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IBM
Research scientists have recently achieved a milestone in creating a
building block for the future of wireless devices. In a paper published
in the magazine Science, IBM researchers announced the first integrated
circuit fabricated from wafer-size graphene, and demonstrated a
broadband frequency mixer operating at frequencies up to 10 gigahertz
(10 billion cycles/second).
Designed
for wireless communications, this graphene-based analog integrated
circuit could improve today’s wireless devices and points to the
potential for a new set of applications. At today’s conventional
frequencies, cell phone and transceiver signals could be improved,
potentially allowing phones to work where they can’t today while, at
much higher frequencies, military and medical personnel could see
concealed weapons or conduct medical imaging without the same radiation
dangers of x-rays.
Graphene,
the thinnest electronic material consisting of a single layer of carbon
atoms packed in a honeycomb structure, possesses outstanding
electrical, optical, mechanical and thermal properties that could make
it less expensive and use less energy inside portable electronics like
smart phones.
Despite
significant scientific progress in the understanding of this novel
material and the demonstration of high-performance graphene-based
devices, the challenge of integrating graphene transistors with other
components on a single chip had not been realized until now, mostly due
to poor adhesion of graphene with metals and oxides and the lack of
reliable fabrication schemes to yield reproducible devices and circuits.
This
new integrated circuit, consisting of a graphene transistor and a pair
of inductors compactly integrated on a silicon carbide (SiC) wafer,
overcomes these design hurdles by developing wafer-scale fabrication
procedures that maintain the quality of graphene and, at the same time,
allow for its integration to other components in a complex circuitry.
“Just
a few days before IBM commemorates its 100th anniversary, our
scientists have achieved a nanotechnology milestone which continues the
company’s century-long pur-suit of innovation and technology
leadership,” said T.C. Chen, vice president, Science and Technology, IBM
Research. “This research breakthrough has the potential to increase the
performance of communication devices that enable people to interact
with greater efficiency.”
The breakthrough is also a major milestone for the Carbon Electronics for RF Applica-tions (CERA) program, funded by DARPA.
In
IBM Research’s demonstration, graphene is synthesized by thermal
annealing of SiC wafers to form uniform graphene layers on the surface
of SiC. The fabrication of graphene circuits involves four layers of
metal and two layers of oxide to form top-gated graphene transis-tor,
on-chip inductors and interconnects.
The
circuit operates as a broadband frequency mixer, which produces output
signals with mixed frequencies (sum and difference) of the input
signals. Mixers are fundamental components of many electronic
communication systems. Frequency mixing up to 10 GHz and excellent
thermal stability up to 125°C has been demonstrated with the graphene
integrated circuit.
The
fabrication scheme developed can also be applied to other types of
graphene materials, including chemical vapor deposited (CVD) graphene
films synthesized on metal films, and are also compatible with optical
lithography for reduced cost and throughput.
Previously,
the team has demonstrated standalone graphene transistors with a
cut-off frequency as high as 100 GHz and 155 GHz for epitaxial and CVD
graphene, for a gate length of 240 and 40 nm, respectively.
