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The miniaturization of electronic devices and the structural optimization of power systems put forward a strict size requirement for passive components such as capacitors. The thickness reduction of dielectric polymer films becomes a necessary and urgent measure for future technology development. This advance leads to a higher capacitance density, less raw resource consumption, and lightweight modules and systems. However, the thickness change inevitably challenges the dielectric properties, the surface condition, and their relationship with the fabrication method of the dielectric films. This review primarily discusses: (1) the influence of polymer film thickness on the dielectric properties, (2) film quality issues in thinner polymer films with different filler contents, (3) high-temperature dielectric polymer engineering, and (4) the major processing methods in decreasing polymer film thickness. In addition, the polymer films also require scalability, processibility, and industrial feasibility in film and component manufacturing. The perspective of future investigations and concerns of dielectric polymer films are shared. It is interesting to see the favorable effect of multilayer polymer films on enhancing the dielectric strength.

The brittle fracture may occur in the application of piezoelectric ceramics, but the traditional research is still limited to the static fracture of the materials. Based on the improved Hopkinson pressure bar loading system and high-speed photography technology, the experimental study on the fracture behavior of piezoelectric ceramics under impact loading was carried out. The dynamic mechanical and electrical response of lead zirconate titanate (PZT) and the possible electric breakdown phenomenon were analyzed. The experimental results show that the output voltage is stable and the maximum output voltage is 889 V when the impact load does not cause the material to fracture. When the material breaks, its macroscopic output voltage fluctuates due to electric breakdown. Combined with the finite element simulation of the impact fracture process, the distribution characteristics of the stress field and electric field near the crack during the fracture process were analyzed. The results show that the sliding between grains formed the crack cavity parallel to the electric field during the impact process. Furthermore, based on the theory of dielectric breakdown, the possibility of electric breakdown in the initial defect and the elliptical cavity formed by the impact is analyzed.

This study is devoted to the improvement of the transformer oil quality, using a new inhibiting additive, since the extensively used inhibitory additive ionol is sensitive to organosulfur compounds of sulfur oils. From the earlier works, the organosulfur compounds are known to affect ambiguously the transformer oils characteristics. Therefore, it was of interest to study the individual sulfides as the inhibitory additives. The goal was achieved by the researches with the use of the model mixtures consisting of the selectively purified transformer oil (free from ionol) along with the individual sulfides, decylcyclohexylsulfide and decylfenylsulfide, at concentration of 0.5 %, Their effect on stability against oxidation of the selectively purified oil, on its electric strength and tangent of the dielectric losses’ angle was studied. The primary results obtained were, firstly, the rate slowing down of water formation in oil and of water-soluble acids formation in oil upon its oxidation in the presence of the individual sulfides, and, secondly, an increase in the electric strength and decrease in the dielectric losses compared to the transformer oil, containing ionol. It was established that decylcyclohexylsulfide inhibitory properties are stronger compared to those of decylfenylsulfide, which was testified by less quantities (by 1.8 times) of the water formed and of water-soluble acids (by 2.22 times). The introduction to oil of 0.5 % decylcyclohexylsulfide and decylfenylsulfide increased the oil electric strength, correspondingly, by 2.6 and by 5.5 times, upon water concentration in oil equal to 15·10-2 g/kg. The significance of the results obtained is in improving the transformer oil quality produced from the sulfur oils with the use of a novel additive.

In this study, the impact of particle form of the Cannabis indica plant biofibers and the fiber’s surface tailoring on the physical, thermal, dielectric, and mechanical properties of unsaturated polyester composite specimens manufactured utilizing nonconventional materials were investigated. The mechanical properties such as compressive, flexural, and tensile strengths of the composite specimens were noticed to increase after functionalization of biofiber with acrylic acid and maximum enhancement was found at 20% of biofiber sacking. The physical characterization was concentrated on the assurance of the dielectric constant, dielectric strength, dielectric loss, moisture absorption, chemical resistance, percentage of swelling, limiting oxygen index, and biodegradation of polymer composites under red soil. An increase in dielectric strength from 28 to 29 kV, limiting oxygen index values from 19% to 23%, and moisture/water absorption behavior was noted for resulted bio-composites after surface tailoring of biofiber. To assess the deterioration of the polymeric materials with the temperature, differential scanning calorimetric and the thermogravimetric tests were carried out and enhancement in thermal stability was noted after fortification of polyester composites with functionalized biofiber.

