Low-Frequency Noise and Resistivity of Hybrid MWCNT/Ni@C/EPOXY Composites

The comprehensive study of resistivity and low frequency (10[Formula: see text]Hz–20[Formula: see text]kHz) noise characteristics of hybrid polymer composites with multi-walled carbon nanotubes (MWCNTs) and onion-like carbon (OLC) particles in one material have been carried out in the wide temperature range ((75–380) K). The characteristic dependences on the fillers density and the dominant conduction mechanisms were investigated. At low temperature ((75–170) K), the resistivity dependences on temperature are well-fitted by the Mott’s formula for the quasi-one-dimensional charge carrier variable range hopping and Arrhenius law. At temperatures above 300[Formula: see text]K, the resistance increases with temperature due to matrix expansion and decreases due to the onset of the conductivity in the matrix. Low frequency voltage noise spectra comprise of 1/[Formula: see text] and Lorentzian-type components with characteristic times in the range from 0.1[Formula: see text][Formula: see text]s to 10[Formula: see text][Formula: see text]s; the noise spectral density in the region of Ohmic resistance is proportional to the voltage square. Therefore, thermally activated charge carrier capture centers randomly modulate the sample’s resistance and control the carrier hopping. Impulse noise and more sudden changes of the noise characteristics were observed at the temperatures, where the conduction mechanisms change.

Resistivity and low frequency (10 Hz – 20 kHz) noise characteristics of composite materials with multi-walled carbon nanotubes (MWCNTs) have been carried out over wide voltage and temperature (73–380 K) ranges. Composite materials with epoxy-grafted (MWCNT's surface covered by liquid epoxy resin) and amino-grafted (MWCNT's surface covered by polyethylene polyamine) MWCNTs were investigated. Low-frequency noise spectra of investigated materials comprise of 1/fα-type components, what indicates that conduction is caused by Mott's hopping between carbon nanoparticles controlled by charge carrier capture and release processes in localized states between them. MWCNT's surface treatment by polyethylene polyamine leads to the larger density of surface states and at the same time more intensive low frequency fluctuations.

Ultra-wide bandgap (UWBG) semiconductors have attracted tremendous amount of interest for applications in high-power electronics and solar-blind UV photodetectors. In particular, β-Ga2O3 has attracted significant research attention in recent years due to its promising electrical and optical characteristics including a large bandgap, high breakdown electrical field, and large Baliga’s figure of merit compared to well-established wide-bandgap technologies such as GaN and SiC [1].Low frequency electronic noise, which is present in all electronic devices, can be used as a diagnostic tool for semiconductor material and device characterization. By studying the low frequency noise in semiconductor materials and devices, the physics associated with the noise properties of bulk and interface defects and traps can be investigated [2]. Measurement of low frequency noise is also crucial for evaluating material quality and device reliability.In this work, we investigate the forward-bias diode parameters and low-frequency electronic noise in Au-W/β-Ga2O3 Schottky barrier diodes. The Schottky contact is formed by depositing 20 nm of Tungsten (W) using dc sputtering followed by 340 nm of Gold (Au) using e-beam evaporation, and subsequent annealing [3].We first measure the I-V characteristics and extract important diode parameters, such as the Schottky barrier height, ideality factor, and series resistance from room temperature forward-bias current-voltage characteristics. The extracted Schottky barrier height for these devices is in the range 0.7-0.8 eV and the ideality factor is approximately 1.2.We next measure the low-frequency electronic noise in Au-W/β-Ga2O3 Schottky diodes at different forward bias voltages at room temperature. We find that the current noise spectral density exhibits 1/f-type behavior for all forward bias voltages at low frequency with an exponent ranging from 0.75 to 1.15, indicating that the low frequency noise of these devices is dominated by excess (flicker) noise. No Lorentzian-shaped generation-recombination (G-R) noise is observed. At low frequencies, the shot noise contribution is found to be negligible for the values of the current in our devices, and the total noise is 1/f-limited.We also investigate the dependence of the current noise spectral density on forward bias current, revealing different relationships in different current regimes. At low currents, the noise spectral density is found to scale approximately as the square of current, whereas at high currents, the noise spectral density begins to saturate. Such noise behavior can be attributed to different noise sources dominating in different current regimes. Furthermore, using the noise figure of merit adapted for ultra-wide bandgap semiconductor devices [4], we find that the Au-W/β-Ga2O3 devices have lower noise levels compared to other emerging UWBG materials and similar noise levels as well-established technologies such as GaN.These results provide important insights into the electronic noise properties of Au-W/β-Ga2O3 Schottky diodes and show that low frequency noise characterization is an important diagnostic tool for assessing the quality and reliability of gallium oxide based wide-bandgap materials and device technologies.

