Resistance Fluctuations Research Articles

UV-Light-Induced Fluctuation Enhanced Sensing by WO3-Based Gas Sensors

WO3-based gas sensors were investigated under UV-light irradiation and at different working temperatures with the object of achieving superior sensitivity and selectivity. Resistance fluctuations in the WO3 layer were studied together with dc resistance measurements. The data were taken in synthetic air, ethanol, nitrogen dioxide, and mixtures of these gases. We conclude that UV irradiation can easily be applied to enhance the gas sensing properties of a WO3 layer.

Detection and Sizing of Single Droplets Flowing in a Microfluidic Device by Impedance Measurement

This article reports on the evaluation of the electrochemical noise technique consisting in measuring the fluctuations of the electrolyte resistance (ER, impedance at high frequency) between two metallic electrodes immerged in a conductive electrolyte to detect and characterize single particles circulating in a microfluidic device. Numerical simulations were performed with the finite element method to study the influence of the dimensions of the channel and the electrodes on the impedance. Excellent agreement was obtained between the theoretical and experimental results, which allowed the diameter of the oil droplets to be estimated with an accuracy of a few percents in the case of droplet diameters ranging from 60 to 100 μm. Developments of smaller microfluidic devices are under progress to detect and characterize particles of a few micrometers, such as biological cells for example.

Composite resistor standard for calibration of measuring transducers in laboratory conditions

Calibration of measuring transducers for precision measurement is done by measuring voltage drop at the resistor standard, produced by output dc current proportional to the input measured value. Resistance fluctuations due to the temperature coefficient of the resistor standard are minor, thanks to the stable temperature conditions in laboratory environment. This fact brings the need to calculate the effect of resistor self-heating on its resistance. This thermal effect, produced by the flow of current through the resistor, is often disregarded. For the precise measurements this can be a significant source of error and must be quantified. This paper describes mathematical model of measurement error, resistor self-heating coefficient is defined, as it?s not usually given in product datasheets. The effect on measurement results is given in detail. Composite resistor standard prototype is described, made from off-the-shelf mass produced components, calculated and hand selected to cancel the self-heating coefficient effects. The prototype is compared to the existing commercially available high performance resistor standard.

Nature of low-frequency noise in homogeneous semiconductors.

This report deals with a 1/f noise in homogeneous classical semiconductor samples on the base of silicon. We perform detail calculations of resistance fluctuations of the silicon sample due to both a) the charge carrier number changes due to their capture–emission processes, and b) due to screening effect of those negative charged centers, and show that proportionality of noise level to square mobility appears as a presentation parameter, but not due to mobility fluctuations. The obtained calculation results explain well the observed experimental results of 1/f noise in Si, Ge, GaAs and exclude the mobility fluctuations as the nature of 1/f noise in these materials and their devices. It is also shown how from the experimental 1/f noise results to find the effective number of defects responsible for this noise in the measured frequency range.

Noise Measurements Of Resistors With The Use Of Dual-Phase Virtual Lock-In Technique

Abstract Measurement of low-frequency noise properties of modern electronic components is a very demanding challenge due to the low magnitude of a noise signal and the limit of a dissipated power. In such a case, an ac technique with a lock-in amplifier or the use of a low-noise transformer as the first stage in the signal path are common approaches. A software dual-phase virtual lock-in (VLI) technique has been developed and tested in low-frequency noise studies of electronic components. VLI means that phase-sensitive detection is processed by a software layer rather than by an expensive hardware lock-in amplifier. The VLI method has been tested in exploration of noise in polymer thick-film resistors. Analysis of the obtained noise spectra of voltage fluctuations confirmed that the 1/f noise caused by resistance fluctuations is the dominant one. The calculated value of the parameter describing the noise intensity of a resistive material, C = 1·10−21 m3, is consistent with that obtained with the use of a dc method. On the other hand, it has been observed that the spectra of (excitation independent) resistance noise contain a 1/f component whose intensity depends on the excitation frequency. The phenomenon has been explained by means of noise suppression by impedances of the measurement circuit, giving an excellent agreement with the experimental data.

Bulk-Induced 1/f Noise at the Surface of Three-Dimensional Topological Insulators.

Slow intrinsic fluctuations of resistance, also known as the flicker noise or 1/f-noise, in the surface transport of strong topological insulators (TIs) is a poorly understood phenomenon. Here, we have systematically explored the 1/f-noise in field-effect transistors (FET) of mechanically exfoliated Bi1.6Sb0.4Te2Se TI films when transport occurs predominantly via the surface states. We find that the slow kinetics of the charge disorder within the bulk of the TI induces mobility fluctuations at the surface, providing a new source of intrinsic 1/f-noise that is unique to bulk TI systems. At small channel thickness, the noise magnitude can be extremely small, corresponding to the phenomenological Hooge parameter γH as low as ≈10(-4), but it increases rapidly when channel thickness exceeds ∼1 μm. From the temperature (T)-dependence of noise, which displayed sharp peaks at characteristic values of T, we identified generation-recombination processes from interband transitions within the TI bulk as the dominant source of the mobility fluctuations in surface transport. Our experiment not only establishes an intrinsic microscopic origin of noise in TI surface channels, but also reveals a unique spectroscopic information on the impurity bands that can be useful in bulk TI systems in general.

