Showing papers on "Breakdown voltage published in 2019"

$\beta$ -Ga 2 O 3 Delta-Doped Field-Effect Transistors With Current Gain Cutoff Frequency of 27 GHz

Abstract: As an ultra-wide bandgap semiconductor, $\beta $ -Ga2O3 has attracted great attention for high-power, high-voltage, and optoelectronic applications. However, until now, high-frequency performance of gallium oxide devices has been limited to relatively low current gain cutoff frequencies below 5 GHz. Here, we show that highly localized delta-doping designs can enable high-sheet-charge density to enable devices with short gate lengths that allow high-frequency operation. Field-effect transistors with a gate length of 120 nm on such delta-doped $\beta $ -Ga2O3 are reported here with extrinsic unity current gain frequency of 27 GHz. The device has a peak drain current of 260 mA/mm, transconductance (gm) of 44 mS/mm, and three-terminal off-state breakdown voltage of 150 V. These results demonstrate that the potential of $\beta $ -Ga2O3 for future RF and millimeter-wave device applications.

Lateral 1.8 kV $\beta$ -Ga 2 O 3 MOSFET With 155 MW/cm 2 Power Figure of Merit

Abstract: Lateral $\beta $ -Ga2O3 MOSFET for power switching applications with a 1.8 kV breakdown voltage and a record power figure of merit of 155 MW/cm2 are demonstrated. Sub- $\mu \text{m}$ gate length combined with gate recess was used to achieve low ON-state resistances with reasonable threshold voltages above −24 V. The combination of compensation-doped high-quality crystals, implantation-based inter-device isolation, and SiN x -passivation yielded in consistently high average breakdown field strengths of 1.8–2.2 MV/cm for gate–drain spacings between 2 and 10 $\mu \text{m}$ . These values outperform the results of more established wide-bandgap device technologies, such as SiC or GaN, and the major Ga2O3 material promise—a higher breakdown strength—is well demonstrated.

High Breakdown Voltage in RF AlN/GaN/AlN Quantum Well HEMTs

Abstract: In evaluating GaN high-electron mobility transistors (HEMTs) for high-power applications, it is crucial to consider the device-level breakdown characteristics. This letter replaces the conventional AlGaN barrier and common AlGaN backbarrier with unstrained AlN, and it assesses the breakdown voltage of AlN/GaN/AlN quantum well HEMTs for gate-drain spacings in the range of 0.27– $5.1~\mu \text{m}$ . The results are highlighted by a high breakdown voltage of 78 V for a gate-drain spacing of 390 nm, among the best reported for submicron-channel devices. In addition, small-signal RF measurements showed record performance for HEMTs on the AlN platform, with $\text {f}_{\text {t}}/\text {f}_{\text {max}} = {161}/{70}$ GHz. The cut-off frequency and corresponding drain bias are benchmarked against the state-of-the-art GaN HEMTs using the Johnson figure of merit, with measured devices highlighted by a JFoM value of 2.2 THz $\cdot $ V. These results illustrate the potential for AlN/GaN/AlN quantum well HEMTs as a future platform for high-power RF transistors.

Design and Fabrication of GaN p-n Junction Diodes With Negative Beveled-Mesa Termination

Abstract: We report on homoepitaxial GaN p-n junction diodes with a negative beveled-mesa termination. The electric field distribution in a beveled-mesa was investigated using TCAD simulation, and the devices were designed using currently available GaN growth techniques. Shallow-angle (ca. 10°) negative bevel GaN p-n junction diodes were fabricated with various Mg acceptor concentrations in the p-layers. The suppression of electric field crowding and improvement of the breakdown voltage were observed, as the Mg concentration was decreased. The parallel-plane breakdown field of 2.86 MV/cm was obtained for a device with the breakdown voltage of 425 V.

