Dielectric Breakdown Characteristics Research Articles

Investigating the Impact of Hardness on Dielectric Breakdown Characteristics of Polyurethane.

Polymeric materials play a vital role in high-voltage insulation, but their insulating properties can deteriorate over time, leading to insulation failures. The presence of voids resulting from manufacturing defects or external stresses can create a highly divergent field, further contributing to this issue. However, certain polymers, such as polyurethane (PU), possess self-healing properties that enable them to repair these voids and restore a uniform electric field distribution, thereby ensuring the reliability of the insulation. Surprisingly, the potential of PU as an insulating material in high-voltage applications remains unexplored. However, the self-healing capability of PU decreases with an increase in the hardness of the material. Therefore, in this study, the dielectric breakdown properties of PU with different levels of hardness, rated on the Shore scale as 40° (soft), 70° (medium), and 90° (hard), were investigated. The AC and DC dielectric breakdown characteristics of these PU variants and dielectric spectra were examined. Additionally, the study explores the relationship between the dielectric properties and the hardness of the material. Our findings revealed that the dielectric breakdown strength of PU increases as the material's hardness is increased under both AC and DC electric stress. However, this may come at the cost of reduced self-healing capabilities of PU. Therefore, there is a need to balance the hardness of the material with its ability to recover from breakdown events. The findings from this study can be useful for researchers and engineers, as they offer valuable insights into the dielectric properties of PU at various hardness levels.

Breakdown Characteristics of Schottky Barrier Diodes Used as Bypass Diodes in Photovoltaic Modules under Lightning Surges

Damage to photovoltaic power-generation systems by lightning causes the failure of bypass diodes (BPDs) in solar cell modules. Bypass diodes damaged by lightning experience high-resistance open- or short-circuit failures. When a bypass diode experiences short-circuit failure due to indirect lightning, the damage may not be immediately visible. When solar radiation is subsequently received, the current circulating in the closed circuit formed by the cell string and short-circuited bypass diode flows, resulting in overheating and burnout of the short-circuited bypass diode. The authors’ research group previously reported that when a bypass diode fails within a range of approximately 10−1 Ω to 10 Ω, the heat generated by the failed bypass diode is high, posing the risk of burnout. However, the detailed failure characteristics of the bypass diode that fail because of indirect lightning surges are not clear. In this study, we performed indirect lightning fracture tests and clarified the dielectric breakdown characteristics of Schottky barrier diodes (SBDs) contained in the bypass diodes of photovoltaic solar cell modules, which are subjected to indirect lightning surges. Furthermore, we attempted to determine the conditions of indirect lightning that resulted in a higher risk of heat and ignition. As a result, short-circuit failures occurred in all the Schottky barrier diodes that were destroyed in the forward or reverse direction because of the indirect lightning surges. Moreover, the fault resistance decreased as the indirect lightning surge charge increased. These results indicate that the risks of heat generation and burnout increase when the Schottky barrier diode fails with a relatively low electric charge from an indirect lightning surge. In addition, we observed that for a forward breakdown of the Schottky barrier diode, the range of the indirect lightning surge that results in a fault condition with a higher risk of heat generation and burnout is wider than that for a reverse breakdown.

진공도에 따른 절연파괴 분석에 관한 연구

This study focuses on investigating the dielectric breakdown characteristics of high-temperature superconducting (HTS) coils, which are increasingly used in various applications such as superconducting cables, superconducting fault current limiters (SFCLs), and superconducting particle accelerators. The research aims to understand how electrical breakdown, induced by high electromotive force and local quenching, can weaken the dielectric stability of HTS magnets. The dielectric experiments were conducted under different vacuum conditions and gaseous helium conditions, and an empirical formula for the electrical insulation design of HTS magnets was developed. Finite element method (FEM) analysis was also performed to simulate various conditions that may cause electrical breakdown, confirming that breakdown could occur at turn-to-turn and layer-to-layer of HTS magnets. As a result, it was confirmed that the magnitude of the induced electromotive force or quench voltage that could cause electrical breakdown of the HTS magnets under various insulating medium conditions such as gaseous nitrogen (GN2), gaseous helium (GHe), and vacuum was deduced.

