Editor's note: this article is by carbon technology research scientist Shu-Jen Han of IBM Research.
Graphene, one of the world’s thinnest electronic
nanomaterials, has long held the promise as a wonder material in everything
from flexible touchscreens to super-fast circuits. It’s that interest in
semiconductors that led my team to build the world’s most advanced,
fully functional integrated circuit made of wafer-scale graphene – 10,000 times
better performance than previously reported efforts.
Our demonstration has the potential to improve today’s wireless devices’
communication speed, and lead the way toward carbon-based electronics device
and circuit applications beyond what is possible with today’s silicon
chips. Integrating graphene radio frequency (RF) devices into today’s low-cost silicon technology could also be a way to enable pervasive wireless communications allowing such things as smart sensors and RFID tags to send data signals at significant distances.
Building a Graphene
The multi-stage graphene
RF receiver integrated circuit consists of three graphene transistors, four inductors, two capacitors, and
two resistors. All circuit components are fully integrated into a 0.6 mm2
area and fabricated in a 200 mm (eight inch) silicon production line, showing
the unprecedented graphene circuit complexity and highest silicon CMOS
What is Graphene?
Graphene is a single layer of carbon atoms packed in a
honeycomb structure. Its electrical, optical, mechanical and thermal properties
make it well-suited for wireless, or RF, communications.
Circuits built on graphene could allow mobile devices –
tablets to wearables – to transmit data much faster, in a more cost-effective manner, than
today’s silicon-based chips. For example, the circuits we built for
wireless receivers consume less than 20 mW power to operate, while also
demonstrating the highest conversion gain of any graphene RF circuits at
multiple GHz frequency – successfully receiving and restoring a digital text
message (“I-B-M”) carried on a 4.3 GHz signal without any distortion.
Fabrication of a true integrated circuit is challenging
because it’s easy to damage a sheet of graphene during the fabrication flow of
conventional integrated circuits. So, while we had shown it was
possible to build an analog graphene integrated circuit with a broadband
frequency mixer in a 2011 proof of concept, the graphene transistor performance was inevitably degraded
due to the harsh fabrication processes.
|Tilted view scanning electron microscopic (SEM) image revealing the integration of key|
components in IC with enlarged view showing the advanced gate structure
of the graphene field-effect transistors (GFET). Inset image shows crosssectional
SEM of embedded T-shaped gate. Scale bar, 500 nm.
The team decided to flip their approach by completely
reversing the conventional silicon integrated circuit fabrication flow, leaving
graphene transistors as the last step of integrated circuit fabrication. This
resulted in preserving graphene device performance. And it resulted in the
first time that graphene devices and circuits could perform modern wireless
communication functions comparable to silicon technology.
*Any opinions, findings and
conclusions or recommendations expressed in this material are those of the
author(s) and do not necessarily reflect the views of the Defense Advanced
Research Projects Agency.
Labels: graphene, nanocircuits, wireless