Measurements Of Current-voltage Characteristics Research Articles

Two-step superconducting-to-normal transitions in frustrated triangular Josephson-junction arrays

Current–voltage characteristics measurements suggest that the superconducting-to-normal transition in triangular Josephson-junction arrays with the frustration index f=1/4 and 1/3, which may have excitations of zero-energy domain walls, occurs in two steps, a vortex-disordering transition followed by a Berezinskii–Kosterlitz–Thouless-like phase-disordering transition at a higher temperature. The transport data also indicate that a similar two-step transition occurs in a weakly frustrated array as well. Experimental findings for a weakly frustrated array are inconsistent with existing theory.

Characterization of two electrode systems for corona-charging of non-woven filter media

Abstract The aim of this paper is to provide a better understanding of the corona-charging process of non-woven electret filters for automotive and medical applications. The experiments were performed on polypropylene samples: 500-μm-thick non-woven fabrics (fiber diameter: 24 μm), laid on a grounded plate electrode and subjected to positive or negative corona generated either by a dual wire–cylinder electrode or by a triode-type electrode set. The paper reports the results of current–voltage characteristics measurements, as well as the repartition of the current density at the surface of the grounded electrode.

Fast and reliable calculation of the two‐diode model without simplifications

ABSTRACTAn algorithm to calculate the current in the two‐diode equivalent circuit of a solar cell is described and characterized in detail. It enables fitting measured current–voltage characteristics with hundreds of voltage points and six fit parameters at practically instantaneous speeds and can handle thousands of voltage points within a few seconds, without simplifications of the two‐diode model. This performance enables routine two‐diode model parameter extraction at in‐line speeds, which may help to enhance cell characterization for module integration. The source code is publicly available. Copyright © 2012 John Wiley & Sons, Ltd.

Rectification effect in poly-p-xylylene-cadmium sulfide graded nanocomposites

The hybrid poly-p-xylylene-cadmium sulfide nanocomposites characterized by gradients of concentrations and sizes of CdS nanoparticles along the lines of an applied electric field have been synthesized using the vapor deposition polymerization in an inhomogeneous electric field. The maximum concentration of cadmium sulfide can exceed 10 vol %, while the average effective sizes of the nanoparticles depend on the concentration and do not exceed 5 nm. The synthesized thin-film nanocomposites exhibit a quantum confinement effect. According to the estimates obtained from the shift of the absorption band edge, the radius of nanoparticles is 2.7 nm near the negative electrode and 3.5 nm near the positive electrode. It has been found that the sample formed in an electric field of 10 kV/cm manifests a rectification effect, which can be associated with the gradient of nanoparticle sizes. The measurements of current-voltage characteristics and photoconductivity have demonstrated that the synthesized samples possess high photoconductivity. The photocurrent in the sample prepared in an electric field of 10 kV/cm can exceed the dark current by two orders of magnitude, and the rectification effect in this case disappears.

Magnetization and electric transport properties of single-crystal MgB2 nanowires

High quality single-crystal magnesium diboride (MgB2) nanowires with lengths exceeding 10 μm were successfully synthesized by hybrid physical chemical vapor deposition. The magnetization and electrical transport properties of single-crystal MgB2 nanowires (NWs) were measured. The superconducting transition temperature of the NWs was 37 K, as confirmed by magnetization measurements. The disordered behavior of the nanowires was observed by four-terminal current–voltage characteristic measurements of an individual NW from T = 10 to 300 K. The temperature-dependent resistivity curves for seven NWs collapsed into a universal curve described by the variable range hopping model, showing intrinsic nonmetallic transport properties. This implies that the granular superconducting defect states are critical to the superconductivity of the individual MgB2 NWs.