This study aims to prepare and examine the structure, thermal and dielectric properties of Polyvinylidene fluoride (PVDF)/Polyvinylpyrrolidone (PVP)/Co0.6Zn0.4Fe2O4 nanocomposite films. The data were collected via X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier-transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA) and dielectric measurements. The XRD spectrum of the Co0.6Zn0.4Fe2O4 ferrite sample showed a spinel crystal structure with an average size 15 nm. In the X-ray diffraction spectra of the PVDF-Co0.6Zn0.4Fe2O4 polymer nanocomposites, β-phase diffraction peak appeared at 2θ = 0.2°. SEM images of all the nanocomposite films exhibited a homogeneous distribution of nanostructured Co0.6Zn0.4Fe2O4. FTIR spectra depicted the absorption bands for α, β and γ-phase of PVDF as well as the carbonyl group of PVP. From TGA analysis, the activation energy for thermal decomposition decreased from 285.73 to 248.97 kJ/mol.K. Besides, there is a decrease in both ΔH and ΔG values with an increase in the Co0.6Zn0.4Fe2O4 concentration. The static dielectric constant (es), the high-frequency dielectric constant (e∞) and the dielectric strength (Δe) for these nanocomposites were lower than the pure PVDF/PVP film. The DC conductivity values were 2.27 × 10−14, 1.63 × 10−8, 2.04 × 10−10 and 1.61 × 10−8 S/cm for 0.0, 1.0, 3.0 and 5.0 wt% of Co0.6Zn0.4Fe2O4.

Flexible polymer dielectrics tolerant to electric field and temperature extremes are urgently needed for a spectrum of electrical and electronic applications. Given the complexity of the dielectric breakdown mechanism and the vast chemical space of polymers, the discovery of suitable candidates is nontrivial. We have laid the foundation for a systematic search of the polymer chemical space, which starts with "gold-standard" experimental measurements and data on the temperature-dependent breakdown strength (Ebd) for a benchmark set of commercial dielectric polymer films. Phenomenological guidelines are derived from this data set on easily accessible properties (or "proxies") that are correlated with Ebd. Screening criteria based on these proxy properties (e.g., band gap, charge injection barrier, and cohesive energy density) and other necessary characteristics (e.g., a high glass transition temperature to maintain the thermal stability and a high dielectric constant for high energy density) were then setup. These criteria, along with machine learning models of these properties, were used to screen polymers candidates from a candidate list of more than 13 000 previously synthesized polymers, followed by experimental validation of some of the screened candidates. These efforts have led to the creation of a consistent and high-quality data set of temperature-dependent Ebd, and the identification of screening criteria, chemical design rules, and a list of optimal polymer candidates for high-temperature and high-energy-density capacitor applications, thus demonstrating the power of an integrated and informatics-based philosophy for rational materials design.

Fluorides and their CO $$_{2}$$ mixtures are considered as promising choices of SF $$_{6}$$ -substitute gases due to their low global warming potentials and high dielectric strength. This paper investigates physical and chemical properties and breakdown characteristics of different common fluorides and their mixtures for application in the power system. For dielectric characteristics of fluorides and their mixtures, their power frequency breakdown voltages are determined experimentally, and the results are compared with SF $$_{6}$$ . For physical and chemical characteristics, the saturated vapor pressures, global warming potentials (GWPs), toxicities, prices of fluorides and their mixtures are calculated, and the corresponding characteristic curves are obtained. Based on characteristics mentioned above, a method for obtaining the optimal gas parameters of a specific fluoride mixture is proposed, which can be used as a feasible solution to find an SF $$_{6}$$ alternative gas that meets the application requirements. The results show that CO $$_{2}$$ mixtures with hexafluoropropene (HFP), 1,1,1,2-tetrafluoroethane (HFC-134a) and perfluoroisobutyronitrile (C4-PFN) are three types of good SF $$_{6}$$ -substitute gases. HFP/CO $$_{2}$$ mixtures with HFP component ratios 0.32 to 0.6 are suitable for applications at 0.1 to 0.3 MPa. HFC-134a/CO $$_{2}$$ mixtures (HFC-134a component ratios from 0.16 to 0.2) are suitable for applications at 0.3 to 0.5 MPa. C4-PFN/CO $$_{2}$$ mixtures (C4-PFN component ratios from 0.09 to 0.12) could be used for the applications at 0.1 to 0.5 MPa, regardless of the gas price.

A multi-physics simulation model of the tri-post insulator in ±800 kV GIL laid horizontally is established to study the effects of gas convection on surface charges and electric field distribution. Results show that gas density together with the dielectric strength around the upper post is reduced over 11% under gas convection generated by the load current. The larger temperature gradient (29 K) along the lower post accelerates more surface charge injection through insulator buck conduction and distorts the electric field around the bottom of the lower post, which is 19.4% higher than that around the bottom of the upper post. The insulation performance of SF 6 /N 2 filled GIL has the most striking spatial distribution characteristics compared with the insulation performance of SF 6 and C 4 F 7 N/CO 2 . Though the flashover voltage is improved with high gas pressure, the flashover is most likely triggered near the lower post of the insulator according to the stream theory. It is hoped that this study can contribute to a useful guide for the design and manufacture of DC-GIL.

