Showing papers on "Breakdown voltage published in 2010"

GaN Power Transistors on Si Substrates for Switching Applications

Abstract: In this paper, GaN power transistors on Si substrates for power switching application are reported. GaN heterojunction field-effect transistor (HFET) structure on Si is an important configuration in order to realize a low loss and high power devices as well as one of the cost-effective solutions. Current collapse phenomena are discussed for GaN-HFETs on Si substrate, resulting in suppression of the current collapse due to using the conducting Si substrate. Furthermore, attempts for normally off GaN-FETs were examined. A hybrid metal-oxide-semiconductor HFET structure is a promising candidate for obtaining devices with a lower on-resistance (Ron) and a high breakdown voltage (Vb).

GaN Power Transistors on Si Substrates for Switching Applications Hybrid MOS-FET transistor devices with low on-resistance, high hold-voltages and high breakdown voltage promise to provide high-power, low-loss operation for switching applications.

Abstract: In this paper, GaN power transistors on Si substrates for power switching application are reported. GaN heterojunction field-effect transistor (HFET) structure on Si is an important configuration in order to realize a low loss and high power devices as well as one of the cost-effective solutions. Current collapse phenomena are discussed for GaN-HFETs on Si substrate, resulting in suppression of the current collapse due to using the conducting Si substrate. Furthermore, attempts for normally off GaN-FETs were exam- ined. A hybrid metal-oxide-semiconductor HFET structure is a promising candidate for obtaining devices with a lower on-resistance ðRonÞ and a high breakdown voltage ðVbÞ.

Effects of nanoparticle charging on streamer development in transformer oil-based nanofluids

Abstract: Transformer oil-based nanofluids with conductive nanoparticle suspensions defy conventional wisdom as past experimental work showed that such nanofluids have substantially higher positive voltage breakdown levels with slower positive streamer velocities than that of pure transformer oil. This paradoxical superior electrical breakdown performance compared to that of pure oil is due to the electron charging of the nanoparticles to convert fast electrons from field ionization to slow negatively charged nanoparticle charge carriers with effective mobility reduction by a factor of about 1×105. The charging dynamics of a nanoparticle in transformer oil with both infinite and finite conductivities shows that this electron trapping is the cause of the decrease in positive streamer velocity, resulting in higher electrical breakdown strength. Analysis derives the electric field in the vicinity of the nanoparticles, electron trajectories on electric field lines that charge nanoparticles, and expressions for the char...

A Watt-Level Stacked-FET Linear Power Amplifier in Silicon-on-Insulator CMOS

Abstract: A single-stage stacked field-effect transistor (FET) linear power amplifier (PA) is demonstrated using 0.28-?m 2.5-V standard I/O FETs in a 0.13-?m silicon-on-insulator (SOI) CMOS technology. To overcome the low breakdown voltage limit of MOSFETs, a stacked-FET structure is employed, where four transistors are connected in series so that their output voltage swings are added in phase. With a 6.5-V supply, the measured PA achieves a small-signal gain of 14.6 dB, a saturated output power of 32.4 dBm, and a maximum power-added efficiency (PAE) of 47% at 1.9 GHz. Using a reverse-link IS-95 code division multiple access modulated signal, the PA shows an average output power of up to 28.7 dBm with a PAE of 41.2% while meeting the adjacent channel power ratio requirement. Using an uplink wideband code division multiple access modulated signal, the PA shows an average output power of up to 29.4 dBm with a PAE of 41.4% while meeting the adjacent channel leakage ratio requirement. The stacked-FET PA is designed to withstand up to 9 V of supply voltage before reaching its breakdown limit. This is the first reported stacked-FET linear PA in submicrometer SOI CMOS technology that delivers watt-level output power in the gigahertz frequency range with efficiency and linearity performance comparable to those of GaAs-based PAs.

Extremely Low On-Resistance and High Breakdown Voltage Observed in Vertical GaN Schottky Barrier Diodes with High-Mobility Drift Layers on Low-Dislocation-Density GaN Substrates

Abstract: Vertical GaN Schottky barrier diodes (SBDs) were fabricated on freestanding GaN substrates with low dislocation density High quality n-GaN drift-layer with an electron mobility of 930 cm2 V-1 s-1 was obtained by optimizing the growth conditions by reducing the intensity of yellow luminescence using conventional photoluminescence measurements The specific on-resistance (RonA) and the breakdown voltage (VB) of the SBDs were 071 mΩ cm2 and over 1100 V, respectively The figure of merit (VB2/RonA) was 17 GW/cm2, which is the highest value among previously reported SBDs for both GaN and SiC