Solution-Processed Zinc Oxide Thin-Film Transistors With a Low-Temperature Polymer Passivation Layer

Bottom-gate top-contact zinc oxide (ZnO) thin-film transistors were fabricated with a low annealing temperature (150 °C) using ammine-hydroxo zinc precursors. The unpassivated devices present profound hysteresis in the measured current-voltage characteristics and a negative output conductance, which were attributed to the interaction of back surface with the oxygen molecules in the ambient atmosphere. To suppress the ambient influence without impacting the device's intrinsic performance, a simple low-temperature (75 °C ) solution-based passivation approach with polydimethylsiloxane was developed. The passivated devices present typical field-effect transistor behaviors of greatly improved device performance.

Theory of Space Charge Limited Currents

Space-charge-limited currents are important in energy devices such as solar cells and light-emitting diodes, but the available theory from the 1950s finds it necessary to postulate defect states that are distributed in energy in order to match data. Here, we show that this postulate is not warranted. Instead, we demonstrate that dopants and the concomitant Frenkel effect, which have been neglected, control the shape of measured current-voltage characteristics. We also account for the observed peak in the noise power. The new theory can anchor efforts to develop experimental techniques to measure deep-trap levels.

Study on the Optical and Electrical Properties of Organic Semiconductor Thin Films for OLEDs

Organic semiconductor thin films of aluminum (III) bis(2-methyl-8-quninolinato)-4- phenylphenolate (BAlq), -naphthylphenylbiphenyl amine (NPB), and tris(8-hydroxy-quinoline) aluminum (AlQ) for organic light-emitting diodes (OLEDs) were deposited by the vacuum sublimation technique. The optical properties in the UV-visible region of the thin films were investigated by optical transmittance and absorption spectra. The band gaps were obtained from direct allowed transitions at room temperature by means of the Tauc plots. The Urbach energy and the slope of Urbach edge were evaluated, respectively according to the Urbach-edges method. The thin film devices of sandwich structure were fabricated using these organic semiconductor materials, in addition, the effective carrier mobility, free carrier density, and electrical conductivity of the thin films were calculated in terms of the measured current-voltage characteristics of the devices.

Electronic system for Langmuir probe measurements

A newly developed Langmuir probe system for measurements of current-voltage (IV) characteristics in the tokamak divertor area is presented and discussed. The system is partially controlled by a computer allowing simultaneous and independent feeding and registration of signals. The system is mounted in the COMPASS tokamak, Institute of Plasma Physics, Academy of Sciences of the Czech Republic.The new electronic circuit boards include also active low-pass filters which smooth the signal before recording by the data acquisition system (DAQ). The signal is thus less noisy and the data processing is much easier. We also designed and built a microcontroller-driven waveform generator with resolution of 1 Ms/s. The power supply is linear and uses a transformer. We avoided the use of a switching power supply because of the noise that it could generate.Examples of measurements of the IV characteristics by divertor probes in the COMPASS tokamak and evaluation of the EEDF are presented.

A simple generator of a stationary flow of non-equilibrium atmospheric-pressure plasma

A simple design of a plasma discharge set up, providing a stationary flow of non-equilibrium atmospheric-pressure plasma is proposed. The non-equilibrium state of plasma is maintained by using a cathode with a weakly conducting liquid like tap water. The anode is formed with a cooled metal ring-shaped inserted in a dielectric barrel. This assembly is fixed at ∼ 1 cm above the water surface. The velocity of the air flow through the anode hole may be changed from 0 m/s up to ∼ 10 m/s. The studied discharge in the open air gap between the tap water surface and the anode ring is powered by direct current I ∼ 0.1 A. The voltage on the air gap is ≥ 1 kV. Measurements of current-voltage characteristics at different flow velocities were carried out. Spectra of radiation of the discharge column and the torch above the anode were measured. The measurement results were compared with the results of radiation spectra modeling for non-equilibrium plasma of humid air. The comparison made possible to determine the characteristics of plasma. The characteristics of the plasma depending on the speed of the airflow and the current are studied.

