Increase In Breakdown Voltage Research Articles

Experimental study on the effects of electrode materials on coal breaking by plasma

The extensively applied plasma technology boasts potential application prospects in the field of coal seam permeability enhancement. However, the effect of electrode materials on coal breaking by plasma (CBP) has not been reported. For this reason, the effects of four kinds of electrode materials, namely aluminum, copper, brass and stainless steel, on CBP were investigated by using a self-built CBP experimental system. The experimentally obtained statistics show that the sizes of coal fragments differ under the action of different electrodes. Specifically, the coal sample tends to be broken into small particles under the action of aluminum electrode, whereas the broken fragments generally have a diameter of larger than 15 mm under the action of brass electrode. The scanning electron microscopy results suggest that the different electrode materials correspond to different modes of crack initiation on coal surface. The results of liquid N2 adsorption show that the aluminum electrode exerts the poorest effect on improving micro-pores in coal, while the copper electrode achieves the best effect. Furthermore, the effects of electrode materials on the current and voltage waveforms at different voltages were analyzed by using a Rogowski coil and a HV test rod, and the effects of electrode materials on deposited energy generated by plasma in the coal were also discussed. The results indicate that at low voltages, the voltage and current waveforms under the action of four electrode materials differ obviously; in contrast, at high voltages, the voltage and current waveforms become almost identical. At the same voltage, the deposited energies formed by different electrode materials also differ due to the difference in breakdown voltages and current waveforms. The deposited energies formed by the aluminum electrode, the brass electrode and the stainless steel electrode inside the coal fall first and then rise with the increase of breakdown voltage, whereas that formed by the copper electrode goes up gradually with the increase of breakdown voltage. Based on the photograph of plasma discharge process shoot by a high-speed camera, the law of plasma propagation inside the coal was analyzed, and the effects of electrode materials on plasma development were discussed. A plasma streamer which is accompanied by dazzling white light and extremely high temperature is formed inside the coal at the moment of discharge, and it continuously expands outward as time passes by. The brightness degrees of plasma streamers formed under the action of electrode materials are different. Among the four electrode materials, the brass electrode forms the brightest light and generates the greatest energy.

Transformer Oil Dielectric Characteristics in Microwave Assisted Reconditioning Processes

Maintenance of transformer oil is needed to maintain the quality of power service. Thermal heating and filtering are the main ways to remove contaminants from the oil. In this research, a preliminary study was carried out using microwaves as thermal heaters in the reconditioning process of used transformer oil. The reconditioning process is carried out by filtering and thermal heating varies from temperatures of 40–100 °C using a microwave oven. Dielectric characteristics are shown by analyzing breakdown voltage, dielectric power loss, viscosity, and dc conductivity measurements. The amount of moisture content is also taken into account in measuring the level of thermal efficiency of the heater. Under the influence of microwaves, an increase in the characteristics of the dielectric strength in the form of an increase in breakdown voltage reaches 140.50%. Microwave heating is very good in reducing the water content in oil with a level of thermal efficiency reaching 25.55–40.40%. Removal of contaminants is better done by microwaves characterized by a decrease in the value of the dielectric power loss and dc conductivity at each treatment.

A novel SOI MESFET to spread the potential contours towards the drain

ABSTRACT This paper presents a new structure of Metal Semiconductor Field Effect Transistor (MESFET) for high power applications. One of the problems that we face in the design of the MESFET devices is that in most cases, the increase of breakdown voltage is accompanied by a decrease in the saturation drain current. Our aim to propose this structure is to improve these two parameters simultaneously. Using the insulator region under the sides of the gate (IR) and the hide field plate (HFP) in the buried oxide (BOX) are the fundamental solution for improving these parameters. We named the proposed structure as spread potential contours towards the drain MESFET (SPC-MESFET). By applying the proposed structure, the drain current and the breakdown voltage improve 20 and 27 percent compared to a conventional structure (C-MESFET), respectively. Therefore, the proposed device has a higher maximum power density than the C-MESFET structure. Also, this idea reduces the gate capacitance and thus the frequency characteristics such as cut off frequency (fT), maximum oscillation frequency (fmax), and Maximum Available Gain (MAG) improve in comparison with the C-MESFET structure.

