SiC FET Research Articles

Solid-State Contactor With Si Thyristor and SiC FET Hybrid Module for High-Efficiency Motor Control

Solid-State Contactor With Si Thyristor and SiC FET Hybrid Module for High-Efficiency Motor Control

Design of a simple and low-cost solid-state ultra-fast high-voltage switch.

Ultra-fast high-voltage switches (UFHVSs) are a core component of time-of-flight mass spectrometers for realizing high accuracy ion acceleration, deceleration, and temporal focusing. The desirable features of high performance UFHVSs include a large range of adjustability of pulse width, a high maximum output amplitude, and minute rising and falling times. Besides the simplicity of the driver circuit, the total cost of the whole device is also critical to its practical applications. In this work, we present a low-cost and easy-fabrication 5000V bipolar solid-state UFHVS for a high-resolution mass spectrometer. A double-pulse transformer isolates the circuit's high- and low-voltage sides and synchronously drives series-connected cascode SiC FETs to form its push-pull topology. This scheme allows transmitting drive signals with long widths but without the magnetic saturation of the transformer. Testing results show that output pulses reach a maximum voltage of 5000V and a width of 150 µs, with rising and falling times of 8.5 and 18.3ns, respectively. More importantly, they have nearly no voltage decay.

A Scalable Enhancement-Mode Junctionless SiC FET with Embedded P+ Pockets in the Oxide Layer for High-Temperature Applications

A Scalable Enhancement-Mode Junctionless SiC FET with Embedded P+ Pockets in the Oxide Layer for High-Temperature Applications

철도 차량용 배터리 충전을 위한 LLC 공진형 컨버터의 SiC FET와 Si FET의 병렬 연결에 관한 연구

Wide-Band-Gap (WBG) switching semiconductor has been improved for higher efficiency and higher power density. Especially, SiC FET is the most attractive switching semiconductor for mid-voltage and high power applications, such as, railway transportation. Its desired features for high power converter are low on-state resistance, thermal stability, no reverse recovery, high switching speed, and so on. However, faster switching speed derives higher dv/dt of drain-source voltage, then this result in larger voltage ringing and worse switching noise. In this paper, parallel configuration of SiC FET and Si FET is proposed to suppress voltage ringing and minimize switching noise. Based on the characteristics of output capacitances of both SiC and Si FETs, the switching performances of single SiC FET and parallel connection of SiC/Si FETs are compared of voltage ringing and switching noise in LLC resonant converter for 10kW battery charging module of railway transportation.

Enabling 99.3% Efficiency in 3.6 kW Totem-Pole PFC Using New 750 V Gen 4 SiC FETs

This article explains how the breakthrough performance of UnitedSiC 750 V Gen 4 SiC FETs enables a simple design of highly efficient totem-pole PFC. Efficiency measurements on the developed unit will demonstrate a 99.3% efficiency rating. Insight into the losses is provided by the new UnitedSiC FET-Jet calculator on-line tool, which are shown to match the actual measurements quite well. Finally, it discusses how the high efficiency of SiC FETs allows further BOM cost reduction for totem-pole PFC.

High energy-efficient electrical drive with multilevel inverter and widebandgap power semiconductors

Multilevel inverters are an alternative for electrical drives with DC link voltage between 560 and 750 V. In this voltage range new wide-bandgap power switches (SiC MOSFET, GaN FET) are available. The paper analyses three-, four-, five- and seven-level inverters. A simulation model of the drive system, including the 11 kW induction motor and motor filter is developed. By replacing IGBTs with SiC FETs, the twolevel inverter achieved a loss reduction of 59 % at 25 °C and 150 °C at nominal motor operation point. By using the five-level inverter with GaN FETs, a further loss reduction of 9 % only at low junction temperature is possible. With a higher number of inverter levels, the size of the motor filter can be reduced. With five inverter levels and 40 kHz switching frequency volume and weight can be reduced by 86 % and 78 % respectively. The overall efficiency of the drive system achieves 98.5 % at 25 °C and 98.1 % at 150 °C. Compared to the state of the art (two-level with IGBTs with 5 kHz), this is an improvement of 2.1 % at 25 °C and 2.7 % at 150 °C.

