Leakage Current Peak Research Articles

Superhydrophobic nanocomposite coatings based on different polysiloxane matrices designed for electrical insulators

The present paper describes for the first time the influence of three different kinds of polysiloxane as hydrophobic agent on superhydrophobic coatings for electrical insulators: a trimethoxy (2,2,4-trimethyl pentyl)-based silane; a mixture of methyl methoxy siloxane with methylsilsesquioxane; a mixture of dimethyl siloxane, methylsilsesquioxanes and n-octyl silsesquioxanes. The polysiloxane properties were investigated by thermogravimetric (TGA) and hydrophobic (contact and sliding angles) analysis, indicating great differences on thermal properties and surface free energy. The polysiloxane binders were loaded with different sizes of microsized alumina trihydrate (ATH) and organophilic nanosilica functionalized with octyl-silane and polydimethylsiloxane (PDMS). The hydrophobicity of the coating was evaluated by water contact angle (WCA) and sliding angle (SA). The morphology and roughness of the coatings were investigated by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Moreover the superhydrophobic durability of the coatings was evaluated by water immersion, hydrophobicity recovery, hydrophobicity transfer and adhesion. The effectiveness of these materials as coatings for glass electrical insulator was evaluated by tracking and erosion resistance using the inclined plane test (IPT). The results showed that the polysiloxane based on a mixture of methyl methoxy siloxane with methylsilsesquioxanee loaded with ATH and PDMS-treated silica exhibited the most promising characteristics as high contact angle, self-cleaning ability, good adhesion to the substrate and low number of leakage current peaks during the tracking and erosion resistance test. Such characteristics can bring benefits on electrical insulators like reducing the formation of conductive surface paths and the consequent degradation of the coating by dry band arcs, increasing its resistance when exposed to the electric field.

(Invited) Fabrication of Ge-on-Insulator By Epitaxial Growth and Ion-Implanted Exfoliation for Electronics and Optoelectronics Applications

1. IntroductionGe has been received much interest as a CMOS channel material and a near-infrared optical material due to its superior characteristics [1,2]. For application use, Ge-on-Insulator (GOI) structure is necessary to suppress large leakage current originated from the narrow bandgap. A method combined wafer bonding and layer splitting by hydrogen ion (H+) implantation, known as Smart-CutTM and realized for Si-on-Insulator fabrication, has been tried to apply for GOI with large diameter, uniform thickness, and single crystal [3-5]. In this study, we fabricated GOI by Smart-CutTM technique and demonstrated electronic and optoelectronic devices on the GOI. Besides, we combined the epitaxial growth method to improve the quality of GOI.2. Experimental, Results, and DiscussionsGOI fabrication procedure by conventional Smar-CutTM method is shown in Fig. 1 [5]. H+ implantation with the dose of 4×1016 cm-2 and energy of 120 keV into Ge was performed through 100 nm-thick SiO2. After SiO2 removal, 3 nm-Al2O3 and 50 nm-SiO2 were formed on the Ge and Si substrates, respectively. Then, the Al2O3/Ge and the SiO2/Si were manually bonded. After annealing in N2 ambient at 300 °C to enhance bonding strength [6], layer splitting was carried out by annealing at 400 °C. GOI thinning by wet etching and surface flatten by chemical mechanical polishing (CMP) were performed. We fabricated both p- and n-MOSFETs with metal source/drain (S/D) on the GOI. The p-MOSFET is an accumulation mode device with ohmic PtGe/Ge S/D. On the other hand, n-MOSFET is an inversion mode device with rectifying TiN/Ge S/D. Both devices work successfully as shown in Fig. 2. We also demonstrate asymmetric metal/Ge/metal photodiode on the GOI. PtGe and TiN are also used as electrodes for hole and electron injection, respectively. Figure 3 shows electroluminescence (EL) spectra for the photodiodes fabricated on the GOI and the bulk Ge. The GOI device shows higher EL intensity than that of bulk Ge. It is considered carrier confinement effect by thin Ge crystal.However, the MOSFETs show a large leakage current at the high drain voltage region. Also, the photodiode on GOI has a broader spectra peak. Figure 4 is the cross-sectional TEM image of the GOI before GOI thinning. There are many defects as black dots near both the split surface and the buried oxide (BOX) interface. The defects near the BOX are serious because this region will be kept after GOI thinning, and cause the degradation of device characteristics (leakage current and broad PL peak). They may be introduced by H+ implantation.To avoid the introduction of the defect during GOI fabrication, we propose an alternative method which is epitaxial growth of a new Ge layer on H+ implanted surface, as shown in Fig. 5. In this method, all defective layer was removed after layer splitting and only epi-Ge layer remains on the handle Si. Figure 5 also shows electron concentrations and mobilities of the GOIs evaluated by Hall effect. The conduction type of the GOI by conventional Smart-CutTM changes from n-type to p-type due to defect introduction. On the other hand, the proposed method successfully keeps the original conduction type (n-type). Although electrical characteristics should be improved more, it is clarified that defect elimination before bonding is important for GOI fabrication by Smart-CutTM.3. ConclusionWe fabricated GOI by Smart-CutTM and demonstrated MOSFETs and photodiode on the GOI. Although both devices successfully work, TEM analysis clarified there are lots of defects near the GOI/BOX interface. Alternative way combined epitaxial growth to eliminate the defects succeeded to improve the electrical characteristics of the GOI.AcknowledgmentThis work is supported by JSPS KAKENHI (No. 19K15028 and 19H05616) and the Research Institute of Electrical Communication, Tohoku University.