Dynamic phase coexistence and non-Gaussian resistance fluctuations inVO2near the metal-insulator transition

We have carried out an extensive investigation on the resistance fluctuations (noise) in an epitaxial thin film of ${\mathrm{VO}}_{2}$ encompassing the metal-insulator transition (MIT) region to investigate the dynamic phase coexistence of metal and insulating phases. Both flicker noise as well as the Nyquist noise (thermal noise) were measured. The experiments showed that flicker noise, which has a $1/f$ spectral power dependence, evolves with temperature in the transition region following the evolution of the phase fractions and is governed by activated kinetics. Importantly, closer to the insulating end of the transition, when the metallic phase fraction is low, the magnitude of the noise shows an anomaly and a strong non-Gaussian component of noise develops. In this region, the local electron temperature (as measured through the Nyquist noise thermometry) shows a deviation from the equilibrium bath temperature. It is proposed that this behavior arises due to current crowding where a substantial amount of the current is carried through well separated small metallic islands leading to a dynamic correlated current path redistribution and an enhanced effective local current density. This leads to a non-Gaussian component to the resistance fluctuation and an associated local deviation of the electron temperature from the bath. Our experiment establishes that phase coexistence leads to a strong inhomogeneity in the region of MIT that makes the current transport strongly inhomogeneous and correlated.

Resistance fluctuations in insulating silicon films with superconducting nanoprecipitates – superconductor-to-metal or vortex matter phase transition?

Silicon films with Ga-rich nanoprecipitates are superconductors or insulators in dependence on their normal state resistance. Even in the insulating state of the film superconducting nanoprecipitates exist below the critical temperature of 7 K and determine its complex transport behavior. In this range sometimes large, random resistance jumps appear that are accompanied by little temperature changes. The resistance fluctuates between a well-defined low-resistance value and a broader band of higher resistances. Jumps to higher resistance are associated with a temperature decrease and vice versa. We present experimental results on these fluctuations and suppose a first order phase transition in the film as probable origin.

Antibiotic resistance monitoring in Vibrio spp. isolated from rearing environment and intestines of abalone Haliotis diversicolor

546 Vibrio isolates from rearing seawater (292 strains) and intestines of abalone (254 strains) were tested to ten antibiotics using Kirby–Bauer diffusion method. Resistant rates of abalone-derived Vibrio isolates to chloramphenicol (C), enrofloxacin (ENX) and norfloxacin (NOR) were <28%, whereas those from seawater showed large fluctuations in resistance to each of the tested antibiotics. Many strains showed higher resistant rates (>40%) to kanamycin (KNA), furazolidone (F), tetracycline (TE), gentamicin (GM) and rifampin (RA). 332 isolates from seawater (n=258) and abalone (n=74) were resistant to more than three antibiotics. Peaked resistant rates of seawater-derived isolates to multiple antibiotics were overlapped in May and August. Statistical analysis showed that pH had an important effect on resistant rates of abalone-derived Vibrio isolates to RA, NOR, and ENX. Salinity and dissolved oxygen were negatively correlated with resistant rates of seawater-derived Vibrio isolates to KNA, RA, and PG.

Universal crossover of the charge carrier fluctuation mechanism in different polymer/carbon nanotubes composites

Carbon nanotubes added to polymer and epoxy matrices are compounds of interest for applications in electronics and aerospace. The realization of high-performance devices based on these materials can profit from the investigation of their electric noise properties, as this gives a more detailed insight of the basic charge carriers transport mechanisms at work. The dc and electrical noise characteristics of different polymer/carbon nanotubes composites have been analyzed from 10 to 300 K. The results suggest that all these systems can be regarded as random resistive networks of tunnel junctions formed by adjacent carbon nanotubes. However, in the high-temperature regime, contributions deriving from other possible mechanisms cannot be separated using dc information alone. A transition from a fluctuation-induced tunneling process to a thermally activated regime is instead revealed by electric noise spectroscopy. In particular, a crossover is found from a two-level tunneling mechanism, operating at low temperatures, to resistance fluctuations of a percolative network, in the high-temperature region. The observed behavior of 1/f noise seems to be a general feature for highly conductive samples, independent on the type of polymer matrix and on the nanotube density.