Variable-Frequency Critical Soft-Switching of Wide-Bandgap Devices for Efficient High-Frequency Nonisolated DC-DC Converters

This paper derives a variable-frequency critical soft-switching control method for nonisolated DC/DC converters using wide-bandgap devices. The critical soft switching control technique under maximum frequency trajectory is introduced to maintain zero voltage switching over a wide range of modulation ratios according to the load variation. The concept prevents turn-on losses that are typically much larger than the turn-off losses in SiC and GaN FETs and the latter can be further reduced by adding external drain-source capacitors. We have derived the boundary conditions for critical soft switching operation. For the reduction of inductor value and volume, a maximum available switching frequency is applied to the converter within the constraints of device requirement and soft switching boundary conditions. We demonstrate experimentally that the proposed concept reduces the power losses in the wide-bandgap devices by a factor of approximately 3, enables an increase of the switching frequency by a factor of about 5, and a decrease of the main inductance by a factor of about 10. Then variable frequency critical soft switching control method is proposed with the constraints to maintain the maximum frequency within soft switching operation. Since our test bench uses off-the-shelf inductors, the inductors are subject to significant high frequency losses. Despite this, the converter efficiency increases by 1%.

Robustness and reliability review of Si and SiC FET devices for more-electric-aircraft applications

Increased electrification of traditionally hydraulic and pneumatic functions on aircrafts has put power electronics at the heart of modern aviation. Aircraft electrical power systems have traditionally operated at 115 V AC and 28 V DC with a constant speed generator and transformer rectifier units converting jet engine power into electrical power. However, due to the increasing trend towards the More Electric Aircraft (MEA), 270 V DC systems are likely in the future. This calls into question, the power semiconductor device technology that enables the on-board power converters needed for electro-mechanical actuation as well as solid-state circuit breakers for system protection. Silicon IGBTs have been the work-horse of power electronics, but as switching speeds increase due to the need for high frequency operation, the bipolar nature of IGBT tail currents become a limiting factor for improved energy conversion efficiency. A number of unipolar FET technologies, including SiC trench MOSFETs, SiC planar MOSFETs, silicon super-junction MOSFETs and SiC JFETs in cascode with a low voltage Si MOSFET, have become commercialized at around 650 V. However, reliability and robustness, especially against single event burn-out and/or single event gate rupture is critical. This paper experimentally investigates the performance of the listed FET devices under Unclamped Inductive Switching and Bias Temperature Instability/gate oxide stress tests.

Compact Modeling of SiC and GaN Junction FETs at High Temperature

High temperatures and other harsh environments are domains of predilection for Junction FETs, particularly when wide band-gap semiconductors such as SiC or GaN are used. The present work describes the new compact model of double gate (DG) JFETs which is compared to TCAD simulations of SiC and GaN JFETs over a wide temperature range up to 500oC. The compact model is shown to be predictive of device behavior, for static (current-voltage) as well as dynamic (capacitance-voltage) behavior of long-channel DG JFETs.

R DS(on) vs. inductance: comparison of SiC MOSFETs in 7pin D2Pak and 4pin TO‐247 and their benefits for high‐power MHz inverters

