Double-pulse Switching Research Articles

A Novel Mixture-Devices-Based Submodule for MMC by Using Low on-State Voltage IGCT and High di/dt Ability IGBT

At present, insulated-gate bipolar transistor (IGBT) is widely used as the converter component in the submodule of modular multilevel converter (MMC) for its excellent performance in driving circuit and switching speed, but the further application is restricted by its high conduction loss and cost rate. Integrated gate-commutated thyristor (IGCT) is another converter device used in MMC with low conduction loss and cost. However, the d <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">i</i> /d <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</i> capability of IGCT is limited so that a snubber circuit is required in the submodule for protection, which generates unwanted power loss for MMC. For better performance and reliability, this paper proposes a mixture-devices-based submodule (MS) for MMC based on the cooperation of parallel IGCT and IGBT devices. Double-pulse switching experiments for the MS are conducted to verify its effectiveness, and to get the data for the follow-up switching power loss calculation. The power loss of MMC based on IGBT, IGCT and mixture devices are calculated based on the model established in this paper. Furthermore, the comprehensive comparison for power loss among IGBT-based, IGCT-based and mixture-device-based MMCs are performed, proving the effectiveness of the mixture topology in terms of power loss reduction. Meanwhile, the proposed MS is cost-competitive.

Influence of Radiation-Induced Displacement Defect in 1.2 kV SiC Metal-Oxide-Semiconductor Field-Effect Transistors.

The effect of displacement defect on SiC metal-oxide-semiconductor field-effect transistors (MOSFETs) due to radiation is investigated using technology computer-aided design (TCAD) simulation. The position, energy level, and concentration of the displacement defect are considered as variables. The transfer characteristics, breakdown voltage, and energy loss of a double-pulse switching test circuit are analyzed. Compared with the shallow defect energy level, the deepest defect energy level with EC − 1.55 eV exhibits considerable degradation. The on-current decreases by 54% and on-resistance increases by 293% due to the displacement defect generated at the parasitic junction field-effect transistor (JFET) region next to the P-well. Due to the existence of a defect in the drift region, the breakdown voltage increased up to 21 V. In the double-pulse switching test, the impact of displacement defect on the power loss of SiC MOSFETs is negligible.

Development of a Device for On-Die Double-Pulse Testing and Measurement of Dynamic On-Resistance of GaN HEMTs

On-die testing can accelerate development of semiconductor devices, but poses certain challenges related to high frequency and high current switching. This paper describes design and development of a tester for double-pulse switching test and measurement of dynamic on-state resistance of unpackaged High-Electron-Mobility Transistors (GaN HEMTs). The tester is capable of switching an inductive load at drain-to-source voltage up to 400 V and drain current up to 10 A. Design challenges resulting from specific properties of GaN HEMTs and on-die measurement are explained, and solutions are proposed. Essential parts of the developed device are described, including low inductance gate-driver and measurement methods. Modified drain voltage clamping circuit for accurate on-state drain voltage measurement is described. The tester is constructed as a printed circuit board, integrated into a probe station. Voltage and current waveforms are measured with oscilloscope and used to calculate the on-resistance. Results of a reference measurement with commercially available packaged transistors are presented. Waveforms measured on experimental unpackaged normally-off GaN HEMT samples are also presented and discussed. The proposed tester device proved to be capable of performing the dynamic on-resistance measurement with satisfactory results.