In this study, three various types of fillers; pristine multi-walled carbon nanotube (MWCNT), hydroxyl functionalized multi-walled carbon nanotube (MWCNT-OH) and carboxyl functionalized multi-walled carbon nanotube (MWCNT-COOH) were used to prepare epoxy (EP) composites via ultrasonication and casting techniques. The effect of pristine MWCNT and functionalized MWCNT (MWCNT-OH and MWCNT-COOH) and fillers loading (0-1.0 vol%) on tensile properties of EP composites were investigated and compared. To identify the effectiveness of functional groups on the EP composites, the MWCNT, MWCNT-OH and MWCNT-COOH were compared through tensile testing. The addition of pristine MWCNT decreased the material’s tensile strength and modulus, while the addition of MWCNT-OH decreased the material’s tensile strength. However, among the EP composites, the 0.4 vol% MWCNT-COOH/EP composite exhibited a 12.80% increase in tensile strength (44 MPa). The tensile modulus of 0.4 vol% MWCNT-OH/EP and MWCNT-COOH/EP composites were found to be significantly higher compared to unfilled epoxy which were approximately 15.60% (2376 MPa) and 18.54% (2436 MPa) respectively. In conclusion, the MWCNT-COOH/EP composite showed slight improvement in both the tensile strength and modulus. The effect of functionalized MWCNT was supported by morphological analysis, which demonstrated an improvement in MWCNT-COOH dispersion with slightly fine agglomerates particles at 0.4 vol%.

In this paper, the forward bias conduction and low frequency noise (LFN) characteristics of GaN Schottky barrier diodes (SBDs) have been measured and studied in the temperature range from 300 K to 450 K. Based on I–V measured results, the temperature dependence of ideality factor and zero bias Schottky barrier height reveals the inhomogeneities of Schottky barriers at the metal-semiconductor (MS) interface. Further study of the LFN measured results shows that the flicker noise ([Formula: see text] noise) is the main component of LFN in GaN SBDs. The current dependence of LFN indicates the influences of the Schottky barrier and the series resistance on [Formula: see text] noise, and the temperature dependence of LFN is analyzed according to Luo’s model and the barrier inhomogeneities model.

In this article, amino functionalized multiwalled carbon nanotubes (MWCNTs) were prepared by chemical modification of the surface of a MWCNTs using γ-aminopropyltriethoxysilane (APTES) and dispersed into the epoxy composition. The modifying agent (APTES) was directly deposited on the MWCNTs surfaces. For the functionalization of MWCNTs, was used not the APTES concentrate, as it had been described in previous works, but its freshly prepared aqueous solution. Properties of APTES-treated MWCNTs were characterized by transmission electron microscope (TEM), Raman spectroscopy and FT-IR. The results showed that the functionalization and chemical compatibility of APTES-treated MWCNTs with epoxy composition provides their best dispersion in the epoxy composition, had important influence on curing behavior, structure and physicochemical properties of the epoxy composites plasticized with trichloroethyl phosphate. The results showed that the functionalization and chemical compatibility of APTES-treated MWCNTs with epoxy composition provides increased of physicomechanical properties of epoxy composites: bending stress increases by 194% and bending modulus increases by 137%, the tensile strength increases by 108% and the tensile elastic modulus increases by 52%, impact strength increases by 300%, in comparison with plasticized epoxy composite that does not contain MWCNTs.

