May 08, 2008

EE Times

Newcomer delivers innovative FETs for less-visible, fragmented market

In a period of vendor mergers and spinouts, a semiconductor startup is a relative rarity.Just as unusual is one which focuses on discrete devices such as transistors, and not for high-volume mass market applications such as cell phone handsets or multimedia.Fabless HVVi Semiconductors, Inc. (Phoeniz, AZ) recently introduced a series of silicon power field-effect transistors (FETs) targeting medium- and high-power pulsed-RF applications at 25 to 300 W levels, such as L-band (1 GHz) radar in commercial and military avionics (both ground-based and airborne), as well as some cellular base-station applications.Why the push into this market?According to Wil Salhuana, President and CEO, RF amplifier component technology had stalled while demand for smaller systems was growing, and there was a significant gap between user needs and vendor offerings, as well as end-market growth niches. Both RF DMOS (double-diffused MOS and LDMOS (laterally diffused MOS) transistor structures were plateauing in performance, packaging, and power, noted Brian Battaglia, Senior RF Applications Engineer, and a new device structure was needed.This led to the company's high-voltage (48 V) vertical FET (HVVFET), developed by founder Bob Davies, who had played a major role in development of 15-year-old incumbent LDMOS.Key to HVVFET performance is the vertical structure which allows heat to flow from the hottest spot of the device directly to the heatsink (less than 10 m), in contrast to a lateral device where the heat must travel through the entire thickness of the wafer to reach the heatsink (typically 100 m).The resulting device offers, according to HVVi, twice the power density, 30% greater efficiency, 3 dB of additional gain, and twice the ruggedness of competitor's products. The ruggedness enhancement is due to both the improved efficiency and thermal characteristics as well as VSWR specification: the FETs can withstand 20:1 VSWR, critical in many RF applications.The venture-backed company has raised over $26 million from Mobius Venture Capital, Advanced Technology Ventures, Horizon Ventures, as well as On Semiconductor, who provides wafer foundry services using conventional silicon-process technology.Of course, HVVi faces established competition, from both broad suppliers as well as those who specialize in these markets, and have both relationships with customers as well as applications expertise.These include Microsemi Corp., Tyco Electronics M/A-Com, NXP Semiconductors, Freescale Semiconductor, and Infineon Technologies AG. Other competition comes from gallium-nitride (GaN) devices, but this is a more limited and costly process, notes Salhuana. Despite our fixation on digital ICs with their multiple millions of transistors, RF applications are still defined by and dependent on iscrete transistor devices and their unique structures, optimized for the frequency, power, and thermal constraints of this analog world.