(Invited) Medium-Voltage SiC Devices for Next Generation of Power Conversion

As a wide bandgap semiconductor, Silicon Carbide (SiC) power switches and diodes offer the promise of lower conduction and switching losses and more efficient power conversion for a wide range of applications that include but not limited to hybrid vehicles, renewable technologies, industrial motors and data centers. However, in present day, SiC solutions for MV-class (>3.3 kV) unipolar switches and diodes suffer from high conduction losses at elevated temperatures, and SiC bipolar devices such as IGBTs require a prohibitive high forward voltage drop of 3V. Therefore, in these systems, the advantage of SiC technology is diminished compared to the incumbent Si IGBT technology. SiC super-junctions (SJ) can break the unipolar limit and offer an improved trade-off between specific on-resistance and blocking voltage for MV-class applications. To date, multi-epitaxial growth and trench-refill approaches have been demonstrated for 1.2kV and 6.5kV SiC SJ devices. Due to low diffusivity of dopants and shallow projectile depth of implanted atoms in SiC, multi-epitaxial solutions are limited to low voltage switches with thinner drift layers (up to 1200V). Alternately, the trench refill approach generates crystallographic defects that result in leakage at high blocking voltages. Furthermore, achieving uniform, target dopant distribution inside re-grown layers requires complex growth conditions and makes the regrowth process challenging. Recently, SiC charge-balanced (CB) diodes and MOSFETs were reported as an alternative solution to SJ devices with a simpler and scalable fabrication process. In these devices, a novel drift layer architecture is implemented with buried p-doped regions inside the drift layers instead of p-doped pillars. This new approach has been adopted for 3.3kV SiC JBS diodes and 4.5kV SiC MOSFET and results in Ron,sp significantly below the 1-D SiC unipolar limit. In the meantime, a new class of SJ devices is being developed that relies on Megavolt-level implantation to form deep p-type and n-type pillars. This multi-epitaxial SJ approach can be implemented in high voltage SiC devices with a smaller number of regrowth steps. In this work, we review fabrication steps for realizing SiC CB diodes and MOSFETs and report static characterization from room temperature up to 175 °C and dynamic response up to 3kV double pulse switching of such diodes and MOSFETs. Furthermore, we report successful fabrication of 2kV SiC SJ PiN diodes as a first building block of deep-implanted SJ technology and will discuss effect of different activation anneal temperatures on recovering lattice damage following high energy implantation.

Coherent control of a surface structural phase transition.

Active optical control over matter is desirable in many scientific disciplines, with prominent examples in all-optical magnetic switching1,2, light-induced metastable or exotic phases of solids3-8 and the coherent control of chemical reactions9,10. Typically, these approaches dynamically steer a system towards states or reaction products far from equilibrium. In solids, metal-to-insulator transitions are an important target for optical manipulation, offering ultrafast changes of the electronic4 and lattice11-16 properties. The impact of coherences on the efficiencies and thresholds of such transitions, however, remains a largely open subject. Here, we demonstrate coherent control over a metal-insulator structural phase transition in a quasi-one-dimensional solid-state surface system. A femtosecond double-pulse excitation scheme17-20 is used to switch the system from the insulating to a metastable metallic state, and the corresponding structural changes are monitored by ultrafast low-energy electron diffraction21,22. To govern the transition, we harness vibrational coherence in key structural modes connecting both phases, and observe delay-dependent oscillations in the double-pulse switching efficiency. Mode-selective coherent control of solids and surfaces could open new routes to switching chemical and physical functionalities, enabled by metastable and non-equilibrium states.

10 kV Silicon Carbide PiN Diodes—From Design to Packaged Component Characterization

This paper presents the design, fabrication and characterization results obtained on the last generation (third run) of SiC 10 kV PiN diodes from SuperGrid Institute. In forward bias, the 59 mm2 diodes were tested up to 100 A. These devices withstand voltages up to 12 kV on wafer (before dicing, packaging) and show a low forward voltage drop at 80 A. The influence of the temperature from 25 °C to 125 °C has been assessed and shows that resistivity modulation occurs in the whole temperature range. Leakage current at 3 kV increases with temperature, while being three orders of magnitude lower than those of equivalent Si diodes. Double-pulse switching tests reveal the 10 kV SiC PiN diode’s outstanding performance. Turn-on dV/dt and di/dt are −32 V/ns and 311 A/µs, respectively, whereas turn-off dV/dt and di/dt are 474 V/ns and −4.2 A/ns.

Polarization switching kinetics of the ferroelectric Al-doped HfO2 thin films prepared by atomic layer deposition with different ozone doses

Ferroelectric switching kinetics of the Al-doped HfO2 (Al:HfO2) thin films prepared by the atomic layer deposition process were investigated by varying the dose time of oxygen precursor (O3). When the O3 dose time was reduced to 3 s, the Al:HfO2 films exhibited an enhanced remnant polarization (2Pr) of 10.2 μC/cm2 due to the suppression of the monoclinic phase and the increase in the ratio of oxygen vacancy. Double-pulse switching and the Kolmogorov–Avrami–Ishibashi model were used to obtain detailed quantitative information on the switching kinetics of the Al:HfO2 films. The estimated values of switching time and activation energy showed the strong dependence of O3 dose. This suggests that the O3 dose condition can be a key control parameter to modulate the ferroelectric polarization switching dynamics of the Al:HfO2 thin films.

