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Temperature-dependent behavior of regular and trench Ni/b-Ga2O3 (001) Schottky barrier diodes (SBDs) was studied. Current-Voltage (I-V) characteristics, ideality factor, and barrier height of trench SBDs were compared with those of regular SBDs at temperatures ranging from 100K to 650 K. The trench SBDs showed a superior performance to regular SBDs. At elevated temperatures (as high as 650 K), the trench SBDs maintained a high ON/OFF current ratio (105), which is four orders of magnitude higher than that in the regular diodes. The current-voltage characteristics of the trench SBDs were recovered when the sample was cooled to room temperature after high temperature measurements, whereas the I-V characteristics of the regular SBDs were degraded. The breakdown voltage (BV) was also measured on asfabricated devices and after high temperature ramp up to 650 K. We observed a reduction in maximum achieved BV from 1084V to 742V on the trench SBDs and from 662V to 488V on regular SBDs, respectively, after temperature-dependent measurements. [ABSTRACT FROM AUTHOR]

CF4 has found industrial applications in power switching and gas insulated circuit breakers although it is considered to be a powerful greenhouse gas. This disadvantage can be overcome by mixing CF4 with gases like Argon and Nitrogen. In order to investigate the dielectric properties of the gases, the breakdown voltages must be measured. An experimental system is used to measure the breakdown voltages of CF4 gas mixtures for different electrode separation between 1 mm and 5mm. By comparing the measured breakdown voltages of CF4+SF6 and CF4+Argon gas mixtures with the corresponding values in the literature, the measurement method and experimental system are verified. Then, the breakdown voltages of CF4+N2 gas mixture is measured, which is lack in the literature.

• Proposes a systematic procedure for designing floating field rings in power devices. • The procedure is demonstrated using TCAD simulations. • 1.7–5.5 kV 4H-Silicon Carbide and 700 V Silicon devices are considered. • Breakdown voltages of the resulting devices exceeded 92% of the plane parallel value. • Yielded termination structures of length 24.5–75% of that reported in literature. Prior work on Silicon Carbide (SiC) power devices has been silent on the exact procedure to be employed for designing the Floating Field Rings (FFRs) meant for raising avalanche breakdown voltage of these devices. On the other hand, prior procedures for designing FFRs in Si devices do not work for kV range breakdown associated with SiC devices, and employ 10's of μm long rings. We propose a systematic procedure for deriving the number and spacing of the FFRs of any ring length required for achieving an arbitrary breakdown voltage. The procedure can be adapted to implement any one of the ring spacing strategies, namely - constant, decreasing or increasing as one moves outward from the main junction. The procedure is demonstrated for the linearly increasing ring spacing case using TCAD simulations, considering 1.7–5.5 kV 4H-Silicon Carbide devices and a 700 V Si device reported in literature. The FFR structures resulting from our procedure are found to have a total length which is 24.5–75% of that published in literature, and breakdown voltage which is more than 92% of the plane parallel value. [ABSTRACT FROM AUTHOR]

This paper is aimed at the comparison of breakdown voltage (BDV) of oil mixtures consisting of Jatropha curcas methyl ester oil (JMEO) extracted from the fruit seeds of jatropha curcas plants, and mineral oil (MO) under AC and DC voltages. Two JMEO/MO oil mixtures were considered: (50% JMEO + 50% MO) and (80% JMEO + 20% MO). The goal was to predict the insulation behavior of power transformers when re-filling with JMEO after they were emptied of mineral oil. The statistical analyses of the experimental data shows that the BDV values conform to normal law. It is shown that the (80%JMEO+20%MO) oil mixture is the most interesting whether under DC or AC as it shows the highest breakdown voltage. The U1% of JMEO under AC voltage is higher than those of the other tested oils. And the U1% of oils mixture (50%JMEO+50%MO) is the lowest one. [ABSTRACT FROM AUTHOR]

The paper presents research results of different properties of mixtures of the synthetic ester with mineral oil and synthetic ester with natural ester. For different concentrations of both mixtures, the following properties were investigated: flash point (open and closed cup), fire point (open cup), net calorific value, breakdown voltage, relative permittivity, dissipation factor, conductivity and dissipation factor. In order to compare results, prepared mixtures and base liquids were carefully arranged under uniform climatic conditions. This meant that the prepared samples had the same relative humidity. The obtained results were compared with the results of the base liquids. In addition, results of the investigation were analyzed in terms of fire safety and changes of electrical properties, in the context of the use of synthetic ester/mineral oil and synthetic ester/natural ester mixtures as insulation liquids in power transformers. [ABSTRACT FROM AUTHOR]