Reducing the effects of mismatch between zinc oxide and silicon by silane plasma modification

We investigated the mismatch between zinc oxide (ZnO) and silicon (Si) upon reduction by silane plasma modification in a plasma-enhanced chemical vapor deposition system. This plasma treatment was only carried out for 10 s and the Si–H bonds that were provided by the silane plasma modification as dangling bonds on the Si wafer in addition to functioning as a conjunction layer to reduce the defects. The X-ray diffraction analysis of the ZnO/p-type silicon structure produced by silane plasma modification has a slightly lower full width at the half maximum, which improved the ZnO film’s crystalline properties. After the silane plasma modification ZnO/Si diode is produced, the measured current–voltage characteristics gave favorable rectifying properties and reverse bias had a low leakage current. The ZnO/Si diode under illumination increased the short-circuit current (Isc) from 7.32 to 19.75 mA/cm2, which is an improvement compared with a conventional bare ZnO/Si diode because of the reduced ZnO/Si interface states. Therefore, the silane plasma modification diminishes the effects of the interface and improves the ZnO/Si diode performance.

Mechanisms of current conduction in Pt/BaTiO3/Pt resistive switching cell

The 80-nm-thickness BaTiO3 (BT) thin film was prepared on the Pt/Ti/SiO2/Si substrate by the RF magnetron sputtering technique. The Pt/BT/Pt/Ti/SiO2/Si structure was investigated using X-ray diffraction and scanning electron microscopy. The current–voltage characteristic measurements were performed. The bipolar resistive switching behavior was found in the Pt/BT/Pt cell. The current–voltage curves were well fitted in different voltage regions at the high resistance state (HRS) and the low resistance state (LRS), respectively. The conduction mechanisms are concluded to be Ohmic conduction and Schottky emission at the LRS, while space-charge-limited conduction and Poole–Frenkel emission at the HRS. The electroforming and switching processes were explained in terms of the valence change mechanism, in which oxygen vacancies play a key role in forming conducting paths.

Physical Parameter-Based SPICE Models for InGaZnO Thin-Film Transistors Applicable to Process Optimization and Robust Circuit Design

In this letter, we show that the physics-based equation that was derived for amorphous oxide semiconductor (AOS) thin-film transistors (TFTs) in our previous work can be successfully incorporated into the SPICE model via Verilog-A. The proposed model and extracted SPICE parameters successfully reproduce the measured current-voltage characteristics of amorphous indium-gallium-zinc-oxide (a-IGZO) TFTs and the load line diagram of a-IGZO TFT inverters. The main advantage of our model is that each parameter has its physical meaning and most of them can be related with the fabrication conditions of AOS TFTs. To show the advantage of the proposed models and extracted SPICE parameters more clearly, we investigate the effect of ionized donor concentration ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">D</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> ) on the inverter circuit operation and determine the optimum value of <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">D</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> and device dimensions considering the tradeoff between the power consumption and the output swing in a-IGZO inverters. The proposed physics-based SPICE model via Verilog-A is expected to play a significant role in the process optimization and circuit design with AOS TFTs.

Electric-field-driven phase transition in vanadium dioxide

We report on local probe measurements of current-voltage and electrostatic force-voltage characteristics of electric-field-induced insulator to metal transition in VO2 thin film. In conducting AFM mode, switching from the insulating to metallic state occurs for electric-field threshold E~6.5\times10^7 Vm-1 at 300K. Upon lifting the tip above the sample surface, we find that the transition can also be observed through a change in electrostatic force and in tunneling current. In this noncontact regime, the transition is characterized by random telegraphic noise. These results show that electric field alone is sufficient to induce the transition; however, the electronic current provides a positive feedback effect that amplifies the phenomena.

Including Radiation Effects and Dependencies on Process-Related Variability in Advanced Foundry SPICE Models Using a New Physical Model and Parameter Extraction Approach

An automated flow is described for total-ionizing dose (TID)-aware SPICE model generation that includes TID response and its dependence on process variability and layout. A memetic algorithm that balances multiple objectives, subject to realistic constraints, is introduced for global optimization of the flow. A differential evolution algorithm is adapted for global exploration, and a modified random pattern search strategy is introduced for local exploitation. The optimizer efficiently reduces the value of different kinds of objective functions in the extraction at reasonable cost and avoids premature convergence in most practical cases. The model is implemented in Verilog-A, can be applied to all foundry model formats, and supports all popular SPICE simulators. To validate the flow, simulations from models extracted from specific targets are compared with measured current-voltage characteristics under various irradiation conditions for 0.35 μm, 0.18 μm, and 90 nm bulk CMOS processes.