In this paper, a novel modification method for biaxially oriented polypropylene (BOPP) membranes is proposed based on surface-grafting technology. The experimental results show that, compared with the pristine samples, the surface-grafted films show better breakdown strength under different voltage stress especially at higher temperatures (85 °C). The DC withstand strength of the surface-grafted PP membranes grows by 42.7% from 386.4 to 551.2 kV/mm. The breakdown strength climbs by 63.5% from 305.9 to 500.2 kV/mm under DC superimposed pulse voltage. Under DC superimposed harmonic stress, the breakdown strength is increased from 175.6 to 587.4 kV/mm by 234%. The influence of surface modification on charge transmission behavior is proposed based on the Density Functional Theory (DFT) simulation. This research provides a theoretical and methodological reference for performance optimization by surface modification for BOPP capacitors.

Summary Polymers with high dielectric breakdown strength (Eb) over a broad temperature range are vital for many applications. The presence of weak points, such as voids and free volume, severely limit the Eb of many high-temperature polymers. Here, we present a general strategy to reduce these weak points by exploiting interchain electrostatic forces in polymer blends. We show that the strong interchain electrostatic interaction between two high-temperature polymers in blends of polyimide (PI) with poly(ether imide) (PEI) yields an extended polymer chain conformation, resulting in dense chain packing and a corresponding decrease in weak spots in the polymers. This leads to a greater than 65% enhancement of Eb at room temperature and 35% enhancement at 200°C. In conjunction with results from blends of PI/poly(1,4-phenylene ether-sulfone) (PSU) and blends of PEI/PSU, we show that this previously unexplored molecular engineering strategy is efficient and straightforward in minimizing weak points in dielectric polymers.

Enhancement of Dielectric strength is an important issue to enhance power system reliability. Insulation filling such as Alumina Trihydrate (ATH) and Silicon dioxide (Sio2) are used to enhance the dielectric strength of polymer insulator. The paper proposes a mathematical model of dielectric strength considering different temperatures and filling percentages using neural network. Moreover, comparison of filling materials is carried out through this model. The comparison shows the superiority of ATH in enhancing the dielectric strength of the polymer. Also, the obtained model will help in getting the best filling concentration without needing to repeat the tests which can be considered as a techno-economical solution to enhance the dielectric strength. Finally, the curve fitting is used to get the dielectric strength model not only as a function of filling concentration percentage but also as a function of temperature.

Fluorine doped tin dioxide (FTO) coatings were deposited on AISI 304 stainless steel (SS) substrates using ultrasonic spray pyrolysis (USP) technique. Four different candidate insulating intermediate layers of TiO2, MgO, Al2O3 and SiO2 were selected and coated on AISI 304 SS using USP and investigated in order to overcome dielectric breakdown of FTO layer due to conductive nature of stainless steel substrate under the applied voltage. After the optimization of the process parameters for the depositions, only TiO2 layer was successfully deposited while other oxides did not form continuous films on AISI-304 SS surface despite the efforts. SEM analysis, supported by back-scatter imaging, revealed thickness values of the layers for FTO and TiO2, individually. Heating performances of the samples with varying sheet resistance values were examined under different applied voltages. Heating experiments showed that 300 °C can be reached with 10 V of applied voltage without occurrence of an electrical breakdown of FTO coating having 160 nm thickness with TiO2 intermediate layer of 660 nm. 28.6% efficiency for the conversion of electrical energy into heat was calculated for FTO coating while bare stainless steel showed only 7.3% efficiency. Later, the heating experiments were repetitively conducted and the samples were tested under high relative humid environment to determine their resistance against moist conditions.

Epoxy polymer-based dielectric materials play a crucial role in advanced electronic devices and power equipment. However, high voltage-stress applications impose stringent requirements, such as a high dielectric strength, on epoxy polymers. Previously reported studies have shown promising material architectures in the form of epoxy polymer-nanoparticle dielectrics, which can restrict the movement of high-energy electrons by the interface charge traps associated with the various interfacial regions. However, these high-energy electrons inevitably traverse the epoxy polymer matrix and destroy the molecular structure, thereby creating a weak link for dielectric breakdown. In this study, a general strategy is developed to improve the dielectric strength by constructing interface charge traps in the molecular structure of the epoxy polymer matrix, using the -CF3 group in partial replacement of the -CH3 group. The proposed strategy increases the dielectric strength (39.5 kV mm-1) and surface breakdown voltage (26.9 kV) of the epoxy polymer matrix by 22.08% and 13.3%, respectively, because the interface charge trap hinders the movement of high-energy electrons. At the same time, the strategy does not degrade the mechanical and thermal properties. The results hold potential for wide application in the manufacturing of advanced future electrical and electronic equipment requiring resilience to high-voltage stress.

In this work, we present the substrate bias enhanced trap effects on time-dependent dielectric breakdown (TDDB) in GaN metal–insulator–semiconductor high electron mobility transistors (MIS-HEMTs) by experiment. Under different substrate biases, the shape parameter $\beta $ and scale factor $\eta $ of the Weibull distribution are extracted from the experimental data. A monotonical decrease in $\beta $ from intrinsic breakdown to extrinsic breakdown relating to the hole-emission from the acceptor-like buffer traps with increased negative substrate biases has been observed, while $\eta $ is increased at large positive substrate biases. This unexpected increase in $\eta $ suggests that the donor-like buffer traps play an important role with a longer lifetime. The trap mechanisms, relating to percolation path establishment, are analyzed based on progressive breakdown (PBD). The capacitance–voltage characteristics are measured during each stress cycle confirming the hole fluence and electron injection in the gate-stack layer with different trap distributions under various substrate biases. Finally, 2-D device simulations are carried out to probe for physical insight into the traps on TDDB failure mechanisms.

