Materials Science Forum Online: 213-1-25 ISSN: 1662-9752, Vols. 74-742, pp 97-973 doi:1.428/www.scientific.net/msf.74-742.97 213 Trans Tech Publications, Switzerland 1 V, 3.3 m SiC bipolar junction transistor power modules M. Domeij 1, A. Konstantinov 1, B. Buono 1, M. Bast 2, R. Eisele 2, L. Wang 3, A. Magnusson 4 1 Fairchild Semiconductor, Isafjordsgatan 32C, 1644 Kista, Sweden 2 University of Applied Sciences Kiel, Grenzstrasse 5, D-24149 Kiel, Germany 3 Lund University, IEA, 22 Lund, Sweden 4 QRTECH AB, Mejerigatan 1, 41276 Gothenburg, Sweden a martin.domeij@fairchildsemi.com, b email, c email Keywords: Power module, inverter, bipolar junction transistor Abstract. Epoxy moulded power modules with a small footprint of 4 mm x 55 mm were fabricated with two switches, each consisting of six parallel 1 V A rated BJTs and Schottky diodes. The SiC-based power modules have very low on-resistance of 3.3 m and a current gain of 8, both at room temperature. An inverter with specially designed drive circuits was constructed using the power modules and an efficiency of 98.5 % was shown for an output power of 12 kw. Introduction Compact power modules with low power losses are important for inverters in hybrid and fully electric vehicles. The low power losses of SiC power devices enables higher current ratings per die area and a SiC-based power module can therefore have a higher current rating compared to a Sibased power module with the same footprint. In this work we present power modules based on 1 V rated SiC bipolar junction transistors (BJTs). The epoxy moulded power modules are designed for high use in inverters with high power levels above kw. Large area 1 V SiC bipolar junction transistors (BJTs) with low on-resistance and fast switching characteristics [1] were used to fabricate power modules with 1 V and A capability. An inverter was constructed using the power modules and the efficiency was measured for output powers up to 12 kw. Fabrication of SiC BJTs Vertical NPN SiC BJTs with a schematic cross-section shown in Fig. 1 were fabricated from mm diameter low-resistive n-type doped wafers of the 4H-SiC polytype. The device process, which is described in more detail in [1], is based on an epitaxially grown NPN structure where dry etching is used to form emitter fingers and to terminate the base-collector junction. The BJT chip has a twolayer metallization system with many emitter fingers under isolation oxide and thick Al pads for wire bonding. The dies which were used in the power modules are designed 1 V rating and operation at A. Design and fabrication of power modules The power module, which is shown in Fig. 2, is epoxy moulded and has a footprint of 4 mm x 55 mm. The circuit and pin-out of the module was designed to be used in a three-phase inverter with electrically separated outputs for the anti-parallel diodes. The circuit and geometric layout of the power module is shown in Fig. 2. Each switch in the power module has six parallel A BJTs and six antiparallel A SiC Schottky barrier diodes (SBDs). The diodes are of the type CPW2-1S and were purchased from Cree. 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, www.ttp.net. (ID: 13.23.136.75, Pennsylvania State University, University Park, USA-8/5/16,23:53:34)
Materials Science Forum Vols. 74-742 971 Emitter contact N Emitter P Base Surface passivation Base contact JTE implant N Collector Base implant N + substrate Collector contact Fig. 1 Schematic cross-section of the BJT active area and junction termination Fig. 2 Circuit diagram, geometric layout and picture of epoxy moulded SiC BJT power module. Ag sinter under high pressure at C was used as die attach to obtain state-of-the-art power cycling capability for automotive applications. Electrical characteristics of the power module The BJT switches of the power module were measured using a Tektronix 371A curve tracer. Fig. 3 shows measured I C -V CE characteristics which show a very low on-resistance of only 3.3 m at room temperature and 4.8 m at. The common emitter current gain at collector currents around - A is 8 at room temperature and 48 at. Fig. 4 displays the measured -V BE characteristics at and at. The steep I-V curve indicates a low series resistance for the base-emitter diode (V BE =3.1-3.2 V gives =3 A) and this is important to achieve high dynamic base currents which are important for fast switching of the power module. Fig. 5 shows the I-V characteristics of one Schottky diode (consisting of six parallel A dies) of the power module. The forward voltage drop V F of the Schottky diode at room temperature and A is more than two times higher than for the BJT switch. This higher V F is the reason why the A Schottky diode dies are significantly larger than the SiC BJT dies, as can be seen in Fig. 2. Inverter fabrication An inverter was fabricated using three power modules. Fig. 6 displays the inverter where the power modules are mounted under the printed circuit board on top of a water cooler. The printed circuit board contains DC link capacitors and drive circuits for the SiC BJTs with current transformers which are used to generate power to the drive circuit from the main current. This concept to achieve energy efficient drive circuits has been described in more detail in [2].
Base current (A) Diode current (A) Collector current (A) Collector current (A) 972 Silicon Carbide and Related Materials 212 =8 A =6 A =4 A =8 A =6 A =2 A =4 A =2 A.5 1 1.5 2 Collector emitter voltage V (V) CE.5 1 1.5 2 Collector emitter voltage V (V) CE Fig. 3 I C -V CE characteristics of one BJT switch in the power module measured using a Tektronix 371A curve tracer at (left) and (right) 3 25 2 15 1 5 1 2 3 4 5 Base emitter voltage V BE (V) Fig. 4 -V BE characteristics of one BJT switch.5 1 1.5 2 2.5 3 3.5 4 Diode voltage V F (V) Fig. 5 I-V characteristics of one Schottky diode Inverter measurements The inverter was operated with a DC link voltage of 33 V and a switching frequency of 1 khz and using a 4 kw induction machine as load for the inverter. The output power was measured using a Yokogawa WT18 instrument. Fig. 7 shows measured power efficiency vs. output power. A maximum efficiency of 98.5 % was measured at 12 kw output power. The inverter was also tested with other load conditions up to 4 kw with a maintained level of efficiency.
Materials Science Forum Vols. 74-742 973 Fig. 6 Picture of the inverter with the SiC BJT power modules mounted under the PCB 1.98.96.94.92.9.88.86.84.82 1181 227 311 4414 5198 6 746 8136 95 18 1111 12155 Output power (W) with only active power with complex power Fig. 7 Measured output efficiency of the inverter Summary Epoxy moulded power modules for 1 V and A with small footprint were fabricated using 1 V SiC BJTs and Schottky diodes. The BJT switches of the power modules have very low onresistance of 3.3 mω and the current gain is 8 at room temperature. Three power modules were deployed to build an inverter and an efficiency of 98.5 % was measured for an output power of 12 kw. Acknowledgements The Swedish Energy Agency and Vinnova are acknowledged for funding the presented work. References [1] M. Domeij et. al., Large area 1 V SiC BJTs with > and ON <3 m cm 2, Materials Science Forum, Vols. 717-72, 212, pp. 1123-1126 [2] L. Wang and H. Baengtsson, How to Control SiC BJT with High, 212 7th International Conference on Integrated Power Electronics Systems (CIPS), 211, p. 4
Silicon Carbide and Related Materials 212 1.428/www.scientific.net/MSF.74-742 1 V, 3.3 mω SiC Bipolar Junction Transistor Power Modules 1.428/www.scientific.net/MSF.74-742.97