Non-ohmic Current-voltage Characteristics Research Articles

Multi-functional properties of CaCu3Ti4O12 thin films

In this work, electric transport properties of CaCu3Ti4O12 (CCTO) thin films were investigated for resistive switching, rectifying and gas sensor applications. Single phase CCTO thin films were produced by polymeric precursor method (PPM) on different substrates and their electrical properties were studied. Films produced on LNO/Si substrates have symmetrical non-ohmic current-voltage characteristics, while films deposited on Pt/Si substrates have a highly asymmetrical non-ohmic behavior which is related to a metal-semiconductor junction formed at the CCTO/Pt interface. In addition, results confirm that CCTO has a resistive switching response which is enhanced by Schottky contacts. Sensor response tests revealed that CCTO films are sensitive to oxygen gas and exhibit n-type conductivity. These results demonstrate the versatility of CCTO thin film prepared by the PPM method for gas atmosphere or bias dependent resistance applications.

New method of accurate estimation of the electron–phonon coupling constants in fractionally charged incommensurate electronic states in molecular systems

The electron-phonon interactions in the fractionally positively charged incommensurate tetrathiafulvalene (TTF) molecular systems are investigated. In particular, since there are fractionally positive charges per TTF molecule, it is very difficult to estimate the vibronic and electron-phonon coupling constants, and thus there have been no reports of the exact calculations in the electron-phonon coupling constants in such fractionally positively charged incommensurate systems. Therefore, in this paper, we suggest new method of accurate estimation of the electron-phonon coupling constants in the fractionally positively charged systems. Total electron-phonon coupling constants for the monocation (l(+100)) of TTF is compared with that for the monoanion (l(-100)) of tetracyanoquinodimethanide (TCNQ). Furthermore, logarithmically averaged phonon frequency for the monocation (ν(ln , +1.00)) of TTF is compared with that for the monoanion (ν(ln , -1.00)) of TCNQ. The C-C and C-S stretching mode of 1599 cm(-1) and the C-S-C and C-C-S bending mode of 472 cm(-1) strongly couple to the b(3)u highest occupied molecular orbital (HOMO) in TTF molecule. The l(+100) value for TTF molecule is estimated to be 0.274 eV, and the ν(ln , +1.00) value for TTF molecule is estimated to be 926 cm(-1). The density of states at the Fermi level (N(NM, crystal)(ε(F))(+0.59, +0.59)) values for TTF(0.59+), which are essential physical values in order to investigate the mechanisms of the non-Ohmic current-voltage characteristics excellently suggested by Cohen and Heeger et al., are also estimated. By comparing the N(NM, crystal)(ε(F))(+0.59, +0.59) values estimated by us with those estimated from the experimental results of the Pauli susceptibility and the current-voltage characteristics in TTF(0.59+) suggested by Cohen and Heeger et al., and from the band calculations, we show that the l(+0.59), ν(ln , +1.00), RE(+0.59), and N(NM, crystal)(ε(F))(+0.59, +0.59) values estimated by our new calculation method are very accurate and reliable.

Non-Ohmic current–voltage characteristics in the positively charged tetrathiafulvalene (TTF) molecular crystals

The mechanism of an extraordinary increase in conductivity at larger applied voltage than the critical voltage generally observed in the one-dimensional electronic systems such as tetrathiafulvalenium–tetracyanoquinodimethanide (TTF–TCNQ) is quantitatively investigated. The tunneling effects of the nondissipative diamagnetic currents between the two neighboring localized TTF unit cells and the current–voltage characteristics at low temperature process (0 K < T < 14 K) are investigated. The transition probability ( P TC) of electrons between two neighboring unit cells is estimated to be in the order of 10 −3–10 −4. The estimated density of states near the Fermi level in the Peierls distorted structures ( N PD( ɛ F)) on the basis of the experimental results of the current–voltage characteristics is always larger than that ( N NM( ɛ F)) in the normal metallic states in TTF–TCNQ molecular crystals. This result can be rationalized from the fact that the density of states near the Fermi level in the Peierls distorted states is enhanced as a result of the congestion of the energy levels. That is, the N PD( ɛ F) values estimated on the basis of the tunneling effect theory suggested in this paper are well rationalized. The tunneling effects theory of the nondissipative diamagnetic currents is compared with the incommensurate charge-density-wave (ICDW) sliding theory. According to our quantitative calculated results, the phenomena described above can be understood if we consider that such an extraordinary increase in conductivity originates from the tunneling effects of the nondissipative localized diamagnetic currents between the two neighboring unit cells.

