Slowly but surely graphene is
been harnessed for producing transistors.
This work is a long ways down the road and we will see this in use rather
quickly.
So far we have been mastering
what we could already do with other materials.
What I find most interesting with graphene is the clear promise to
engineer completely new solutions not otherwise possible. That will soon be a big part of this
developing story.
The revolution in materials science
and electronics brought on by graphene has barely begun.
Innovation is step toward digital graphene transistors
by Staff Writers
Researchers are making progress in creating digital transistors using a
material called graphene,
potentially sidestepping an obstacle thought to dramatically limit the
material's use in computers and consumer electronics. This composite image
shows the circuit schematics of a new type of graphene inverter, a critical
building block of digital transistors, left, and scanning electron microscope
images of the fabricated device. Credit: Hong-Yan Chen, Purdue University
Birck Nanotechnology
Center
Researchers are making progress in creating digital transistors using a
material called graphene, potentially sidestepping an obstacle thought to
dramatically limit the material's use in computers and consumer electronics.
Graphene is a one-atom-thick layer of carbon that conductselectricity with
little resistance or heat generation. After its discovery in 2004 - which earned
a Nobel Prize in physics - it was touted as a potential replacement for
silicon, possibly leading to ultrafast devices with simplified circuits that
might be less expensive to manufacture.
However, graphene's luster has dulled in recent years for digital
applications as researchers have discovered that it has no "band
gap," a trait that is needed to switch on and off, which is critical for
digital transistors.
"The fact that graphene is a zero-band-gap material by nature has
raised many questions in terms of its usefulness for digital
applications," said Purdue doctoral student Hong-Yan Chen.
Electrons in semiconductors like silicon exist at two energy levels,
known as the valence and conduction bands.
The energy gap between these two levels is called the band gap. Having the
proper band gap enables transistors to turn on and off, which allows digital
circuits to store information in binary code consisting of sequences of ones
and zeroes.
Chen has led a team of researchers in creating a new type of graphene
inverter, a critical building block of digital transistors. Other researchers
have created graphene inverters, but they had to be operated at 77 degrees
Kelvin, which is minus 196 Celsius (minus 320 Fahrenheit).
"If graphene could be used in digital applications, that would be
really important," said Chen, who is working with Joerg Appenzeller, a
professor of electrical and computer engineering and scientific director ofnanoelectronics at
Purdue's Birck Nanotechnology Center
The Purdue researchers are the first to create graphene inverters that
work at room temperature and have a gain larger than one, a basic requirement
for digital electronics that enables transistors to amplify signals and control
its switching from 0 to 1.
Findings were detailed in a paper, "Complementary-Type Graphene
Inverters Operating at Room-Temperature," presented in June during the
2011 Device Research Conference in Santa
Barbara , Calif.
Thus far graphene transistors have been practical only for specialized
applications, such as amplifiers for cell phones and military systems. However,
the new inverters represent a step toward learning how to use the material to
create graphene transistors for broader digital applications that include
computers and consumer electronics.
To create electronic devices, silicon is impregnated with impurities to
change its semiconducting properties. Such "doping" is not easily
applicable to graphene. However, the researchers have potentially solved this
problem by developing "electrostatic doping," which makes it possible
for graphene inverters to mimic the characteristics of silicon inverters.
Electrostatic doping is induced through the electric field between
metal gates, which are located 40 nanometers away from graphene channels. The
doping can be altered by varying the voltage, enabling researchers to test
specific doping levels.
"This will allow us to find the sweet spot for operating the
device," Chen said.
Further work will be needed to integrate the prototype into a working
graphene circuit for digital applications.
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