Single and multi-fin normally-off Ga 2 O 3 vertical transistors with a breakdown voltage over 2.6 kV

Abstract: We demonstrate record-high performance in normally-off single and multi-fin b-Ga 2 O 3 vertical power transistors. The effective channel mobility is significantly improved up to ~130 cm2/V•s with a post-deposition annealing process. With a fin-channel width of 0.15 µm, true normally-off operation is achieved with a threshold voltage of >1.5 V; a record-high breakdown voltage of 2.66 kV (at V gs =0 V) and a specific on-resistance of 25.2 mW•cm2 are obtained in multi-fin devices, corresponding to a Baliga’s figure-of-merit of 280 MW/cm2, which is the highest among all Ga 2 O 3 transistors. Devices with (100)-like fin-channel sidewalls exhibit the lowest interface trapped charge density and a significantly higher current than other fin orientations. These findings offer important insights on the development of Ga 2 O 3 MOSFETs and show great promise of Ga 2 O 3 vertical power devices.

Application of C6F12O/CO2 mixture in 10 kV medium-voltage switchgear

Abstract: Due to the high global warming potential (GWP) of SF 6 , the use of new gases in electrical equipment has drawn increasing attention. Here, the application of environmental-friendly gas dodecafluoro-2-methylpentan-3-one (C 6 F 12 O) and CO 2 mixture in 10 kV medium-voltage switchgear is studied. First, the basic physical and chemical properties of C 6 F 12 O were discussed, and the toxicity and safety of its application in equipment was analysed. Then, the breakdown voltage was measured in the laboratory. The power-frequency breakdown test was carried out with the mixing ratio of 2, 4 and 6% at 0.1~0.2 MPa, and the influence of utilisation coefficient of electric field on the breakdown performance was analysed. Finally, the appropriate mixing ratio was determined and tested in the load switch cabinet and the circuit breaker switch cabinet, including the power frequency withstand voltage test and the lightning impulse test. The test results show that 4% C 6 F 12 O and CO 2 meet the standard value tested at a pressure of >0.14 MPa, which has the potential to be used as an insulating gas in a 10 kV switchgear.

An Over 20-W/mm S-Band InAlGaN/GaN HEMT With SiC/Diamond-Bonded Heat Spreader

Abstract: This letter reports on an InAlGaN/GaN high-electron-mobility transistor (HEMT) employing a SiC/diamond-bonded heat spreader with a record high output power density of 22.3 W/mm. A quaternary In-added InAlGaN barrier enabled both the large current of over 1 A/mm and the high breakdown voltage of 257 V. The drain bias was increased as high as 100 V for the S-band load-pull measurement, leading to high power operation. Furthermore, the thermal resistance was reduced by 60%, from 18.8 to 7.2°C/W, by employing the SiC/diamond heat spreader. This large heat dissipation effect was clearly observed in the output power density for the load-pull measurement. Our results demonstrate that the GaN HEMT with an In-added barrier layer is promising not only for millimeter-wave applications but also for high output power microwave amplifiers.

Fluorine-Implanted Termination for Vertical GaN Schottky Rectifier With High Blocking Voltage and Low Forward Voltage Drop

Abstract: In this letter, fluorine-implanted termination (FIT) has been demonstrated in vertical GaN-on-GaN Schottky barrier diodes (SBDs). Owing to the unique feature of F ions that can become negative fixed charges in GaN, the electric field crowding at the junction edge can be mitigated and the breakdown voltage ( BV ) of the vertical GaN SBDs can be effectively enhanced. For SBDs, it is challenging to simultaneously achieve both high BV and low forward voltage drop ( ${V}_{{F}}$ ). Thanks to the effective leakage suppression by FIT, a high BV of ~800 V is realized in an FIT-SBD even with a low ${V}_{{F}}$ value of 0.85 V (at 100 A/cm2). By incorporating an AlGaN tunneling-enhancement layer, the FIT-SBD can achieve further improved BV of ~1020 V and ${V}_{{F}}$ of 0.83 V. Fast reverse recovery performance has also been realized in the FIT-SBDs.

A field-plated Ga2O3 MOSFET with near 2-kV breakdown voltage and 520 mΩ · cm2 on-resistance

Abstract: A composite field-plated Ga2O3 MOSFET with highly doped ohmic-capping layer is fabricated. An output current of 20 mA mm−1 and on-resistance of 520 mΩ cm2 shows big improvement upon the previous experiment on similar field plated devices. The breakdown voltage is measured to be 1975 V on an L gd = 25 μm device. At elevated temperatures, the breakdown voltage decreases to <1 kV at 130 °C, while the on-resistance and saturation current are almost unchanged. The breakdown may be limited by the dielectric liquid strength. The on-resistance is limited by high interface state density that is attributed to the thermal process during the field oxide deposition.