High Breakdown ( $> \hbox{1500\ V}$ ) AlGaN/GaN HEMTs by Substrate-Transfer Technology

Abstract: In this letter, we present a new technology to increase the breakdown voltage of AlGaN/GaN high-electron-mobility transistors (HEMTs) grown on Si substrates. This new technology is based on the removal of the original Si substrate and subsequent transfer of the AlGaN/GaN HEMT structure to an insulating carrier wafer (e.g., glass or polycrystalline AlN). By applying this new technology to standard AlGaN/GaN HEMTs grown on Si substrate, an AlGaN/GaN HEMT with breakdown voltage above 1500 V and specific on resistance of 5.3 mΩ·cm2 has been achieved.

A mathematical model of the modified Paschen's curve for breakdown in microscale gaps

Abstract: Traditionally, Paschen’s curve has been used to describe the breakdown voltage for gaseous ionization between two electrodes. However, experiments have shown that Paschen’s curve, which is based on Townsend effects, is not necessarily accurate in describing breakdown between electrodes spaced less than 15 μm apart. In this regime, electron field emission plays a significant role in the breakdown phenomenon, and recently an alternative mathematical description that accounts for ion-enhanced field emission was proposed to describe the breakdown voltage in small gaps. However, both Paschen’s curve and the small gap equation only work in certain regimes, and neither predicts the transition that occurs between Townsend and field emission effects—the so-called modified Paschen’s curve. In this work, a single, consistent mathematical description of the breakdown voltage is proposed that accounts for both Townsend ionization and ion-enhanced field emission mechanisms. Additionally, microscale breakdown experiment...

AlGaN/GaN/GaN:C Back-Barrier HFETs With Breakdown Voltage of Over 1 kV and Low $R_{\scriptscriptstyle{\rm ON}} \times A$

Abstract: A systematic study of GaN-based heterostructure field-effect transistors with an insulating carbon-doped GaN back barrier for high-voltage operation is presented. The impact of variations of carbon doping concentration, GaN channel thickness, and substrates is evaluated. Tradeoff considerations in on-state resistance versus current collapse are addressed. Suppression of the off-state subthreshold drain-leakage currents enables a breakdown voltage enhancement of over 1000 V with a low on-state resistance. Devices with a 5-μm gate-drain separation on semi-insulating SiC and a 7-μm gate-drain separation on n-SiC exhibit 938 V and 0.39 mΩ·cm2 and 942 V and 0.39 m Ω·cmcm2, respectively. A power device figure of merit of ~ 2.3 × 109 V2/Ω·cm2 was calculated for these devices.

Over 100 A operation normally-off AlGaN/GaN hybrid MOS-HFET on Si substrate with high-breakdown voltage

Abstract: The demonstration of a normally-off n-channel AlGaN/GaN hybrid metal–oxide–semiconductor heterojunction field-effect transistor (MOS-HFET) on Si substrate for large-current operation is reported. The AlGaN/GaN hybrid MOS-HFET has the merits of both a MOS channel and an AlGaN/GaN heterostructure with high mobility two dimensional electron gases (2DEG). The maximum drain current of over 100 A with 2 μm channel length and 340 mm channel width is performed. This is the best value for a normally-off GaN-based field-effect transistor. The specific on-state resistance is 9.3 mΩ cm 2 . The fabricated device also exhibits good normally-off operation with the threshold voltage of 2.7 V and the breakdown voltage of over 600 V.

AlGaN/GaN/AlGaN DH-HEMTs Breakdown Voltage Enhancement Using Multiple Grating Field Plates (MGFPs)

Abstract: GaN-based high-electron mobility transistors with planar multiple grating field plates (MGFPs) for high-voltage operation are described. A synergy effect with additional electron channel confinement by using a heterojunction AlGaN back barrier (BB) is demonstrated. Suppression of the OFF-state subthreshold gate and drain leakage currents enables breakdown voltage enhancement over 700 V and a low ON-state resistance of 0.68 mΩ × cm2. Such devices have a minor tradeoff in ON-state resistance, lag factor, maximum oscillation frequency, and cutoff frequency. A systematic study of the MGFP design and the effect of Al composition in the BB is described. Physics-based device simulation results give insight into electric field distribution and charge carrier concentration, depending on the field plate design.