In this work, the authors present their investigations of the benefits of combining the latest silicon carbide MOSFETs with novel packages for electronic ballasts of inductively coupled plasmas. Such plasmas require MHz inverters with output powers above 2 kW. Additionally, for a breakthrough of the technology efficiencies >90% have to be realised. It has been shown that a combination is achievable with SiC FETs. Nevertheless, even though the transistors have undergone significant development in recent years, one limiting factor has mostly remained untouched. The common TO-247 package does not fit to the requirements of a fast switching application. Within the latest launch of the new generations of SiC MOSFETs, some are available in novel packages with kelvin source connection, like 4pin TO-247 and 7pin D2Pak. The authors compare three versions of the latest generation in a resonant full-bridge inverter and in application-oriented test. Thereby, the 7pin D2Pak and one of the 4pin TO-247 transistors were 65 mΩ devices and the second 4pin TO-247 FET was a 45 mΩ device. For the investigations, the authors made simulations, built three MHz inverters, and conducted measurements. Consequently, efficiencies of 93.9% could be achieved at a switching frequency of 2.5 MHz and an output power of P out =2.6 kW.

Design and Implementation of a GaN-Based, 100-kHz, 102-W/in3Single-Phase Inverter

High power density is a desirable feature of power electronics design, which prompts economic incentives for industrial applications. In this paper, a gallium nitride (GaN)-based 2-kVA single-phase inverter design was developed for the Google Little Box Challenge, which achieves a 102-W/in $^{3}$ power density. First, the static and dynamic temperature-dependent characteristics of multiple SiC and enhancement-mode GaN FETs are investigated and compared. Based on the device testing results, several topologies of the inverter stage and different power decoupling solutions are compared with respect to the device volume, efficiency, and thermal requirements. Moreover, some design approaches for magnetic devices and the implementation of gate drives for GaN devices are discussed in this paper, which enable a compact and robust system. Finally, a dc notch filter and a hard switching full-bridge converter are combined as the proposed design for the prototype. A 2-kVA prototype is demonstrated, which meets the volume, efficiency, and thermal requirements. The performance of the prototype is verified by the experimental results.

SiC-FET Sensors for Selective and Quantitative Detection of VOCs Down to Ppb Level

With the increased interest in development of cheap, simple means for indoor air quality monitoring, and specifically in relation to certain well-known pollutant substances with adverse health effects even at very low concentrations, such as different Volatile Organic Compounds (VOCs), this contribution aims at providing an overview of the development status of the silicon carbide field effect transistor (SiC FET) based sensor platform for ppb level detection of VOCs. Optimizing the transducer design, the gas-sensitive material(s) composition, structure and processing, its mode of operation - applying temperature cycled operation in conjunction with multivariate data evaluation - and long-term performance it has been possible to demonstrate promising results regarding the sensor technology's ability to achieve both single-digit ppb sensitivity towards e.g. naphthalene as well as selective detection of individual substances in a mixture of different VOCs.

Power Loss, System Efficiency, and Leakage Current Comparison Between Si IGBT VFD and SiC FET VFD With Various Filtering Options

SiC devices are gaining acceptance in the motor drive industry. This paper compares the power loss and efficiency between two options that can be used with SiC-based variablefrequency drives (VFDs). In the first option, the SiC VFD is equipped with an output sine-wave filter with carrier frequency at 50 kHz. A $dv/dt$ filter is used for the second option with the carrier frequency reduced to 8 kHz. Both options are compared with a standard Si insulated-gate bipolar transistor (IGBT) VFD operating at a carrier frequency of 8 kHz with no output filter. The focus of this paper is to present different filtering options for SiC VFDs. The $dv/dt$ filter is designed to meet the same specification as that of the standard Si IGBT VFD with no output filter, so as to present a fair comparison between a standard Si IGBT VFD and the next-generation SiC VFD. Results using a 460-V 11-kW system show that the SiC VFD with an output sine-wave filter has a lower efficiency compared with SiC VFD with a $dv/dt$ filter. Influence of the various filtering options on leakage current in the motor drive system has also been studied, and the results are presented in this paper.