Film thickness-dependent ferroelectric polarization switching dynamics of undoped HfO2 thin films prepared by atomic layer deposition

Metal-ferroelectric-metal capacitors were fabricated to evaluate the ferroelectricity and switching dynamics of the undoped-HfO2 thin films prepared by atomic layer deposition. The film thickness was controlled to be 9 to 16 nm as an important control parameter. The value of remnant polarization (Pr) decreased with increasing the film thickness owing to the modulations in amounts of ferroelectric orthorhombic phase. The 11-nm-thick HfO2 thin film, which was strategically suggested as a critical film thickness, showed the Pr value of 8.47 μC/cm2. Based on the accurately calculated Pr by double-pulse switching measurement and Kolmogorov-Avrami-Ishibashi (KAI) model, the ferroelectric polarization switching time (ts) and the activation electric field (Ea) for polarization reversal were estimated with the variations in film thickness of the HfO2 thin films. The ts and Ea showed decreasing and increasing trends with increasing the film thickness, respectively. The values of Pr for the MFM capacitor were also found to be gradually modulated by controlling the ferroelectric partial polarization with pulse-width and pulse-number modulations, which corresponded to the emulations of assigning the synaptic weights for the synapse device applications.

Self-Sustained Turn-Off Oscillation of SiC MOSFETs: Origin, Instability Analysis, and Prevention

This paper presents a comprehensive investigation on the self-sustained oscillation of silicon carbide (SiC) MOSFETs. At first, based on the double pulse switching test, it is identified that the self-sustained oscillation of SiC MOSFETs can be triggered by two distinct test conditions. To investigate the oscillatory criteria of the two types of self-sustained oscillation, a small-signal ac model is introduced to obtain the transfer function of the oscillatory system. The instability of the oscillation is thereby determined by the two conjugate pole pairs of the transfer function. By analyzing the damping ratios of the two pole pairs, the parametric sensitivity of various circuit and device’s parameters on the two types of self-sustained oscillation are obtained. The analyses reveal the oscillatory criteria of the self-sustained oscillation for SiC MOSFETs. Based on the oscillatory criteria, necessary methods are proposed to prevent the oscillation. The proposed oscillation suppression methods are validated by the experiment at the end of the paper.

Integrated Gate Commutated Thyristor-Based Modular Multilevel Converters: A Promising Solution for High-Voltage dc Applications

This article proposes that a modular multilevel converter (MMC) based on the integrated-gate commutated thyristor (IGCT) is a promising solution for future highvoltage dc (HVdc) applications. The system-level scheme and technical issues of the IGCT MMC are proposed, and the commutation behaviors of the IGCT and the snubber circuit in the MMC are analyzed. On this basis, the optimal designs of the anode inductor, power supply system, valve series, and submodule structure are proposed, and a comprehensive experimental platform is built. Detailed experiments are conducted, including a double-pulse switching experiment, a back-to-back power cycling experiment, and an MMC operation experiment. Furthermore, the correctness and effectiveness of the proposed IGCT MMC solution are verified.

Investigation on the Self-Sustained Oscillation of Superjunction MOSFET Intrinsic Diode

This paper presents the analyses on the self-sustained oscillation of superjunction MOSFET intrinsic diode. At first, the characteristics of the self-sustained oscillation for the superjunction MOSFET intrinsic diode are identified by the double-pulse switching test. The test results show that the self-sustained oscillation with significant self-amplification phenomenon can be triggered during the reverse recovery transient of superjunction MOSFET intrinsic diode. Based on the Sentaurus TCAD simulation, the self-sustained oscillation is reproduced. The simulation results reveal the root cause of the self-sustained oscillation. Due to the snappy reverse recovery of superjunction MOSFET intrinsic diode, the steep slope of diode snap off current can generate high voltage across the common source inductance, which drives the gate–source voltage and turns on the high-side MOSFET. The unexpected MOSFET turn-on can, in return, enhance the steepness of the current slope when the diode snap off. This leads to a positive feedback process and self-sustained oscillation is generated. In the end, based on the theoretical analyses and experimental results, the necessary methods that can suppress the oscillation are presented.