This paper presents experimental results of a comparative study of the characteristics of streamers propagating in olive oil and breakdown voltage with mineral oil, rapeseed oil (natural ester) and tetra-ester and methyl oleate (synthetic ester liquids). The comparison focuses more particularly on the pattern, stopping length, associated current and electrical charge of streamers propagating in a point-plane electrodes geometry under (1.2/50 μs) lightning impulse (LI) voltage as well as breakdown voltages under AC and LI voltages. A statistical analysis of breakdown voltages is also achieved. It is shown that the streamer characteristics (streamers shape, stopping length, associated current and electrical charge) of olive oil in small gaps are comparable to those of mineral oil. Breakdown voltages under AC and LI voltages are found to be higher in olive oil than in mineral oil. Consequently, olive oil can constitute a potential substitute for mineral oil in in high voltage power transformers. [ABSTRACT FROM AUTHOR]

The present work aims at investigating the possibility of mixtures between naphthenic transformer mineral oil (MO) and natural ester olive oil (VO). Ten mixture ratios between the two non-inhibited oils have been constituted. The variations of the electrical and physicochemical checking parameters (density, color number, water content, acidity, breakdown voltage and dissipation factor) are first analyzed and discussed in comparison with their initial values and those recommended by standards. Then, DC fields are applied during 3000 s and isothermal charging current measurements are made. The two original oils are both uninhibited, new and contain water contents in the limits of their saturation levels. The study reveals a favor for the vegetable oil and mixtures up to 15 % of mineral oil, especially with regard to breakdown voltage and charging current behavior. On the other hand, the addition of VO amounts until 15% improves significantly all the properties of the MO in spite of the high water amounts contained in the base VO. [ABSTRACT FROM AUTHOR]

Breakdown in dielectrics, the mechanism of which is still not yet fully revealed, exhibits very complicated test phenomena and characteristics. The breakdown voltage of a dielectric is believed to be related not only to the dielectric properties but also to the waveform of the applied voltage. For most dielectrics, the impulse breakdown voltage decreases with increasing wavefront time. However, we found for oil-impregnated paper (OIP) used in power transformers, increasing wavefront time in lightning impulses (at microsecond timescales) may lead to a significant increase in breakdown voltage. In contrast, the variation in the wavetail time produces very little effect on breakdown voltage. Combined with our previous test results on the space charge distributions in OIP, we tried to provide two explanations regarding this interesting phenomenon: First, the wavefront time of the applied impulse voltage affects the movement process of the positive particles in the oil-filled micro cavities in OIP, which is strongly related to the local electric field in the oil filled micro cavities and the breakdown voltage of the OIP. Moreover, the wavefront time is closely related to the trapping and detrapping process of the dielectrics. Therefore the effects of the traps in dielectric on the breakdown characteristics are different when the wavefront time varies. [ABSTRACT FROM AUTHOR]

This article presents the results of the studies on lightning properties of two synthetic ester liquids and mineral oil. The measurements concern the standard lightning impulse voltage at both polarities and a point-to-sphere electrode system representing highly divergent electric field distribution. The studies were based on the IEC 60897 Standard wherein the standard recommendations were extended to include light emission registration using a photomultiplier technique. Comparisons of the lightning impulse breakdown voltages (LIBV), times to breakdown (TtB) and light waveforms were made. The results concerning LIBV and TtB showed that at negative polarity both the esters have almost the same lightning characteristics which are slightly below the characteristics of mineral oil. At positive polarity the results indicated an improvement. Regarding the light emission, the mineral oil tested seemed to be more resistant against the appearance of fast light pulses indicating the intense stepwise propagating discharges. [ABSTRACT FROM AUTHOR]

