Resistance Fluctuations Research Articles

Effect of ambient on the resistance fluctuations of graphene

In this letter, we present the results of systematic experimental investigations of the effect of different chemical environments on the low frequency resistance fluctuations of single layer graphene field effect transistors. The shape of the power spectral density of noise was found to be determined by the energetics of the adsorption-desorption of molecules from the graphene surface making it the dominant source of noise in these devices. We also demonstrate a method of quantitatively determining the adsorption energies of chemicals on graphene surface based on noise measurements. We find that the magnitude of noise is extremely sensitive to the nature and amount of the chemical species present. We propose that a chemical sensor based on the measurement of low frequency resistance fluctuations of single layer graphene field effect transistor devices will have extremely high sensitivity, very high specificity, high fidelity, and fast response times.

Memory characteristics of flexible resistive switching devices with triangular-shaped silicon nanowire bottom electrodes

In this paper, we demonstrate the bipolar resistive switching characteristics of flexible resistive random access memory (ReRAM) devices, whose bottom electrodes are made of silicon nanowires (Si NWs) with a triangular structure, which offer preferential sites for the filaments. The temperature dependence of the low resistance state (LRS) of the resistive Al2O3/ZnO bilayers of ReRAM devices reveals that Ag filaments originating from the top Ag electrodes are responsible for bipolar resistive switching. With respect to the endurance characteristics of the LRS, resistance fluctuation is negligible because of the filaments generated at the specific sites of the vertices of the Si NW bottom electrodes. In addition, the resistive switching characteristics are maintained even after 1000 bending cycles.

Analytical fluctuation enhanced sensing by resistive gas sensors

Resistance fluctuations across polarised resistive gas sensors were studied in detail to evaluate sensor working conditions for detecting methane and ammonia at various concentrations. The 1/f noise component typically dominates other noise sources up to a few kHz and can be utilised to improve gas selectivity when compared with measurements of the sensor DC resistance. The Arrhenius plot was created and the activation energy for the investigated gases was evaluated. Using this method, different ambient gases can be potentially detected only by means of a single commercial Taguchi gas sensor and 1/f noise measurements at different temperatures of the gas sensing layer without a need of intense computations to get reliable results.

Virtual instruments in low-frequency noise spectroscopy experiments

Low-frequency noise spectroscopy (LFNS) is an experimental technique to study noise spectra, typically below 10 kHz, as a function of temperature. Results of LFNS may be presented as the ?so-called? noise maps, giving a detailed insight into fluctuating phenomena in electronic devices and materials. The authors show the usefulness of virtual instrument concept in developing and controlling the measurement setup for LFNS experiments. An example of a noise map obtained for polymer thick-film resistors (PTFRs), made of commercial compositions, for temperature range 77 K - 300 K has been shown. The experiments proved that 1/f noise caused by resistance fluctuations is the dominant noise component in the studied samples. However, the obtained noise map revealed also thermally activated noise sources. Furthermore, parameters describing noise properties of resistive materials and components have been introduced and calculated using data from LFNS. The results of the work may be useful for comparison of noise properties of different resistive materials, giving also directions for improvement of thick-film technology in order to manufacture reliable, low-noise and stable PTFRs.

New approaches for improving selectivity and sensitivity of resistive gas sensors: a review

Purpose – This paper aims to present the methods of improving selectivity and sensitivity of resistance gas sensors. Design/methodology/approach – This paper compares various methods of improving gas sensing by temperature modulation, UV irradiation or fluctuation-enhanced sensing. The authors analyze low-frequency resistance fluctuations in commercial Taguchi gas sensors and the recently developed tungsten trioxide (WO3) gas-sensing layers, exhibiting a photo-catalytic effect. Findings – The efficiency of using low-frequency fluctuations to improve gas detection selectivity and sensitivity was confirmed by numerous experimental studies in commercial and prototype gas sensors. Research limitations/implications – A more advanced measurement setup is required to record noise data but it will reduce the number of gas sensors necessary for identifying the investigated gas mixtures. Practical implications – Fluctuation-enhanced sensing can reduce the energy consumption of gas detection systems and assures better detection results. Originality/value – A thorough comparison of various gas sensing methods in resistance gas sensors is presented and supported by exemplary practical applications.