Failure of Switching Operation of SiC-MOSFETs and Effects of Stacking Faults on Safe Operation Area

When developing silicon carbide (SiC) devices, the reliability of the internal body diode is an important issue. Stacking faults (SFs) are expanded from basal plane defects by using a body diode. Although it is well known that ON-voltage degradation occurs due to SFs, their effects on dynamic reliability have not been studied well. Furthermore, including the effects of SFs, there are not many reports about the dynamic reliability of SiC-MOSFETs. In this paper, a double-pulse switching test using 3.3-kV SiC-MOSFETs was carried out to clarify the failure mechanism of the switching operation of SiC-MOSFETs and effects of SFs on the safe operation area (SOA). Before the switching test, current stress was applied to the body diode of the devices under test (DUTs) to expand the SFs. The circuit configuration was half-bridge type, and a double-pulse gate signal was applied to the lower arm DUT. The switching voltage was 1.8 kV, and the switching current increased at about 8-A steps to failure. As a result, reverse recovery SOA (RRSOA) reliability decreased depending on the amount of SFs in the SiC-MOSFET. Because RRSOA failure was caused by avalanche due to the hole concentration during reverse recovery and the SFs raised local current density, reverse bias SOA (RBSOA) hardly decreased even if SFs containing SiC-MOSFETs were used. This is because RBSOA failure was caused by degradation of the gate isolation layer due to overheating and the temperature coefficient of the SFs electric resistance indicated negative.

Analysis of GaN HEMTs Switching Transients Using Compact Model

This paper presents a methodology to model GaN power HEMT switching transients. Thus, a compact model to predict devices’ pulse switching characteristics and current collapse reliability issue has been developed. Parasitic RC subcircuits and a standard double-pulse switching tester to model intrinsic parasitic effects and to analyze power dissipation of GaN power HEMT are proposed and presented. Switching transient including gate-lag and drain-lag is predicted for ideal (without trap) and nonideal (with trap) devices. The results are validated by and compared to 2-D finite-element technology computer-aided design simulations. The original aim of this exercise is to develop a fast (near-real-time) model which can predict dynamic behavior of single and multiple power GaN HEMTs used for the switching transients of GaN power devices at circuit level.

A Built-In High Temperature Half-Bridge Power Module with Low Stray Inductance and Low Thermal Resistance for In-Wheel Motor Application

In order to integrate a five-phase inverter system into the limited space of an in-wheel motor, a high temperature low stray inductance SiC half-bridge power module with a volume of about 5 ml was designed, fabricated and tested. The stray inductance in the module was calculated by an electromagnetic simulator and confirmed by measurements to be 4.4 nH. Double-pulse switching tests were conducted at temperatures up to 200°C. Thermal resistance, including that of the substrate, was calculated to be 0.153 °C/W. Fast switching capability was accomplished with an external gate resistance of 1 Ω.

Modeling Inductive Switching Characteristics of High-Speed Buffer Layer IGBT

In this study, a physics-based compact model for high-speed buffer layer insulated gate bipolar transistor (IGBT) is proposed. The model utilizes the 1-D Fourier-based solution of ambipolar diffusion equation (ADE) implemented in MATLAB and Simulink. Based on the improved understanding on the inductive switching behavior of a high-speed buffer layer IGBT, the ADE is solved for all injection levels instead of high-level injection only as usually done. Assuming high-level injection condition in the buffer layer, the excess carrier transport, redistribution and recombination in the buffer layer are redescribed. Moreover, some physical characteristics such as the low conductivity of N-base at turn-on transient and free holes appeared in the depletion layer during turn-off process are also considered in the model. Finally, the double-pulse switching tests for a commercial field stop IGBT and a light punch-through carrier-stored trench bipolar transistor are used to validate the proposed model. The simulation results are compared with experiment results and good agreement is obtained.