In the present study, the MWNT/epoxy composites are prepared with three weight percentages (0.0, 0.3, and 0.5%) of multiwall carbon nanotube (MWNT). The temporal response of multi-wall carbon nanotube (MWNT)/epoxy composite with different wt% of multi-wall carbon nanotube (MWNT) is measured by experiment. Also, a cavity-type measuring system is designed to experimentally measure the surface temperatures and obtain the thermal conductivity of these composites at different heating rates. It is found that the responses of the 0.3 and 0.5% weight percentage of multi-wall carbon nanotube (MWNT)/epoxy composites are found to be about 25 and 47.8%, respectively, faster than that of the pure epoxy resin. Both the responding characteristics and the variation trends of the measured surface temperatures of these composites can be well predicted by the lumped-heat capacity model. Besides, the higher the weight percentage (wt%) of multi-wall carbon nanotube (MWNT) in the composite, the larger is the thermal conductivity. Relative to the pure epoxy, the thermal conductivities for the composites with 0.3 and 0.5% of multi-wall carbon nanotube (MWNT) increase by 15.9 and 44.9%, respectively. For the weight percentages studied, the thermal conductivity of these composites is found to increase mildly at low heating rates; however, it remains nearly constant at high heating rates.

In this work we propose a measurement setup topology suitable for the automatic DC and low frequency noise (LFN) characterization of field effect transistors at wafer level. The system is composed of source and measure units (SMUs), by a custom-built low noise amplifier (LNA), and by a PC based spectrum analyzer. No bias filters and switch matrices are used, allowing fast switching between DC and LFN measurements together with low leakage. The programmable LNA can reach background noise levels in the order of fA/Hz1/2, while DC performances are limited by the SMUs. The main feature of the proposed system is the high degree of operational flexibility due to the complete PC-based software control. LFN characterization, down to bias DC currents of 1pA, in organic thin film transistors is reported to demonstrate system operation and performances.

A hetero‐structured hybrid was produced by grafting one‐dimensional (1D) amine‐functionalized multiwalled carbon nanotubes (MWCNTs) onto the basal plane of two‐dimensional (2D) graphene oxide (GO) via an amine‐epoxy ring‐opening reaction, and such hybrid was further applied for reinforcing epoxy composites. Based on this hybrid design, 1D MWCNTs anchored on the 2D GO nanosheets resisted the re‐stacking of GO nanosheets while GO improved the MWCNTs' dispersion state. Attributing to the synergistic effect of GO and MWCNTs, a multi‐dimensional conducting network within epoxy matrix was constructed and efficiently transferred stress and heat between hybrid and matrix. When just 0.5 wt% hybrids were incorporated, the mechanical properties, thermal stability and thermal conductivity of hybrid‐filled epoxy composites were significantly improved, compared with pure epoxies. This work gives a promising method for designing and preparing polymer composites for thermal management and protection applications. Highlights A hetero‐structured hybrid consisting of MWCNTs and GO was obtained. Better dispersion of GO–MWCNTs within matrix was achieved. A multi‐dimensional GO–MWCNTs conducting network in matrix was constructed. Enhanced properties were due to the synergistic effect of GO and MWCNTs. Structural performance of GO and MWCNTs was maximized.

In the present investigation, two methods were used for addition multiwall carbon nanotubes (MWCNTS) into carbon fiber (CF)/epoxy resin composite system. The mechanical properties of the prepared samples were compared to show the best method for addition of MWCNTS from point of view of mechanical properties. The introduction of carbon nanotubes (CNTs) into fiber reinforced polymer composites has been achieved mainly via two routes: mixing CNTs entirely throughout the matrix (matrix modification) or attaching CNTs onto reinforcing fibers (interface modification). In all previous references the addition of CNTs occur through one route from the two routes but in this research, we introduced MWCNTS into CF/epoxy resin composite through the two routes at the same time. Three CF composite samples were prepared CF/epoxy resin composite (C1), CF/1wt% MWCNTS /epoxy resin composite (C2) in which MWCNTS added via one route (epoxy resin system) and the third sample was CF/1wt% MWCNTS / epoxy resin composite (C3) in which MWCNTS added via two routes (epoxy resin and CF fabric). The result shows that the mechanical properties of C3>C2>C1, for example, the flexural strength of C3 higher than C2 by 19% and C2 higher than C1 by 51% respectively. This is because addition MWCNTS via two routes increase the ability of good mixing of CNTS with epoxy resin and good dispersion of CNTs into the CF fabric surface and this leads to improve the interface bonding between the CF and epoxy so improve the mechanical properties.