Equivalence between C5F10O Addition and PTFE Vapor Contamination in the Particle Composition and Critical Electric Field Strength of High‐Temperature CO2/O2 Gas Mixture

AbstractSF6 has been introduced as an insulating and extinguishing gas in gas circuit breakers. However, its global warming potential is significantly high at approximately 25 200. Therefore, development of alternative gases is essential. We have been investigating the dielectric breakdown characteristics of high temperature CO2 gas contaminated by various gases. This study discusses the equivalent condition between high temperature CO2/O2/C5F10O gas mixture and CO2/O2 gas mixture contaminated with PTFE (C2F4) vapor because both gas mixtures consist of C, O, and F atoms. It is concluded that when the mole fractions of every atom are equivalent between both gas mixtures, both gas mixtures have the same characteristics as each other, such as the particle composition and critical electric field strength. © 2023 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.

Influence of Thermal Aging on Dielectric Properties of High Voltage Cable Insulation Layer

Thermal aging is one of the main reasons for the degradation of insulation properties of high voltage cable. Dielectric properties and breakdown strength are important parameters to reflect the insulation performance of the cable insulation materials. In the work, the influence of thermal aging on dielectric and breakdown performance of the cable insulation layer was studied. Firstly, XLPE cable insulation samples were prepared and the thermal aging treatment was carried out. Secondly, the microstructure and molecular structure of XLPE samples under different thermal aging time were analyzed. The dielectric properties and breakdown characteristics of XLPE samples under different thermal aging times were characterized in macro aspect. Finally, the effects of different temperatures on the molecular microstructure of XLPE were studied. The results show that with the extension of thermal aging time, the microstructure of XLPE molecule is destroyed, the macromolecular chain is gradually cleaved, and the carbonyl absorption intensity increases. At power frequency, the breakdown strength decreases from 75.37 kV/mm to 62.18 kV/mm, the relative permittivity increases from 2.44 to 2.51, and the dielectric loss increases from 1.47 × 10−4 to 3.10 × 10−3. The free volume rate of XLPE molecules increases with the increasing temperature, and the mean square displacement gradually increases. The work has good guiding significance for the safe operation and condition assessment of high-voltage cables.

Negative DC Dielectric Breakdown Characteristics and Synergistic Effect of HFO-1336mzz(E) Mixtures

HFO-1336mzz(E), a substitute for sulfur hexafluoride (SF6), has received much attention owing to its excellent insulation and environmental performance. To provide a reference for selecting suitable buffer gas type and mixing ratio in engineering applications, this article investigated the saturated vapor pressure characteristics, negative direct current (−dc) breakdown properties, and synergistic effect of HFO-1336mzz(E)/CO2 and HFO-1336mzz(E)/N2 mixtures. Experimental results show that although the allowable percentage of HFO-1336mzz(E) in the HFO-1336mzz(E)/CO2 mixture is lower than that of the HFO-1336mzz(E)/N2 at the same gas pressure and limiting temperatures, the former one has a higher breakdown voltage in the gas pressure range from 0.1 to 0.7 MPa. Compared with HFO-1336mzz(E)/N2, the shorter distance within the bimolecular composite structures of HFO-1336mzz(E)/CO2 leads to stronger interaction energy ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${E}_{\text {int}}$ </tex-math></inline-formula> ). As a result, HFO-1336mzz(E)/CO2 has a better synergistic effect in view of breakdown voltage. Based on the comprehensive analysis of saturated vapor pressure, liquefaction temperature, and insulation properties of HFO-1336mzz(E)/buffer gas mixtures, CO2 is superior as a buffer gas to N2 being mixed with HFO-1336mzz(E). The negative dc breakdown voltage of 0.7 MPa HFO-1336mzz(E)/CO2 occupies 99.17%, 93.03%, and 85.92% of that of 0.7 MPa 20%SF6/80%N2 mixture under −5 °C, −15 °C, and −25 °C limiting temperatures, guaranteeing its application as an insulation medium in electrical equipment under 220 kV.