Shock waves generated by underwater pulsed discharge have been applied to industrial and bio-medical treatments, and the key technology is to induce high intensity shock waves. Based on the underwater pulsed discharge platform, the effect of the electrical breakdown modes on the shock wave intensity in water is discussed in the positive pin-to-plane configuration. Experimental results demonstrate that the amplitude of applied voltage have a significant influence on the breakdown modes as well as the shock wave intensity. Based on the analysis of discharge images captured by a high-speed camera, it can be concluded that the breakdown modes are classified as subsonic bush-like streamers or supersonic filamentary streamers. The mechanism of subsonic streamer in lower applied voltage is more likely an electro thermal process. The micro-bubbles are firstly generated, and then discharge occurs in the bubble cluster. The bubble volume grows until a breakdown of the underwater gap, and the shock wave is the generated. The time to breakdown of subsonic streamers is commonly within hundreds of microseconds at the experimental condition. In higher applied voltage, the energy loss in the pre-breakdown process is reduced significantly as well. In our experiment, a threshold value of 22.5 kV is necessary for the subsonic streamer mode transition into supersonic streamer mode. The energy conversion efficiency, the time to breakdown and the influence of the applied voltage are discussed at different breakdown modes. The shock wave intensity differs 2–4 times in different breakdown modes even in the same applied voltage, thus increasing the applied voltage may be a remarkable way to enhance the shock wave intensity. [ABSTRACT FROM AUTHOR]

Statistical results have shown that the waveforms of impulses invading power transformers differ from those of the standard impulse voltage recommended by the IEC Standard. However, the effect of such differences on the modification effect of nano-modified transformer oil has rarely been studied. The present work therefore experimentally investigated the effects of impulse waveform parameters on the breakdown characteristics of nano-TiO 2 modified transformer oil (NMTO). We determined the breakdown characteristics of NMTO with different nano-particle concentrations, and compared the breakdown characteristics under both standard impulse voltage and non-standard impulse voltage. Specifically, the influence of the wave front time and wave tail time of the applied voltage on the breakdown characteristics of NMTO were experimentally identified. Finally, mechanisms of observed phenomena were analyzed. Test results indicate that both the waveform parameters and polarity have important effects on the modification effect of NMTO. Such effects are attributed to the migration of positive particles and charged nano-particles. [ABSTRACT FROM AUTHOR]

This paper presents experimental studies of streamer propagation and breakdown in a mineral oil and a synthetic ester liquid under both positive and negative DC voltages. A point-plane electrode configuration with a point tip radius of 10 μm was used. Characteristics of streamer including length, propagation velocity and shape were analysed based on shadowgraph images obtained at a gap distance of 10 mm using a multi-channel ultra-high speed camera. Under positive polarity, the streamers in both liquids propagate in the 2nd mode; the stopping length of the synthetic ester is longer than that of the mineral oil at the same applied voltage level. However there is no obvious streamer propagation (less than 10% of the gap distance) under negative polarity even when the applied voltage approaches to the breakdown voltage; the streamers in both liquids stay in the 1st mode. Breakdown tests at various gaps of 2 mm, 5 mm, 10 mm, 20 mm and 30 mm were also investigated. 50% breakdown voltages of the synthetic ester liquid are lower than those of the mineral oil at all the gap distances investigated under both polarities. [ABSTRACT FROM AUTHOR]

Metal particles, such as copper and iron, not only reduce the breakdown voltage but also accelerate the oxidation of insulating oils. The effects of metal particles on the dielectric properties of mineral and natural ester insulating oils were investigated in this work. The experimental results indicate that the AC and impulse breakdown voltages of the insulating oil decrease with the increase of the size and the quantity of the metal particles. The positive breakdown voltages V b+ of insulating oils decrease moderately in the beginning, while the particles quantity increases to a certain extent, the V b+ decreases significantly. In comparison, the metal particles always reduce the negative impulse breakdown voltage V b− significantly. The effect of the copper particles on the insulating oils is slightly greater than that of the iron particles due to their higher conductivity. The permittivity of contaminated insulating oils increases quasi-linearly with the concentration of copper particles. Improved models considering the polarization of the surface oxidation layer of copper particles were proposed, and the calculated data were in good agreement with the measured permittivity of the contaminated insulating oil. [ABSTRACT FROM AUTHOR]

Abstract This paper presents an investigation on the current and breakdown voltage measurements in thermoset-thermoplastic blends based on an epoxy-amine/poly-etherimide phase separated material. Thermoset-thermoplastic separated blends could be a novel material for insulation applications and can be compared to epoxy/inorganic composites systems. Pure epoxy network as well as the blends with 10 wt% of PEI were studied in terms of conduction and transient currents. An ohmic behavior below the threshold field (E th) and space-charge-limited conduction (SCLC) above E th are pointed out. Contact emission phenomenon was investigated by means of Schottky model and seems to be valid for both materials. The addition of 5 and 10 wt% of PEI into the epoxy system showed an increase in the values of breakdown voltage with the increase of the PEI amount. Highlights • Electrical characterization of an epoxy/thermoplastic blend is examined • Current is controlled by volume phenomena through SCLC approach • Epoxy and blends showed contact emission at the electrode/sample interface • Breakdown voltage increased with the increase of the percentage of thermoplastic [ABSTRACT FROM AUTHOR]