Formulation of voids and impurities inside the power cable insulation may be found based on fabrication or installation processes that lead to the formation of high electrical stress and collapse of the insulation material of the power cable with cable aging. In this research, it has been investigated on possibility of nanoparticles for developing polyvinyl chloride that is used in power cable fabrication. Therefore, new polyvinyl chloride (PVC) nanocomposites have been fabricated and experimentally tested under high voltage tester. In this paper, it has been investigated on the effect of nanoparticles on electrostatic field distribution inside three-core power cables insulation in presence of air, water and copper impurities with different shapes (rectangle, circle and ellipse). Finite element method has been used to calculate the electrostatic field distribution in power cable insulation. This research success to design innovative patterns of polyvinyl chloride insulation materials for enhancing the electrical stress according to type and concentration of nanoparticles. Also, a comparative study of partial discharges in three-core power cables has been investigated on conventional PVC structure material and new nanocomposites industrial materials.

Materials exhibiting high energy/power density are currently needed to meet the growing demand of portable electronics, electric vehicles and large-scale energy storage devices. The highest energy densities are achieved for fuel cells, batteries, and supercapacitors, but conventional dielectric capacitors are receiving increased attention for pulsed power applications due to their high power density and their fast charge-discharge speed. The key to high energy density in dielectric capacitors is a large maximum but small remanent (zero in the case of linear dielectrics) polarization and a high electric breakdown strength. Polymer dielectric capacitors offer high power/energy density for applications at room temperature, but above 100 °C they are unreliable and suffer from dielectric breakdown. For high-temperature applications, therefore, dielectric ceramics are the only feasible alternative. Lead-based ceramics such as La-doped lead zirconate titanate exhibit good energy storage properties, but their toxicity raises concern over their use in consumer applications, where capacitors are exclusively lead free. Lead-free compositions with superior power density are thus required. In this paper, we introduce the fundamental principles of energy storage in dielectrics. We discuss key factors to improve energy storage properties such as the control of local structure, phase assemblage, dielectric layer thickness, microstructure, conductivity, and electrical homogeneity through the choice of base systems, dopants, and alloying additions, followed by a comprehensive review of the state-of-the-art. Finally, we comment on the future requirements for new materials in high power/energy density capacitor applications.

This study investigates the effect of various amounts of silica nanoparticles on electrical properties of RTV-SiO2 nanocomposite. The effect of increasing the amounts of filler in the RTV1 polymer matrix on the dispersion and dispersibility of nanoparticles has also been investigated through microscopic images. SEM images demonstrated that surface roughness excessed with increasing filler percentage, so that the non-uniformed distribution of the fillers will occur and the surface morphology will change. Electrical results indicated an increase in dielectric loss factor and a decrease in volume resistance via addition of 1, 3, and 5%wt nano-silica in composites. Also, there was a significant decrease in the dielectric strength by adding 3%wt of nano-silica. However, the dielectric constant and surface resistance did not change. Tracking test demonstrated that the erosion resistance of the sloping surface was greatly improved by increasing the nano-silica content, and this is very important for the application of this specific nanocomposite as a high-voltage insulators coating.

A series of (1-x) (BaO–TiO2–SiO2–Al2O3–B2O3)-xHfO2 (abbreviated as (1-x)BTSAB-xH) glass-ceramics were designed and prepared by traditional melt quenching and heat treatment method. The dielectric and energy storage properties of the glass-ceramics were studied systematically. The results of X-ray diffraction indicate that the main crystal phase of (1-x) BTSAB-xH glass-ceramics is BaTiO3. It should be noted that the addition of HfO2 can not only increase the dielectric constant, but also enhance the breakdown dielectric strength, resulting in high theoretical energy storage density. The max theoretical energy storage density can reach up to 7.07 J/cm3. The discharged energy storage density is 0.73 J/cm3 measured at 300 kV/cm @ room temperature. These results show that Hf doped barium titanate-based glass-ceramics are promising materials for application in dielectric capacitor with high energy storage density.

SF6 has been extensively deployed in high voltage gas insulated equipment to be used as a dielectric medium since 1960 because of its excellent dielectric strength and arc interruption performance. This research proposes promising substitute of SF6, by investigating a refrigerant gas such as Chlorodifluoromethane (CHClF2) with a mixture of CO2/N2/Air to mitigate environmental hazards of SF6. R22 has less atmospheric life and low cost as compared to SF6. It has less GWP (1,810) as compared to SF6 (23,900). In this research, the AC and DC breakdown properties of R22 mixtures along with varying ratios of CO2, N2, and Air were investigated. The best alternative to SF6 has been found to be a mixture of R22 + N2 which is close to 81% of SF6 dielectric strength. The dielectric strength of different optimal mixtures was found in the order of SF6 > R22 + N2 > R22 + Air > R22 + CO2 under AC voltage at 0.4 MPa. Moreover, the boiling point and GWP were further reduced by adding the buffer gases such as N2,, CO2, and Air. R22 also has acceptable insulation self-recoverability and liquefaction temperature. The results of this study are promising in terms of low cost and environment-friendly alternative to SF6.