Solar blind Schottky photodiode based on an MOCVD-grown homoepitaxial β-Ga2O3 thin film

Abstract: We report on a high performance Pt/n−Ga2O3/n+Ga2O3 solar blind Schottky photodiode that has been grown by metalorganic chemical vapor deposition. The active area of the photodiode was fabricated using ∼30 A thick semi-transparent Pt that has up to 90% transparency to UV radiation with wavelengths < 260 nm. The fabricated photodiode exhibited Schottky characteristics with a turn-on voltage of ∼1 V and a rectification ratio of ∼108 at ±2 V and showed deep UV solar blind detection at 0 V. The Schottky photodiode exhibited good device characteristics such as an ideality factor of 1.23 and a breakdown voltage of ∼110 V. The spectral response showed a maximum absolute responsivity of 0.16 A/W at 222 nm at zero bias corresponding to an external quantum efficiency of ∼87.5%. The cutoff wavelength and the out of band rejection ratio of the devices were ∼260 nm and ∼104, respectively, showing a true solar blind operation with an excellent selectivity. The time response is in the millisecond range and has no long-time decay component which is common in photoconductive wide bandgap devices.We report on a high performance Pt/n−Ga2O3/n+Ga2O3 solar blind Schottky photodiode that has been grown by metalorganic chemical vapor deposition. The active area of the photodiode was fabricated using ∼30 A thick semi-transparent Pt that has up to 90% transparency to UV radiation with wavelengths < 260 nm. The fabricated photodiode exhibited Schottky characteristics with a turn-on voltage of ∼1 V and a rectification ratio of ∼108 at ±2 V and showed deep UV solar blind detection at 0 V. The Schottky photodiode exhibited good device characteristics such as an ideality factor of 1.23 and a breakdown voltage of ∼110 V. The spectral response showed a maximum absolute responsivity of 0.16 A/W at 222 nm at zero bias corresponding to an external quantum efficiency of ∼87.5%. The cutoff wavelength and the out of band rejection ratio of the devices were ∼260 nm and ∼104, respectively, showing a true solar blind operation with an excellent selectivity. The time response is in the millisecond range and has no long-ti...

High Performance and Highly Robust AlN/GaN HEMTs for Millimeter-Wave Operation

Abstract: We report on a 3 nm AlN/GaN HEMT technology for millimeter-wave applications. Electrical characteristics for a 110 nm gate length show a maximum drain current density of 1.2 A/mm, an excellent electron confinement with a low leakage current below $10~\mu \text{A}$ /mm, a high breakdown voltage and a FT/Fmax of 63/300 GHz at a drain voltage of 20V. Despite residual trapping effects, state of the art large signal characteristics at 40 GHz and 94 GHz are achieved. For instance, an outstanding power added efficiency of 65% has been reached at VDS = 10V in pulsed mode at 40 GHz. Also, an output power density of 8.3 W/mm at VDS = 40V is obtained associated to a power added efficiency of 50%. At 94 GHz, a record CW output power density for Ga-polar GaN transistors has been reached with 4 W/mm. Additionally, room temperature preliminary robustness assessment at 40 GHz has been performed at VDS = 20V. 24 hours RF monitoring showed no degradation during and after the test.

Part I: Physical Insight Into Carbon-Doping-Induced Delayed Avalanche Action in GaN Buffer in AlGaN/GaN HEMTs

Abstract: Physics behind the improvement in breakdown voltage of AlGaN/GaN HEMTs with carbon-doping of GaN buffer is discussed. Modeling of carbon as acceptor traps and self-compensating acceptor/donor traps is discussed with respect to their impact on avalanche breakdown. Impact of carbon behaving as a donor as well as acceptor traps on electric field relaxation and avalanche generation is discussed in detail to establish the true nature of carbon in GaN that delays the avalanche action. This understanding of the behavior of carbon-doping in GaN buffer is then utilized to discuss design parameters related to carbon doped buffer. Design parameters such as undoped channel thickness and relative trap concentration induced by carbon-doping are discussed with respect to the performance metrics of breakdown voltage, leakage current, sheet charge density, and dynamic ON-resistance.