A long uniform low-temperature discharge is achieved inside a 1 mm radius fused silica tube using plane parallel linear electrodes. At a driving frequency of 13.56 MHz, a pure helium discharge is generated from 10 Torr to atmospheric pressure without any gas flow. Depending on the applied power and pressure, the discharge occurs either in the Ω or in the γ mode. As long as the gas flow is zero, the discharge shows no gradient along the electrodes. Consequently, the length of the discharge is only limited by the axial dimension of the electrodes. As the pressure increases, the Ω to γ transition occurs at higher and higher power densities. The breakdown voltage is minimum at 75 Torr with a power density down to 0.1 W cm−3. However, below 20 Torr, charged particle losses become very important so that the breakdown and maintaining voltages increase drastically. Regardless of the pressure, the gas temperature is found to always lie between 300 and 520 K. [ABSTRACT FROM AUTHOR]

New AlGaN/GaN high electron mobility transistors (HEMTs) that their barrier layers under the gate are divided into two regions horizontally are presented in this work. Upper region is Si 3 N 4 (SI-HEMT) or un-doped AlGaN (UN-HEMT) and lower region is AlGaN with heavier doping compared to barrier layer. Upper region in SI-HEMT and UN-HEMT reduces peak electric field in the channel and then improves breakdown voltage considerably. Lower region increases electron density in the two dimensional electron gas (2-DEG) and enhances drain current significantly. For instance, saturated drain current in SI-HEMT is about 100% larger than that in the conventional one. Moreover, the maximum breakdown voltage in the proposed structures is 65 V. This value is about 30% larger than that in the conventional transistor (50 V). Also, suggested structure reduces short channel effect such as DIBL. The maximum g m is obtained in UN-HEMT and conventional devices. Proposed structures improve breakdown voltage and saturated drain current and then enhance maximum output power density. Maximum output power density in the new structures is about 150% higher than that in the conventional. [ABSTRACT FROM AUTHOR]

A novel dual channel three-terminal np-LDMOS power device with both electrons and holes for conduction is proposed in this paper. Based on a new approach of inducing a large-signal which is processed by a simple circuit for controlling the gate of p-LDMOS inside the device, the new np-LDMOS only requires one external gate controlling voltage signal that can be performed as an n-LDMOS device. The SOA of the new device is improved in comparison with the n-LDMOS device, since the counteracting of electric flux density produced by the both type of carriers' currents. Furthermore, the specific on-resistance of the np-LDMOS device is reduced by about 19% when comparing with that of the conventional one. The control method and performances of the proposed power device are investigated and authenticated by numerical simulations. [ABSTRACT FROM AUTHOR]

Studying the effect of adding nanosized ZrO2 to mineral transformer oil on the AC breakdown voltage is presented. The study is carried out considering different concentration levels of nanosized ZrO2. These concentrations are 0, 0.001, 0.002, 0.003 and 0.006%w. The AC breakdown voltage of both nanofilled and base oil is measured according ASTM D1816 standard at room temperature. The evaluation is carried out based on AC breakdown voltage for the nanofilled and base oil considering average and Weibull statistical techniques. Both 50 and 10% breakdown voltage probabilities are obtained and analysed for all samples. Also, the effect of temperature (to take the effect of real operating conditions) on breakdown voltage of base and nanofilled oil is experimentally evaluated. The studied temperatures are 50, 80 and 130°C. The obtained results show that the performance of nanoparticles is significantly affected by increasing the temperature of nanofilled transformer oil. Finally, a proposed mechanism for the effect of temperature on the nanofluids breakdown strength is introduced. [ABSTRACT FROM AUTHOR]

Atmospheric pressure plasmas have achieved great scientific and technological advances for a wide range of applications including the field of antimicrobial treatment. In this paper, a home-made atmospheric pressure plasma jet device was built and the effects of air plasma treatments on the inactivation of pure bacterial culture (Escherichia coli ATCC 8739) deposited onto the surface of agar plates were investigated. Plasmas were generated using high voltage discharge for 30, 60 and 90 s. The number of viable microorganisms was determined using a plate count method. Microbial Log10 reduction depended on the time of exposure and feed gas flow. A significant reduction of about 2.5 Log10 for E. coli was achieved within 60 s of plasma treatment. This result can be related to the presence of reactive species in the plasma volume, in particular, O radicals. [ABSTRACT FROM AUTHOR]