GaN FET를 적용한 인터리브 CRM PFC의 효율특성에 관한 연구

This paper presents the efficiency analysis of a critical current mode interleaved PFC rectifier, in which each of three different semiconductor switches is employed as the active switch. The Si FET, SiC FET, and GaN FET are consecutively used with the prototype PFC rectifier, and the efficiency of the PFC rectifier with each different semiconductor switch is analyzed. An equivalent circuit model of the PFC rectifier, which incorporates all the internal losses of the PFC rectifier, is developed. The rms values of the current waveforms main circuit components are calculated. By adapting the rms current waveforms to the equivalent model, all the losses are broken down and individually analyzed to assess the conduction loss, switching loss, and magnetic loss in the PFC rectifier. This study revealed that the GaN FET offers the highest overall efficiency with the least loss among the three switching devices. The GaN FET yields 96% efficiency at 90 V input and 97.6% efficiency at 240 V, under full load condition. This paper also confirmed that the efficiency of the three switching devices largely depends on the turn-on resistance and parasitic capacitance of the respective switching devices.

C-H surface diamond field effect transistors for high temperature (400 °C) and high voltage (500 V) operation

By forming a highly stable Al2O3 gate oxide on a C-H bonded channel of diamond, high-temperature, and high-voltage metal-oxide-semiconductor field-effect transistor (MOSFET) has been realized. From room temperature to 400 °C (673 K), the variation of maximum drain-current is within 30% at a given gate bias. The maximum breakdown voltage (VB) of the MOSFET without a field plate is 600 V at a gate-drain distance (LGD) of 7 μm. We fabricated some MOSFETs for which VB/LGD > 100 V/μm. These values are comparable to those of lateral SiC or GaN FETs. The Al2O3 was deposited on the C-H surface by atomic layer deposition (ALD) at 450 °C using H2O as an oxidant. The ALD at relatively high temperature results in stable p-type conduction and FET operation at 400 °C in vacuum. The drain current density and transconductance normalized by the gate width are almost constant from room temperature to 400 °C in vacuum and are about 10 times higher than those of boron-doped diamond FETs.

SiC–FET based SO2 sensor for power plant emission applications

Thermal power plants produce SO2 during combustion of fuel containing sulfur. One way to decrease the SO2 emission from power plants is to introduce a sensor as part of the control system of the desulphurization unit. In this study, SiC–FET sensors were studied as one alternative sensor to replace the expensive FTIR (Fourier Transform Infrared) instrument or the inconvenient wet chemical methods. The gas response for the SiC–FET sensors comes from the interaction between the test gas and the catalytic gate metal, which changes the electrical characteristics of the devices. The performance of the sensors depends on the ability of the test gas to be adsorbed, decomposed, and desorbed at the sensor surface. The feature of SO2, that it is difficult to desorb from the catalyst surface, makes it known as catalyst poison. It is difficult to quantify the SO2 with static operation, even at the optimum operation temperature of the sensor due to low response levels and saturation already at low concentration of SO2. The challenge of SO2 desorption can be reduced by introducing dynamic operation in a designed temperature cycle operation (TCO). The intermittent exposure to high temperature can help to desorb SO2. Simultaneously, additional features extracted from the sensor data can be used to reduce the influence of sensor drift. The TCO operation, together with pattern recognition, may also reduce the baseline and response variation due to changing concentration of background gases (4–10% O2 and 0–70% RH), and thus it may improve the overall sensor performance. In addition to the laboratory experiment, testing in the desulphurization pilot unit was performed. Desulphurization pilot unit has less controlled environment compared to the laboratory conditions. Therefore, the risk of influence from the changing concentration of background gas is higher. In this study, linear discriminant analysis (LDA) and partial least square (PLS) were employed as pattern recognition methods. It was demonstrated that using LDA quantification of SO2 into several groups of concentrations up to 2000ppm was possible. Additionally, PLS analysis indicated a good agreement between the predicted value from the model and the SO2 concentration from the reference instrument of the pilot plant.

