On the second day of PCIM Europe 2008, SiC took center stage with two companies demonstrating products and more companies presenting papers during the afternoon technical sessions. TranSiC AB was showing the first completely SiC half-bridge module, Cree was demonstrating its latest advances in SiC diodes. Authors from Mitsubishi Electronics, Siemens, and Infineon Technologies presented papers on developments in SiC technology.
TranSiC won the race to develop the first completely SiC power module and presented a 1,200V, 6A half-bridge module with SiC switches as well as SiC diodes. The chips are rated for operation up to 225°C. Using the company’s first-generation BitSiC™ npn bipolar junction transistors, the modules provide a lower V-sat compared with silicon IGBTs. The storage time delay is specified as "negligible." Production is scheduled for fourth quarter of this year or early 2009.
Over a few rows in the exhibit hall, Cree was demonstrating the selection criteria for SiC Schottky diodes in continuous conduction mode power factor (CCM PFC) applications. According to Cree, "SiC is fundamentally more reliable than silicon." The company claims that SiC diodes have achieved production volumes that make them cost-effective in converters as small as 300W.
Selection of a SiC Schottky boost diode is different from its counter part Si ultra-fast soft-recovery diode which is normally oversized due to the excessive reverse recovery energy loss. Cree has developed a Mathdcad file to provide power supply designers a detailed explanation and calculation on how to select appropriate SiC Schottkys for different power rated CCM PFC boost converters.
Matthias Neumeister, with Siemens AG, presented an "Investigation of Surge Current Capability of SiC MPS (Merged-Pin Schottky) Diodes," he had prepared with co-authors representing Chemnitz University of Technology, Chemnitz, Germany, and Infineon, AG. The study found that under surge current conditions the diodes have to withstand high temperatures. The MPS diodes produced by Infineon were destroyed by the temperature limitation of the aluminum metallization (melting point). To improve the ruggedness of such diodes against surge current, a thicker metallization and/or a higher number of bond wires will be useful.
Next, Katsumi Satoh and Gourab Majumdar with the Power Device Works of Mitsubishi Electric in Japan presented, "1200V SiC SBD chip evaluation at ultra high current density." The electrical characteristics and the reliability of SiC SBD were evaluated under the condition of ultrahigh current density, showing superior static and reverse recovery properties as compared with Si diode.
In addition, the authors found that the power loss in the module of IGBT-SiC diode combination under the inverter operation is significantly lower than that generated using Si pin diode. They concluded that the results suggest that the enhanced features of SiC SBD with small chip size is capable of allowing higher switching frequencies and improving IGBT reliability in the IGBT power semiconductor systems, as well as reducing the cost in the application of SiC devices.