Low On-Resistance High-Breakdown Normally Off AlN/GaN/AlGaN DHFET on Si Substrate

Abstract: Ultrathin-barrier normally off AlN/GaN/AlGaN double-heterostructure field-effect transistors using an in situ SiN cap layer have been fabricated on 100-mm Si substrates for the first time. The high 2DEG density in combination with an extremely thin barrier layer leads to enhancement-mode devices with state-of-the-art combination of specific on-resistance that is as low as 1.25 m?·cm2 and breakdown voltage of 580 V at V GS = 0 V . Despite the 2-?m gate length used, the transconductance peaks above 300 mS/mm. Furthermore, pulsed measurements show that the devices are dispersion free up to high drain voltage V DS = 50 V. More than 200 devices have been characterized in order to confirm the reproducibility of the results.

A Universal Grid-Connected Fuel-Cell Inverter for Residential Application

Abstract: This paper describes a universal fuel-cell-based grid-connected inverter design with digital-signal-processor-based digital control. The inverter has a direct power conversion mechanism with a high-frequency zero-voltage-switched dc/ac primary-side converter followed by a pair of ac/ac cycloconverters that operates either in parallel or in series to simultaneously address the issues of universal output and high efficiency. The critical design issues focus on the impact and optimization of transformer leakage inductance with regard to effectiveness of zero voltage switching of a primary-side converter, duty-cycle loss, resonance, and voltage spike that has effect on the breakdown voltage rating of the cycloconverter devices. An additional concept of dynamic transformer tapping has been explored to address the impact of varying input voltage on secondary-side voltage spike and inverter efficiency. Finally, detailed grid-parallel and grid-connected results are presented that demonstrate satisfactory inverter performances.

Nanorod based Schottky contact gas sensors in reversed bias condition

Abstract: There has been significant interest in using electronically contacted nanorod or nanotube arrays as gas sensors, whereby an adsorbate modifies either the impedance or the Fermi level of the array, enabling detection. Typically, such arrays demonstrate the I-V curves of a Schottky diode that is formed using a metal-semiconductor junction with rectifying characteristics. We show in this work that nanostructured Schottky diodes have a functionally different response, characteristic of the large electric field induced by the size scale of the array. Specifically, they are characterized by a low reverse breakdown voltage. As a result, the reverse bias current becomes a strong function of the applied voltage. In this work, for the first time, we model this unique feature by describing the enhancement effect of high aspect ratio nanostructures on the I-V characteristics of a Schottky diode. A Pt/ZnO/SiC nanostructured Schottky diode is fabricated to verify the theoretical equations presented. The gas sensing properties of the Schottky diode in reversed bias is investigated and it is shown that the theoretical calculations are in excellent agreement with measurements.

Silicon Substrate Removal of GaN DHFETs for Enhanced (<1100 V) Breakdown Voltage

Abstract: In this letter, we present a novel approach to enhance the breakdown voltage (VBD) for AlGaN/GaN/AlGaN double-heterostructure FETs (DHFETs), grown by metal-organic chemical vapor deposition on Si (111) substrates through a silicon-substrate-removal and a layer-transfer process. Before removing the Si substrate, both buffer isolation test structures and DHFET devices showed a saturation of VBD due to the electrical breakdown through the Si substrate. We observed a VBD saturation of 500 V for isolation gaps larger than 6 μm . After Si removal, we measured a VBD enhancement of the AlGaN buffer to 1100 V for buffer isolation structures with an isolation gap of 12 μm. The DHFET devices with a gate-drain (LGD) distance of 15 μm have a VBD > 1100 V compared with ~300 V for devices with Si substrate. Moreover, from Hall measurements, we conclude that the substrate-removal and layer-transfer processes have no impact on the 2-D electron gas channel properties.

High Al Composition AlGaN-Channel High-Electron-Mobility Transistor on AlN Substrate

Abstract: AlGaN-channel high-electron-mobility transistor (HEMT) with high Al composition of 0.51 has been developed. The epitaxial layers were grown on a free-standing AlN substrate to improve crystalline quality. The fabricated device exhibited a maximum drain current (Idsmax) of 25.2 mA/mm with a maximum transconductance (gmmax) of 4.7 mS/mm. The characteristic features of the device were a high source-to-drain breakdown voltage of 1800 V and a high applicable gate-to-source voltage of 4 V in the forward direction. Temperature dependence of DC characteristics demonstrated that the drain current degradation at elevated temperatures for the AlGaN-channel HEMT was appreciably small as compared with the conventional AlGaN/GaN HEMT. This is the first report showing successful DC operation of AlGaN-channel HEMT with high Al composition of over 0.5.

