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Growing Europe’s nanowires
EUROPEAN researchers have developed “One of the problems of the [current]
state-of-the-art nanowire ‘growing’ top-down approach is that it
technology, opening the way for faster, introduces harsh environments and you
smaller microchips and creating a promising end up with devices that may be
new avenue of research and industrial dominated by defects.”
development in Europe. Nanowires are a
promising new technology that could meet NODE’s nanowires are ‘grown’ from the
rapidly rising performance requirements for bottom up, like crystals, into vertical
integrated circuit design over the next ten structures. “We call it ‘guided self-
years. They are tiny wires just tens of assembly’, and it is a ‘bottom-up’ process
nanometres in diameter and micrometers in that can result in fewer defects,” Samuelson characteristics
length. They could mean smaller, faster and says. Vertical nanowires can consist of of potential devices,
lower power electronics, and lead to entirely different materials, by simply altering the such as field effect transistors (FET). Finally,
novel architectures such as 3D microchips – depositing material, so the wire takes on the team looked at integrating these devices
a vertical stack of circuitry that can layers with different characteristics. “There into circuits.
massively increase the size of circuits for the are many potential opportunities for
same footprint. developing new technologies,” he says. It is a huge body of work and led to some
“This vertical arrangement may be the route real breakthroughs. “One of the
Nanowires are so narrow they are often to 3D circuit design as well as to realise breakthroughs was the perfect deposition of
called ‘one-dimensional’ structures because monolithic on-chip optoelectronics.” high-K dielectrics coating the nanowires and
the width of the wire constrains the serving as a dielectric in the wrap-gate
sideways movement of electrons as they NODE focused on combining silicon with transistors,” reveals Samuelson. “We
pass through the wire. Also, the cylindrical indium arsenide (Si:InAs) and silicon with developed a very good technique for this.”
geometry allows the most efficient silicon germanium (Si:SiGe), two very
electrostatic gating technology. promising materials. “Indium arsenide is High-K dielectrics overcome some of the
inherently very fast and, as such, it was of limits of silicon dioxide at very small scales
Unsurprisingly at this scale, nanowires particular interest to our work,” remarks and are a promising strategy for further
demonstrate many characteristics that offer Samuelson. miniaturisation of integrated circuits.
the potential for novel circuits and
architectures, and physicists are very The project looked at every link in the “As part of this research, we have also
excited. The Japanese pioneered the field nanowire production chain, from growth, encountered problems and possible
with the USA taking up the work, and with processing on an industrial scale, to roadblocks [to further] development, such
a few European teams entering soon after. characterisation and integration. “And one of as quite severe problems in growing Si
the big challenges of the project was the nanowires using gold catalysts”, adds
But the Europeans are on their way. Recent integration of our work with current silicon Samuelson.
work at the NODE project led to world- processing technology, so there was a big
class technology and 40 patents. “Silicon effort on processing,” Samuelson stresses. “This technology is not ready for industrial
technology becomes very challenging when applications, and whether it will be three, six
you get down to 10-15nm,” explains Lars For this, characterisation studies were or nine years before it appears industrially, I
Samuelson, director of the Nanometer important to examine the different materials cannot say,” Samuelson warns. “But we
Structure Consortium at Lund University and used and the effects induced by the established the state of the art, we have the
coordinator of the NODE project. nanowire structure. NODE also examined best results.”
Yale researchers use benzene as single-molecule semiconductor
WHILE it has been revealed as a scientific breakthrough - and not not feasible at small scales in computer circuits and, as such,
a practical application - only, researchers have found a benzene scientists want to use molecules as semiconductors, although Mark
molecule attached to gold behaves like silicon. Researchers have Reed, the Harold Hodgkinson professor of engineering and applied
revealed that a benzene molecule attached to gold contacts science at Yale, said the practical application of faster and smaller
behaves like a silicon transistor, which could open up the “molecular computers” could be decades away.
progression of single-molecule semiconductors.
“We’re not about to create the next generation of integrated
The team from Yale University and the Gwangju Institute of Science circuits. But after many years of work gearing up to this, we have
and Technology in South Korea manipulated the molecule’s different fulfilled a decade-long quest and shown that molecules can act as
energy states by applying various voltages through the contacts, transistors,” he stated. Benzene is widely used in the production of
controlling the current passing through it. Traditional transistors are rubbers, dyes and plastics and is highly flammable.
10 www.compoundsemiconductor.net January/February 2010
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