GaN players aim for defense market

Amid the heat of Atlanta s Georgia World Congress Center, GaN RF electronics emerged as one of the hottest topics at this year s MTT-S International Microwave Symposium. In fact, while wondering if the heated GaN discussions could actually cause a fire, one delegate questioning the safety of the venue commented: "If it catches light, you ll never get all of these people out."

While commercial GaN applications, such as amplifiers for cable TV and wireless communications base stations, are just getting going, it s the military whose interests are particularly inflamed by the wide-bandgap semiconductor. With the GaN RF products offering particularly high performance, it seemed at the conference that defense companies will pay a premium to secure the benefits of this up-and-coming technology.

Their interest can only have been spurred on even more by company announcements of GaN transistor portfolios boasting record performance at the symposium (see "MTT-S IMS 2008 GaN records"). Among these, RF Micro Devices (RFMD) particularly caught the delegates eyes with its 400 W S-band radar power amplifier.

As well as an impressive power output, which RFMD claims is unmatched by any US companies in the GaN area, the device s bandwidth is another standout feature. RFMD s amplifier spanned twice the range of a competing 300 MHz bandwidth module and the company says that it can push this to 1 GHz in the 2.5–3.5 GHz domain.

The Japanese firm Eudyna, which dominates the high-power RF GaN market, was not impressed by RFMD s 400 W module. It demonstrated a 500 W amplifier operating at 1.5 GHz at the 2006 MTT-S show, and Warren Gould, Eudyna s senior director of business development, felt that this reflected the company s overall hold in the area. "They re all trying to get into our customers and it s tough," he said. "We ve got higher breakdown voltages, better performance and we re already in production."

While RFMD agrees that Eudyna was there first, it is hoping to reap the benefit from domestic interest fueling the powerful US military market.

"Our customers tell us that the only other people that they can get these parts from are the Japanese and there are problems sourcing those into the US," said Jeff Shealy, vice-president and general manager of RFMD s Aerospace and Defense Business Unit. "We re in discussions with every major defense manufacturer in the US as well as multiple companies abroad interested in our amplifier technology."

Shealy pointed out that, although GaN devices may still need to be linked together for kilowatt output radar, combining higher-power modules ultimately produces lower loss than would be incurred by lower-power solid-state devices. This in turn finally makes solid-state RF electronics a feasible replacement for microwave tubes at high powers. "The customers are very interested in replacing very heavy, bulky tube technology with a solid-state rack-mounted unit," Shealy explained.

However, despite the boon of highly reliable government-sponsored orders, the shroud of secrecy surrounding the defense market means that it is very hard to determine what dollar value the interest in the area is likely to turn into.

Shealy admits limited visibility into the total military RF GaN market size, but at least he knows that the market is attractive to RFMD. "The volumes in the radar market are very small, but the selling prices are very good," he commented.

Despite being almost entirely prevented from talking about its business by the defense cloak, RFMD s North Carolina neighbor Nitronex paints a similar picture of a vibrant GaN business. "We can t make enough devices," admitted Ray Crampton, the company s marketing director. "It s insanely busy."

Nitronex s latest, higher-power GaN devices are RF transistors that cover the frequency range from DC to 2.7 GHz, with power outputs of up to 200 W. These powers are partly limited by their silicon substrates, which have a lower thermal conductivity than the SiC substrates that are used by most other companies. This makes it much more challenging to reach the full performance potential of GaN, and Nitronex has worked hard on its device designs to improve heat flows.

However, the payback comes in the form of cheaper devices and the potential to use larger wafers. Nitronex is already working on 4 inch GaN-on-silicon wafers whereas the SiC substrate community still uses 3 inch diameter wafers or even smaller (table 1).

Crampton explains that many of Nitronex s devices, including its latest ones, are being sought out specifically for use in unnamed narrowband 2.5 GHz applications. Although Crampton could not be drawn on what these applications might be, he did concede that in 2008 and 2009 the vast majority (he feels that about two-thirds is a good estimate) of Nitronex s business would be with defense companies. Perhaps the firm s importance to the defense industry is best reflected by how it is addressing its current capacity constraints – with the support of military funds that are being pumped into the company specifically to finance work on enhancing its yields.

The success of Nitronex s business is doubly obscured, by its military work and by the fact that it isn t publicly listed and therefore its accounts are less readily available. However, Crampton says that although the company is not quite profitable, it s getting ever closer to recording its first net income.

Although US GaN firms are clearly reaping the benefit of international military politics, other compound semiconductor companies also stand to gain. On the one hand, where the sale of RF components to certain countries is restricted, bespoke design houses and foundries are stepping in to provide the desired functions. On the other, countries with their own defense interests at heart are just as likely to spot the GaN opportunity as the US is.

This is very much the case at NXP, the Dutch semiconductor company pushing the commercial side of Europe s GaN efforts. It is collaborating with the United Monolithic Semiconductors foundry, in which the defense giant EADS owns a 50% stake, and Germany s Fraunhofer Institute of Applied Solid-State Physics.

As the commercial partner, NXP is setting itself some very clear goals, including the release of 100 W GaN transistors for WCDMA base stations in 2009. Perhaps thanks to this, the company seems to have one of the clearest perspectives on the overall potential of the GaN market, including the opaque military angle.

NXP says that ultimately there is enough business for just three RF GaN foundries worldwide. It predicts that these will be distributed evenly between Asia, the US and Europe – another clear sign that national interests will have a strong role to play in the destiny of the GaN industry.

Further reading
A Maekawa et al. 2006 IMS Digest 722.
K Krishnamurthy et al. 2008 IMS Digest 303.   

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