Improvement of resistive switching fluctuations by using one step lift‐off process

Bipolar resistive switching characteristics are investigated in ZrO2 containing Cu thin layer devices, particularly for the self‐isolated‐structure device fabricated by one step lift‐off process. Compared with the traditional‐structure device, the self‐isolated‐structure device shows more uniform resistive switching characteristics. This is because the isolation of each device cell has negligible influence on each other and thus mitigates possible crosstalk between each cell. These results suggest that the feasibility of good stabilization of the resistive switching parameters can be obtained through one step lift‐off process. (© 2015 WILEY‐VCH Verlag GmbH &amp;Co. KGaA, Weinheim)

Wearable Electronics of Silver-Nanowire/Poly(dimethylsiloxane) Nanocomposite for Smart Clothing.

Wearable electronics used in smart clothing for healthcare monitoring or personalized identification is a new and fast-growing research topic. The challenge is that the electronics has to be simultaneously highly stretchable, mechanically robust and water-washable, which is unreachable for traditional electronics or previously reported stretchable electronics. Herein we report the wearable electronics of sliver nanowire (Ag-NW)/poly(dimethylsiloxane) (PDMS) nanocomposite which can meet the above multiple requirements. The electronics of Ag-NW/PDMS nanocomposite films is successfully fabricated by an original pre-straining and post-embedding (PSPE) process. The composite film shows a very high conductivity of 1.52 × 104 S cm−1 and an excellent electrical stability with a small resistance fluctuation under a large stretching strain. Meanwhile, it shows a robust adhesion between the Ag-NWs and the PDMS substrate and can be directly machine-washed. These advantages make it a competitive candidate as wearable electronics for smart clothing applications.

Resistive switching phenomena: A review of statistical physics approaches

Resistive switching (RS) phenomena are reversible changes in the metastable resistance state induced by external electric fields. After discovery ∼50 years ago, RS phenomena have attracted great attention due to their potential application in next-generation electrical devices. Considerable research has been performed to understand the physical mechanisms of RS and explore the feasibility and limits of such devices. There have also been several reviews on RS that attempt to explain the microscopic origins of how regions that were originally insulators can change into conductors. However, little attention has been paid to the most important factor in determining resistance: how conducting local regions are interconnected. Here, we provide an overview of the underlying physics behind connectivity changes in highly conductive regions under an electric field. We first classify RS phenomena according to their characteristic current–voltage curves: unipolar, bipolar, and threshold switchings. Second, we outline the microscopic origins of RS in oxides, focusing on the roles of oxygen vacancies: the effect of concentration, the mechanisms of channel formation and rupture, and the driving forces of oxygen vacancies. Third, we review RS studies from the perspective of statistical physics to understand connectivity change in RS phenomena. We discuss percolation model approaches and the theory for the scaling behaviors of numerous transport properties observed in RS. Fourth, we review various switching-type conversion phenomena in RS: bipolar-unipolar, memory-threshold, figure-of-eight, and counter-figure-of-eight conversions. Finally, we review several related technological issues, such as improvement in high resistance fluctuations, sneak-path problems, and multilevel switching problems.

High-Performance Sensors Based on Resistance Fluctuations of Single-Layer-Graphene Transistors.

One of the most interesting predicted applications of graphene-monolayer-based devices is as high-quality sensors. In this article, we show, through systematic experiments, a chemical vapor sensor based on the measurement of low-frequency resistance fluctuations of single-layer-graphene field-effect-transistor devices. The sensor has extremely high sensitivity, very high specificity, high fidelity, and fast response times. The performance of the device using this scheme of measurement (which uses resistance fluctuations as the detection parameter) is more than 2 orders of magnitude better than a detection scheme in which changes in the average value of the resistance is monitored. We propose a number-density-fluctuation-based model to explain the superior characteristics of a noise-measurement-based detection scheme presented in this article.

Metal nano-film resistivity chemical sensor.

In this work, we present a study on reusable thin metal film resistivity-based sensor for direct measurement of binding of thiol containing molecules in liquid samples. While in bulk conductors the DC current is not influenced by the surface events to a measureable degree in a thin metal layer the electrons close to the surface conduct a significant part of electricity and are influenced by the surface interactions. In this study, the thickness of the gold layer was kept below 100 nm resulting in easily measureable resistivity changes of the metal element upon a surface SH-groups binding. No further surface modifications were necessary. Thin film gold layers deposited on a glass substrate by vacuum sputtering were photolithographically structured into four sensing elements arranged in a Wheatstone bridge to compensate for resistance fluctuations due to the temperature changes. Concentrations as low 100 pM provided measureable signals. The surface after the measurement could be electrolytically regenerated for next measurements.