Vertical GaN p–n diode with deeply etched mesa and the capability of avalanche breakdown

Abstract: A simple structure with high breakdown voltage and a low leakage current of a vertical GaN p–n diode on a GaN free-standing substrate is demonstrated. We describe a vertical p–n diode with a simple edge termination that has a drift layer etched deeply and vertically. A device simulation revealed that the electric field was more relaxed at the device edge and applied uniformly in the entire device with increasing etching depth. We fabricated the simulated structure and succeeded in reducing the leakage current and improving the breakdown voltage. With this structure, a stable avalanche breakdown can be observed.

GaN power devices: current status and future challenges

Abstract: The status and challenges in the development of GaN power devices are reviewed. At present, normally-off gate injection transistors (GITs) on Si are commercially available. The updated structure known as a hybrid-drain-embedded GIT provides superior reliability that contributes to the stable operation of compact power switching systems with high efficiency. The fabricated vertical GaN transistor on GaN as a future challenge demonstrates extremely low specific on-state resistance and high breakdown voltage. Metal-insulator-semiconductor-gate GaN transistor is also a technical challenge for faster switching, since it would give greater freedom of gate driving as a result of both high threshold voltage and widened gate voltage swing. Normally-off operation free from hysteresis in the current–voltage characteristics is confirmed in a recessed-gate AlGaN/GaN heterojunction field effect transistor using AlON as a gate insulator. Fast switching characteristics are experimentally confirmed for both of the newly developed GaN devices, indicating their great potential for practical use.

Silicon–germanium avalanche photodiodes with direct control of electric field in charge multiplication region

Abstract: A CMOS-compatible avalanche photodiode (APD) with high speed and high sensitivity is a critical component of a low-cost, high-data-rate, and energy-efficient optical communication link. A novel waveguide-coupled silicon–germanium APD detector with three electric terminals was demonstrated with breakdown voltage of −6 V, bandwidth of 18.9 GHz, DC photocurrent gain of 15, open-eye diagram at a data rate of 35 Gb/s, and sensitivity of −11.4 dBm at a data rate of 25 Gb/s. This three-terminal APD allows high-yield fabrication in the standard CMOS process and provides robust high-sensitivity operation under small voltage supply.

Analysis of AlGaN/GaN HEMT using discrete field plate technique for high power and high frequency applications

Abstract: In this paper, the RF and DC characteristics of AlGaN/GaN High electron mobility transistor is analysed using discrete field plate technique. Surprisingly, it reduces the device parasitic capacitance exhibiting very low CGS and CGD of 5.8 × 10−13 F/mm and 4.2 × 10−13 F/mm respectively to improve the cut off frequency (fT) from 17.5 GHz to 20 GHz. The discrete field plate suppresses the maximum electric field between gate and drain region to achieve the high breakdown voltage of 330 V. The maximum transconductance (gm) achieved is 275 mS/mm, ensuring the better DC operation of the device. The simulated results clearly show that, the discrete field plate HEMTs are superior in performance over conventional GaN FP-HEMTs for future high frequency and high power applications.

Fin-channel orientation dependence of forward conduction in kV-class Ga2O3 trench Schottky barrier diodes

Abstract: Ga2O3 vertical trench Schottky barrier diodes with four different fin-channel orientations are realized on (001) substrates and compared. Fin-channels along the [010] direction with (100)-like sidewalls result in the highest forward current, while other channel orientations all lead to a shallow turn-on behavior and much lower forward current, indicative of severe sidewall depletion attributed to negative interface charges. The comparison indicates that the interface charge density is the smallest on the (100)-like surfaces. The breakdown voltage of the diodes with 1-μm fin width is around 2.4 kV, with no apparent dependence on the channel orientation.