We prepared a dielectric elastomer actuator composed of hydrogenated carboxylated acrylonitrile-butadiene rubber (HXNBR)/nitrile group (CN)-modified and non-modified titanium oxide (TiO2) particles with insulation properties. The CN group-containing silane coupling agent was synthesized via a thiol–ene reaction between acrylonitrile and 3-mercaptpropyltrimethoxysilane and immobilized onto the TiO2 particle surface. The HXNBR/CN-modified and non-modified TiO2 particle composite elastomer showed a high relative dielectric constant and generated stress in a low electric field. The relative dielectric constant increased proportionally with the amount of CN-modified TiO2 particles, showing a value of 22 at 100 Hz. As the dielectric constant increased, the volumetric resistivity decreased; however, the dielectric breakdown strength was maintained at 95 V/mm. The generated stress of the composite elastomer increased in proportion to the relative dielectric constant, showing a maximum of 1.9 MPa. The card-house structure of TiO2 particles in the composite elastomer is assumed to suppress the dielectric breakdown in a low electric field. Thus, we demonstrated that an elastomer containing a high dipole group on an insulating particle surface is capable of improving the power performance of soft actuators.

Silicon-carbide metal–oxide–semiconductor field-effect transistors (SiC-MOSFETs) are core devices for future power electronics. The factors limiting their automotive applications are currently under investigation. Postoxidation annealing in NO gas is a key technology to achieving high carrier mobility in SiC-MOSFETs. In this article, we study the NO annealing effects on time-dependent dielectric breakdown (TDDB) reliability by the constant voltage stress (CVS) method at room temperature (RT). We show that heavy NO annealing enhances hole trapping near the SiO2/SiC interface and leads to a rapid increase in the gate current ( $I_{\text {g}}$ ) and results in shorter time-to-breakdown ( $t_{\text {BD}}$ ) and smaller Weibull slope of $t_{\text {BD}}$ in comparison to light NO annealing case. However, the detailed examination of the $I_{\text {g}}$ behavior reveals that the charge-to-breakdown ( $Q_{\text {BD}}$ ) and its distribution do not deteriorate. Therefore, we must reconsider the use of the CVS method by examining the $I_{\text {g}}$ behavior during stress, which strongly depends on NO annealing conditions.

Silicone rubber (SR) and ethylene-propylene-diene monomer (EPDM) are widely-used polymers as housing for high voltage insulators. In this work, SR/EPDM/clay nanocomposites were obtained by two-roll mill mixing for outdoor polymeric insulators. Morphology, dielectric properties, dielectric breakdown strength (DBS), and surface and volume resistivity of different weight contents of nanoclay (Cloisite 15A) incorporated in SR, EPDM, and SR/EPDM hybrid nanocomposites were characterized. In addition, the distribution of breakdown voltages was fit to the distribution of Weibull and estimated the scale and shape parameters. The polar groups of the clay particles enhanced the polarization capability of the nanocomposites. Moreover, DBS results showed an enhancement of the dielectric strength proportional to clay content. Finally, the surface and volume resistance of all nanocomposites decreases but maintains very high electrical resistance. The experimental data presented in this study will be useful for designing and manufacturing the outdoor insulators.

The objective is to compare the electrical performance of a tubular barrier made of silicone and glass protecting an air gap with an alternating electric field. This investigation is focused on rod–rod and rod–plane electrode systems with variable interelectrode distance. An experimental device consists of wooden support in U shape. The air space disruption tests of the two systems with tubular barriers were supported by a visualization of the path of their electrical rupture. A disruption model of a non-uniform electric field air gap was developed in this study. Using the experimental results of dielectric breakdown of the considered systems, this model characterizes the flashover voltage as a function of the barrier insulation’s nature. In addition, it allows an easy comparison of its electrical insulation capacity under these conditions. Under pollution, no protection is provided by a glass barrier to the two systems due to the highly conductive behaviour of the pollution layer covering its surface. On the other hand, that offered by a tubular silicone barrier is by far the best because of the flashover discharge’s presence on its surface under these conditions. In a clean and dry atmosphere, the electrical insulation power of the systems is more efficient with a silicone barrier than with a glass one, because of its more advantageous dielectric properties and its lightness.

