SiC Bipolar Power Transistors - Design and Technology Issues for Ultimate Performance
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SiC Bipolar Power Transistors - Design and Technology Issues for Ultimate Performance Mikael Östling1, Martin Domeij1,2, Carina Zaring2, Andreij Konstantinov2, Reza Ghandi1, Benedetto Buono1, Anders Hallen1, Carl Mikael Zetterling1 1 School of ICT, KTH Royal Institute of Technology, E229, SE-16440 Kista, Sweden 2 TranSiC AB, Electrum 207, SE-16440 Kista, Sweden ABSTRACT Silicon carbide (SiC) semiconductor devices for high power are becoming more mature and are now commercially available as discrete devices. Schottky diodes have been on the market since a few years but also bipolar junction transistors (BJTs), JFETs and MOSFETs are now reaching the market. The interest is rapidly growing for these devices in high power and high temperature applications. The BJTs have low conduction losses, fast switching capability, operate in normally-off mode, have high radiation hardness, and can handle high power density. This paper will review the current state of the art in active switching device performance with special emphasis on BJTs. Device performance has been demonstrated over a wide temperature interval. A very important feature in high power switch applications is the low on-resistance of a device. Better material quality and epi processes suppress the amount of basal plane dislocations to avoid stacking fault formation generated during high current injection. This has long been a concern for bipolar SiC devices but several research reports and long term reliability measurements of pnjunctions show that the bipolar degradation problem can be solved by a fine-tuned epitaxial technique. A discussion on surface passivation control is included. Finally, an example of a power switching module is given also demonstrating the excellent paralleling capability of BJTs. INTRODUCTION Silicon carbide device technology has matured greatly over the past 20 years when Cree Inc. started pioneering this technology. A great number of scientific device technology papers have been published and comprehensive text books or book chapters have been written. In [1] a full technology review of SiC process technology is given and in [2] a device review of rf and power devices can be found. The device technology is greatly dependent on substrate and epitaxial material quality and the number of detrimental defects. Over the years this has been one of the limiting factors for a commercial success of the high voltage and high current device market. Today the materials quality of 4H-SiC wafers and epitaxy is at such a high quality that many companies are offering commercial SiC wafers and epitaxy on 4H-SiC with wafer diameter 100 mm. The main SiC power device products are still rectifiers based on Schottky or junction barrier diodes. A few companies are offering active power devices switches as engineering samples based on MOSFETs, JFETs and BJTs. The application areas of the rectifying devices are as free-wheeling diodes in various DC-DC converters
and drives. The main advantage is the lack of reverse recovery and subsequent low swi
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