Simulation of AlGaN/GaN HEMTs’ Breakdown Voltage Enhancement Using Gate Field-Plate, Source Field-Plate and Drain Field Plate

Abstract: A 2-D simulation of off-state breakdown voltage (VBD) for AlGaN/GaN high electron mobility transistors (HEMTs) with multi field-plates (FPs) is presented in this paper. The effect of geometrical variables of FP and insulator layer on electric field distribution and VBD are investigated systematically. The FPs can modulate the potential lines and distribution of an electric field, and the insulator layer would influence the modulation effect of FPs. In addition, we designed a structure of HEMT which simultaneously contains gate FP, source FP and drain FP. It is found that the VBD of AlGaN/GaN HEMTs can be improved greatly with the corporation of gate FP, source FP and drain FP. We achieved the highest VBD in the HEMT contained with three FPs by optimizing the structural parameters including length of FPs, thickness of FPs, and insulator layer. For HEMT with three FPs, FP-S alleviates the concentration of the electric field more effectively. When the length of the source FP is 24 μm and the insulator thickness between the FP-S and the AlGaN surface is 1950 nm, corresponding to the average electric field of about 3 MV/cm at the channel, VBD reaches 2200 V. More importantly, the 2D simulation model is based on a real HMET device and will provide guidance for the design of a practical device.

Vertical geometry 33.2 A, 4.8 MW cm2 Ga2O3 field-plated Schottky rectifier arrays

Abstract: The performance of arrays consisting of 21 β-Ga2O3 field-plated rectifiers fabricated on thick epitaxial layers (n-type carrier concentration ∼1.6 × 1016 cm−3) grown on conducting substrates (carrier concentration 3 × 1019 cm−3) is reported. We show that by interconnecting the output of 21 smaller (0.4 × 0.4 mm2 to 1 × 1 mm2, total area 0.09 cm2) individual rectifiers using e-beam deposited Au, we can achieve a high total forward output current of 33.2 A, at 4.25 V in the single-sweep voltage mode, and a low forward turn-on voltage of 2.9 V (defined at 100 A cm−2) and maintain a reverse breakdown voltage of 240 V (defined at 1 μA cm−2). The current density was 376 A cm−2, and the on-state resistance was 0.012 Ω cm2. The total forward current was 10 A at 1.9 V and 22 A at 3 V. The power figure-of-merit for the array, VB2/RON, was 4.8 MW cm−2, with a reverse recovery time of individual rectifiers of 32 ns. The on/off ratio of the rectifier array was in the range of 105–1010 for +1 V/−1 to −100 V.

Effect of gate dielectric thicknesses on MOS photodiode performance and electrical properties

Abstract: Different film thickness was used to investigate the effect of the Al2O3 as a dielectric material for the fabrication of Al/AL2O3/Si/Al MOS diode. Chemical spray pyrolysis method was employed in this work. A high rectification behavior was observed from current-voltage (I-V) measurements in forward and reverse in dark. Optimum ideality factor of (2.36) at 5 sprayed layers was observed, the breakdown voltage found to be 5 MV cm−1 while the barrier height was (0.65 eV) at the same layer thickness. Capacitance-voltage (C–V) measurements was carried out which ensure the formation of abrupt junction; the incorporating built-in potential (Vbi) was estimated and found to be (0.8 eV). In addition, the photodiode shows a good Responsivity of about (1.4, 1.8) Amp/watt at Uv and IR region respectively.

Experimental study on the partial discharge and AC breakdown properties of C4F7N/CO2 mixture

Abstract: As an environmental friendly insulating medium, C 4 F 7 N has received extensive attention in the past two years In this study, the partial discharge (PD) and breakdown characteristics of C 4 F 7 N/CO 2 gas mixture were investigated using the gas insulation performance test platform The influence of gas pressure and mixing ratio on the PD initial voltage (PDIV) and breakdown voltage of C 4 F 7 N/CO 2 gas mixture in different electric fields was tested It was found that the PDIV and breakdown voltage of gas mixture with 2–8% C 4 F 7 N in the highly non-uniform field showed a linear saturation increasing trend with the change of gas pressure and mixing ratio The breakdown voltage of gas mixture increases linearly with gas pressure in the quasi-uniform electric field The relative breakdown voltage of gas mixture in the highly non-uniform field under high-pressure conditions is inferior to those of low-pressure conditions The C 4 F 7 N/CO 2 gas mixture containing 2–8% C 4 F 7 N is sensitive to the non-uniformity of electric field According to the PD and breakdown tests results, C 4 F 7 N/CO 2 gas mixture with 2–8% C 4 F 7 N has the potential to replace SF 6 using in gas-insulated equipment

