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Controlling
power consumption in mobile devices and large scale data centers is a
pressing concern for the computer chip industry. Researchers from Penn
State and epitaxial wafer maker IQE have created a high performance
transistor that could help solve one of the vexing problems of today’s
MOSFET technology—reducing the power demand whether the transistors are
idle or switching.
Today’s
digital information processing systems, from data centers to mobile
laptops to smart phones, consume and dissipate significant power due to
the constant power demand of the billions of transistors packed into the
logic circuits on digital electronic devices. In traditional MOSFETs
(metal-oxide semiconductor field-effect transistors), the building
blocks of today’s digital technology, a supply voltage of around one
volt is required to gradually turn on the transistor. The current
transistor technology faces inherent limits to reducing the power demand
in electronic circuits due to physical laws related to the MOSFET
design. Meanwhile, power demand will increase as the size of next
generation transistors decreases and more devices are packed onto a
computer chip.
In
a paper delivered at the International Electron Devices Meeting
in Washington DC on Dec. 7, 2011, Penn State doctoral candidate Dheeraj
Mohata will discuss a new materials and device architecture that
provides power savings and instant transistor on-off capability for
future electronics. The paper, titled “Demonstration of MOSFET-Like
On-Current Performance in Arsenide/Antimonide Tunnel FETs with Staggered
Hetero-junctions for 300mV Logic Applications,” reports the fabrication
of a heterojunction field effect tunnel transistor with a 650% increase
in drive current.
“This
is the first time a tunneling field effect transistor has had a
MOSFET-like On-state current,” says Mohata’s adviser Suman Datta,
professor of electrical engineering. “By choosing two dissimilar
semiconductor materials, Indium Gallium Arsenide and Gallium Arsenic
Antimonide, and adjusting their composition, Deheeraj was able to
engineer Hetero Tunnel FETs with a 7.6-times improvement in drive current
over the control sample.”
Tunneling
FETs use the quantum mechanical property in which electrons are able to
pass through a physical barrier if the barrier is thin enough. By
increasing the drive current, the team was able to operate the Tunnel
FET at reduced voltage, 300 mV compared to one V, thereby
offering considerable power savings.
“If
one can pick a proper combination of two different semiconductors and
adjust their composition such that their band alignment results in a
staggered configuration, it’s possible to significantly increase the
tunneling rate and enhance the drive current of the Tunnel FET,” Datta
explains.
The
Penn State researchers designed and partnered with IQE, who produced
the atomically precise multi-layer epiwafers using molecular beam
epitaxy on which the transistors are built. The Penn State team then
used advanced nanofabrication techniques to fabricate vertically
oriented tunnel FET devices on the epiwafers in the Materials Research
Institute’s Nanofabrication Facility, whose director, professor of
electrical engineering Theresa Mayer, was the co-principal investigator
on the project. Comparing experimental results against the computer
models used in the design phase enabled the researchers to verify their
device simulations, and determine that Hetero Tunnel FETs would perform
in a similar manner in the next generations of semiconductor devices,
including future 7nm technology node devices.
“Work
has to go on to see if this device can be further scaled to smaller
dimensions and integrated on an industrial scale,” Datta concludes. “If
so, the impact will be significant in terms of low power integrated
circuits that can work at 300 millivolts and below. This raises the
possibility for self-powered circuits in conjunction with energy
harvesting devices for active health monitoring, ambient intelligence,
and implantable medical devices where the batteries haven’t scaled in
step with the devices.”
Other
members of the Penn State team along with Mohata, Datta, and Mayer
include current and former graduate students, respectively, R. Bijesh
and Salil Mujumdar in electrical engineering, graduate student Craig
Eaton and assistant professor Roman Engel-Herbert in materials science
and engineering, and Vijaykrishnan Narayanan, professor of computer
engineering. Their research on Heterojunction Tunnel FETs was funded by
Intel Corporation and the Nanoelectronics Research Institute
(NRI)-supported Midwest Institute of Nanoelectronic Discovery (MIND).
The Materials Research Institute’s Nanofabrication Facility is a member
of the National Nanofabrication Infrastructure Network (NNIN).