Design, characterization, modeling and analysis of high voltage silicon carbide power devices

This research focuses on the design, characterization, modeling and analysis of high voltage Silicon Carbide (SiC) metal-oxide-semiconductor field effect transistors (MOSFET), insulated gate bipolar transistors (IGBT) and emitter turn-off thyristors (ETO) to satisfy the stringent requirements of advanced power electronic systems. The loss information, frequency capability and switching ruggedness of these 10-kV SiC power devices are studied extensively in order to provide their application prospects in solid-state transformers (SST).Among 10-kV SiC power devices, SiC MOSFETs are of the greatest interest due to their lower specific on-resistance compared to silicon MOSFETs, and their inherently fast switching speed due to their majority carrier conduction mechanism. Therefore, 10-kV SiC MOSFETs are studied first in this dissertation. The characterization, modeling and analysis of 10-kV SiC MOSFETs were investigated extensively. The low losses and high switching frequency of 10-kV SiC MOSFETs were demonstrated in characterization study and a 4-kV 4 kW boost converter.The on-resistance of SiC MOSFETs increases rapidly with increased junction temperature and blocking voltage. This makes their conduction losses possibly unacceptable for applications where high DC supply voltages (&ge10-kV) and high temperature operation are used. This warrants the development of SiC bipolar devices (IGBTs and thyristors) to achieve smaller conduction losses due to the conductivity modulation of their thick drift layers, especially at elevated temperatures. Therefore, design, characterization and optimization of 10-kV SiC IGBT and ETO were discussed.A 4H-SiC p-channel IGBT with improved conduction characteristics was developed and characterized experimentally as well as analyzed theoretically by numerical simulations. The device exhibited a differential on-resistance of 26 mOcm2 at a collector current density of 100 A/cm 2 at room temperature. The SiC IGBT showed a turn-off time of 1 mus in an inductive load circuit with a DC-link voltage of 4-kV and a collector current density of 150 A/cm2 at room temperature. The possible approaches to achieve a better performance trade-off between forward voltage drop and turn-off energy loss were investigated using numerical simulations.In order to maintain the superior conduction characteristics of SiC GTO and improve its dynamic characteristics, high voltage SiC ETO was developed. The experimental demonstration of the world's first 4.5-kV SiC ETO prototype shows a four time higher switching frequency and a much higher power density than its silicon counterparts. Numerical simulations and theoretical analysis have been carried out to show the potentially improved performance of 10-kV SiC ETO. The results show that 10-kV SiC n-type ETO has much better performance trade-off than that of the p-type ETO due to a smaller current gain of the lower bipolar transistor. Further improvement of SiC ETO can be done by developing SiC n-type GTO.The characteristics and losses of 10-kV SiC MOSFET, p-IGBT and ETO were compared using the experimental measurement results, PSPICE simulations and numerical simulations. Using the extracted loss information of SiC power devices and method of loss calculation in SST, the frequency capability of these 10-kV SiC power devices in a 20 kVA SST was investigated and compared in the same power loss density of 300 W/cm2 and junction temperature of 125°C. The comparison shows that 10-kV SiC MOSFET has the highest switching frequency amongst 10-kV SiC power devices in the AC/DC rectifier stage and DC/DC converter stage of SST when their active chip size is more than 5 mm 2. Using 10-kV SiC MOSFET, a switching frequency of more than 20 kHz in the SST can be achieved by choosing an optimum chip size of the SiC MOSFET, which can greatly reduce the size and weight of the SST.