The driving force for the use of SiC in high voltage switches is the potential benefit from considerably reduced static losses and reduced number of devices in serial connection compared with Si-IGBTs. As an appropriate design for high voltage applications we choose a bipolar normally-on JFET structure (so called BIFET, Bipolar Injection FET), which promises additional advantages in a serial connection in a “supercascode” circuit. Simulations of such BIFETs for an aimed blocking voltage of 4.5 kV and minority carrier lifetimes between 0.5 μs and 5 μs demonstrate a reduction of the static loss by more than 25 % compared to the unipolar JFET for the same blocking voltage. Experimentally achieved forward characteristics of BIFETs show a forward voltage of less than 6 V at 70 A/cm2 and Tj = 150°C. The breakdown of these first BIFETs exhibits an avalanche-like behaviour at 2.5 kV , i.e. approximately 70 % of the planar breakdown. The dynamic performance was investigated in a cascode configuration in a chopper circuit with a clamped inductive load. Introduction The demand for devices able to block several kilovolts is still increasing. In power distribution systems, e.g., today many single switches are connected in series in order to obtain high blocking voltages. Another trend is the fact that the users prefer IGBT like switches with powerless voltage control despite their deficiencies of lower blocking voltage compared with thyristors or GTO’s. The requirements typical for these applications are at least several 100 Amps, so that parallel connection of switches becomes mandatory. The driving force for the use of SiC in high voltage switches is the potential benefit from considerably reduced static losses and reduced number of devices in the serial connection. Above 4 kV the power loss should be less in bipolar than in unipolar SiC switches because of the bipolar conductivity modulation. The task of developing bipolar switches, however is not easy to solve since for bipolar SiC switches physical parameters like minority carrier lifetime and its adjustment are a challenge of design and technology. A simple transfer from experience with silicon won’t work. In silicon, state of the art bipolar switches like IGBTs utilise a p-type substrate. However, using the available p-type SiC substrates, all advantages from conductivity modulation gained from bipolar effects are overcompensated by the high resistivity of the substrate (s. Fig.1: VFsubstrate = 5,25 V). Using n-type substrates will overcome this situation, but in consequence the drift zone needs to be p-type, where the carrier transport properties and defect density are today less analysed compared with n type layers. Therefore one has to look for an high emitter efficiency and a suited lifetime management in order to efficiently modulate the drift zone conductivity . Materials Science Forum Online: 2004-06-15 ISSN: 1662-9752, Vols. 457-460, pp 1245-1248 doi:10.4028/www.scientific.net/MSF.457-460.1245 © 2004 Trans Tech Publications Ltd, Switzerland All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications Ltd, www.scientific.net. (Semanticscholar.org-11/03/20,15:23:55)