27 kV, 20 A 4H-SiC n-IGBTs

In this work, we report our recently developed 27 kV, 20 A 4H-SiC n-IGBTs. Blocking voltages exceeding 24 kV were achieved by utilizing thick (210 μm and 230 μm), lightly doped N-drift layers with an appropriate edge termination. Prior to the device fabrication, an ambipolar carrier lifetime of greater than 10 μs was measured on both drift regions by the microwave photoconductivity decay (μPCD) technique. The SiC n-IGBTs exhibit an on-state voltage of 11.8 V at a forward current of 20 A and a gate bias of 20 V at 25 °C. The devices have a chip size of 0.81 cm2 and an active conducting area of 0.28 cm2. Double-pulse switching measurements carried out at up to 16 kV and 20 A demonstrate the robust operation of the device under hard-switched conditions; coupled thermal analysis indicates that the devices can operate at a forward current of up to 10 A in a hard-switched environment at a frequency of more than 3 kHz and a bus voltage of 14 kV.

High Junction Temperature and Low Parasitic Inductance Power Module Technology for Compact Power Conversion Systems

Advanced power module technology capable of taking advantage of the superior features of next-generation power devices, such as those fabricated with SiC and GaN, must be developed to create much more compact and cost-effective power conversion systems. New power modules based on such technology are especially required to allow fast switching of power devices in the extended junction temperature range. This paper describes the major technical challenges involved in sufficiently improving the thermal stress reliability of the critical package systems in SiC power modules and in markedly reducing internal parasitic inductance. Thermal stress reliabilities of the die attachment system, wire bonding system, and encapsulant system are successfully improved, all of which are shown to be able to achieve common life targets: 1) 3000 h for a storage test at 250 °C and 2) 3000 cycles for thermal cycling between −40 °C and 250 °C. A novel phase-leg power module capable of substantially reducing the loop inductance along the principal current tracks is proposed and fabricated by applying SiC-JFETs, SiC-Schottky barrier diodes, and the abovementioned reliable thermal stress package systems. Double pulse switching testing of the module reveals smaller drain-source voltage spikes and ringing even in turn-ON and turn-OFF transients at very high slew rates of current and voltage. Finally, a 0.34 L forced-air-cooled dc 600 V input ac 50 Hz 400 V 25 kW output three-phase SiC inverter is fabricated using three-phase leg modules and its operation is demonstrated at high-power levels.

Physically based 2D compact model for power bipolar devices

AbstractThe two‐dimensional (2D) physical compact model for advanced power bipolar devices such as injection enhanced gate transistor (IEGT) or Trench IGBT is presented in this paper. In order to model the complex 2D nature of these devices the ambipolar diffusion equation has been solved simultaneously for different boundary conditions associated with different areas of the device. The IEGT compact model has been incorporated into the SABER simulator and tested in standard double‐pulse switching test circuit. The compact model has been established to model a 4500V‐1500A flat pack TOSHIBA IEGT. Copyright © 2004 John Wiley &amp; Sons, Ltd.

A 2D physically based compact model for advanced power bipolar devices

A two-dimensional (2D) physical compact model for advanced power bipolar devices such as Injection Enhanced Gate Transistor (IEGT) or Trench IGBT is presented in this paper. In order to model the complex 2D nature of these devices, the ambipolar diffusion equation has been solved simultaneously for different boundary conditions associated with different areas of the device. The IEGT compact model has been incorporated into the SABER simulator and tested in standard double-pulse switching test circuit. The compact model has been established to model a 4500V–1500 A flat pack TOSHIBA IEGT.

Threshold switching polycrystalline NbO2: Decay and recovery of the on state at room and low temperatures and its relationship to trapping centers

Double pulse switching experiments, performed on polycrystalline NbO2 at 300 and 15 K, reveal properties strongly associated with electronic, nonthermal, threshold switching. The data indicate a trapped carrier lifetime of 200 ns, agreeing with our previous measurements on polycrystalline NbO2 devices (data that had been obtained by a different method). The study also shows the functional increase of on-state lifetime with increasing overvoltage and the effect of overvoltage on the on-state I-V characteristics during fast polarity reversal. These results, coupled to previous work, are explicable in terms of a trap-limited transition to a metal-like state induced by a critical electric field and carrier concentration.