Electrical breakdown of tap water (350 μS.cm-1) under sub-millisecond pulses (0.5 ms) with a gap distance of 3–35mm has been investigated. It was found that the gap distance has a great influence on the polarity effect of underwater electrical breakdown, including breakdown mode, breakdown voltage, and pre-breakdown time delay. Under positive voltage impulses, the breakdown voltage increases with the gap distance; meanwhile, the pre-breakdown time delay decreases, and both of them show a saturation trend. Under negative voltage impulses, the breakdown voltage and prebreakdown time delay increase with the gap distance, and the pre-breakdown time delay shows a saturation trend. Consequently, the polarity effect on the breakdown characteristics is varied with the gap distance. Further investigation by high speed optical observation confirmed that the polarity effect variation is closely related to the breakdown mode transition of positive polarity with the gap distance. Finally, a simple model based on the linear propagation assumption was proposed to predict the variation of the breakdown voltage with the gap distance. [ABSTRACT FROM AUTHOR]

A Metal-Insulator-Metal (MIM) capacitor with high capacitance, high breakdown voltage, and low leakage current is aspired so that the device can be applied in many electronic applications. The most significant factors that affect the MIM capacitor's performance is the design and the dielectric materials used. In this study, MIM capacitors are simulated using different dielectric materials and different number of dielectric layers from two layers up to seven layers. The effect of the different dielectric constants (k) to the performance of the MIM capacitors is also studied, whereas this work investigates the effect of using low-k and high-k dielectric materials. The dielectric materials used in this study with high-k are Al2O3 and HfO2, while the low-k dielectric materials are SiO2 and Si3N4. The results demonstrate that the dielectric materials with high-k produce the highest capacitance. Results also show that metal-Al2O3 interfaces increase the performance of the MIM capacitors. By increasing the number of dielectric layers to seven stacks, the capacitance and breakdown voltage reach its highest value at 0.39 nF and 240 V, respectively. [ABSTRACT FROM AUTHOR]

The statistical delay of microplasma breakdown in GaP light-emitting diodes with the green-emission spectrum is studied. The unusual profound effect of deep centers on the statistical delay of avalanche breakdown is observed in the temperature range of 300-380 K; this effect is caused by a variation in the charge state of these centers due to a reduction in the reverse bias applied to the p- n junction. Four deep levels are revealed and their parameters are determined. [ABSTRACT FROM AUTHOR]

In this paper, we report a diamond-shaped body contact (DSBC) for silicon-on-insulator (SOI) LDMOSFET. Several DSBC devices along with conventional body contact (CBC) structures are laid out using 0.35 μm SOI MOSFET foundry process. The DSBC device is designed using the same standard layers as in the CBC structure and the contact layout is adapted to process design rules. Experimental characterization of the CBC and DSBC devices in terms of off-state breakdown voltage (BVoff), on-state breakdown voltage (BVon), on-resistance (Ron) and device foot print showed 19% improvement in BVon compared DSBC device with that of the CBC structure. BVoff and Ron of both of the devices are identical. The device foot print is smaller in DSBC device by 11% compared with that of the CBC structure leading to enhanced “On-resistance × Area” figure of merit where smaller high voltage SOI LDMOSEFT reduces the area and cost of power integrated circuits. In order to explain BVon improvement of DSBC structures, three-dimensional (3-D) device simulation is carried out to clarify the lateral BJT action and breakdown mechanism. It is demonstrated that the number of P+ diffusions in DSBC device can be increased to improve BVon without increasing “On-resistance × Area”. The on-state breakdown voltage improvement and area efficiency of the diamond-shaped body contact proposes it as a promising candidate for reliable operation of SOI LDMOSFET. [ABSTRACT FROM AUTHOR]

In this paper, the 4H–SiC metal semiconductor field effect transistor with symmetric lightly doped drain (SLDD-MESFET) is improved and a 4H–SiC MESFET with recessed and multi-concentration doped channel (RMDC-MESFET) is proposed. According to the 2-D simulation results, it is found that compared with the SLDD structure, the saturation current of RMDC-MESFET is increased from 373 mA/mm to 480 mA/mm, which is 29% higher. The breakdown voltage remains stable, resulting in a 25% increase in maximum output power density, from 5.89 W/mm to 7.34 W/mm. At the same time, the transconductance of the proposed structure is increased by 28% from 68 mS/mm to 87 mS/mm, resulting in an 18% increase in the cut-off frequency from 21.45 GHz to 25.3 GHz. The DC and RF performances of the RMDC-MESFET are improved simultaneously, so the structure has good prospects for high-power and RF applications. • An improved 4H–SiC MESFET with recessed and multi-concentration doped channel is proposed. • The optimal size of the recessed region of the device is obtained as L=W=0.1μm. • The saturation current of this device is increased by 29% and the maximum output power density is increased by 25%. • The transconductance of this device is increased by 28% and the cut-off frequency is increased by 18%. [ABSTRACT FROM AUTHOR]