Optical Investigation of Proton‐Irradiated Metal Organic Chemical Vapor Deposition AlGaN/GaN High‐Electron‐Mobility Transistor Structures

About 2 MeV proton numerical calculation damage indicates that a quasiflat profile is introduced into the GaN buffer layer of high‐electron‐mobility transistor (HEMT) templates. A previous transport study of such HEMT structures showed increased breakdown voltage and reduced GaN buffer layer leakage after proton irradiation. Hyperspectral electroluminescence measurements detected the emission band in the spectral region between 700 and 800 nm. This emission is assumed to be associated with the generation of trap levels responsible for the device failure. To obtain insights into the nature of radiation‐generated traps, detailed low‐temperature photoluminescence (PL) and cathodoluminescence (CL) experiments are conducted in a set of virgin and proton‐irradiated device structure templates. Both the PL and CL spectra show large intensity variations of all emission bands, in the spectral range between 330 and 890 nm, with increasing proton dosage. This is consistent with the introduction of compensating and/or nonradiative recombination centers in the GaN buffer layer. Luminescence measurements carried out under various excitation conditions show different recombination rates for emission bands observed near 420 and 550 nm, indicating different free carrier capture rates. Spectral analysis suggests that these two emission bands have different dependences on proton irradiation dosage, consistent with different chemical natures.

Electrical Characteristics of AlGaN/GaN High-Electron-Mobility Transistors Fabricated with a MgF2 Passivation Layer

We have demonstrated AlGaN/GaN high-electron-mobility transistors (HEMTs) fabricated with aMgF2 passivation layer. Upon MgF2 passivation using an e-beam evaporator, the HEMT showed a maximum drain saturation current of 508 mA/mm, a maximum transconductance of 136 mS/mm, a significantly reduced gate forward leakage current, a low gate reverse leakage current of 1.8 × 10−7 A/mm at gate bias voltage of −10 V, and an increased breakdown voltage of 563 V. This suggests that the MgF2 film is quite useful as a passivation layer for AlGaN/GaN HEMTs.

Vertical Leakage in GaN-on-Si Stacks Investigated by a Buffer Decomposition Experiment

We investigated the origin of vertical leakage and breakdown in GaN-on-Si epitaxial structures. In order to understand the role of the nucleation layer, AlGaN buffer, and C-doped GaN, we designed a sequential growth experiment. Specifically, we analyzed three different structures grown on silicon substrates: AlN/Si, AlGaN/AlN/Si, C:GaN/AlGaN/AlN/Si. The results demonstrate that: (i) the AlN layer grown on silicon has a breakdown field of 3.25 MV/cm, which further decreases with temperature. This value is much lower than that of highly-crystalline AlN, and the difference can be ascribed to the high density of vertical leakage paths like V-pits or threading dislocations. (ii) the AlN/Si structures show negative charge trapping, due to the injection of electrons from silicon to deep traps in AlN. (iii) adding AlGaN on top of AlN significantly reduces the defect density, thus resulting in a more uniform sample-to-sample leakage. (iv) a substantial increase in breakdown voltage is obtained only in the C:GaN/AlGaN/AlN/Si structure, that allows it to reach VBD > 800 V. (v) remarkably, during a vertical I–V sweep, the C:GaN/AlGaN/AlN/Si stack shows evidence for positive charge trapping. Holes from C:GaN are trapped at the GaN/AlGaN interface, thus bringing a positive charge storage in the buffer. For the first time, the results summarized in this paper clarify the contribution of each buffer layer to vertical leakage and breakdown.

Meandering Gate Edges for Breakdown Voltage Enhancement in AlGaN/GaN High Electron Mobility Transistors

Herein, a unique device‐design strategy is reported for increasing the breakdown voltage and hence Baliga figure of merit (BFOM) of III‐nitride high electron mobility transistors (HEMTs) by engineering the gate edge toward the drain. The breakdown of such devices with meandering gate‐drain access region (M‐HEMT) are found to be 62% more compared with that of conventional HEMT whereas the on‐resistance suffers by 76%, leading to an overall improvement in the BFOM for by 28%. The 3D technology computer‐aided design simulations show that the decrease in the peak electric field at the gate edge was responsible for increased breakdown voltage.