Modelling and detection of failure in medical electrodes

In this paper we have studied the failures in medical electrodes such as electroencephalogram electrodes (EEG) being used for collecting brain signals. As those electrodes have to guarantee high level of reliability it is important to explore and predict the possible occurrence of failures in there structure. The electrode tip (needle) made of stainless steel is covered with thin oxide film acting as a dielectric and determing the total electrode resistance. In fact, studying the fluctuations of that resistance gives the insight into defects of the whole structure. The electrical properties of the oxide layer are characterized by charge hopping mechanism and the total resistance could be modeled by implementing random resistance network (RRN) methodology.The applied computational algorithm is based on Monte Carlo simulation procedure with direct and iteration methods. The obtained simulation results show non-gaussian Bramwell-Holdsworth-Pinton (BHP) distribution of the total resistance fluctuations, and they verified by the experiments.

Improvement of resistive switching memory achieved by using arc-shaped bottom electrode

We demonstrated a resistive switching Pt/InGaZnO/Al memory device based on an arc-shaped bottom electrode (BE), which was fabricated by using a polystyrene (PS) nanosphere template. For the device without an arc-shaped BE, netlike conducting filaments (CFs) are easily formed, resulting in an incomplete rupture and a large resistance fluctuation. In comparison, the electric field direction would point to the center of the arc, instead of being vertical to the planar electrode. Therefore, the CFs prefer to form a simple, radial structure around the arc-shaped BE, and the simplified CFs are effective for achieving a narrower resistance distribution and RS improvement.

All-electrical frequency noise reduction and linewidth narrowing in quantum cascade lasers

A novel all-electrical method of frequency noise reduction in quantum cascade lasers (QCLs) is proposed. Electrical current through the laser was continuously adjusted to compensate for fluctuations of the laser internal resistance, which led to an active stabilization of the optical emission frequency. A reduction of the linewidth from 1.7 MHz in the standard constant current mode of operation down to 480 kHz is demonstrated at 10-ms observation time when applying this method to a QCL emitting at 7.9 μm.

Determining the electrical resistivity of coke powder

In order to improve means of determining the electrical resistivity of coke powder, existing methods are analyzed. Their basic deficiency is that it is difficult to identify and eliminate the influence of transient electrical resistance between the electrodes and the coke-powder sample, because it is impossible to ensure constant packing density of the powder column at constant pressure. Therefore, to eliminate fluctuations in the transient resistance, constant packing density of the sample is required. That may be ensured if the pressure varies over the sample. The influence of transient resistances on the measurement result may be eliminated by improving the pressing system and constructing a two-probe cell and also by replacing the potentiometer, milliammeter, voltmeter, rheostat, and battery with an up-to-date measuring module. Recommendations for improvement in the apparatus and method used in determining the resistivity of coke are developed, for use in a prototype system. In improving the resistivity determination, the constant parameters are the sample mass; the volume of the sample (and hence its density); and the current passing through the sample. The variable is the pressure applied to the coke sample. A method of determining the electrical resistivity of coke powder is developed, and three improved systems are created. Two undergo industrial tests at PAO Zaporozhkoks and ChAO Makeevkoks. The tests confirm the known dependence of the resistivity on the final coke temperature (in the range 900–1150°C) and the possibility of using the resistivity in judging the condition of the coke and correcting the coking temperature of the batch. Since the final coking temperature determines the size and strength of the coke particles, other conditions being equal, the condition of the coke (its readiness for use) may be assessed on the basis of a set of physicochemical characteristics.

Probing a spin-glass state inSrRuO3thin films through higher-order statistics of resistance fluctuations

The complex perovskite oxide ${\mathrm{SrRuO}}_{3}$ shows intriguing transport properties at low temperatures due to the interplay of spin, charge, and orbital degrees of freedom. One of the open questions in this system is regarding the origin and nature of the low-temperature glassy state. In this paper we report on measurements of higher-order statistics of resistance fluctuations performed in epitaxial thin films of ${\mathrm{SrRuO}}_{3}$ to probe this issue. We observe large low-frequency non-Gaussian resistance fluctuations over a certain temperature range. Our observations are compatible with that of a spin-glass system with properties described by hierarchical dynamics rather than with that of a simple ferromagnet with a large coercivity.

