Operation and Performance of state-of-the-art High Temperature SiC Switches

This paper outlines recent developments in two dominant classes of Silicon Carbide based switches – the Super Junction Transistor (SJT) for 1.2kV-6.5kV pulse width modulated switching; and Thyristors for >6.5kV cycloconverter and pulsed power operation. The high-temperature (> 200 °C) blocking voltage, on-state and switching performance of recently fabricated 1200 V-class, 4H-SiC Super Junction Transistors (SJT) are presented. The SiC SJT developed by GeneSiC is a Normally-OFF, Gate oxide-free transistor, which can be operated in a Gate-voltage or Gate-current control mode. Unlike competing SiC transistor technologies, the Super Junction Transistor is designed to successfully exploit many superior properties of 4H-SiC resulting in operating temperatures > 250 °C, high DC figure of merit (V B 2 /r on,sp), and ultra-fast switching transients. The SJT avoids the gate-oxide reliability issues associated with MOSFETs, especially at high temperatures and yet provides superior on-state characteristics over normally-ON SiC JFETs, especially at temperatures in excess of 150 °C. In this work, SJTs with chip areas of 4 mm 2 and 16 mm 2 were fabricated. Nearly temperature independent Drain-Source blocking voltages as high as 1400 V and Drain-Gate blocking voltages as high as 1650 V were measured on the fabricated SJTs up to temperatures as high as 250 °C. A modest increase in the device on-resistance from 5.8 mΩ-cm 2 at 25 °C to 9.5 mΩ-cm 2 at 200 °C was recorded. For a 4 mm 2 SJT, a Drain current of 9.8 A required minimum Gate input currents of 125 mA and 200 mA at 25 °C and 175 °C, respectively. The SJT provides a desirable normally-OFF circuit operation, with a + 2.65 V Gate threshold voltage at 25 °C, which decreases to + 2.3 V at 200 °C. Detailed results from high-temperature electrical characterization of the SJTs including switching performance after packaging and demonstration of an inductively loaded chopper circuit with SiC SJTs will be presented. In addition to unipolar devices like SJTs, there is a strong interest for the development of high voltage (>6.5kV) power Silicon Carbide (SiC) based Gate Turn Off (GTO) Thyristors for various power conditions applications working at at high temperature. Experimental studies are presented on parameters of interest towards high temperature switching operation, including rise time, delay time, turn-off gain and turn-off time. Large area (4.2x4.2 mm and 8.8x8.8 mm) >8 kV SiC GTOs were designed, fabricated and characterized. The GTOs fabricated in this work have a 5x10 …