Formation of Remote Quantum Point Contact Inside Dielectric Medium of an AlO x /SiO x ReRAM

Remote quantum point contact (QPC) far from the metal electrodes was observed in forming free aluminum oxide (AlOx)/silicon oxide (SiOx) resistive random access memory (ReRAM) cell, which was resolved at low bias. QPC behavior of the cell was attributed to confined oxygen vacancies across uncorrelated narrow grain boundaries of intermediate O3 treated thin AlOx layer of the stack, which was designed to restrict vacancy channeling between the two immediate reservoirs; i.e., from beneath SiOx to the top as-deposited AlOx layer. From time dependent dielectric breakdown (TDDB) characteristics of the cell while assessed under low stress biases, we found one to one correspondence between TDDB and its bias dependent QPC. Furthermore, we found that, under steady state and especially at low biases progressive breakdown (PBD) of the dielectric exhibited two-level random telegraph noise (RTN) like conductance fluctuations, which occurred in the magnitude of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${G}_{{0}}$ </tex-math></inline-formula> or in its multiples depending on applied bias to the cell, that demonstrated a correlation between electron trapping and maximum QPC instability during filament growth. Low voltage QPC-based switching under dc bias sweep, its correlation with TDDB and RTN under the steady state thus provided us a framework to analyze the evolution of QPC well before reaching the SET state in an AlOx/SiOx cell, which is different from the usual QPC evolution as found near contact regions in a conventional SiOx cell without accompanying engineered AlOx barrier.

Three-Dimensional Metal-Insulator-Metal Decoupling Capacitors with Optimized ZrO2 ALD Properties for Improved Electrical and Reliability Parameters

Embedded three-dimensional (3-D) metal-insulator-metal (MIM) decoupling capacitors with high-κ dielectric films of high capacitance and long-life time are increasingly needed on integrated chips. Towards achieving better electrical performance, there is a need for investigation into the influence of the variation in atomic layer deposition (ALD) parameters used for thin high-κ dielectric films (10 nm) made of Al2O3-doped ZrO2. This variation should always be related to the structural uniformity, the electrical characteristics, and the electrical reliability of the capacitors. This paper discusses the influence of different Zr precursor pulse times per ALD cycle and deposition temperatures (283 °C/556 K and 303 °C/576 K) with respect to the capacitance density (C-V), voltage linearity and leakage current density (I-V). Moreover, the dielectric breakdown and TDDB characteristics are evaluated under a wide range of temperatures (223-423 K).

An Improved Design Procedure for a 10 kHz, 10 kW Medium-Frequency Transformer Considering Insulation Breakdown Strength and Structure Optimization

Medium-frequency transformer (MFT) is an essential device in the smart solid-state transformer (SST) prototype. Compared with the well-defined principle design of magnetic core and windings in MFT, insulation issues are barely concerned. This article focuses on improved design optimization of an MFT, considering the main insulation strength and structure. Dielectric breakdown characteristics of epoxy resin insulating material were studied. An obvious reduction of dielectric strength occurred at high frequency and high temperature in thick samples, which is used for the design of insulation clearance and margin. Moreover, a modified insulation loss evaluation was used, involving the square wave with spike voltages. Through introducing a strategy of multilayered insulation in the windings, the insulation structure is optimized. A 10-kW, 10-kHz, 1-kV/750-V MFT used in the 10-kV SST system was designed by considering the insulation research. Finally, experimental verifications of the MFT performance were carried out by a resonant dc–dc converter. It appears that the optimized MFT exhibits low electric field, small temperature rise, and high efficiency at a 10-kW load. This research provides the basic principles for insulation design in high-voltage and high-power MFT.