Resistance of helical edges formed in a semiconductor heterostructure

Time-reversal symmetry prohibits elastic backscattering of electrons propagating within a helical edge of a two-dimensional topological insulator. However, small band gaps in these systems make them sensitive to doping disorder, which may lead to the formation of electron and hole puddles. Such a puddle -- a quantum dot -- tunnel-coupled to the edge may significantly enhance the inelastic backscattering rate, due to the long dwelling time of an electron in the dot. The added resistance is especially strong for dots carrying an odd number of electrons, due to the Kondo effect. For the same reason, the temperature dependence of the added resistance becomes rather weak. We present a detailed theory of the quantum dot effect on the helical edge resistance. It allows us to make specific predictions for possible future experiments with artificially prepared dots in topological insulators. It also provides a qualitative explanation of the resistance fluctuations observed in short HgTe quantum wells. In addition to the single-dot theory, we develop a statistical description of the helical edge resistivity introduced by random charge puddles in a long heterostructure carrying helical edge states. The presence of charge puddles in long samples may explain the observed coexistence of a high sample resistance with the propagation of electrons along the sample edges.

Higher resources decrease fluctuating selection during host-parasite coevolution.

We still know very little about how the environment influences coevolutionary dynamics. Here, we investigated both theoretically and empirically how nutrient availability affects the relative extent of escalation of resistance and infectivity (arms race dynamic; ARD) and fluctuating selection (fluctuating selection dynamic; FSD) in experimentally coevolving populations of bacteria and viruses. By comparing interactions between clones of bacteria and viruses both within- and between-time points, we show that increasing nutrient availability resulted in coevolution shifting from FSD, with fluctuations in average infectivity and resistance ranges over time, to ARD. Our model shows that range fluctuations with lower nutrient availability can be explained both by elevated costs of resistance (a direct effect of nutrient availability), and reduced benefits of resistance when population sizes of hosts and parasites are lower (an indirect effect). Nutrient availability can therefore predictably and generally affect qualitative coevolutionary dynamics by both direct and indirect (mediated through ecological feedbacks) effects on costs of resistance.

Measurements of Low Frequency Noise of Infrared Photo-Detectors with Transimpedance Detection System

Abstract The paper presents the method and results of low-frequency noise measurements of modern mid-wavelength infrared photodetectors. A type-II InAs/GaSb superlattice based detector with nBn barrier architecture is compared with a high operating temperature (HOT) heterojunction HgCdTe detector. All experiments were made in the range 1 Hz - 10 kHz at various temperatures by using a transimpedance detection system, which is examined in detail. The power spectral density of the nBn’s dark current noise includes Lorentzians with different time constants while the HgCdTe photodiode has more uniform 1/f - shaped spectra. For small bias, the low-frequency noise power spectra of both devices were found to scale linearly with bias voltage squared and were connected with the fluctuations of the leakage resistance. Leakage resistance noise defines the lower noise limit of a photodetector. Other dark current components give raise to the increase of low-frequency noise above this limit. For the same voltage biasing devices, the absolute noise power densities at 1 Hz in nBn are 1 to 2 orders of magnitude lower than in a MCT HgCdTe detector. In spite of this, low-frequency performance of the HgCdTe detector at ~ 230K is still better than that of InAs/GaSb superlattice nBn detector.

Low-frequency resistance fluctuations in a single nanowire (diameter ≈ 45 nm) of a complex oxide and its relation to magnetic transitions and phase separation

We report measurement of low frequency resistance noise spectroscopy in a single strand of a nanowire (NW) (diameter ≈ 45 nm) of a complex oxide manganite La0.5Sr0.5MnO3, that showed ferromagnetic transition (TC ≈ 315 K), an antiferromagnetic transition (TN ≈ 210 K) and a phase-separated region below TN. We demonstrated that noise spectroscopy in a single NW can cleanly detect the magnetic transitions including the phase-coexistence that may not be possible to do by magnetic measurements. The normalized noise in the single NW is an order less than that reported in ultralow-noise Si Junction Field Effect Transistor.

