inserted between the Au source/drain electrodes and the single crystal to reduce hole-injection barrier heights. The μ reached 3.2cm2V−1s−1 in the [7]phenacene single crystal FET with a Ta2O5 gate dielectric, and a low absolute threshold voltage |VTH| (6.3V) was observed. Insertion of 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ) in the interface produced very a high μ value (4.7–6.7cm2V−1s−1) in the [7]phenacene single crystal FET, indicating that F4TCNQ was better for interface modification than TCNQ. A single crystal electric double-layer FET provided μ as high as 3.8×10−1cm2V−1s−1 and |VTH| as low as 2.3V. These results indicate that [6]phenacene and [7]phenacene are promising materials for future practical FET devices, and in addition we suggest that such devices might also provide a research tool to investigate a material’s potential as a superconductor and a possible new way to produce the superconducting state.

Inverter‐based second‐order sigma‐delta modulator for smart sensors

Presented is a fully-differential inverter-based switched-capacitor second-order sigma-delta modulator for smart sensor applications. To reduce the supply voltage, the power consumption and the chip area, a simple inverter is used to replace the operational transconductance amplifier in the traditional integrator. The supply voltage can be lower than the summation of the absolute threshold voltages of the PMOS and NMOS transistors in the inverter. The described modulator has been designed and fabricated in AMI 0.5 µm CMOS process. Measurement shows that it can work under 1.5 V supply voltage and provide 55.39 dB signal-to-noise and distortion ratio (SNDR). Simulation also shows that the modulator can work under 0.7 V supply voltage and provide 59.38 dB SNDR in IBM 180 nm CMOS process.

Radio frequency cavity analysis, measurement, and calibration of absolute Dee voltage for K-500 superconducting cyclotron at VECC, Kolkata

Variable Energy Cyclotron Centre has commissioned a K-500 superconducting cyclotron for various types of nuclear physics experiments. The 3-phase radio-frequency system of superconducting cyclotron has been developed in the frequency range 9-27 MHz with amplitude and phase stability of 100 ppm and ±0.2(0), respectively. The analysis of the RF cavity has been carried out using 3D Computer Simulation Technology (CST) Microwave Studio code and various RF parameters and accelerating voltages ("Dee" voltage) are calculated from simulation. During the RF system commissioning, measurement of different RF parameters has been done and absolute Dee voltage has been calibrated using a CdTe X-ray detector along with its accessories and known X-ray source. The present paper discusses about the measured data and the simulation result.

Bipolar switching polarity reversal by electrolyte layer sequence in electrochemical metallization cells with dual-layer solid electrolytes

Bipolar switching behaviours of electrochemical metallization (ECM) cells with dual-layer solid electrolytes (SiOx-Ge0.3Se0.7) were analyzed. Type 1 ECM cell, Pt (bottom electrode)/SiOx/Ge0.3Se0.7/Cu (top electrode), exhibited typical eightwise current-voltage (I-V) hysteresis of ECM cells whereas Type 2 ECM cell, Pt (bottom electrode)/Ge0.3Se0.7/SiOx/Cu(top electrode), showed counter-eightwise hysteresis. In addition, absolute off-switching voltage in Type 2 cell is lower than that in Type 1 cell while on-switching voltage in both cells is almost the same. An attempt to understand this electrolyte-stack-sequence-depending switching polarity reversal was made in terms of the ECM cell potential change upon the electrolyte stack sequence and the consequent change in Cu filament growth direction. Relevant experimental evidence for the hypothesis was obtained regarding the switching behaviours. Furthermore, given the switching polarity reversal, feasibility of serial complementary resistive switches was also demonstrated.