Significant Differences in BTI and TDDB Characteristics of Commercial Planar SiC-MOSFETs

Silicon carbide (SiC) metal-oxide-semiconductor field-effect transistors (MOSFETs) have been produced by several vendors for commercial applications. SiC-MOSFET reliability was assessed using bias-temperature instability (BTI) and time-dependent dielectric breakdown (TDDB) characteristics. Here, we compared two planar SiC-MOSFET samples (A and B) from different vendors. The samples exhibited significantly different positive and negative BTI, time-dependent gate-current, TDDB lifetime statistics, and temperature dependence. These differences suggest NO (nitric oxide)-annealing variations.

Effects of filler composition, loading, and geometry on the dielectric loss, partial discharge, and dielectric strength of liquid metal polymer composites

With the goal of enabling the design of liquid metal polymer composites (LMPCs) with desired electrical and mechanical properties while preventing premature dielectric aging and failure, the dielectric breakdown characteristics of LMPCs containing galinstan (GaInSn), barium titanate (BTO), iron (Fe), and mixtures thereof are investigated. The dielectric properties including dielectric loss (tan δ), partial discharge inception electric field (PDIE), and breakdown electric field (Ebd) are investigated. According to the study, LMPCs with a higher overall filler concentration tend to show higher tan δ, lower PDIE, and lower Ebd. The study also demonstrates that these dielectric properties vary by the type of filler even with an equally maintained filler concentration. This is due to the distinct filler conductivity, permittivity, and geometry that cause differences in the electric field distribution within the composites. To provide further insights into the observed experimental results, finite element analysis (FEA) models were developed and analyzed.

Effect of barrier thickness of Polytetrafluoroethylene on the Direct Current breakdown characteristics of liquid nitrogen

When high-temperature superconducting (HTS) tapes in high voltage DC HTS devices are quenched, amounts of thermal bubbles are generated in liquid nitrogen (LN2) that will reduce the insulation strength greatly. Especially when resistive-type superconducting fault current limiters meet a short-circuit fault, the insulation strength of the LN2 decreased significantly due to the thermal bubbles and electrothermal pressure. Solid insulating barriers can improve the insulation strength of the LN2. The objective of this study is to obtain the effect of barrier thickness on the DC dielectric breakdown characteristics of LN2. Insulating barrier Polytetrafluoroethylene with three different thicknesses were tested. Three types of electrodes such as rod-plane, needle-plane, and plane-plane were applied. The results showed that the barriers can increase the negative and positive breakdown voltage both with and without thermal bubbles in a slightly non-uniform field (SNF) and non-uniform field (NF). For the SNF, the DC breakdown voltage is higher when the barrier is thinner. The effect of the barrier thickness in the NF is lower than that in the SNF field. For the NF, the positive breakdown voltage is higher when the barrier is thicker.

Effects of Annealing Temperature on TiN/Hf0.5Zr0.5O2/TiN Ferroelectric Capacitor Prepared by In-Situ Like Consecutive Atomic Layer Deposition

In this letter, the ferroelectric characteristics and reliability of TiN&#x002F;Hf_0.5Zr_0.5O₂&#x002F;TiN Metal-Ferroelectric-Metal (MFM) capacitor fabricated using the <i>&#x2018;&#x2018;in-situ&#x2019;&#x2019;</i> like consecutive atomic layer deposition (<i>C-ALD</i>) and the <i>&#x201C;ex-situ&#x201D;</i> deposition techniques are compared for different post metal annealing (PMA) temperatures. We suggested that <i>C-ALD</i> deposition improves the interface of the ferroelectric HZO film and the higher PMA temperature further improves the crystal quality. We found that <i>wake-up</i> tends to happen for both types of samples with lower PMA temperature, indicating the possible higher dependence of <i>&#x201C;wake-up&#x201D;</i> on crystallinity. Nevertheless, <i>C-ALD</i> and higher PMA temperature are both required to prevent early breakdown. <i>C-ALD</i> samples combined with 600 &#x00B0;C PMA showed the excellent remanent polarization (2P_r) of 53 &#x03BC;C&#x002F;cm², endurance properties of 10¹¹ cycles, and outstanding time-dependent dielectric breakdown (TDDB) characteristics.

