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news digest ♦ Power Electronics


applications in the alternative energy, industrial and consumer markets. The firms say the dramatic reduction in form factor and figures-of- merit put this 1200V MOSFET device in a class of its own.


Table 1 : Comparison of Cree SiC MOSFET, the UniSiC Stack-Cascode MOSFET and a projected 1200V silicon superjunction device


Figure 1: Comparison of Die Sizes


Figure 1 shows the die sizes of a 1200V IGBT with co-packaged diode, a 1200V competitor SiC MOSFET and the AOS UniSiC stack- cascode device. The small die size shows the tremendous potential this device creates for future miniaturisation of power circuits given how much it cuts conduction and switching losses.


The UniSiC MOSFET provides very low Rdson and gate charge Qg, an excellent body diode with virtually no stored charge and a low diode forward voltage drop. The device can be used in applications used by conventional MOSFETs or IGBTs with standard gate drives. It can be switched over a wide speed range – as fast as a superjunction MOSFET, or as slow as an IGBT.


Alpha and Omega says the device has far superior characteristics compared to existing IGBTs, silicon power MOSFETs and the best competitive SiC 1200V MOSFET as shown in the table below.


The UniSiC device is formed by stacking a specially designed low voltage silicon MOSFET over a normally-on SiC JFET. The SiC JFET is provided by SemiSouth, one of the leading suppliers of SiC JFET technology.


The low voltage MOSFET is specially engineered to allow optimal operation of the composite device with clean switching, low Rdson, gate charge and superb diode characteristics. It is intended to provide great ease of use, working with standard drive circuitry, and drastically improving circuit efficiencies over the whole range of load current.


“Using the superb characteristics of SiC JFETs for high voltage applications, and solving the switching problems that have plagued cascode devices in the past, AOS is in a position to offer the power electronics community a dream switch,” said Anup Bhalla, Vice President of High-Voltage Discretes at AOS. “The devices can be used like conventional discrete IGBTs and FETs using the same gate drives, allowing the user to realise huge efficiency gains without too much re-engineering.”


“We are very pleased with the introduction of this new high voltage technology, which, in partnership with SemiSouth laboratories, allows AOS to bring a truly revolutionary device to the


204 www.compoundsemiconductor.net January / February 2012


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