Power trends: Silicon carbide makes the drop

March 09, 2018 // By Nick Flaherty
Dr Chris Dries and his partners bought United SiC eight years ago to develop a new kind of silicon carbide device that is now coming to market.

Based on technology developed at Rutgers University in the US, the new devices are drop in replacements for existing silicon MOSFETs, offering more efficiency and power capability while using the same gate drivers.

This required a whole new approach, and he is realistic about the time it takes for development. “It’s generally in 15 to 20 years for a new material system to demonstrate efficacy to really mainstream,” said Dries (above).  “Diodes were important in the 2000s but the SiC transistor technologies hadn’t taken off and we wanted to do it in a very different way. The first thing we did was go fabless, compared to Cree, Infineon and Rohm.”

“That was particularly effective back then that the wafer diameters matched legacy silicon fabs that were transitioning out, so we started on a 4in GaAs and InP line then onto an automotive qualified 6in line and we have brought both of those up at a time when the demand is surging and what’s driving that is automotive. So much of our business is growing in Asia while i

n the US people are slower to latch onto it. Europe designs in SiC in a big way.”

“To be successful in a fragmented market like this we have to do something unique,” he said. “What we make is not a traditional SiC MOSFET – we make a normally on SiC JFET and co-package with a custom low voltage silicon MOSFET in an always off device. The retained charge (Qrr) is about 3x lower than a silicon MOSFET and so has the gate drive – the downside is the added packaging complexity, but we can use an 8in mainstream silicon foundry for that.”

“What’s happening in the market is the user doesn’t care [what the device structure is]. This lends itself to more sophisticated levels of integration – I can co-package a JFET with on-chip silicon MOSFET with its own gate driver and controller IC, which allows you to put an LLC stage in a package so what we see in the next two or three years is why not have a whole flyback converter in a chip. We are solving all the problems of co-packing already so the next logical level is the integration.”


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