INFLUENCE OF ANODIC ALUMINA USED AS SEPARATING DIELECTRIC OF SILICON AVALANCHE LEDs ON DIODE CHARACTERISTICS

A study of the influence of the formation regimes of avalanche LEDs based on nanostructured silicon on the parameters of the formed devices, such as the light emission voltage and the stability of operation has been performed. These parameters are an important factor for the practical use of avalanche LEDs in the development of silicon photonics products, the progress of which is associated with the future of integrated electronics. For the first time, the technological operation of local through electrochemical anodizing of aluminum in various electrolytes for the formation of a separating dielectric of Schottky contacts is presented. The influence of the built-in electric charge in the separation dielectric of silicon avalanche LEDs on their current-voltage characteristics is studied. It was found that the built-in negative electric charge increases the breakdown voltage of the Schottky contact, which results in an increase of the light emission efficiency of the diode structures. An explanation of this effect is presented on the basis that the built-in negative electric charge inside the anode oxide also creates a space charge region in silicon, which helps to reduce the effect of the concentration of field lines at the edges of diode structures, performing the function of protecting the Schottky contact from edge effects as well as protective areas do. It has been established that the highest avalanche breakdown voltage is observed in diode structures with anodic oxide formed in an electrolyte based on an aqueous solution of phosphoric acid. An analysis of the characteristics of LEDs at different temperatures of silicon substrates showed an increase of breakdown voltage with increasing temperature, which is typical for avalanche breakdown during impact ionization. Stable light emission of the formed LEDs was demonstrated in a wide range of operating voltages (8–16 V). The use of silicon avalanche LEDs both as discrete devices and in integrated electronics in general has been discussed.

Solution-Processed Li2O-Al2O3/TiO2 Nanolaminate Stacks Containing Mobile Lithium Ions and with Increased Breakdown Voltages.

An aqueous solution approach has been utilized to prepare nanolaminates of TiO2 and ionically conductive Li2O-Al2O3 (LiAlO). This new approach utilizes low curing temperatures, resulting in fully oxidized films as demonstrated by Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy. The layered structures have been characterized by scanning electron microscopy, X-ray diffraction, and X-ray reflectivity. Incorporation of sufficiently thick (13 and 27 nm) ion blocking TiO2 layers into nanolaminate structures with LiAlO layers resulted in an increase in breakdown voltage by more than a factor of two, relative to LiAlO. Nanolaminate structures also preserve the large double layer capacitance of the ionically conductive layer. Increased breakdown strength coupled with large capacitances results in a doubling of ultimate charge storage capacity, illustrating how nanolaminates can be used to improve properties relevant for energy/charge storage applications.

Arc ablation behavior and microstructure evolution of plastically deformed and micro-alloyed Cu–Cr–Zr alloys

Cu–Cr–Zr alloys are often subjected to premature failures due to arc erosion at moment of their breakdown. In this paper, a series of simulated high-voltage arc ablation experiments were conducted to systematically investigate arc ablation characteristics of Cu–Cr–Zr alloys, their microstructure evolutions and anti-ablation properties after plastic deformation and microalloying. Results showed that during their arc ablation processes, a halo pattern was firstly formed on the surface under the action of high-temperature arc. This is followed by partial melting and splashing of Cu, forming of uneven and rough surfaces, and finally significant burning of the alloy. The degree of ablation of alloy is aggravated with the increased breakdown voltage. Due to a combined effect of solid solution strengthening, fine grain strengthening and deformation strengthening, the ablation resistance of the micro-alloyed and plastically deformed alloy has been significantly improved. The breakdown field strengths of commercial Cu–Cr–Zr alloy, heat-treated and deformed one, micro-alloyed and heat-treated one are 1.46 × 106 V/m, 1.67 × 106 V/m and 1.90 × 106 V/m, respectively. However, the breakdown strength of alloys after microalloying is unstable. Results show that there are no preferred phases for the first breakdown of arc ablation of Cu–Cr–Zr alloys. The second-phase particles with high-hardness and high-melting temperature hinder the splashing and flow of the molten copper, and inhibit the movement of the cathode spots during the ablation process.

Breakdown Walkout in Polarization-Doped Vertical GaN Diodes

We demonstrate the avalanche capability and the existence of breakdown walkout in GaN-on-GaN vertical devices with polarization doping. By means of combined electrical and optical characterization, we demonstrate the following original results: 1) vertical p-n junctions with polarization doping have avalanche capability; 2) stress in avalanche regime induces an increase in breakdown voltage, referred to as breakdown walkout; 3) this process is fully-recoverable, thus being related to a trapping mechanism; 4) temperature-dependent measurements of the breakdown walkout identify $\text{C}_{N}$ defects responsible for this process; and 5) capacitance deep level transient spectroscopy (C-DLTS) and deep level optical spectroscopy (DLOS) confirm the presence of residual carbon in the devices under test. A possible model to explain the avalanche walkout is then proposed.