Doped ZnO Nanorod Array for Ultra Low NO2 Sensing

NO2 is an important marker in the human breath for asthma whose concentration is proportional to the amount of inflammation in the lungs caused by infections. NO2 is also present in the exhaust of the vehicles and the OSHA recommends no more than 5 ppm NO2 in air. Currently 235 million people are suffering from asthma worldwide and the number is expected to increase drastically owing to the increase in global pollution level and dependence on fossil fuel. Metal oxide semiconductors such ZnO have remarkable sensing properties for, NO2. Sensor response (S) is a function of the resistance of the ZnO on inter-digitated Au electrodes which is given by the following equation: S = Rair/Rgas , where, Rgas is the resistance of the film in presence of testing analyte and Rair is the resistance of the film in air. The gas detection occurs because of the reaction on the ZnO surface in presence of the NO2 molecule which causes a reduction in electron concentration and hence fluctuation in electrical resistance. This can be explained by the following equation: NO2 + e- = NO+ + O- ads Here we report synthesis of TiO2 coated ZnO, Mg, Co, and Ag doped as well as undoped thin ZnO nanorod array directly on Au interdigitated electrodes using a low cost, environmentally friendly and large area application two-step chemical bath deposition (CBD) technique [1, 2] for selective detection of ultralow (0.1 ppm) NO2 in humid air at 280 °C. The structure and morphology of the ZnO films prepared by CBD has been probed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM). The as-prepared doped and undoped ZnO sensors were tested for the detection of NO2 (0.1-5 ppm in simulated breath) in the temperature range of 50-280 ˚C as shown in the figure 1. Characteristics such as sensitivity, selectivity, limit of detection, reproducibility, and stability will be reported. Role of dopants in enhancing the selectivity will be explained. The selectivity for the interfering analytes such as humidity, CO2, NO2, H2 and ammonia will also be investigated. Finally the sensing mechanism will be discussed in detail.

Ultra low 1/f noise in suspended bilayer graphene

We have studied 1/f noise power SI in suspended bilayer graphene devices. Around the Dirac point, we observe ultra low noise amplitude on the order of f*SI/Ib2=10−9. The low frequency noise level is barely sensitive to intrinsic carrier density, but temperature and external doping are found to influence the noise power. In our current-annealed samples, the 1/f noise is dominated by resistance fluctuations at the contacts. Temperature dependence of the 1/f noise suggests the presence of trap states in the contact regions, with a nearly exponential distribution function displaying a characteristic energy of 0.12 eV. At 80 K, the noise displays an air pressure sensitivity that corresponds to ∼0.3 ppm gas detection sensitivity; this indicates the potential of suspended graphene as a platform for gas sensing applications.

Gate-controlled semimetal-topological insulator transition in an InAs/GaSb heterostructure

We report a gate-controlled transition of a semimetallic InAs/GaSb heterostructure to a topological insulator. The transition is induced by decreasing the degree of band inversion with front and back gate voltages. Temperature dependence of the longitudinal resistance peak shows the energy gap opening in the bulk region with increasing gate electric field. The suppression of bulk conduction and the transition to a topological insulator are confirmed by nonlocal resistance measurements using a dual lock-in technique, which allows us to rigorously compare the voltage distribution in the sample for different current paths without the influence of time-dependent resistance fluctuations.

Noise Properties Of Thick-Film Conducting Lines For Integrated Inductors

Abstract Studies of noise properties of thick-film conducting lines from Au or PdAg conductive pastes on LTCC or alumina substrates are reported. Experiments have been carried out at the room temperature on samples prepared in the form of meanders by traditional screen-printing or laser-shaping technique. Due to a low resistance of the devices under test (DUTs), low-frequency noise spectra have been measured for the dc-biased samples arranged in a bridge configuration, transformer-coupled to a low-noise amplifier. The detailed analysis of noise sources in the signal path and its transfer function, including the transformer, has been carried out, and a procedure for measurement setup self-calibration has been described. The 1/f noise component originating from resistance fluctuations has been found to be dominant in all DUTs. The analysis of experimental data leads to the conclusion that noise is produced in the bends of meanders rather than in their straight segments. It occurs that noise of Au-based laser-shaped lines is significantly smaller than screen-printed ones. PdAg lines have been found more resistive but simultaneously less noisy than Au-based lines.

Critical slowing down of the charge carrier dynamics at the Mott metal-insulator transition.

We report on the dramatic slowing down of the charge carrier dynamics in a quasi-two-dimensional organic conductor, which can be reversibly tuned through the Mott metal-insulator transition (MIT). At the finite-temperature critical end point, we observe a divergent increase of the resistance fluctuations accompanied by a drastic shift of spectral weight to low frequencies, demonstrating the critical slowing down of the order parameter (doublon density) fluctuations. The slow dynamics is accompanied by non-Gaussian fluctuations, indicative of correlated charge carrier dynamics. A possible explanation is a glassy freezing of the electronic system as a precursor of the Mott MIT.