Graphene has been
touted as the next silicon, with one major problem—it is too conductive to be
used in computer chips. Now scientists from the University of Manchester
have given its prospects a new lifeline.
In a paper
published in Science, a Manchester team lead by Nobel
laureates Professor Andre Geim and Professor Konstantin Novoselov has literally
opened a third dimension in graphene research. Their research shows a
transistor that may prove the missing link for graphene to become the next
silicon.
Graphene is a
remarkable material with endless unique properties, from electronic to chemical
and from optical to mechanical.
One of many
potential applications of graphene is its use as the basic material for
computer chips instead of silicon. This potential has alerted the attention of
major chip manufactures, including IBM, Samsung,
Texas Instruments, and Intel.
Individual transistors with very high frequencies—up to 300 GHz—have already
been demonstrated by several groups worldwide.
Unfortunately,
those transistors cannot be packed densely in a computer chip because they leak
too much current, even in the most insulating state of graphene. This electric
current would cause chips to melt within a fraction of a second.
This problem has
been around since 2004 when the Manchester
researchers reported their Nobel-winning graphene findings and, despite a huge
worldwide effort to solve it since then, no real solution has so far been
offered.
The University of
Manchester
scientists now suggest using graphene not laterally (in plane)—as all the
previous studies did—but in the vertical direction. They used graphene as an
electrode from which electrons tunneled through a dielectric into another
metal. This is called a tunneling diode.
Then they
exploited a truly unique feature of graphene—that an external voltage can
strongly change the energy of tunneling electrons. As a result they got a new
type of a device—vertical field-effect tunneling transistor in which graphene
is a critical ingredient.
Leonid
Ponomarenko, PhD, who spearheaded the experimental effort, said: "We have proved
a conceptually new approach to graphene electronics. Our transistors already
work pretty well. I believe they can be improved much further, scaled down to
nanometer sizes and work at sub-THz frequencies."
"It is a new
vista for graphene research and chances for graphene-based electronics never
looked better than they are now," adds Novoselov.
Graphene alone
would not be enough to make the breakthrough. Fortunately, there are many other
materials, which are only one atom or one molecule thick, and they were used
for help.
The Manchester team made the
transistors by combining graphene together with atomic planes of boron nitride
and molybdenum disulfide. The transistors were assembled layer by layer in a
desired sequence, like a layer cake but on an atomic scale.
Such layer-cake
superstructures do not exist in nature. It is an entirely new concept
introduced in the report by the Manchester
researchers. The atomic-scale assembly offers many new degrees of
functionality, without some of which the tunneling transistor would be
impossible.
"The demonstrated
transistor is important but the concept of atomic layer assembly is probably
even more important," explains Geim.
Novoselov added: "Tunneling transistor is just one example of the inexhaustible collection of
layered structures and novel devices which can now be created by such assembly.
"It really offers
endless opportunities both for fundamental physics and for applications. Other
possible examples include light emission diodes, photovoltaic devices, and so
on."
SOURCE
