June 03, 2003
For decades, researchers have been eager to overcome the obstacles preventing true commercialization of gallium nitride (GaN). GaN, a III-V compound, has a number of properties that enable high-power, high-frequency and high-temperature microelectronics and blue, green and ultraviolet optoelectronic devices. The long-standing problem, however, is that an ideal substrate on which to grow GaN does not exist. Both silicon carbide and sapphire have proved viable, but these substrates are small and expensive. Raleigh, N.C.-based Nitronex is developing technology that enables standard silicon wafers to serve as a substrate for GaN crystal growth.
Four North Carolina State Univ. materials engineering students, Kevin Linthicum, Mark Johnson, Warren Weeks and Thomas Gehrke, founded Nitronex in Feb. 1999. All four were working on various ways to perfect the growth of gallium nitride, serving as research assistants to NCSU's well-known wide-bandgap semiconductor expert Robert Davis. Since its founding, Nitronex has grown to about 60 employees, most of whom are either materials engineering or device engineering specialists.
Nitronex brought in Jack Hillson to serve as CEO. Prior to joining Nitronex, Hillson held the position of VP of operations for both TeraConnect and Corning Lasertron. He also served as senior VP and GM at Digital Microwave. Earlier, he spent 11 years at M/A-COM in a variety of technical and operations roles.
In return for an equity stake in the company, NCSU transferred an IP package to Nitronex covering a number of methods and processes for growing GaN. Nitronex has raised $34.5 million in funding over two rounds from TPG Ventures, Alliance Technology Ventures, VantagePoint Venture Partners, Academy Centennial Fund, Boston University's Community Technology Fund, Contender Capital, and Southeast Interactive Technology Funds. Investors also include John Marren, a partner at the Texas Pacific Group, and RF Micro Devices' David Norbury.
Nitronex expects the high-frequency performance of GaN will make it highly desirable for power applications, and is thus initially targeting the RF power amplifier market.
While most compound semiconductors have a cubic or diamond crystal structure, GaN has a hexagonal structure; this lattice mismatch makes it very difficult to deposit GaN on cubic structures such as silicon. Over the years, another material with a hexagonal structure matured, silicon carbide, which proved to be an adequate substrate for growing GaN crystals; the lattice mismatch between GaN and silicon carbide is only about 3%, while the mismatch between GaN and silicon is about 18%. After silicon carbide, researchers figured out how to grow GaN on sapphire.
However, both silicon carbide and sapphire substrates are small diameter, expensive and difficult to work with. By developing a means to deposit GaN on silicon, Nitronex created a potentially huge disruptive technology that will not only enable volume production of high-performance devices, it will do so at low cost by leveraging the enormous manufacturing infrastructure set up around silicon.
The technical challenges are daunting. In addition to the lattice mismatch, Nitronex had to deal with the chemical incompatibility of GaN and silicon--if the crystal is not grown correctly, the result is a useless mess. Another significant hurdle is the thermal expansion co-efficients. During cooling after growing a crystal at high temperature, the substrate will contract at a different rate than the GaN, which adds stress to the material. The resulting stress of growing the crystal on sapphire is compressive, but on silicon it is in tension, creating a tendency for the GaN to crack.
Nitronex has been able to address all three of these problems?lattice mismatch, thermal expansion coefficients, and growing GaN in a way that does not react with the silicon. The material component of Nitronex's IP, which it calls SIGANTIC?, addresses the buffer layer, which is the layer that enables the transition from a silicon cubic lattice to a hexagonal lattice. The company's PENDEO? process involves a method of growing GaN laterally--changing the crystal growth environment to promote the lateral growth front over the vertical growth front?to significantly reduce the number of imperfections inherent to GaN crystal growth on non-GaN wafers.
Nitronex is far enough ahead of anyone else working on GaN-on-silicon that it does not worry nearly as much about competitors sneaking up on its heels as it does about LDMOS?the incumbent technology in the power amplifier space the company is targeting. The company's imperative is to hit the market with a solution that is not only better than LDMOS, but one that will also be bolstered by enough testing data that customers concerned about employing a brand new technology will be satisfied.
As it is still in development mode, Nitronex is not ready yet to discuss details about how its GaN-on-silicon technology compares to LDMOS, although it says that it will initially be comparable in terms of efficiency, gain and linearity. In the long run, however, the nature of the material promises higher frequencies, higher usable bandwidth and, ultimately, higher operating voltage. According to Nitronex, LDMOS cannot be extended much further in terms of the bandwidth frequency or supply voltage, while its GaN-on-silicon roadmap has great long-term potential.
Nitronex has been sampling devices for more than a year, so its customers have proof in their hands that the company can do what it claims. These were early devices, but the company will be sampling a next round of devices in June with some of its major customers. By the end of the year, Nitronex hopes to launch a device into the market that significantly challenges LDMOS.
Jim Vorhaus, VP of GaN device design, joined Nitronex in 2002 from photonics startup Sparkolor. Before that, he was VP and GM of Litton Industries' semiconductor products group, and managed the design and development of Avantek 's semiconductor products.
The company's European managing director, Paul Williams, joined Nitronex in 2002 from Sanmina-SCI, where he was worldwide program manager. For 11 years before that, Williams held various senior technical positions at Nokia Networks, including R&D manager, manufacturing manager, and business development manager.
Ray Vasquez is Nitronex's director of wafer fabrication. Most recently, Vasquez was VP of operations for Corning Lasertron and, prior to that, was a senior engineering manager for Silterra Semiconductor Foundry in Malaysia. Earlier, he was a device-engineering manager at Intel for seven years. Vasquez also held various engineering positions at Submicron Technology, Motorola and BOWMAR.
Jim DeVivo, director of finance, joined Nitronex from Bear Stearns and Companies, where he specialized in financial consolidation and regulatory filings for the firm's European subsidiaries. Previously, he audited commercial real estate companies and small businesses with the public accounting firm Friedman Alpren and Green.
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