Lifetime and reliability in realistic operating conditions are important parameters for the application of thin-film piezoelectric microelectromechanical systems (piezoMEMS) based on lead zirconate titanate (PZT). Humidity can induce time-dependent dielectric breakdown at a higher rate compared to dry conditions, and significantly alter the dynamic behavior of piezoMEMS-devices. Here we assess the lifetime and reliability of PZT-based micromirrors with and without humidity barriers operated at 23°C in an ambient of 0 and 95 % relative humidity. The correlation of the dynamic response, as well as the ferroelectric, dielectric, and leakage properties, with degradation time was investigated. In humid conditions, the median time-to-failure was increased from ${2.7\times }{10}^{4}{[1.9\times }{10}^{4}{-4.0\times }{10}^{4}{]}$ s to ${1.1\times }{10}^{6}{[0.9\times }{10}^{6}{-1.5\times }{10}^{6}{]}$ s at 20 $\text{V}_{{\mathrm {AC}}}$ continuous unipolar actuation, by using a 40 nm thick Al2O3 humidity barrier. However, the initial maximum angular deflection, polarization, and dielectric permittivity decreased by about 6, 11, and 12 %, respectively, for Al2O3 capped devices. For both bare and encapsulated devices, the onset of electrothermal breakdown-events was the dominant cause of degradation. Severe distortions in the device’s dynamic behavior, together with failure from loss of angular deflection, preceded time-dependent dielectric breakdown in 95% relative humidity. Moreover, due to the film-substrate stress transfer sensitivity of thin-film devices, water-induced degradation affects the reliability of thin-film piezoMEMS differently than bulk piezoMEMS. [2020-0228]

In this research, the mesomorphic properties, thermal conductivity, and dielectric strength of a liquid-crystalline epoxy resin with hybrids of cellulose nanofiber and boron nitride nanosheet are studied. The thermal conductivity of LCER with hybrid fillers at a loading of 30 wt% demonstrated approximately 387% of that of the neat LCER and 246% of that of the nanocomposites with single BNNS fillers. The hybrid nanocomposite also demonstrates comparable dielectric strength and greater water contact angles in contrast to nanocomposites with single BNNS fillers. Furthermore, the nanocomposites with hybrid fillers show greater resistance to electrical erosion during the breakdown testing due to the greater thermal conductivity induced by enhanced filler dispersion.

Herein, a type of syntactic foam, consisting of silicone-modified resin and hollow polymer microspheres, is developed and tested for the application of a composite cross-arm. The physical properties, electrical properties, and hydrolysis-resistance are tested and analyzed. Suitable microspheres can reduce the density of the syntactic foam to 46.63% of the resin. The dielectric strength of the syntactic foam decreases from 37.9 to 26.1 kV/mm with increasing microsphere content, which is still much higher than the operational requirement of 3 kV/mm. The water-absorption rate (

Dielectric spectroscopic measurements of five homologous series of orthoconic antiferroelectric liquid crystalline (OAFLC) esters (S)-MHPOBC ((S)-4-(1-methylheptyloxy) carbonyl phenyl 4’-octyloxy-4...

The thickness scaling of the ferroelectric (FE) hafnium zirconium oxide (HZO) down to sub-10 nm is essential in non-volatile memory devices. In this study, high remnant polarization (Pr), low thermal budget, low operation voltage, and high endurance are demonstrated in the FE HZO thin films with thickness shrinkage from 10 to 3 nm. Due to the in-plane tensile stress induced by the TiN capping layer and the initial island growth on the platinum bottom electrode, record-high Pr ∼24.8 μC cm−2 is realized in the 6 nm HZO layer. Good ferroelectricity with Pr ∼10.8 μC cm−2 and low saturation voltage (∼0.7 V) is also achieved in the 3 nm HZO thin film. The wake-up effect is insignificant as the HZO thickness is greater than 5 nm, while an obvious wake-up effect is observed in sub-5 nm HZO thin films. This result can be ascribed to the increasing stability of the tetragonal phase with a decrease of the HZO thickness as supported by the dielectric constant measurement. The dielectric breakdown strength of the HZO layers was evaluated by the time-zero dielectric breakdown test. The dielectric breakdown strength increases rapidly with a decrease of the HZO thickness, which leads to a significant endurance improvement with ∼1011 electric field cycling without breakdown in the 3 nm HZO thin film. The favorable FE properties demonstrated in the sub-5 nm HZO thin films provide a promising approach in future FE non-volatile memory applications.

Polymer insulation is an integral part of electrical equipment. For an electrical insulation system, electrical, mechanical and thermal properties of polymer play a critical role in performance of insulation. Therefore, for reliable insulation system it is imperative to enhance and upgrade the insulating materials properties. In this context nanodielectrics materials can play a crucial role for next generation of insulating materials. Development of nanodielectrics materials with enhanced properties is a complex interplay between filler particle size, its functionalization and uniform dispersion in polymer matrix. In this paper, we report preparation of epoxy nanocomposites with silica particles having varying size and functionality. The epoxy nanocomposite composites were evaluated for their dielectric strength, dielectric dissipation and water absorption and impact properties. Our results shows improvement in dielectric and impact properties for epoxy nanocomposites with functionalized fumed silica nano-particles. Addition of colloidal silica did not show noticeable improvement in dielectric and mechanical properties. Our results for epoxy nanocomposite shows that enhancement of epoxy nanocomposite properties are function of particles size and chemical functionality of filler particles.