Effects of frequency and thermal conductivity on dielectric breakdown characteristics of epoxy/cellulose/BN composites fabricated by ice-templated method

Epoxy resin has been extensively used in the electrical systems and electronic devices. However, it is still a challenge to fabricate highly thermally conductive but electrically insulating epoxy composites. In this work, epoxy/cellulose/BN (EP/C-BN) composites were fabricated by ice-templated method. More importantly, the effects of frequency and thermal conductivity on dielectric breakdown characteristics, supported by the experiments of dielectric breakdown characteristics, infrared thermal imaging and finite simulation analysis, were studied. The as-prepared EP/C-BN composites exhibit a maximum thermal conductivity of 1.19 W/(m·K), and notably improved breakdown time at high frequency (324% higher than that of EP at 44 kHz). This work gives significant insight into the design of the thermal management polymers working at high frequency and high voltage fields.

Reliability Analysis on TiN Gated NMOS Transistors

Compared to poly Si gate, metal gate has no gate depletions and experiences inversion capacitance gain, which makes an advantage for devices scaling. In this paper, we investigated the gate oxide leakage current and Time Dependent Dielectric Breakdown (TDDB) characteristics of TiN and poly Si electrodes with a 3.5 to 5 nm SiO2 dielectric thickness range. According to the Transmission Electron Microscope (TEM) analysis there is difference in oxide thickness. The SiO2 thickness of TiN gate electrode has been reduced by ~0.25 nm, considerably because of a scavenging effect. We normalized the reduced SiO2 thickness with an electrical oxide field, and there were no differences between the two electrodes in gate leakage current, accumulation breakdown voltage (BV), and accumulation TDDB lifetime. Therefore, we found the scavenging effect of TiN electrodes seems to affect little the leakage current and TDDB reliability of SiO2 dielectric. On the other hand, the BV and TDDB lifetime of TiN electrode in the inversion region are little bit better than that of the poly electrode. We think this differences are originated from the difference between TiN/SiO2 and poly Si/SiO2 interfaces.

HVDC 케이블 접속재용 실리콘고무/나노 실리콘카바이드 콤포지트의 전기적 특성

In order to develop HVDC cable accessory, space charge exists at the interface between XLPE and EPDM composite or at the interface between XLPE and SiR. The larger the difference in ratio between the dielectric constant and the electrical conductivity of the two insulators, the greater the amount of space charge appears at the interface. The more and more space charges are stored at the interface, the higher the electric field distortion occurs. Therefore, in developing HVDC cable connection materials, Silicone rubber/nano silicon carbide (SiC) contents composites related to insulation and electrical conduction were manufactured. Nano SiC, a semiconducting inorganic material, has been modified to reinforce the interface of the composite mixed with silicon rubber.In addition, in order to study electrical ±HVDC dielectric breakdown characteristics and dielectric characteristics, modified ano SiC was filled with 0, 1, 3, 5, 7, 9wt%, dispersed, and nanocomposite was developed.