High-Voltage β-Ga2O3 Schottky Diode with Argon-Implanted Edge Termination

Abstract: The edge-terminated Au/Ni/β-Ga2O3 Schottky barrier diodes were fabricated by using argon implantation to form the high-resistivity layers at the periphery of the anode contacts. With the implantation energy of 50 keV and dose of 5 × 1014 cm−2 and 1 × 1016 cm−2, the reverse breakdown voltage increases from 209 to 252 and 451 V (the maximum up to 550 V) and the Baliga figure-of-merit (VBR2/Ron) also increases from 25.7 to 30.2 and 61.6 MW cm−2, about 17.5% and 140% enhancement, respectively. According to the 2D simulation, the electric fields at the junction corner are smoothed out after argon implantation and the position of the maximum breakdown electric filed, 5.05 MV/cm, changes from the anode corner at the interface to the overlap corner just under the implantation region. The temperature dependence of the forward characteristics was also investigated.

Leakage and breakdown mechanisms of GaN vertical power FinFETs

Abstract: This work studies the leakage and breakdown mechanisms of 1.2 kV GaN vertical power FinFETs with edge termination. Two competing leakage and breakdown mechanisms have been identified. The first mechanism is dominated by the electric field, with the leakage current dominated by the electric field in the drift region and destructive breakdown voltage by the peak electric field at the edge termination. The second leakage and breakdown mechanism is controlled by an energy (or potential) barrier in the fin channel. This energy barrier suffers from the drain-induced barrier lowering (DIBL) effect and is highly dependent on gate/drain biases, fin geometries, and GaN/oxide interface charges. The electrons injected into the drift region due to the DIBL effect further lead to trap-assisted space-charge-limited conduction, which results in a nondestructive early breakdown. The barrier height in the fin channel determines which mechanism is dominant; the same device could show either destructive or nondestructive breakdown at different gate biases. To enable the normally off power switching, it is important to suppress the leakage from the second mechanism and maintain a sufficiently high energy barrier in the fin channel up to high drain voltages. Finally, the key device parameters determining the energy barrier in the fin channel have been identified. The findings in this work provide critical device understanding and design guidelines for GaN vertical power FinFETs and other “junctionless” vertical high-voltage power transistors.

4.9 kV breakdown voltage vertical GaN p–n junction diodes with high avalanche capability

Abstract: In order to avoid sudden catastrophic hard breakdown in high breakdown voltage vertical GaN p–n junction diodes, punch-through induced breakdown structures have been newly considered. Mg acceptor concentration in the p-GaN layer was reduced so that the punch-through breakdown occurred before the hard breakdown. By using a wafer with triple drift layers and the p-GaN layer with lowered Mg concentration of 3 × 1017 cm−3 grown on a freestanding n-GaN substrate, the diode showed a high breakdown voltage of 4.9 kV with high reverse avalanche capabilities against sudden increase of reverse current over 5 orders of magnitudes. No degradation was observed after fifteen repetitive measurements.

A Promising Nano-Insulating-Oil for Industrial Application: Electrical Properties and Modification Mechanism.

Abstract: Despite being discovered more than 20 years ago, nanofluids still cannot be used in the power industry. The fundamental reason is that nano-insulating oil has poor stability, and its electrical performance decreases under negative impulse voltage. We found that C60 nanoparticles can maintain long-term stability in insulating oil without surface modification. C60 has strong electronegativity and photon absorption ability, which can comprehensively improve the electrical performance of insulating oil. This finding has great significance for the industrial application of nano-insulating oil. In this study, six concentrations of nano-C60 modified insulating oil (CMIO) were prepared, and their breakdown strength and dielectric properties were tested. The thermally stimulated current (TSC) curves of fresh oil (FO) and CMIO were experimentally determined. The test results indicate that C60 nanoparticles can simultaneously improve the positive and negative lightning impulse and power frequency breakdown voltage of insulating oil, while hardly increasing dielectric loss. At 150 mg/L, the positive and negative lightning impulse breakdown voltages of CMIO increased by 7.51% and 8.33%, respectively, compared with those of FO. The AC average breakdown voltage reached its peak (18.0% higher compared with FO) at a CMIO concentration of 200 mg/L. Based on the test results and the special properties of C60, we believe that changes in the trap parameters, the strong electron capture ability of C60, and the absorption capacity of C60 for photons enhanced the breakdown performance of insulating oil by C60 nanoparticles.