Effects of multi-walled carbon nanotubes (MWNTs) on flame retardation as well as thermal stabilization efficiency of two phosphorus-containing flame retardant systems i.e., ammonium polyphosphate/pentaerythritol (APP/PER) and red phosphorus (RP) in polypropylene (PP) have been investigated. Limiting oxygen index, thermo-gravimetric analysis, melt flow index, and tensile tests have been performed in this study. Moreover, the structure of the nanocomposites was characterized by scanning electron microscopy (SEM). SEM images revealed good dispersion of fillers in the polymer matrix. Furthermore, it was shown that the addition of MWNTs alone at a minimum loading level of 4 wt% improves thermal stability of PP considerably without any undesirable effect on its flow-ability and mechanical properties. Moreover, addition of MWNTs alone resulted in a slight improvement of flammability of the polymer. However, comparison between thermal stability and flame retardancy of PP samples containing a combination of MWNTs and APP/PER or RP and those of the samples containing APP/PER or RP alone proved that MWNTs interfere with thermal stabilization and flame retardation efficiency of both APP/PER and RP in the polymer.

Low-Frequency Noise in Advanced CMOS Devices begins with an introduction to noise, describing the fundamental noise sources and basic circuit analysis. The characterization of low-frequency noise is discussed in detail and useful practical advice is given. The various theoretical and compact low-frequency (1/f) noise models in MOS transistors are treated extensively providing an in-depth understanding of the low-frequency noise mechanisms and the potential sources of the noise in MOS transistors. Advanced CMOS technology including nanometer scaled devices, strained Si, SiGe, SOI, high-k gate dielectrics, multiple gates and metal gates are discussed from a low-frequency noise point of view. Some of the most recent publications and conference presentations are included in order to give the very latest view on the topics. The book ends with an introduction to noise in analog/RF circuits and describes how the low-frequency noise can affect these circuits.

Electrical conductivity of chemically modified multiwalled carbon nanotube/epoxy composites

ABSTRACTA new compatibilizer [P(GMA‐co‐VCz) copolymer] containing carbazole moiety and reactive epoxide group, which can functionalize multiwalled carbon nanotubes (MWCNTs) for making superior epoxy composites, was prepared by a simple one‐pot free radical polymerization. The designed compatibilizer could noncovalently functionalize multiwalled carbon nanotube (MWCNTs) via π‐π interaction as evidenced from fluorescence, Raman, and FTIR spectra analysis, and efficiently disperse MWCNTs in organic solvents. TEM images suggest a good wrapping of P(GMA‐co‐VCz) on MWCNTs surface. P(GMA‐co‐VCz) functionalized MWCNTs were more homogeneously dispersed in epoxy matrix than the case without compatibilizer, indicating that the compatibilizer improves the compatibility between MWCNTs and epoxy resin. In addition, the presence of epoxide groups in compatibilizer could generate covalent bonds with the epoxy matrix and improve the interface interaction between MWCNTs and epoxy matrix. As a result, mechanical and electrical properties of the epoxy composites with compatibilizer were largely improved as compared with those of composites without compatibilizer. The addition of as little as 0.15 wt % of MWCNTs to epoxy matrix affords a great increase of 40% in storage modulus and 52.5% in elongation at break. Furthermore, a sharp decrease of almost 9 orders of magnitude in volume resistivity of epoxy composite is observed. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45022.

This work presents Low Frequency Noise (LFNoise) characterization and modeling performed on DPSASEG SiGe HBT integrated in a 55-nm CMOS node. The aim of this study is to evaluate the advantage brought by the implementation of a Dynamic Surface Annealing (DSA) in addition to the well-known Spike Annealing process. The HBTs are supplied by STMicroelectronics Crolles and present transit (fT) and maximum oscillation (fMAX) frequencies in the 320-370 GHz range. Spectra can be affected by the presence of generation-recombination (GR) components. The 1/f noise amplitude is modeled following the SPICE compact model, and the 1/f parameters KF and AF are calculated. The extracted figure of merit KB = KFAe has a very good value of 6.8 10-10 μm² for transistors processed using the DSA technique.