High-Performance Integrated Dual-Gate AlGaN/GaN Enhancement-Mode Transistor

Abstract: In this letter, we present a new AlGaN/GaN enhancement-mode (E-mode) transistor based on a dual-gate structure. The dual gate allows the transistor to combine an E-mode behavior with low on-resistance and very high breakdown voltage. The device utilizes an integrated gate structure with a short gate controlling the threshold voltage and a long gate supporting the high-voltage drop from the drain. Using this new dual-gate technology, AlGaN/GaN E-mode transistors grown on a Si substrate have demonstrated a high threshold voltage of 2.9 V with a maximum drain current of 434 mA/mm and a specific on-resistance of 4.3 m Ω·cm2 at a breakdown voltage of 643 V.

Reversed bias Pt/nanostructured ZnO Schottky diode with enhanced electric field for hydrogen sensing

Abstract: In this paper, the effect of electric field enhancement on Pt/nanostructured ZnO Schottky diode based hydrogen sensors under reverse bias condition has been investigated. Current–voltage characteristics of these diodes have been studied at temperatures from 25 to 620 °C and their free carrier density concentration was estimated by exposing the sensors to hydrogen gas. The experimental results show a significantly lower breakdown voltage in reversed bias current–voltage characteristics than the conventional Schottky diodes and also greater lateral voltage shift in reverse bias operation than the forward bias. This can be ascribed to the increased localized electric fields emanating from the sharp edges and corners of the nanostructured morphologies. At 620 °C, voltage shifts of 114 and 325 mV for 0.06% and 1% hydrogen have been recorded from dynamic response under the reverse bias condition.

Temperature Dependence of Avalanche Breakdown in InP and InAlAs

Abstract: Simple analytical expressions for temperature coefficients of breakdown voltage of avalanche photodiodes (APDs) utilizing InP or InAlAs are reported. The work is based on measurements of temperature dependence of avalanche breakdown voltage in a series of InP and InAlAs diodes at temperatures between 20 and 375 K. While avalanche breakdown voltage becomes more temperature sensitive with avalanche region thickness for both materials, the InAlAs diodes are less sensitive to temperature changes compared to InP diodes.

Gate‐recessed normally‐off GaN‐on‐ Si HEMT using a new O2‐BCl3 digital etching technique

Abstract: A new, semi-self-limiting, digital etch process using separate oxygen (O2) and boron trichloride (BCl3) plasmas to sequentially remove layers of material from AlGaN/GaN high electron mobility transistors (HEMTs) on the order of a few angstroms per cycle is presented. This novel digital or atomic layer etching (ALE) technique was used for the conversion of AlGaN/GaN HEMT devices from depletion mode (normally-on operation) to enhancement mode (normally-off operation). For a fixed BCl3 time of 60 sec per cycle, the etch rate per cycle was increased from 1.4 nm/cycle to 2.5 nm/cycle by increasing the O2 time per cycle from zero to 15 seconds, and remained fairly constant with higher O2 time per cycle for a self-limiting etch process. Two GaN-on-Si wafers from the same CVD growth were processed side-by-side using the device layout and process steps, except for the depletion-to-enhancement conversion step, to compare ALE and fluorine treatment. The ALE-processed had a peak gm of 250 mS/mm, 67% higher than the fluorine-treatment process. The ALE process resulted in a threshold voltage variation of +/- 150 mV across the 3 inch wafer (σ = 63 mV), which was less than half of that of the fluorine-treatment wafer. The three-terminal breakdown voltage of the ALE-processed wafer exceeded 1100 V, which is the first demonstration of such a high voltage device using GaN-on-Si and a gate recess technique, and the drain leakage current was in the μA/mm range at 1100 V. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Experimental and simulation study of breakdown voltage enhancement of AlGaN/GaN heterostructures by Si substrate removal

Abstract: The breakdown mechanism in GaN-based heterostructures (HFETs) grown on silicon substrate is investigated in detail by TCAD simulations and silicon substrate removal technique. High-voltage electrical measurements show that the breakdown voltage saturates for larger gate-drain distances. This failure mechanism is dominated by the avalanche breakdown in the Si substrate. High-voltage TCAD simulations of AlGaN/GaN/Si substrate structures show higher impact ionization factor and electron density at the Si interface indicating a leakage current path where avalanche breakdown occurs. Experimentally, by etching off the Si substrate the breakdown voltage no longer saturates and linearly increases for all gate-drain gaps. We propose the silicon removal technique as a viable way to enhance the breakdown voltage of AlGaN/GaN devices grown on Si substrate.