A UNIVERSAL SOI-BASED HIGH TEMPERATURE GATE DRIVER INTEGRATED CIRCUIT FOR SiC POWER SWITCHES WITH ON-CHIP SHORT CIRCUIT PROTECTION

In recent years, increasing demand for hybrid electric vehicles (HEVs) has generated the need for reliable and low-cost high-temperature electronics which can operate at the high temperatures under the hood of these vehicles. A high-voltage and high temperature gate-driver integrated circuit for SiC FET switches with short circuit protection has been designed and implemented in a 0.8-micron silicon-on-insulator (SOI) high-voltage process. The prototype chip has been successfully tested up to 200°C ambient temperature without any heat sink or cooling mechanism. This gate-driver chip can drive SiC power FETs of the DC-DC converters in a HEV, and future chip modifications will allow it to drive the SiC power FETs of the traction drive inverter. The converter modules along with the gate-driver chip will be placed very close to the engine where the temperature can reach up to 175ΰC. Successful operation of the chip at this temperature with or without minimal heat sink and without liquid cooling will help achieve greater power-to-volume as well as power-to-weight ratios for the power electronics module.

Use of Vacuum as a Gate Dielectric: The SiC VacFET

We introduce the vacuum field-effect transistor (VacFET), the first SiC FET to use a vacuum-sealed cavity in place of the traditional, solid gate dielectric. This device architecture eliminates the need to thermally oxidize the SiC surface, a practice which has been widely reported to inhibit the performance and reliability of SiC MOSFETs. Using a combination of batch-compatible electronics and micromachining processing techniques, a polycrystalline SiC bridge is suspended above a 4H-SiC substrate, and the underlying cavity is sealed under vacuum. The fundamental studies made possible by such a device could shed much-needed light on the basic electronic properties of an inverted SiC surface. In this introductory report, we detail the analytical design and fabrication necessary to manufacture the VacFET, and we also demonstrate proof of the concept using turn-on and output characteristics of the first functional SiC device.

A Universal BCD-on-SOI Based High Temperature Short Circuit Protection for SiC Power Switches

In recent years, the rapid increase in the market for hybrid electric vehicles has generated great demand for low-cost, high-volume, high-temperature power converters that can work in harsh environment (temperature ≥ 150°C) conditions. Most of the commercially available power semiconductor devices and associated control electronics are rated for maximum of 85°C ambient temperature. Under this circumstance, wide bandgap (WBG) semiconductors have become a better alternative due to their ability to operate at much higher temperatures (≥500°C) than conventional bulk silicon based devices. As with any other power devices, SiC switches also require fault detection and protection mechanisms for their reliable application to real systems. One severe fault situation is the short circuit at the load end, which can cause very high surge currents that flow through the power switches. Quick detection and removal of the short circuit fault current by external circuitry is required to protect the power switch as well as the power converter module. This work presents a high-temperature (≥200°C), high-voltage short circuit protection (SCP) for SiC power devices. The circuit is designed using a resistor sensing method to provide protections for both “normally ON” and “normally OFF” SiC FET switches. A rail-to-rail input comparator is employed to ensure that the circuit operates under different power supply levels. The prototype circuit is implemented using a 0.8-micron, 2-poly, and 3-metal BCD-on-SOI process. The die size for the protection circuit is 0.52 mm2 (845 μm × 612 μm). The circuit has been successfully tested up to 200°C ambient temperature under power supplies ranging from 10 V to 30 V without any heat sink or cooling mechanism.

Improved Efficiency in Power Factor Correction Circuits with a pn-Gated SiC FET

The purpose of this paper is to present an all-SiC switched AC-DC converter using active power factor correction. The typical boost-converter approach is employed using continuous conduction mode. A SiC Schottky barrier diode performs the free-wheeling diode function, and a 600 V, 0.12 % SiC vertical junction field effect transistor performs the switching function under the control of a Fairchild ML4821 integrated circuit. The converter is operable off-line over the full universal voltage range (85-260 VAC), but it was optimized for a 400-600 W application operating at 208 VAC. Results are presented that demonstrate extremely high efficiency at a switching frequency of 500 kHz, the highest operating frequency of the ML4821.