Nonlinear current-voltage characteristics of nanochannels

Like ion channels, nanochannels are known to exhibit curious non-Ohmic current-voltage (I-V) characteristics with an approximate piece-wise constant differential resistance. Using a nanoslot model and a nonequilibrium ion transport theory, we attribute the nonlinear resistance to overlapping double layers inside and an extended polarized layer of space charge outside the nanochannel. The overlimiting current beyond a critical voltage is shown to develop when the polarized layer is destabilized by a microvortex instability at one entrance. By extending earlier nanochannel and polarized layer models to include this instability, nonideal ion permselectivity and field-focusing effect, quantitative predictions-together with explicit differential resistance expressions-are offered for the nonlinear I-V features of a nanochannel surrounded by microreservoirs from a simple pseudo-one-dimensional model.

Electrical Characterization of ZnO Single Nanowire Device for Chemical Sensor Application

Vertically well-aligned high quality ZnO nanowires were grown on GaN epilayer on c-plane sapphire via a vapor-liquid-solid (VLS) process by introducing an Au thin film (3 nm) as a catalyst. ZnO single nanowire device was ingenuously fabricated by combining conventional optical lithography and high resolution electron beam lithography and its current-voltage characteristics were measured with doing the post process to acquire reproducible performance as a chemical gas sensor. And its temperature dependent current-voltage characteristics were measured to investigate temperature dependant electrical transport. The ZnO nanowire device showed slightly non-ohmic current-voltage characteristics which may be due to back-to-back configuration of the diodes with the insulating contact barriers and showed an relatively small activation energy of 0.2 eV. To test our device as a chemical sensor, the NO2 gas response was reported at the elevated temperature.

Non-Ohmic Current-Voltage and Impedance Characteristics of Electroadsorptive Zn2SnO4

Although is known as a CO-selective gas sensor that responds to CO gas more sensitively than to gas, non-ohmic curves and thus voltage-dependent sensitivity were observed when used with Pt electrodes. In order to study the observed voltage-dependent resistance, one side of was contacted with ZnO (or In this configuration, the asymmetric curve was shown due to the ohmic interface between ZnO (or and and the non-ohmic interface between Pt and The impedance spectra of the layered sample also indicated that the interfacial resistance of increased with applied bias. The time-dependent current and potential measurements showed the slowly increasing resistance when was positively biased, This observation was explained by the field-induced adsorption of oxygen gas (or the electroadsorptive effect). © 2001 The Electrochemical Society. All rights reserved.

Non-ohmic current–voltage characteristics in single-wall carbon nanotube network

The non-ohmic current–voltage ( I– V) characteristics of the single-wall carbon nanotube network were investigated at low temperatures. The temperature dependence of resistivity at low current ( I<10 μ A) shows non-metallic negative d ρ/d T from T=1.4–300 K. Below T<15 K, gradual decreases of resistivity are observed as the applied currents increase, showing significant non-ohmic behavior at high electric field. The I– V curves in the non-ohmic regime can be fitted well by the fluctuation-induced tunneling model, indicating the importance of inter-tubular contacts or inherent energy barriers inside the tubes.

Current–voltage characteristics and selective CO detection of Zn 2SnO 4 and ZnO/Zn 2SnO 4, SnO 2/Zn 2SnO 4 layered-type sensors

The current–voltage characteristics and the CO gas-sensing properties of porous Zn 2SnO 4 were examined. ZnO/Zn 2SnO 4 and SnO 2/Zn 2SnO 4 layered-type samples were also fabricated for the investigation of the interfacial effect between ZnO (or SnO 2) and Zn 2SnO 4 by sequentially die-pressing respective powders. To form a stable contact between ZnO (or SnO 2) and Zn 2SnO 4, the composition and thus the sinterability of ZnO (or SnO 2) was controlled. The electrical and gas-sensing properties of the layered samples were compared with those of individual ZnO, SnO 2 and Zn 2SnO 4. Zn 2SnO 4 showed the higher sensitivity values to CO gas than to H 2 gas at relatively low temperature. The sensitivity of Zn 2SnO 4 decreased with the increasing magnitude of applied voltage at high temperature. Both SnO 2/Zn 2SnO 4 and ZnO/Zn 2SnO 4 layered-type samples showed the sensing characteristics varying with the direction of applied bias. The interface between Pt and Zn 2SnO 4 was responsible for the observed non-ohmic current–voltage characteristics and the resultant gas sensitivity.

レーザーアブレーション法により作製されたＺｎＯ／Ｐｒ６Ｏ１１積層薄膜のバリスタ特性

ZnO-Pr6O11 varistors exhibit non-ohmic current-voltage characteristics due to the double Schottky barrier formed at the interface between ZnO grains and intergranular phases of Pr6O11. In this paper, the I-V characteristic of ZnO/Pr6O11 multilayerd films with different thickness fabricated by pulsed laser ablation method are studied. In spite of decreasing the film thickness, the films with 5000-500A thickness exhibit nonlinear I-V characteristic. The values of breakdown voltage (Vb) and non-linear coefficient (a) are estimated as Vb=0.19-0.30V, α=2.5-4.1. Therefore, thin ZnO/Pr6O11 multilayered films prepared by PLD method show lower breakdown voltage.