Conductivity noise study of the insulator-metal transition and phase coexistence in epitaxial samarium nickelate thin films

Interaction between the lattice and the orbital degrees of freedom not only makes rare-earth nickelates unusually "bad metal", but also introduces a temperature driven insulator-metal phase transition. Here we investigate this insulator-metal phase transition in thin films of $\mathrm{SmNiO_3}$ using the slow time dependent fluctuations (noise) in resistivity. The normalized magnitude of noise is found to be extremely large, being nearly eight orders of magnitude higher than thin films of common disordered metallic systems, and indicates electrical conduction via classical percolation in a spatially inhomogeneous medium. The higher order statistics of the fluctuations indicate a strong non-Gaussian component of noise close to the transition, attributing the inhomogeneity to co-existence of the metallic and insulating phases. Our experiment offers a new insight on the impact of lattice-orbital coupling on the microscopic mechanism of electron transport in the rare-earth nickelates.

Electrical resistance and 1/f fluctuations in thin titanium films

The thickness of a metallic layer has been determined and the resistivity and spectral density of voltage fluctuations in thin titanium films with initial thicknesses of 5–100 nm, which were obtained by magnetron sputtering and intended for promising elements of the neutron optics, have been investigated. It has been found that a continuous metallic layer necessary for functioning is retained even in thinnest samples, and excess fluctuations of the layer resistance with the 1/f-type spectrum are observed. It has been shown that the method of measuring film resistivity can be used as effective express-method of determining the thickness of metallic nanolayers.

Voltage noise across a metal/metal sliding contact as a probe of the surface state

We report a complete experimental study and a physical modelling of the long-term evolution of the main electrical properties of a metal ring/wire sliding contact, the wire, and the ring being coated with a thin Au film. The long-term evolution of the Au/Au sliding contact was characterized through the measurement and tracking of relevant quantities such as the voltage noise across the contact, revealing the ageing of the contact. A phenomenological approach to the sliding contact, coupling both electrical and mechanical aspects, allows a sensible interpretation of the experimental results. This approach retains three contributions to the voltage noise operating at different scales, namely the rings surface geometry, chemical composition fluctuations of the coated rings, and the mesoscopic structure of the contact. A fundamental distinction between these sources is established, owing to their effects relying on either the mechanical contact losses or resistance fluctuations. We finally show that the determination and tracking of these noise sources using reasonable specific indexes lead to reliable criterions of the electrical contact quality.

Piezoresistive Properties of Ag/Silica Nano‐Composite Thin Films Close to the Percolation Threshold

The effect of mechanical stress on the electrical properties of Ag/silica nano‐composite sol–gel films, fabricated using an ultra‐violet (UV) photo‐reduction process, is studied over a large range of Ag volume fractions, φ. The ability to finely tune φ in situ by varying the UV exposure time enables the direct identification of the critical volume fraction, φ* ≈ 13.1%, around which the resistance changes by 6 orders of magnitude and the average piezoresistive gage factor, <G>, peaks at 4330. <G> is orders of magnitude larger than that of bulk silicon and φ* is close to the value expected for percolation in 3 dimensions. It is shown experimentally that this giant piezoresistance is the result of a stress‐induced change in the average Ag cluster size that significantly modifies the sample resistance when φ ∼ φ*. In terms of the potential use of any composite material as a sensitive strain sensor, a sensor figure‐of‐merit (F) that accounts for both <G> and for the measured, expected divergence in resistance fluctuations close to φ* is defined. It is shown that maximum F is achieved in composites slightly to the metallic side of the percolation transition. In the case studied here, the maximum value of F, which is 5–10 times larger than that measured on commercial strain gages under the same conditions, is obtained for φ ≈ 13.4%. The ability to finely tune φ in‐situ therefore suggests that Ag/silica nano‐composites could be the basis for a highly sensitive, low power, strain sensing technology.

Degradation Phenomenon of Electrical Contacts by Oscillating Mechanisms - Modeling about Fluctuation of Contact Resistance -

Degradation Phenomenon of Electrical Contacts by Oscillating Mechanisms - Modeling about Fluctuation of Contact Resistance -

Degradation Phenomenon of Electrical Contacts by using a Micro-Sliding Mechanism -Modeling about Fluctuation of Contact Resistance-

Degradation Phenomenon of Electrical Contacts by using a Micro-Sliding Mechanism -Modeling about Fluctuation of Contact Resistance-