Our society is insatiable as far as the transfer of data is concerned. Consequently,
increasingly faster and cheaper transistors are being developed. In row in recent
months, researchers from ETH
Zurich have now broken the world record for the switching speed of nitride-based
transistors that use silicon as a substrate several times.
 | | The transistors are produced under clean-room conditions in the Firstlab. (Photo: O. Ostinelli/ETH Zurich) |
The transistors are produced under clean-room conditions in the Firstlab.
(Photo: O. Ostinelli/ETH Zurich) (more pictures) Although Youtube was for example
only founded in 2005, 100 million videos are watched daily on its platform,
and the amount of digital information in our society is constantly rising. In
2006, for example, 161 billion gigabytes of digital information were produced
– three million times as much information ever stored in books. What’s
more, by 2010 this figure will already have increased to about 1000 billion
gigabytes per year.
Few people are aware that not only does one always need better software to
process such enormous amounts of data, but that the demands on hardware also
continually increase. Transistors are pivotal elements in this struggle: small
semiconductor components that can be controlled through the flow of electrons
to work like microscopic switches or amplifiers in the nanometer scale.
Faster and faster the goal
Colombo Bolognesi, Professor of TeraHertz Electronics at the Laboratory
of Electromagnetic Fields and Microwave Electronics, and his group are experts
when it comes to fast transistors. Their goal is to improve their speed of operation.
After all, the faster a transistor operates, the more information it can process
in a given time. The researchers therefore combine semiconductor materials in
different layers to enable the electrons to flow as quickly as possible. They
also try to make the transistors as small as possible so that the electrons
travel shorter distances, thereby enhancing the operation speed of the devices.
These semiconductor layers have to be prepared under the cleanest conditions
as they are often only as thick as a few atomic layers. Bolognesi’s research
group is thus one of the principal users of the FIRST Lab (http://www.first.ethz.ch/)
on the Hönggerberg. One of the special transistor technologies that Bolognesi’s
group is working on is based on aluminium gallium nitride (AlGaN/GaN) and has
high electron mobility, thus belonging to the “High Electron Mobility
Transistors (HEMTs)” class of transistors.
AlGaN/GaN HEMTs are of technological importance because they can support large
current flows and high voltages while remaining functional at elevated temperatures.
Over the last few months, Bolognesi and his students have managed to beat the
record for the switching speed of AlGaN/GaN HEMTs on silicon substrates several
times in a row: the record is now 108 GHz. “Other groups had only managed
28 GHz up to now using similar technology, so we are almost four times as fast”,
says Bolognesi, putting his team’s achievement into perspective.
Price is the deciding factor
Usually, sapphire or silicon carbide is used as the substrate material
for AlGaN/GaN HEMTs. However, in consumer electronics the part price plays a
big role, as does device performance. For large scale production, every cent
you save on a transistor means a better profit. This is why intensive research
is being conducted worldwide on realizing efficient AlGaN/GaN transistors on
low-cost silicon substrates.
Silicon is cheaper than the customary substrates currently available as it
is extremely abundant in nature, constituting about 26 percent by weight of
the earth’s crust. For Bolognesi, likely high-volume applications for
AlGaN/GaN HEMTs on silicon will be in automotive anti-collision radars which
operate at 77 GHz, or in mobile telephone base station transmitter systems.
In particular, such transmitters could save energy through components that also
work with a much better efficiency than currently available alternatives. This
would not only be good for the mobile phone operators’ wallets, but also
for the environment. However, Bolognesi states that the direct commercial application
is not the primary aim of his team’s research: “We are looking to
demonstrate what is possible in practically manufacturable devices while trying
to push their physical limits of operation.”
Posted September 9th, 2009
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