Vortex dynamics and non-Ohmic current-voltage characteristics of high- T c layered superconductors

We have calculated the non-Ohmic current-voltage characteristics of anisotropic three-dimensional Josephson-junction arrays as a model of layered high- T c oxides. Langevin dynamic simulations are performed for various Josephson-coupling anisotropies ( γ = J | c / J ⊥ c ) at finite temperature in zero and finite magnetic fields. We find that interlayer coupling gives rise to the non-vanishing critical current ( I c ), and that the low-temperature phase displays non-Ohmic power-law behavior ( V ( I − I c ) α−1 ). Moreover, in the γ-dependence of I c , we see the two-to three-dimensional crossover associated with thermally excited vortex-antivortex pairs.

Analysis of nonohmic current-voltage characteristics in a Cu-compensated GaAs photoconductor

An analysis of observations of nonohmic current conduction in a copper-compensated GaAs (GaAs:Cu) photoconductive switch is presented. It is demonstrated that conduction during illumination and at modest current densities can be attributed to an optically injected plasma influenced by single-injection contact effects. However, at higher current densities, a double-injection model is more suitable. We provide further evidence that the transition from a single-injection process to a double-injection process is accompanied by the formation of at least one current filament with cross-sectional area of 5×10−4 cm2, and a peak current density greater than 103 A/cm2. We finish by suggesting avalanche breakdown at the n+−i anode junction as a possible mechanism for the onset of significant hole injection at the anode, a condition necessary to justify the use of a double-injection-dominated transport model in an essentially n-i-n device.

Zinc oxide varistors

An overview is given of zinc oxide varistors, which are made of semiconducting ceramics with highly nonohmic current-voltage characteristics, which originate at the grain boundaries. These varistors are widely utilized to protect electric power lines and electronic components against dangerous voltage surges. This overview covers electrical characteristics, fabrication methods, effects of additives, microstructures, the conduction mechanism, degradation, and applications.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Non-Ohmic Properties of ZnO-Rare Earth Metal Oxide-Co3O4 Ceramics

Zinc oxide ceramics containing rare earth metal oxide and cobalt oxide which exhibit non-ohmic current-voltage characteristics were studied. The nonlinearity was similar to that of the zinc oxide varistor containing Bi2O3 and other additives. According to microstructural observations, the intergranular layer of the ceramics was found to be a rare earth metal oxide compound without Zn and Co atoms, and its thickness was expected to be less than 100 Å. The nonlinear characteristics are attributed to the potential barrier due to the depletion layer formed in the interfacial region of the ZnO grainboundaries doped with Co atoms. Qualitative analysis of capacitance-voltage relations confirmed this model.

Trap-controlled space charge currents in liquid benzene?

With a specially prepared palladium black electrode, non-ohmic current voltage characteristics with a steep rise of current at a certain voltage have been observed. They will be explained as space charge limited currents of negative charge carriers influence by traps.

Non-Ohmic Conduction in Germanium under a Strong Magnetic Field

A distinct non-ohmic current-voltage characteristics in n -type germanium containing 10 20 to 10 22 impurity atoms/m 3 under a strong impulsive magnetic field was found at liquid hydrogen temperatures. The effect was also observed in p -type germanium with appropriate impurity concentrations for the transverse magnetic field stronger than 1 Wb/m 2 . Essential mechanism underlying this effect would be a “transverse breakdown” introduced by M. Toda et al. In the present case, however, “transverse impact ionization” should be more appropriate than “transverse breakdown”. Necessary conditions for the occurrence of this non-ohmic effect are (1) the existence of the strong Hall field and (2) neutralized donors or acceptors in germanium crystals. Some peculiar phenomena associated with this effect i.e. , a kind of instability in electric current, negative differential drift mobility and the anomalous electric field dependence of the Hall angle were also observed.

Non-ohmic behavior of carbon black-loaded rubbers

Non-ohmic current—voltage characteristics of carbon black-loaded rubber vulcanizates are explained by tunnelling effects. In samples containing 40 pbw of HAF black in different dispersions, tunnelling parameters are found to depend on the degree of dispersion. In a second series the concentration of MT black varied between 10 and 50 pbw.The non-ohmic behavior of all these samples can be described by approximately the same equation, but tunnelling between impurities appears to predominate. A series of samples containing 50 pbw of six different blacks (MT, regal SRF, FEF, HAF, ISAF, SAF) appear to follow Ohm's law.