In this paper, we report a 1.84 kV GaN-on-GaN Schottky barrier diode (SBD) corresponds to a low on-resistance of 1.98 mΩ-cm2. The GaN epi-layer was etched to the multi-fins-structure with optimized bevel angle. The fins structure enables to improve the breakdown voltage by means of the uniforme electric field distribution. Afterwards, the GaN fins were capped by atomic layer deposition (ALD)-grown AlN film. The AlN served as a tunneling-barrier layer, which not only passivated the GaN surface but also decreased the turn-on voltage. The AlN-capped SBD shows a turn-on voltage at 0.18 V. Furthermore, the temperature-dependent transfer characteristics suggest the different current tunneling mechanisms at low and high electric field conditions, respectively. The time-dependent dielectric breakdown (TDDB) measurement suggests the surface traps were well passivated by ALD-AlN, which implies that the AlN cap-layer enables to improve the device reliability.

Molecular dynamics of ionic liquids in an electric field can be decomposed into contributions from translational motions of ions, rotational motions of permanent dipoles and - in the case of ions equipped with long alkyl-chains - motions of ionic aggregates. The discrimination of these contributions in the dielectric spectrum is quite involved, resulting in numerous controversies in the literature. Here, we use dielectric spectroscopy at ambient and elevated pressures of up to 550 MPa to monitor the changes of the observed processes in five supercooled ionic liquids with octyl-chains independent of pressure and temperature. In most of the ionic liquids under investigation two dynamical processes are observed, one of them is identified as the ion hopping process, which we describe by the MIGRATION model. It turns out that this process is closely connected to the glass transition step as measured by differential scanning calorimetry. Concerning the second process, we rule out motions of aggregated ions to be its origin by comparison of our results with X-ray scattering literature data at elevated pressure. Instead, we tentatively ascribe it to dipolar reorientations and show that the dielectric strength of this slow process decreases as a function of increasing relaxation time, i.e. for decreasing temperatures and increasing pressures. We compare this behavior with literature data of other ion conducting systems and discuss its microscopic origin.

Polymer-based dielectrics have been attracted much attention to flexible energy storage devices due to their rapid charge–discharge rate, flexibility, lightness and compactness. Nevertheless, the energy storage performance of these dielectric polymers was limited by the weak dielectric breakdown properties. Crosslinked structure has been proven efficient to enhance breakdown strength (Eb) and charge–discharge efficiency (η) of polymer film capacitors. However, crosslinked networks usually lead to low electric displacement of dielectric capacitors, which greatly restrict their energy storage density (Ud). In this work, we present a tri-layered composite via layer-by-layer casting technology, where crosslinked polyvinylidene fluoride (c-PVDF) was used as the inter-layer to offer high breakdown strength, and the outer ternary fluoropolymer layers with high dielectric constant could provide high electric displacement. The optimal tri-layered composites exhibit an ultrahigh discharge energy density of 18.3 J cm−3 and a discharge efficiency of 60.6% at 550 kV mm−1. This energy density is much higher than that of the PVDF terpolymer and commercially biaxially oriented polypropylene (BOPP, 1–2 J cm−3). The simulation results prove that the enhanced energy density originates from the effectively depressed charge transport in crosslinked structure at high applied electric field. Moreover, this work provides a feasible method for developing flexible all-organic high-energy-density composites for polymer capacitors.

Constant-voltage time-dependent dielectric breakdown (TDDB) measurements are performed on recently manufactured commercial 1.2 kV 4H-SiC power metal-oxide-semiconductor (MOS) field-effect transistors (MOSFETs) from three vendors. Abrupt changes of the electric field acceleration parameters ( $\gamma $ ) are observed at oxide electric fields ( $E_{ox}$ ) around 8.5 MV/cm to 9 MV/cm for all commercial MOSFETs. Gate leakage currents and threshold voltage shifts are also monitored under different oxide fields ( $E_{ox}= {\mathrm {8 MV/cm}}$ and 10 MV/cm). The results suggest the failure mode under high oxide electric field is modified by impact ionization or Anode Hole Injection (AHI) induced hole trapping. This observation agrees with previously published oxide reliability studies on SiC MOSFETs and suggests that constant-voltage TDDB measurements need to be carefully performed under low oxide fields to avoid lifetime overestimation caused by hole trapping. The extrapolated $t_{63\%}$ lifetimes (times to 63% failures) from TDDB measurements performed at $E_{ox} < {\mathrm {8.5 MV/cm}}$ are longer than 108 hours at 150°C for all vendors. The predicted lifetimes at $E_{ox}= {\mathrm {4 MV/cm}}$ demonstrate more than 105 times increases than the oxide lifetimes reported a decade ago, showing promising progress in SiC technology.