О возможности использования токов утечки для оценки состояния изоляции асинхронного двигателя

The need to improve the reliability and reduce the stator winding-related accident rates of asynchronous electric drives is what makes this topic relevant. The goal hereof is to find how capacitive leakage currents could be used to indicate the condition of the stator winding insulation in an asynchronous motor. The paper presents some results of studies into the stator winding insulation leakage currents generated by rectangular voltage pulses at 100 to 2000 Hz. The researchers have verified the ability to register leakage current parameters as a function of voltage pulse amplitude and frequency in order to use such data to find the insulation condition. It is shown that rectangular voltage pulses can produce sufficiently large leakage currents for easier use. Even rather simple and low-cost equipment is usable to that end. However, reliable determination of the leakage current peaks amplitude requires a very long measurement with numerous transmitted pulses; alternatively, one could use very high-resolution equipment with a sampling time of 10-6 s or less. Nevertheless, the equipment used in the tests does extract the data regarding the effective capacitive leakage currents, which could be used to diagnose the insulation.

Facet dependence of leakage current and carrier concentration in m-plane GaN Schottky barrier diode fabricated with MOVPE

In this study, GaN m-plane Schottky barrier diodes fabricated with a metalorganic vapor-phase epitaxy on a GaN substrate were investigated using emission microscope, photoluminescence, and cathodoluminescence. In addition, facet dependence of leakage current under reverse-biased condition was observed. We showed that the leakage-current distribution was caused by the facet dependence of the carrier concentration and oxygen concentration. These results can provide important suggestions for the fabrication of m-plane devices. (a) four-faceted hillocks on m-plane GaN MOVPE sample, facet dependence of (b) leakage current and (c) PL peak intensity of the m-plane GaN Schottky barrier diode.

Time–frequency analyses of leakage current waveforms of high voltage insulators in uniform and non‐uniform polluted conditions

This study deals with the analysis of the leakage current (LC) in both time and frequency domains, for different configurations of polluted high voltage insulators (i.e. for clean and polluted insulator surfaces). The characteristic parameters of the recorded LC waveforms up to flashover namely the peak value, the phase shift, the total harmonic distortion and the harmonic contents are investigated. It is shown that the LC peak value and the phase shift cannot be a trustworthy indication of the surface activity related to partial discharges and waveform type whereas the harmonic components magnitude can be well correlated with the LC distortions; it is shown that in the early stages, the fifth and seventh harmonics contribute to the distortion of the LC whereas for advanced stage, the third harmonic contribution is the most significant. A time–frequency analysis is also carried out to better understand the LC behaviour. The spectrogram of the different stages of LC activity is computed using Matlab toolbox. The results show that time–frequency analysis can be used as a tool for patterns recognition and classification of the LC.