A novel superjunction (SJ) reverse-blocking (RB) insulated gate bipolar transistor (IGBT) is proposed and investigated for the first time. The device features a shorted collector trench (SCT) at the bottom, an SJ structure in the drift region, and an N1-layer as well as N2-layer at the bottom and top side of N-pillar, respectively. First, the SCT combined with the N2 enables the SJ RB-IGBT to sustain a high reverse breakdown voltage (BV \textit {R} ). The SCT assists in depleting the N1 in the reverse blocking state, enabling a high BV \textit {R} under the condition of a high N1 doping that is required to maintain a high forward breakdown voltage (BV \textit {F} ). The N2 acts as a field-stop layer in the reverse blocking state. Second, unlike the conventional SJ IGBT, the SJ RB-IGBT maintains bipolar conducting mode in the ON-state even with high N/P pillar doping of 6 \times 10^15 cm ^\mathrm -3 , due to carrier store effect induced by N2. Thus, a low ON-state voltage ( \textV\mathrm{\scriptscriptstyle ON} ) is obtained. Third, the SJ junction extracts the plasma into separate pillars during turn OFF, enabling a fast turn-OFF speed that is comparable with unipolar devices. The SJ RB-IGBT realizes bidirectional blocking capability >1200V and turn-OFF loss 80% lower than that of the state-of-the-art RB-IGBT. [ABSTRACT FROM PUBLISHER]

In view of the maloperation problem in traditional distance protection zone-III caused by overload in lines, an adaptive overload identification method based on the complex phasor plane is proposed in this paper. First, according to the geometric distribution of the measured phasors under different operating conditions, the virtual voltage drop phasor equation is established. And then, the adaptive setting coefficient is calculated and the adaptive overload identification criterion of distance protection zone-III is formed. Finally, by combining the identification criterion with the operating characteristic of traditional distance protection zone-III, the overload in lines can be distinguished from symmetrical faults. Simulation tests on the IEEE 10-machine 39-bus system verify that, the proposed method is able to prevent the distance protection zone-III from maloperating in the case of overload. Furthermore, in the case of overload and symmetrical fault coexisting, the proposed distance protection scheme can also play the role of backup protection effectively. [ABSTRACT FROM PUBLISHER]

The results of experimental study of streamer and spark processes under a standard lightning voltage pulse are shown for different degrees of electric-field nonuniformity in sphere-plane and sphere-sphere electrode systems. The possibility of introducing similarity relations for streamer processes is considered. The applicability of various numerical methods for determining the breakdown voltage is analyzed. [ABSTRACT FROM AUTHOR]

Nitrogen polar SiNx/AlGaN/GaN/AlGaN metal– insulator–semiconductor high-electron-mobility transistors (MIS-HEMTs) with 28.6-nm equivalent GaN channel thickness grown by metal–organic chemical vapor deposition on sapphire substrate with a high combination of current/power gain cutoff frequencies ( fT/f\max ) and three-terminal breakdown voltage (BVDS) are demonstrated. fT /BVDS of 103 GHz/114 V and f\max /BVDS of 248 GHz/114 V were achieved in devices with the gate widths of 2 \times 50\mu \textm and 2 \times 25\mu \textm , respectively, comparing well with recent reports of fully passivated and vertically scaled Ga-polar GaN HEMTs. Devices with a gate width of 2 \times 75 \mu \textm showed the peak output power densities of 5.74 W/mm at 4 GHz and 6.29 W/mm at 10 GHz obtained by load-pull measurements. [ABSTRACT FROM PUBLISHER]

We study the voltage-current characteristics of gas discharges driven by field emission of electrons at the microscale. Particle-in-cell with Monte Carlo collision calculations are first verified by comparison with breakdown voltage measurements and then used to investigate atmospheric discharges in nitrogen at gaps from 1 to 10 µm. The results indicate the absence of the classical glow discharge regime because field electron emission replaces secondary electron emission as the discharge sustaining mechanism. Additionally, the onset of arcing is significantly delayed due to rarefied effects in electron transport. While field emission reduces the breakdown voltage, the power required to sustain an arc of the same density in microgaps is as much as 30% higher than at macroscale. [ABSTRACT FROM AUTHOR]

