Silicon Carbide Power Components Are Making Strides

Mar 23, 2005 6:32 PM
By David Morrison, Editor, PETech

Though silicon carbide (SiC) has long been deemed a power technology of the future, recent developments suggest the technology may finally be entering the mainstream. In his plenary session talk at the recent Applied Power Electronics Conference in Austin, Texas, J.C. Zolper of the Defense Advanced Research Projects Agency (DARPA) discussed how some of the obstacles to commercialization of SiC semiconductors are being overcome and the timeframe for development of new SiC devices.

In “Emerging Silicon Carbide Power Electronics Components,” Zolper, who is the deputy director of the Microsystems Technology Office at DARPA, discussed how limitations in existing CMOS and bipolar silicon technologies will require a switch to alternate materials. Until now, geometric scaling has been the usual method for reducing power losses in silicon switches, such as those used in low-voltage dc-dc converters.

However, geometric scaling of silicon switches has its limits. For example, with CMOS devices, scaling can lower on-state and switching losses but will not address off-state losses. Zolper noted that at low voltages, scaling is not enough and alternative materials such as SiC are required. Zolper pointed out that for the same gate thickness, SiC can withstand 10 times the voltage of silicon. That characteristic permits the development of more efficient semiconductor components capable of operation at high voltages. One of the market factors supporting the adoption of SiC power components is the availability of high-quality material due to its growing use in LEDs.

Zolper said there have been two main obstacles to commercialization of SiC components—material quality and availability. In the past, yields on SiC wafers were poor due to defects such as “micropipes,” which reflected insufficient quality in core materials. However, the improvements in the wafer technology have reduced the incidence of these yield-lowering defects. And, Zolper stated, there are no fundamental barriers to making SiC materials much better.

Recent successes in improving SiC fabrication are reflected in the attempts by SiC manufacturers to build their devices on larger wafers. For example, after previously building SiC devices on 3-in. wafers, one SiC device manufacturer is now trying to fabricate 4-in. wafers.

The speaker also mapped out some of the expected milestones for commercialization of SiC power devices in the coming years. SiC Schottky diodes rated at 1200 V are currently available. Similarly rated MOSFET switches are expected in the next two to three years. Meanwhile, MOSFETs rated at 5 kV to 10 kV are expected in three to five years. In that same timeframe, there are plans for PIN diodes rated at 5 kV or above. Beyond the five year mark, it’s projected that IGBTs rated at 10 kV or higher will be available.

Zolper noted that the necessary cost reductions will come with volume manufacturing and multiple suppliers, both of which are now emerging. As the new components enable increased efficiency and power density, SiC devices will enable new system capabilities and capture significant market share.

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