news review NXP GaN development
RECOGNISED as a compelling alternative to silicon for many RF applications, GaN technology has generated significant industry interest due to its performance advantage.
However, this material has faced significant challenges related to cost but according to NXP, this may be a thing of the past. Core to that vision is the concept of “mainstream GaN” – bringing economies of scale and over 30 years of experience in RF power transistors to enable innovation and a secure, reliable supply chain for RF GaN products.
“SINCE announcing our commitment to ‘mainstream GaN’ last year, we’ve received a great deal of interest in our GaN offerings and have worked intensively with a handful of key customers to refine our first-generation GaN portfolio,” says Mark Murphy, director of marketing, RF power product line, NXP Semiconductors. “By offering our customers a choice between high-performance GaN and LDMOS, we’re in the unique position of being able to offer unbiased choices for fully optimised designs, depending on the specific requirements of each application.”
NXP currently offers engineering samples of its first-generation GaN products, including the CLF1G0035-50 and CLF1G0035-100 amplifiers for 50W and 100W broadband applications. Based on a 0.5µm gate-length technology developed in collaboration with the Fraunhofer IAF Institute in Freiburg, as well as United Monolithic Semiconductors (UMS) in Ulm, Germany. NXP’s collaboration with UMS and Fraunhofer IAF Institute establishes a Europe-based supply chain for GaN technology. NXP will be ramping up for volume production and offering engineering samples of additional amplifiers in Q3 and Q4.
2GHz power amplifler for communications
MITSUBISHI ELECTRIC has developed a prototype high-output, high-efficiency 2GHz power amplifier for mobile communications base stations. The amplifier, which features a GaN transistor on a silicon substrate instead of more costly SiC, achieves a conversion efficiency rating of 70%. This, says the firm, is unprecedented among 2GHz power amplifiers with outputs of 150W or higher.
The amplifier is expected to lead to the development of smaller and more power- efficient base station transmitters. The installation of such equipment in tighter spaces will help expand wireless network coverage to accommodate increasing wireless traffic due to smartphone proliferation.
While amplifiers that use GaN transistors consume less power and have a higher output than amplifiers made with silicon transistors, they typically require a more robust substrate made SiC, which elevates
the cost. Initial efforts to develop a GaN transistor using a silicon substrate were hampered by deformation between the GaN layer and Si substrate, which led to increased loss and decreased power conversion efficiency. Eventually the company designed a high-performance transistor by optimising the GaN crystal structure and inserting a buffer layer between the GaN layer and Si substrate.
Could this buffer be aluminium nitride?
Mitsubishi has remained tight-lipped about this but it is known from literature that using this material as a buffer layer can minimise wafer bow and strain in the full structure of GaN-on silicon devices.
Mitsubishi Electric’s new GaN power amplifiers made with cheap silicon substrates achieve a power conversion efficiency of 70% at 2.1GHz, largely improving upon the 58% conversion efficiency of silicon transistor amplifiers currently available commercially.
July 2012
www.compoundsemiconductor.net 9
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