Ionization gas sensors using vertically aligned multi-wall carbon nanotubes (MWCNT) are demonstrated. The sharp tips of the nanotubes generate large non-uniform electric fields at relatively low applied voltage. The enhancement of the electric field results in field emission of electrons that dominates the breakdown mechanism in gas sensor with gap spacing below 14 μm. More than 90% reduction in breakdown voltage is observed for sensors with MWCNT and 7 lm gap spacing. Transition of breakdown mechanism, dominated by avalanche electrons to field emission electrons, as decreasing gap spacing is also observed and discussed. [ABSTRACT FROM AUTHOR]

This study relates to the delay of secondary electrostatic discharges (ESDs). The first motivation for this study is the fact that the delay value is a required input parameter for the simulation of the secondary ESD. The second motivation is that this delay is one limiting factor for the usage of spark gaps as protection devices. The objective is to determine the delay for different intended and unintended spark gap structures as this time delay will influence the peak current and rise time of the secondary ESD across these gaps. The intended application is ESD protection in consumer products, for that reason 0.5–3 mm gap distances and voltages up to 14 kV are considered at different humidity levels. Very long time lags are observed for clean sphere-to-sphere gaps requiring average field strengths >200 kV/cm to achieve a breakdown in a few nanoseconds in dry air. Humidity is shown to strongly reduce the time lag. However, if printed circuit board (PCB) spark gap geometries are considered the time lags are much smaller. Similar shorter lag times have been found in geometries that resemble more unintentional breakdown locations in a product. [ABSTRACT FROM PUBLISHER]

This study focuses on the area of the epitaxial design, fabrication and characterization of a 1µm gate-length InP-based pseudomorphic high electron mobility transistor (pHEMT) using InGaAs-InAlAs material systems. The advanced epitaxial layer design incorporates a highly strained aluminum-rich Schottky contact barrier, an indium-rich channel and a double delta-doped structure, which significantly improves upon the conventional low-noise pHEMT which suffers from high gate current leakage and low breakdown voltage. The outstanding achievements of the new design approach are 99% less gate current leakage and a 73% increase in breakdown voltage, compared with the conventional design. Furthermore, no degradation in RF performance is observed in terms of the cut-off frequency in this new highly tensile strained design. The remarkable performance of this advanced pHEMT design facilitates the implementation of outstanding low-noise devices. [ABSTRACT FROM AUTHOR]

Enhanced performance of RF power modules is required in a next-generation information society. To satisfy these requirements, we designed a novel high-electron mobility transistor (HEMT) structure employing wider bandgap AlGaN for a channel layer, which we called AlGaN channel HEMT, and investigated it. The wider bandgap is more effective for higher voltage operation of HEMTs and contributes to the increase of output power in RF power modules. As a result, fabricated AlGaN channel HEMTs had much higher breakdown voltages than those of conventional GaN channel HEMTs with good pinchoff operation and sufficiently high drain current density without noticeable current collapse. Furthermore, specific on-state resistances of fabricated AlGaN channel HEMTs were competitive with the best values of reported GaN- and SiC-based devices with similar breakdown voltages. These results indicate that the proposed AlGaN channel HEMTs are very promising not only for an information–communication society but also in the power electronics field. [ABSTRACT FROM AUTHOR]

Research on the sparkover characteristics of long air gaps under composite voltages has important significance on the design and operation of transmission lines and equipment. In this paper, corona charge injection prior to sparkover in an inversed rod-plane gap under composite voltages was studied. The variation of charge injection to the initiation of leader and breakdown was measured by a capacitor divider. Two photomultipliers were positioned to study corona development at two positions between the tip of the rod and the plane, from which the light output could be compared with the charge injected into the gap. When a positive prestress voltage is employed at the plane, charge injection is enhanced and leader inception and breakdown occur at lower voltages than with prestress voltage of opposite polarity. The U50\% sparkover voltages are in inverse proportion to the charge and power inputs up to the time of the leader initiation. The results of corona charge injection to sparkover are helpful for understanding the physical process of the gap breakdown in depth. [ABSTRACT FROM AUTHOR]

