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Microwave gallium nitride high-power transistors


Objectives and content
The use of high efficiency power devices based on silicon
or Gallium Arsenide (GaAs) has led to lower cost and
higher functionality in a wide range of applications,
ranging from wireless access networks to television
transmitters, and has allowed the development of many
others, from mobile telephone to (potentially) automotive
warning radar. After more than twenty-five years of
development, current solid state devices for generating
microwave power, based on GaAs, are approaching their
theoretical power limits (typically about 10W at 10GHz).
The generation of higher levels of microwave power is one
of the few areas which is still the preserve of vacuum
tubes. Applications requiring such levels of microwave
power include air traffic control systems, satellite
systems for communications and remote environmental
sensing, and high definition terrestrial television
systems. The vacuum tubes used for these applications
are bulky, heavy, expensive, require high voltage levels
for operation and, most importantly, are significantly
less reliable than solid state devices. A solid state
replacement would therefore be highly desirable.
Recent developments in the growth of wide band-gap
semiconductors, and in particular the Gallium Nitride
(GaN) based materials, have already had a major impact on
another area previously inaccessible to solid state
devices, namely the generation of blue and white light.
These developments in GaN-based materials are now making
solid state devices capable of generating high levels of
microwave power a realistic possibility. Predictions of
the power capability of GaN-based devices show that they
can exceed the performance of GaAs devices by as much as
a factor of 100, slightly greater than for SiC.
The primary aims of this project are to establish the
technology for the growth and fabrication of GaN-based
microwave power devices and to demonstrate this within
the project through devices capable of delivering 5W at
10GHz. This will form the basis for the subsequent
development of very high power devices (up to and above
50W at 10GHz) as well as microwave power circuits capable
of more complex functions. The industrial partners
expect to see the first commercial exploitation within
three years of the end of this project.
The highest priority research task is to establish the
growth of device-quality materials. While the growth of
GaN for blue LEDs has progressed rapidly in recent years,
the materials requirements for electronic and
optoelectronic devices differ and it is not yet clear
which is the most appropriate growth technique. With
bulk GaN not yet available, there is also the issue of
the choice of substrate. The consortium includes
specialist experience in all realistic growth methods and
covers all practical choices for substrates, with a major
objective of the mid-project review being a detailed
recommendation on the most appropriate combination. The
second priority is the development of process technology
for these materials, which is expected to reflect
extensively the expertise within the consortium on
manufacturing microwave devices based on GaAs, but with
significant new aspects due to the chemical stability of GaN and the high temperatures at which it will be required to work.



Participants (5)

St. Martin Strasse 53
81609 Muenchen
Interuniversitair Mikro-Electronika Centrum VZW
9000 Gent
Thomas Swan Scientific Equipment Limited
United Kingdom
1C Button End, Harston
CB2 5NX Harston - Cambridge
Domaine De Corbeville
91404 Gometz La Ville
United Kingdom
University Park