Electrical and magnetic properties of bilayered BaTiO3–Ni thick films prepared via a combined method of electrophoretic deposition and screen printing

Thick film BaTiO3 (BTO)–Ni composites were prepared on alumina substrates via a combined method of electrophoretic deposition (EPD) and screen printing technique. During the EPD process, a Ni/alumina substrate was used as a deposited electrode (cathode), which was prepared via the screen printing method. Microstructures, electrical property and magnetic property of the layered composites were studied. Results reveal that the porous composites present non-ferroelectric property and negative resistance effect, in which the former could be attributed to the fact that the sintering was conducted in a reducing atmosphere. Furthermore, the out-of-plane and in-plane leakage current characteristics could testify the homogeneity of the thick films in different directions via the electric fields which correspond to the leakage current peaks. The non-uniformity of the composite in the vertical direction may be related to the instability of BTO particles in suspension. Also, the dielectric constant in the out-of-plane mode decreases with increasing frequency owing to the existence of space charges. In addition, the bilayered films exhibit magnetic anisotropy, which could be ascribed to the interfacial stress between alumina substrates and Ni layers.

Oxygen-vacancy-mediated negative differential resistance in La and Mg co-substituted BiFeO3 thin film

The conductive characteristics of Bi0.9La0.1Fe0.96Mg0.04O3 (BLFM) thin film are investigated at various temperatures and a negative differential resistance (NDR) is observed in the thin film, where a leakage current peak occurs upon application of a downward electric field above 80 °C. The origin of the NDR behavior is shown to be related to the ionic defect of oxygen vacancies (VO••) present in the film. On the basis of analyzing the leakage mechanism and surface potential behavior, the NDR behavior can be understood by considering the competition between the polarized distribution and neutralization of VO••.

Optical Detection of Partial Discharges on Insulator Strings of High-Voltage Transmission Lines

Leakage current detection is a promising method for measuring pollution levels on insulators of overhead transmission lines. This paper describes the development of a leakage current sensor based on a fiber-coupled light-emitting diode, as well as the development of a processing module that detects, stores, and classifies leakage current peaks that are directly related to partial discharges on the surface of the high-voltage insulators. The relative humidity is also detected and stored for further analysis. The processing module uses a PIC 16F877A microcontroller and can register the rate of partial discharges for two months on three different levels.

Letter to the Editor: Variation of Leakage Current with SDD on an Artificially Polluted Porcelain Pin Insulator—An Experimental Study

Working insulators begin to fail as airborne contaminants and moisture from natural wetting combine on the surface of insulator to cause an increase in surface conductivity. This enables current to conduct across the insulators, thereby changing the electrical conductivity exhibited by the insulators when clean. If the change in conductivity is severe enough, then the leakage current may escalate into a service interruption due to flashover. This flashover results in an outage that in turn degrades power quality and hence affects reliability. To improve power quality, it is necessary to select proper insulator(s) depending on the level of the pollution. The leakage current mainly depends on salt deposit density (SDD) on the insulator surface, but this dependency is not yet investigated completely. This work is an attempt towards this direction, to study experimentally the variation of the leakage current with SDD. Experimental results reveal that the peak value of the leakage current remains almost same in magnitude for different SDD values and the time of occurrence of the leakage current peak is delayed for lower values of SDD.

Nonstandard method for accelerated ageing tests of nonceramic insulators

A methodology for testing accelerated ageing of nonceramic insulators (NCI) is presented based mainly on polluting the insulators with several substances, such as kaolin, lime, fertilizer and natural field pollutants. The polluted insulators are evaluated inside a salt fog chamber by applying cycles of salt fog, clean fog, drying and constant voltage. During the tests, clear evidence of tracking, erosion, chalking and puncture was observed on the insulators. Flashover takes place on the early damaged insulators in a relatively short time with respect to the test time of 5000 h recommended by IEC 61109. Based on the results obtained it is necessary to modify the standard continuous 5000 h salt fog test to evaluate the long-term performance of NCI. The new test must consider low salinity, clean fog and drying periods and an initial pollution coating. Under these conditions, the leakage current magnitude is smaller and consequently much more discharge activity occurs over the polluted insulator surface leading to surface deterioration, since hydrophobicity recovery of the insulator surface is allowed during the drying period. Measurements show that the leakage current peak values were in a range from 50 to 120 mA.

Hot-electron-induced minority-carrier generation in bipolar junction transistors

The authors report on the observation and analysis of minority-carrier generation in the collector and the substrate of n-p-n bipolar junction transistors as a result of photons which are generated in the collector-base depletion region. Both the substrate current and the additional leakage current peak at V/sub BE/ approximately 0.8 V. In the authors' model of the phenomena, the photons induce the generation of carriers both in the depletion region and in the neutral region. The generated minority carriers in the neutral region diffuse and contribute to the substrate current and the junction leakage current. The contribution of the carriers that are generated in the depletion region is not dominant. >