We have investigated the effect of pre-ionization by a radioactive ^137 \Cs\ \gamma-ray source on the atmospheric air breakdown conditions in a high-voltage spark gap. A standoff millimeter-wave (mmW) system was used to monitor the breakdown properties. A decrease in breakdown threshold was observed with an increase of radiation dose. We attribute this to a space charge-controlled electron diffusion process in a cloud of radiation-induced ion species of both polarities. The space charge-dependent diffusion coefficient was determined from the measurement data. In addition, we found that the breakdown process shows random spikes with Poisson-like statistical feature. These findings portend the feasibility of remote detection of nuclear radiation using high-power mmWs. [ABSTRACT FROM AUTHOR]

We fabricated gallium oxide (\Ga2 \O3) Schottky barrier diodes using \beta-\Ga2 \O3 single-crystal substrates produced by the floating-zone method. The crystal quality of the substrates was excellent; the X-ray diffraction rocking curve peak had a full width at half-maximum of 32 arcsec, and the etch pit density was less than \1 \times \10^4 \ \cm^-2. The devices exhibited good characteristics, such as an ideality factor close to unity and a reasonably high reverse breakdown voltage of about 150 V. The Schottky barrier height of the \Pt/\beta–\Ga2 \O3 interface was estimated to be 1.3–1.5 eV. [ABSTRACT FROM PUBLISHER]

A novel silicon-on-insulator (SOI) high breakdown voltage (BV) power device with interlaced dielectric trenches (IDT) and N/P pillars is proposed. In the studied structure, the drift region is folded by IDT embedded in the active layer, which results in an increase of length of ionization integral remarkably. The crowding phenomenon of electric field in the corner of IDT is relieved by the N/P pillars. Both traits improve two key factors of BV, the ionization integral length and electric field magnitude, and thus BV is significantly enhanced. The electric field in the dielectric layer is enhanced and a major portion of bias is borne by the oxide layer due to the accumulation of inverse charges (holes) at the corner of IDT. The average value of the lateral electric field of the proposed device reaches 60 V/μm with a 10 μm drift length, which increases by 200% in comparison to the conventional SOI LDMOS, resulting in a breakdown voltage of 607 V. [ABSTRACT FROM AUTHOR]

The effects of the airflow on plasma-assisted combustion actuator (PACA) characteristics are studied in detail. The plasma is characterized electrically, as well as optically with a spectrometer. Our results show that the airflow has an obvious influence on the PACA characteristics. The breakdown voltage and vibrational temperature decrease, while the discharge power increases compared with the stationary airflow. The memory effect of metastable state species and the transportation characteristics of charged particles in microdischarge channel are the dominant causes for the variations of the breakdown voltage and discharge power, respectively, and the vibrational temperature calculated in this work can describe the electron energy of the dielectric barrier discharge plasma in PACA. These results offer new perspectives for the use of PACA in plasma-assisted combustion. [ABSTRACT FROM AUTHOR]

An ultra-low specific on-resistance (Ron,sp) oxide trench-type silicon-on-insulator (SOI) lateral double-diffusion metal–oxide semiconductor (LDMOS) with an enhanced breakdown voltage (BV) is proposed and investigated by simulation. There are two key features in the proposed device: one is a U-shaped gate around the oxide trench, which extends from source to drain (UG LDMOS); the other is an N pillar and P pillar located in the trench sidewall. In the on-state, electrons accumulate along the U-shaped gate, providing a continuous low resistance current path from source to drain. The Ron,sp is thus greatly reduced and almost independent of the drift region doping concentration. In the off-state, the N and P pillars not only enhance the electric field (E-field) strength of the trench oxide, but also improve the E-field distribution in the drift region, leading to a significant improvement in the BV. The BV of 662 V and Ron,sp of 12.4 mΩ·cm2 are achieved for the proposed UG LDMOS. The BV is increased by 88.6% and the Ron,sp is reduced by 96.4%, compared with those of the conventional trench LDMOS (CT LDMOS), realizing the state-of-the-art trade-off between BV and Ron,sp. [ABSTRACT FROM AUTHOR]

A new SOI power device with multi-region high-concentration fixed charge (MHFC) is reported. The MHFC is formed through implanting Cs or I ion into the buried oxide layer (BOX), by which the high-concentration dynamic electrons and holes are induced at the top and bottom interfaces of BOX. The inversion holes can enhance the vertical electric field and raise the breakdown voltage since the drain bias is mainly generated from the BOX. A model of breakdown voltage is developed, from which the optimal spacing has also been obtained. The numerical results indicate that the breakdown voltage of device proposed is increased by 287% in comparison to that of conventional LDMOS. [ABSTRACT FROM AUTHOR]