Influence Of Electrical Stress Research Articles

Influence of the stoichiometric ratio on the material properties and the aging behavior of anhydride-cured epoxy systems

Abstract When partial discharge and dielectric heating effects can be excluded, comparatively little is known about the aging behavior of polymeric insulation materials under combined environmental and electric field stress. Since it was found in an earlier study that hygroelectrical stress leads to a strong reduction in the residual breakdown strength of anhydride-cured epoxy samples, the goal of this contribution is to determine if a material modification could enhance the insulation performance under hygroelectrical stress. For this purpose, epoxy samples of different stoichiometric ratios (SRs) were manufactured and hygroelectrically stressed. The material properties were evaluated by AC breakdown strength measurements as well as by Fourier-transform infrared (FTIR) spectroscopy before and after each aging sequence. Gravimetric analysis quantified the water diffusion behavior and the (steady-state) water absorption during exposure to different relative humidity levels at room temperature. The breakdown strength decreases for both increasing and decreasing SR compared to S R = 95 % . Moreover, FTIR measurements revealed that an increase of the SR leads to a higher amount of unreacted anhydride which correlates with an increasing amount of absorbed water. Thus, the mutual presence of water in the atmosphere and of unreacted anhydride in the epoxy material is identified as the main risk factor for epoxy degradation under the influence of electrical stress, since unreacted anhydride favors stronger water absorption and the presence of water inside the material is attributed to a lowering of the potential barrier for molecular bond breaking. Remarkably, the breakdown strength of non-aged samples is lower at S R = 80 % compared to S R = 95 % , but the long-term performance with respect to insulation aging is enhanced, which correlates with the non-/less-existing unreacted anhydride in the material.

Study of the electrical stress effect on the SiC-SiO2 interface by inelastic electron tunneling spectroscopy

The influence of electrical stress on the behavior of traps at SiC-SiO2 interface are studied by inelastic electron tunneling spectroscopy (IETS). Measured IETS demonstrate the characteristic vibration modes contributed from defects at both metal-oxide and SiC-SiO2 interface. The observed distinct peaks in IETS provide unambiguous evidence to the existence of disordered carbon cluster at SiC-SiO2 interface. By performing bias-dependent IETS measurement, trap-assisted electron tunneling and charge-trapping process were observed and the defect level were determined for SiC-SiO2 interface. Moreover, the influence of electrical stress on the IETS peak-valley intensity and position was investigated and its origination was discussed.

Influence of electrical stress on printed polymer resistors filled with carbon nanomaterials

Superior electrical properties of carbon nanotubes were utilized by the authors in the fabrication of printed resistors. In common applications such as electrodes or sensors, only basic electrical and mechanical properties are investigated, leaving aside other key parameters related to the stability and reliability of particular elements. In this paper we present experimental results on the properties of printed resistive layers. One of the most important issues is their stability under high currents creating excessive thermal stresses. In order to investigate such behavior, a high direct current stress test was performed along with the observation of temperature distribution that allowed us to gain a fundamental insight into the electrical behavior at such operating conditions. These experiments allowed us to observe parametric failure or catastrophic damage that occurred under excessive supply parameters. Electrical parameters of all investigated samples remained stable after applying currents inducing an increase in temperature up to 130 °C and 200 °C. For selected samples, catastrophic failure was observed at the current values inducing temperature above 220 °C and 300 °C but in all cases the failure was related to the damage of PET or alumina substrate. Additional experiments were carried out with short high voltage pulse stresses. Printed resistors filled with nanomaterials sustained similar voltage levels (up to 750 V) without changing their parameters, while commonly used graphite filled polymer resistors changed their resistance value.

Fabrication of ZrO2 layer through electrohydrodynamic atomization for the printed resistive switch (memristor)

The insulating active layer has a vital role in the MIM (Metal–Insulator–Metal) structure of resistive switch (memristor). Different fabrication technologies are being used to the deposition of the active layer to explore the resistive switching in metal oxides. Electrohydrodynamic atomization (EHDA) has been used in this brief to deposit an active layer for the printed resistive switch (memristor). A thin liquid jet of solution containing ZrO2 (Zirconium Dioxide) nanoparticles was generated through a metallic capillary with a constant flow rate under the electrical forces. Liquid jet was further disintegrated into small droplets, containing nanoparticles, under the influence of electrical stresses and were collected on the ITO coated PET (Polyethylene Terephthalate) to form uniform layer of ZrO2 nanoparticles. A smooth thin film was observed with an average thickness of 67 nm. Resistive (memristive) behavior was observed in the deposited thin film with ITO (Indium-Tin Oxide) as a bottom electrode and Ag as a top electrode. Bipolar reversible resistive switching was analyzed by setting different current compliances. Results reveal that EHDA has full potential to fabricate the active layer in resistive switches for printed electronics.

Effects of electrical stress on mid-gap interface trap density and capture cross sections in n-MOSFETs characterized by pulsed interface probing measurements

High field electrical stress effects on the mid-gap interface trap density ( D it0) and geometric mean capture cross sections ( σ 0) in n-MOSFETs have been studied using the pulsed interface probing method. The results show that the PIP technique is sensitive to changes in mid-gap trap cross section values caused by the Fowler–Nordheim (F–N) electrical stress. The decrease of mid-gap trap cross sections following the F–N tunneling injection is found. Our works also provide further insight into the influence of electrical stress on mid-gap interface trap generation in n-MOSFETs without the assumption of the constant capture cross section value during F–N stresses.

The influence of electric stress on morphological changes occurring by surface diffusion on a body with anisotropic surface energy

The time evolution of the surface morphology of a long single-crystal (initially cylindrical) wire which forms the central electrode of a coaxial capacitor is discussed for mass transport by (isotropic) surface diffusion but allowing for anisotropic surface energy γ. Radial changes in the shape of the wire are shown to be retarded by the electric stress when the γ anisotropy is small. As Nichols and Mullins have shown, the wire is unstable to longitudinal perturbations; their treatment is generalized to incorporate both γ anisotropy and electric stress. The dominant wavelength in the evolving unstable axial profile is related to a γ anisotropy factor involving an out-of-plane second derivative of γ averaged over directions in the radial plane. The electric stress enhances or inhibits the instability depending upon the magnitude of this anisotropy factor. Some tentative remarks, based upon a conjectured extrapolation of the perturbation treatment developed here, are addressed to the problem of the ovulation of a semi-infinite cylinder.

Residual air and moisture in impregnated paper insulation-II

The paper describes further experiments on the drying and impregnating processes of impregnated paper insulation for high-voltage cables. Conclusions are reached as to the relative advantages of drying at atmospheric pressure and under vacuum. The qualities of the product are discussed from the standpoint of conductivity, dielectric absorption, and power factor. The influence of electric stress on impregnated paper and the progressive change in power factor under stress are studied in accelerated overvoltage tests. Evidence is presented as to the nature of certain interesting types of progressive change of power factor in their relation to the amount of residual air.