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Record power SiC devices enhance radar

The superior physical properties of SiC are helping US semiconductor manufacturer Microsemi to increase the range and amount of information derived from aerospace radar.

Microsemi has used SiC to produce what it claims are the most powerful radio-frequency transistors yet made for VHF and UHF radar applications.

The company launched two kilowatt-scale SiC static-induction transistors (SITs) on October 6 that are already in “pilot” production.

“The critical electric field of SiC is an order of magnitude higher than silicon,” pointed out Mike Mallinger, Microsemi s director of business development for wide-bandgap products. “That means I can operate the transistor at much higher bias voltages.”

“We can create a transistor approximately the same size with a much higher power level that then adds to the capability of the overall system,” he told compoundsemiconductor.net.

The company s Bend, Oregon, fab makes millimeter-dimension chips based on out-sourced 3-inch SiC epiwafers prior to back end processing at its Santa Clara, California site. Connecting the transistors in parallel, rather than simply producing larger chips that are more likely to contain device-killing SiC material defects, enables high-power operation.

The device that targets VHF radio wavelengths at 150-160 MHz typically produces 1400 W signals, while the 406-450 MHz UHF transistor can reach 1100 W. They provide 9 dB and 8 dB of gain respectively.

“Here in the States, we had a major event occur back on September 11, 2001,” said Mallinger. “As a result of that, our airline industry began to understand the need to increase the range and identification on radar systems.”

This demands more from the radar semiconductor components. Increased signal pulse length means that the transistors heat up more, while shorter periods between pulses gives them less opportunity to cool.

Here, the high-temperature operating capability and threefold thermal conductivity improvement that SiC offers over silicon comes into play. Microsemi has shown that its components can operate at 300°C, compared to 150°C for its silicon transistors.

“What that allows the radar to do is not only range the target, but also read the target in much more detail,” Mallinger explained.

The SIT technology was developed originally at Northrop Grumman, but was then transferred to Advanced Power Technology (APT) in 2005. Microsemi bought APT later that year.

The company s focus with these devices is the defense market. The technology is supported by a US Air Force contract, and Microsemi is working closely to advance with customers through what can be a lengthy design cycle.

As well as the SITs, Microsemi intends to launch SiC MESFETs for high-power S-band radar early in 2009. It is also in the process of upgrading the Bend fab to use 4-inch SiC wafers and adding epiwafer suppliers to support its primary source, Cree.

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