Impact of N2O admixture on the characteristics of pulsed dielectric barrier discharges in N2 at atmospheric pressure

The impact of N2O admixtures on the inception and development of pulsed dielectric barrier discharges (DBDs) in N2 at atmospheric pressure is studied using optical and electrical diagnostics supported by 0D modelling of the reaction kinetics. The N2O concentration in the N2–N2O gas mixture was varied between virtually pure N2 and 10 vol% N2O. A significant impact of N2O on the discharge characteristics was found for concentrations above 1000 ppm. In particular, a decrease of the transferred charge, and discharge energy and an increase of breakdown voltage, maximal discharge current, discharge emission diameter and velocity of the cathode-directed ionisation front (positive streamer) were observed. Additionally, a strong increase of breakdown voltage and discharge inception jitter accompanied by a decrease of the emission duration was found for N2O concentrations above 1 vol%. The modelling results indicate that for N2O concentrations in this range a transition from an electropositive to an electronegative regime takes place.

Experimental study on the effect of coal thickness and breakdown voltage on energy conversion during electrical disintegration

The high-voltage electrical pulse coal fracturing technology based on the principle of electrical disintegration (ED) has been put forward, but the voltage and current waveform are rarely reported. In this study, effects of coal thickness and breakdown voltage on voltage and current waveforms in during ED in air environment were investigated. Besides, the changes of peak current, electric breakdown delay and instantaneous power with the variations of coal thickness and breakdown voltage were analyzed, and the changes of deposited energy and energy conversion rate with the variations of thickness and breakdown voltage were discussed. The results show that coal thickness and breakdown voltage have notable effects on deposited energy. Under the same breakdown voltage, the deposited energy inside coal samples with different thicknesses differs. In contrast, with the same coal thickness, the deposited energy in coal sample increases with the increase of breakdown voltage. The energy conversion rate increases first and then decreases with the increase of coal thickness, while it decreases first and then increases with the increase of voltage. Therefore, with certain coal thickness, there is an optimum breakdown voltage which enables the energy conversion efficiency to reach the optimal.

Frequency-independent breakdown strength of dielectric elastomers under AC stress

Soft insulators are the main component used in dielectric elastomer actuators (DEAs). It follows that dielectric properties like permittivity and dielectric strength of the insulator can strongly influence the maximum dynamic actuation performance of DEA devices. We observed an increasing breakdown voltage with increasing driving AC voltage frequency for silicone-based dielectric films. Despite the breakdown voltage increase, we demonstrate that there is no actual breakdown electric field rise with varying frequencies. We show that the voltage behavior is rather compatible with a constant dielectric breakdown field model and the slow mechanical response of the elastomer.

Impact of interface traps/defects and self‐heating on the degradation of performance of a 4H‐SiC VDMOSFET

The reliability of silicon carbide metal oxide semiconductor field-effect transistors remains a challenge in power applications and relates to the SiO2–SiC interface. The presence of unwanted interface traps/defects degrades the device performance. The impact of acceptor traps/defects on the performance of a 4H-SiC vertical Diffused Metal Oxide Semiconductor Field Effect Transistor (DMOSFET) with a breakdown voltage of 1700 V is investigated. - and - characteristics were simulated, using a drift-diffusion model coupled to Fourier heat equations, and are in a good agreement with experimental results. The presence of interface traps/defects were shown to produce degradation of threshold voltage, but the impact diminishes as temperature increases. A threshold voltage shift of 3.5 V occurs for a trap concentration of 2 × 1013 cm–2/eV at room temperature. The transfer characteristics obtained from electro-thermal modelling show a larger degradation than those at a constant temperature. This degradation increases with the drain bias increase. The threshold voltage from the electro-thermal simulations is 5 V compared to 4 V observed in constant 423 K temperature simulations at. Finally, the interface traps/defects increases breakdown voltage exhibiting a strong dependency on the trap density and their energy decay characteristics.