Novel Vertical Heterojunction Field-Effect Transistors with Re-grown AlGaN/GaN Two-Dimensional Electron Gas Channels on GaN Substrates

Abstract: Novel vertical heterojunction field-effect transistors (VHFETs) with re-grown AlGaN/GaN two-dimensional electron gas (2DEG) channels on free-standing GaN substrates have been developed. The VHFETs exhibited a specific on-resistance (RonA) of 7.6 mΩ cm2 at a threshold voltage (VTH) of -1.1 V and a breakdown voltage (VB) of 672 V. The breakdown voltage and the figure of merit (VB2/RonA) are the highest among those of the GaN-based vertical transistors ever reported. It was demonstrated that the threshold voltage can be controlled by the thickness of AlGaN layers and a normally-off operation was achieved with a 10-nm-thick Al0.2Ga0.8N layer.

Schottky-Drain Technology for AlGaN/GaN High-Electron Mobility Transistors

Abstract: In this letter, we demonstrate 27% improvement in the buffer breakdown voltage of AlGaN/GaN high-electron mobility transistors (HEMTs) grown on Si substrate by using a new Schottky-drain contact technology. Schottky-drain AlGaN/GaN HEMTs with a total 2-?m-thick GaN buffer showed a three-terminal breakdown voltage of more than 700 V, while conventional AlGaN/GaN HEMTs of the same geometry showed a maximum breakdown voltage below 600 V. The improvement of the breakdown voltage has been associated with the planar contact morphology and lack of metal spikes in the Schottky-drain metallization.

Off-State Breakdown Characterization in AlGaN/GaN HEMT Using Drain Injection Technique

Abstract: AlGaN/GaN high-electron mobility transistor's (HEMT's) off-state breakdown is investigated using drain-current injection techniques with different injection current levels. Competitions between the source leakage and gate leakage, pure leakage and impact ionization, and source- and gate-injection-induced impact ionization during the drain-injection measurement are discussed in detail. It was found that the breakdown originates from the source/gate leakage at low drain injection levels but is dominated by source/gate-induced impact ionization process at high drain injection currents. The source-induced impact ionization usually precedes the gate-induced impact ionization in low-gate leakage devices, resulting in a premature three-terminal off-state breakdown. We also found that the gate-bias value affects the breakdown voltage in the conventional three-terminal off-state breakdown I-V measurement and should be carefully considered.

Blocking-voltage boosting technology for GaN transistors by widening depletion layer in Si substrates

Abstract: We propose a novel technique to boost the blocking voltage of AlGaN/GaN hetero junction field effect transistors (HFETs) by widening a depletion layer in highly resistive Si substrate. The blocking-voltage boosting (BVB) technology utilizes ion implantation at the peripheral area of the chip as channel stoppers to terminate the leakage current from the interfacial inversion layers at AlN/Si. A depletion layer is widened in the substrate by the help of the channel stopper, which increases the blocking voltage of the HFET. The off-state breakdown voltage of the HFETs is increased up to 1340V by the BVB technology from 760V without the channel stoppers for the epitaxial GaN as thin as 1.4µm on Si. This technology greatly helps to increase the blocking voltage even for thin epitaxial GaN on Si, which leads to further reduction of the fabrication cost.

Enhancement-mode GaN MIS-HEMTs for power supplies

Abstract: In this paper, we present the current status of GaN-high electron mobility transistor (HEMT) for power-supply-applications. Advantages of GaN HEMT are summarized with discussing required characteristics applying for power supplies. Then, we introduce our Enhancement-mode (E-mode) GaN MIS-HEMT technology. We focused on realizing both normally-off operation and high current density with high breakdown voltage. Detailed results are discussed in this paper. In particular, we developed a unique device structure called triple layer cap structure. High current density with normally-off mode was successfully achieved, which is preferable for power-supply application. We also demonstrated high speed performance with low on-resistance.

Breakdown properties of transformer oil-based TiO 2 nanofluid

Abstract: A new class of colloidal dielectric fluids is formulated by mixing TiO 2 nanoparticle with transformer oil in order to enhance the dielectric performance of mineral oil. To investigate the impact of this change, both AC and lightning breakdown voltage tests were carried out according to IEC standard respectively. The results of AC tests indicate that mean value and 1% probability breakdown voltage of nanofluid achieves an increase of 1.15 and 1.43 times that of transformer oil respectively. For lightning breakdown voltage, nanofluid was 13.3KV higher than that of transformer oil. It is considered to be mainly attributed to polarization of TiO 2 nanoparticles, which may act as electron traps in the process of electron transfer in electrically stressed nanofluids. Furthermore, the high specific surface area of nanoparticles also increases the probability of electron scattering in the nanofluids, which reduces the impact energy of electrons and prevents the oil from ionizing. All these results confirmed that transformer oil modified with TiO 2 nanoparticles hold a promise to improve its insulating properties.