Dielectric breakdown properties of Al-air mixtures

In order to investigate the influence of aluminum vapor on the breakdown performance of air, this paper makes a study of the dielectric breakdown characteristics of Al-air mixture in the temperature range of 300–5000 K at atmospheric pressure. A Boltzmann analysis method is used to deal with the electron energy distribution function (EEDF), the reduced ionization coefficients (α/N), the reduced attachment coefficients (η/N) and the critical reduced breakdown strength ((E/N)cr) so as to explore the influence of temperature and mixing ratio on the dielectric breakdown properties. In the temperature range of 300–2000 K, the property of the mixture is mainly determined by the mixing proportion of aluminum vapor because the composition of particles remains unchanged. In the temperature range of 2000–2500 K, the decomposition of Al2O2 leads to the increase of aluminum oxides and NO, and a rise in the percentage of high-energy electrons as well as the increment of α/N. Also, the joint action of O2 and NO makes η/N increase first and then decrease, and (E/N)cr goes down to a smaller temperature range. An increase in the proportion of aluminum vapor causes (E/N)cr to decrease in the low-temperature region and to increase in the high-temperature region, which will reduce the transition between these two temperature regions.

Impact of O2 post oxidation annealing on the reliability of SiC/SiO2 MOS capacitors* *Project supported by the General Program of the National Natural Science Foundation of China (Grant No. 61974159) and the Youth Innovation Promotion Association of the Chinese Academy of Sciences and Scientific Instrument Developing Project of the Chinese Academy of Sciences (Grant No. YJKYYQ20200039).

The effects of dry O2 post oxidation annealing (POA) at different temperatures on SiC/SiO2 stacks are comparatively studied in this paper. The results show interface trap density (D it) of SiC/SiO2 stacks, leakage current density (J g), and time-dependent dielectric breakdown (TDDB) characteristics of the oxide, are affected by POA temperature and are closely correlated. Specifically, D it, J g, and inverse median lifetime of TDDB have the same trend against POA temperature, which is instructive for SiC/SiO2 interface quality improvement. Moreover, area dependence of TDDB characteristics for gate oxide on SiC shows different electrode areas lead to same slope of TDDB Weibull curves.

Electric stress and dielectric breakdown characteristics under high-frequency voltages with multi-harmonics in a solid-state transformer

Mixed-frequency electric stress and the thermal issue by rapid semiconductor switching and circuit topology cause the unexpected insulation breakdown, indicating a key issue on medium-high frequency (MF-HF) transformers. This work focuses on the effects of frequency and temperature on the breakdown strength of used epoxy resin insulation. An experimental method containing the power supply and breakdown measurement unit was constructed under high sinusoidal voltages with harmonic components. A continuous boost method was used to induce dielectric breakdown. Meanwhile, high voltage and current probes were employed to capture the breakdown voltage and current waveforms. The results indicate the reduction in the breakdown strength of the epoxy resin with the increase in frequency and temperature. Furthermore, the effects of temperature (up to 120 °C) on breakdown strength were no more obvious than those of frequency (up to 8 kHz). That is mainly derived from the glass transition of epoxy resin. Through discussing the dielectric loss and energy dissipation by FEM simulations together with the complex permittivity of epoxy resin, it could be concluded that the dielectric heating contributes to the acceleration of electric breakdown under high-frequency voltages. In addition to the fundamental frequencies, the harmonic voltages introduced high electric stresses and dielectric loss, resulting in a decrease in breakdown strength. The dielectric heating related to the electric stresses and frequencies should be considered in the insulation design of MF-HF transformers.

Pre-Deposition Interfacial Oxidation and Post-Deposition Interface Nitridation of LPCVD TEOS Used as Gate Dielectric on 4H-SiC

In this work, the influence of pre-deposition interfacial oxidation or post-deposition interface nitridation on the performance of 4H-SiC MOS capacitors was investigated. The gate oxide was deposited by LPCVD using TEOS as a precursor. Interface breakdown strength was derived from leakage current and Time-Zero Dielectric Breakdown characteristics whereas interface quality was assessed by the determination of interface state density from the comparison of quasi-static and high frequency capacitance-voltage characteristics using high-low method. In the experimental results, it is demonstrated that the gate oxide deposited by LPCVD using TEOS which is post-deposition annealed in nitric oxide ambient is advantageous for trench-gate MOSFET due to its effectiveness for improving the interface quality and oxide reliability, whereas pre-deposition interfacial oxidation is deleterious to interface state density and breakdown strength.