COMPACT CAPACITANCE MODEL FOR PRINTED THIN FILM TRANSISTORS WITH NON-IDEAL CONTACTS

We report on a compact capacitance model that accurately describes both the gate length dependent and the gate length independent frequency dispersion observed in C-V curves for printed thin film transistors with non-ideal contacts. We also show that modeling the drain current with two adjacent subthreshold regions (instead of just one in the previous RPI TFT model) is needed to match the measured current-voltage characteristics. We show that Elmore model which accounts for channel length transit time is not sufficient for describing the frequency dispersion in C-V curves for printed TFTs and present the new Variable Dispersion Model (VDM). VDM reproduces the experimentally observed gate length independent dispersion arising due to the finite time of the electron exchange between the localized states in the mobility gap and the states above the mobility edge in amorphous semiconductors. The combined Elmore-VDM model has been implemented in AIM-Spice and showed good agreement with measured C-V data.

Local leakage current behaviours of BiFeO3 films

The leakage current behaviours of polycrystalline BiFeO3 thin films are investigated by using both conductive atomic force microscopy and current-voltage characteristic measurements. The local charge transport pathways are found to be located mainly at the grain boundaries of the films. The leakage current density can be tuned by changing the post-annealing temperature, the annealing time, the bias voltage and the light illumination, which can be used to improve the performances of the ferroelectric devices based on the BiFeO3 films. A possible leakage mechanism is proposed to interpret the charge transports in the polycrystalline BiFeO3 films.

Determining the thermal generation rate of minority charge carriers at semiconductor-ultrathin oxide interfaces

A simple proximate method for determining the generation rate G s of electron-hole pairs in metal-ultrathin oxide-semiconductor (MOS) structures is proposed. This method is based on measurements of dynamic current-voltage characteristics of MOS structures in the region of deep depletion of the semiconductor surface and on the comparison of these data to a quasi-equilibrium volt-farad characteristic (VFC) of an ideal MOS structure. This approach to determining G s from the value of the structure capacitance is insensitive either to a shift of the VPC, which is caused by the presence of built-in charges, or a recharge of localized electron states in the oxide and at the Si-SiO2 interface. The proposed technique also allows one to take the influence of a tunneling current through an insulator on the measurement results into account. The algorithm was tested in studies of generation and annihilation processes of centers of generation of electron-hole pairs in n-Si-based MOS structures with an ultrathin (≅4 nm) oxide.

Large-area and nanoscale n-ZnO/p-Si heterojunction photodetectors

The article reports the results of our experimental investigation on the effect of UV light on the characteristics of n-ZnO/p-Si heterojunction. c-Axis oriented zinc oxide (ZnO) films were deposited by thermal evaporation technique on p-type silicon (Si) substrates to form ZnO/Si heterojunctions. Both large-area and nanoscale heterojunction configurations were studied. The measured current–voltage characteristics in dark and illuminated conditions confirm the rectifying behavior of the heterojunctions and an excellent UV response. The responsivity values were measured to be of 0.18 and 0.12 A/W to UV light (365nm) for large-area and nanoscale heterojunctions, respectively. The values are comparable with those offered by other commercial UV detectors. The nanoscale heterojunction device can find applications in nanophotonics.

Field-effect mobility extraction in nanowire field-effect transistors by combination of transfer characteristics and random telegraph noise measurements

A technique based on the combined measurements of random telegraph-signal noise amplitude and drain current vs. gate voltage characteristics is proposed to extract the channel mobility in inversion-mode and accumulation-mode nanowire transistors. This method does not require the preliminary knowledge of the gate oxide capacitance or that of the channel width. The method accounts for the presence of parasitic source and drain resistance effect. It has been used to extract the zero-field mobility and the field mobility reduction factor in inversion-mode and junctionless transistors operating in accumulation mode.