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SiC and silicon combined produce ultra-high performance MOSFETs

The UniSiC 1200V device is formed by stacking a specially designed low voltage silicon MOSFET above a normally-on silicon carbide JFET

 Alpha and Omega Semiconductor (AOS) and SemiSouth Labs have jointly demonstrated UniSiC, a 1200V, 90 mΩ MOSFET in a TO262 package.

The device is designed to meet the growing need for energy efficient switching devices for high performance power conversion 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.

 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.

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

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 world of power conversion," commented Mike Chang, President and CEO of AOS. "Products like these will set AOS apart as the high voltage supplier of choice, facilitating our twin goals of product diversification and rapid growth."

"SemiSouth is excited to see the performance achieved by AOS using our SiC power JFET die. First released in 2008, we have seen our JFET products gain rapid adoption in the market, and this first-ever stack-cascode demonstration from AOS really takes the performance and ease of use to the next level. We are pleased to have this relationship with AOS as a valued customer," said Jeff Casady, President and CTO of SemiSouth Laboratories.
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