5kV/200ns Pulsed Power Switch based on a SiC-JFET Super Cascode

Abstract

In many pulse power applications there is a trend to modulators based on semiconductor technology. For these modulators high voltage and high current semiconductor switches are required in order to achieve a high pulsed power. Therefore, often high power IGBT modules or IGCT devices are used. Since these devices are based on bipolar technology the switching speed is limited and the switching losses are higher. In contrast to bipolar devices unipolar ones (e.g. SiC JFETs) basically offer a better switching performance. Moreover, these devices enable high blocking voltages in case large bandgap materials as SiC are used. At the moment SiC JFET devices with a blocking voltage of 1.5 kV per JFET are available. Alternatively, the operating voltage could be increased by connecting N JFETs and a low voltage MOSFET in series resulting in a Super Cascode switch with a blocking voltage N-times higher than the blocking voltage of a single JFET. In order to evaluate the achievable switching speed of the Super Cascode and its applicability in solid state modulators, the performance of such a SiC switch is examined in this paper. Furthermore, the performance of the Super Cascode is compared with 4.5 kV IGBTs made by Powerex, which are mounted in a special low inductive housing for minimising the rise and fall times.