We present the dielectric relaxation properties of the ferroelectric smectic-A (SmAPF) phase formed by a mixture of bent-shaped dimeric molecules α,ω-bis(4-alkoxyanilinebenzylidene-4′-carbonyloxy)pentanes with different alkyl chain lengths. The SmAPF phase shows a Goldstone-like mode at approximately 500 Hz, which can be attributed to the ferroelectricity and huge dielectric strength (Δe). Δe varies dramatically with the cell thickness; in particular, it attains more than 7000 in a 50 μm-thick cell, which is much higher compared to that reported in the bent-shaped molecules.

Cryogenic dielectrics are a crucial component for applied superconducting systems such as high-temperature superconductor (HTS) cables. Here two types of polymer nanocomposites were investigated as dielectrics for cryogenic applications. Both polyimide (PI) and polyamide (PA) nanocomposites showed exceptional performance as dielectrics, with PI as the stronger material. Significant dielectric strength improvement was observed for samples tested in the cryogenic environment when compared to those tested at the room temperature. The PI exhibited a high dielectric strength of 347 ± 67 kV/mm at 92 K, while its nanocomposites were in the range of 261-280 kV/mm. The performance change of these dielectrics was influenced by a number of factors including the density of free charge carriers, localized heat generation and material degradation, thermal contraction of polymers, and polymer-nanoparticle interfacial changes at cryogenic temperatures. The findings from this research can help advance the understanding of breakdown failures in cryogenic dielectrics.

Small and light fly ash is a by-product of thermal power plants, in which oxides mainly present in fly ash are suitable to reinforce composite materials. Its content accounts for 10, 20, 30, 40, and 50% of those materials. However, due to the smooth surface, it cannot stick completely in plastics. Therefore, in this work, it was studied to combine nanoclay additive (I.30 E) with 1, 3, and 5% by weight to synergize to improve mechanical strength, fire retardation, and electrical properties. Mechanical properties and flame retardant properties have improved markedly. At the combined ratio of 40% by weight of fly ash and 3% nanoclay, nanocomposites have tensile strength values of 64.12 MPa, flexural strength of 89.27 MPa, compressive strength of 215.23 MPa, and impact resistance of Izod 14.45 kJ/m2, oxygen index limited to 26.8% of fire retardant material. In terms of dielectric strength, the electric strength of pure epoxy is 17.5 kV/mm, higher than that before adding nanoclay (12.7 kV/mm). The presence of nanoclays in the material creates a tortuous electric path, slowing the propagation of the power plant, which is the main factor that improves the breaking strength of the nanocomposite.

To verify an increase in porosity due to small pores dose not reduce the dielectric breakdown strength (DBS) of alumina ceramics, we sinter a SiO2-CaO co-doped 95 wt% alumina ceramic via step-controlled atmosphere sintering (first sintering in oxygen, then sintering in air) and conventional sintering (sintering in air) to fabricate samples of different porosities. The dielectric breakdown (DB) test under an AC high voltage shows that the two samples have almost equal DBS in spite of different porosities. Microscopic analysis reveals that the conventionally sintered sample contains more small pores of size range 5–25 μm than the step-controlled atmosphere sintered sample, so the increase in the small pores does not reduce the DBS of the alumina ceramic. The partial discharge in the small pores does not occur before the DB of the alumina ceramic, and this is the reason why the two samples have equal DBS.

A stochastic reaction–diffusion drift model is used to simulate the time kinetics of interface and bulk oxide traps responsible for bias temperature instability (BTI), stress-induced leakage current (SILC), and time-dependent dielectric breakdown (TDDB) in MOSFETs. Trap generation and passivation are calculated using dissociation and repassivation of trap precursors and simultaneous diffusion and/or drift of atomic, molecular, and/or ionic species. The average of multiple stochastic simulations is used to qualitatively explain the measured BTI and SILC data. The difference in BTI and SILC time kinetics, variation in SILC time kinetics across reports, and oxide thickness dependence of TDDB Weibull slope variation are also qualitatively explained.

Sulphur hexafluoride (SF6), the most popular dielectric medium adopted in compressed gas insulated equipment, has been identified as a highly potent greenhouse gas. This has led to increased interest in finding a more environmentally friendly replacement candidate. In this paper, the technical viability of C3F7CN/CO2 gas mixtures was assessed as a potential retro-fill solution for existing SF6-filled gas insulated lines (GIL) and busbars (GIB). A reduced-scale coaxial prototype was developed to establish the breakdown strength of 20% C3F7CN / 80% CO2 and 16% C3F7CN / 84% CO2 gas mixtures in direct comparison with pure SF6 under the standard lightning impulse (1.2/50 μs). Breakdown results demonstrate that a mixture of 20% C3F7CN / 80% CO2 exhibits comparable insulation capability to pure SF6 in coaxial geometries with similar field uniformity to GIL / GIB. This initial finding has led to the construction of a full-scale GIB demonstrator rated for 420/550 kV. Type tests according to IEC 62271-204 showed that the 20% C3F7CN / 80 % CO2 gas mixture has passed all the required voltage levels as SF6. The research findings in this paper are an encouraging step towards a technically viable SF6-free retro-fill solution for existing GIL / GIB installed for the 400 kV transmission network in the UK.