A new method to evaluate the effectiveness of impulse voltage for detecting insulation defects in GIS equipment

Lightning impulse (LI) test is an effective means to detect insulation defects in gas-insulated metal-enclosed switchgear (GIS) equipment. However, the LI test wavefront time Tf will exceed the standard value of 1.2 μs ± 30% for large test load capacitance. Whether extending the Tf will influence defect detection effectiveness should be a concern. In this study, a generating system of impulses with different wavefront parameters was established. The insulation characteristics of a coaxial cylinder structure with an SF6 gas gap with conductive protrusion in a bus under impulses with different wavefront parameters were studied. Experimental results show that the voltage–time curve of the gap shows a bathtub trend that has a flat part in the range of 1 μs to 5 μs. With a Tf increase, the 50% breakdown voltage increases. Whether extending the Tf will influence defect detection effectiveness is analyzed from the standpoint of the different meaning of the breakdown voltage in voltage-time curve and 50% breakdown voltage. The essence of detection effectiveness under impulse voltages with different wavefront parameters is a comparison of the probability of detecting the same insulation defect. Based on the discharge probability distribution, a new quantitative method to evaluate the insulation defect detection effectiveness of impulse voltages for GIS equipment is proposed. The method, based on the 90% discharge voltage value of an insulation defect under a standard LI, normalizes the discharge probability under different wavefront parameters.

InGaN/(GaN)/AlGaN/GaN normally-off metal-oxide-semiconductor high-electron mobility transistors with etched access region

The proposal and processing aspects of the prove-of-concept InGaN/GaN/AlGaN/GaN metal-oxide-semiconductor (MOS) high-electron mobility transistor with etched access regions are addressed. Full strain and decent quality of the epitaxial system comprising 4 nm In0.16Ga0.84N/3 nm GaN/5 nm Al0.27Ga0.73N are observed using a high-resolution transmission-electron microscopy and by deformation profile extractions. Large negative polarization charge in the MOS gate stack provides the HEMT normally-off operation, while free electrons are populated at access regions after etching. Consecutive passivation by 10 nm Al2O3 together with annealing at 300 °C improved the Al2O3/semiconductor interface, with the threshold voltage (VT) reaching 1 V. Improvements of the present concept in comparison to the previous one with a gate recess were proved by showing the decreased drain leakage current and increased breakdown voltage.

Temperature dependent lateral and vertical conduction mechanisms in AlGaN/GaN HEMT on thinned silicon substrate

This paper presents the influence of Si substrate thinning by grinding and dicing on the mechanical and electrical properties of AlGaN/GaN HEMT grown on 6-inch Si substrate. By experimentally removing 96% of the Si substrate, an increase in the lateral breakdown voltage by 13% is achieved for a wide temperature range. A decreasing vertical breakdown voltage with substrate thinning shows the necessity of substrate replacement to maintain the vertical isolation. Poole-Frenkel and space charge limited conduction mechanisms are identified for the vertical leakage in forward and reverse bias down to thicknesses of 200 μm, respectively. The increase in chip bow and the resulting increase in tensile strain in the epitaxial layers resulting from the substrate removal are correlated to a 40% decrease in 2DEG charge carrier concentration along with a 27% increase in threshold voltage. These findings are explained by strain-induced gate barrier and polarization charge variations.

Total-Ionizing-Dose Irradiation-Induced Dielectric Field Enhancement for High-Voltage SOI LDMOS

Breakdown voltage (BV) shifting behavior induced by total-ionizing-dose (TID) irradiation is investigated for high-voltage SOI LDMOS, in this letter. The BV increase caused by irradiation is present for the first time, and the degradation mechanism is revealed by modeling and simulation. Irradiation-induced electric field modulation exerts an impact on the competition between the lateral BV and vertical BV and results in BV shifting. The dielectric field is enhanced by irradiation-induced positive oxide trapped charges in the BOX layer, which is responsible for the BV increasing after irradiation. A TID radiation hardening approach is proposed so that the lateral BV is required to be properly higher than vertical BV instead of pursuing equality.

Numerical simulation of the effect of water admixtures on the evolution of a helium/dry air discharge

In this study, a 1D plasma fluid model is used to shed light into the evolution of a He/dry air (500 ppm, 79% N2 and 21% O2) dielectric barrier discharge (DBD) under different levels of water admixtures (20 to 2000 ppm). The model considers the analytical chemistry between helium, nitrogen, oxygen and water species and it is verified with experimental results to ensure its correctness. The simulation results show that water admixtures highly affect the discharge characteristics and the dominant ions in the mixture. In particular, it was observed that the increase of water in the mixture up to 600 ppm causes the reduction of the breakdown voltage, while above 600 ppm the breakdown voltage increases. Furthermore, the simulation results show that the most important positive ion in the mixture is H2O+ for 20–100 ppm of water admixtures and for 100–2000 ppm of admixtures. The most abundant negative charged species is found to be electrons for the range of water admixtures considered in this study. To interpret these results and to get an insight into the discharge evolution, the main reaction pathways of ion production are investigated and analyzed.