1.6 kV Vertical Ga 2 O 3 FinFETs With Source-Connected Field Plates and Normally-off Operation

Abstract: High performance Ga 2 O 3 vertical FinFETs with a breakdown voltage of 1.6 kV, a drain current density of 600 A/cm2 have been demonstrated in this work. Fin-shaped channels with sub-micron widths lead to a high threshold voltage of 4 V, and also provide strong RESURF effects to reduce the drain leakage current and increase the breakdown voltage. A low leakage current of lower than 10−3 A/cm2 is maintained until the hard breakdown of the transistor. In order to sustain high voltage, a source-connected field plate (FP) supported by a dielectric layer is implemented at the outer edge of the gate pad as the edge termination, which enabled a breakdown voltage almost 2 times as high as those without FP. Device simulation shows that the highest electric field peak appears at the FP edge, which suggests further improvement of the breakdown voltage is possible by optimizing the FP design or implementing additional edge terminations.

Design of Transistors Using High-Permittivity Materials

Abstract: The design and modeling of dielectric superjunction transistors using combinations of ultrahigh permittivity materials and high-mobility materials are described. We show that placing high dielectric permittivity materials in the gate–drain depletion region can reduce electric field variations by screening the field due to depleted charges. This enables simultaneously high sheet charge density and breakdown voltage for scaled field-effect transistors. Using detailed 2-D device simulation of dc and high frequency characteristics, we show that extreme dielectric constant engineering provides unique opportunities for transistor design and has the potential to perform better than state-of-the-art millimeter-wave and terahertz frequency transistors.

Statistical Investigation of AC Dielectric Strength of Natural Ester Oil-Based Fe 3 O 4 , Al 2 O 3 , and SiO 2 Nano-Fluids

Abstract: This paper deals with the effects of conductive and insulating nanoparticles at various sizes and concentrations on the ac dielectric strength of natural ester oil, namely, MIDEL 1204. The investigated nanoparticles are conductive (Fe 3 O 4 ) and two insulating (Al 2 O 3 and SiO 2 ). The measurements of breakdown voltages are achieved according to IEC 60156 standard. Experimental findings show that the investigated nanoparticles have not a significant influence on insulation performances of natural ester oil as it is the case with mineral oils and synthetic esters. The best improvement does not exceed 7%; it is obtained with Fe 3 O 4 (50nm) at a concentration of 0.4 g/L and Al 2 O 3 (13 nm) at a concentration of 0.05 g/L. In some cases, the addition of nanoparticles even reduces the dielectric strength of natural ester oil. Indeed, a decrease of 15% is observed with SiO 2 at a concentration of 0.05 g/L. The statistical analysis of experimental results is performed using two probabilistic functions, namely, normal and Weibull laws. It is shown that the breakdown voltage values of the investigated nano-liquids generally obey the normal and Weibull distributions. In addition, the breakdown voltage with a risk of 1% and 50% probability is deduced.

The Transition to Paschen's Law for Microscale Gas Breakdown at Subatmospheric Pressure.

Abstract: The decrease in electronic device size necessitates greater understanding of gas breakdown and electron emission at microscale to optimize performance. While traditional breakdown theory using Paschen’s law (PL), driven by Townsend avalanche, fails for gap distance d $$\lesssim $$ 15 μm, recent studies have derived analytic equations for breakdown voltage when field emission and Townsend avalanche drive breakdown. This study derives a new analytic equation that predicts breakdown voltage VB within 4% of the exact numerical results of a previously derived theory and new experimental results at subatmospheric pressure for gap distances from 1–25 μm. At atmospheric pressure, VB transitions to PL near the product of pressure and gap distance, pd, corresponding to the Paschen minimum; at lower pressures, the transition to PL occurs to the left of the minimum. We further show that the work function plays a major role in determining which side of the Paschen minimum VB transitions to PL as pressure approaches atmospheric pressure while field enhancement and the secondary emission coefficient play smaller roles. These results indicate that appropriate combinations of these parameters cause VB to transition to PL to the left of the Paschen minimum, which would yield an extended plateau similar to some microscale gas breakdown experimental observations.