Graphene-on-SiC - ISOM

TECHNOLOGY GaN POWER ELECTRONICS
Boosting GaN-on-silicon
blocking voltages
A misconception is holding back the development and deployment of
GaN devices that are built on silicon substrates. This platform is widely
blamed for compromising blocking voltages, but it doesn’t: It is possible to
make diodes and HEMTs on silicon that have breakdown voltages of well
over 2 kV, according to Timothy Boles and Douglas Carlson from M/A-COM
Technology Solutions, Tomas Palacios from MIT and Mike Soboroff, who
recently moved from the US Department of Energy to Rock Creek Strategies.
GaN HEMTs arE oN THE vErGE of
revolutionizing the power electronics industry,
thanks to their capability to take device
performance to a new level. Their tremendous
promise has already spurred widespread
academic and industrial development of
transistors for power switching applications
that have an impressive set of attributes: power
densities of more than 2 W/mm; continuous
current handling capabilities of 10 a or more; and
very high reverse breakdown blocking voltages,
which typically exceed 1 kv. Prototypes of these
transistors have been built on sapphire, SiC and
silicon − three platforms with differing pros and
cons.
Efforts at device development have delivered
much heralded, well-deserved technical
successes, but this is yet to lead to significant
commercial adoption of GaN. There are many
explanations for this, and they tend to revolve
around the view that while GaN diodes and
transistors produce impressive results, they are
far more expensive than their silicon rivals. or, to
put it in simper terms, they don’t get close to the
bang-per-buck of the incumbent technology.
This explains what is happening in the
marketplace today. In this arena, the limited
success of GaN products can be accounted for
by citing a widely held mantra: once the minimum
level of performance needed for the application
is achieved, the cheapest solution will win. So, in
order for GaN-based products to realize their full
potential in a broader marketplace, two changes
must take place: The cost of material must
plummet; and device manufacturers must target
applications that cannot be addressed by lowercost
rival technologies, such as those based on
silicon.
Figure 1. A typical GaN
HEMT epitaxial structure
one route to driving down the cost of GaN devices
involves building them on silicon and processing
them in silicon lines. Staff at the US Department
of Energy (DoE) subscribe to that view, and
they are funding a project to investigate and
ultimately commercialize GaN-on-silicon power
device technology. We are all involved, and we
42 www.compoundsemiconductor.net April/May 2013