IEEE Spectrum October, 2016 - 11

Short StACk: Imec
constructed transistors from
stacks of horizontal silicon
nanowires (cross section of
array shown here).

the next hiGhPerformanCe
transistor

toP: imeC; Bottom: eRik VRielink

A potential FinFet successor is made
from stacks of lateral nanowires

ba sed i n L euven, Belgium, have constructed
gate-all-around transistors from dense stacks
of 8 -n a nome te r -w id e
nanowires on a convent iona l silicon su r face.
Although engineering hurdles remain, the coming
years could see further
i mprovements to t h is
basic approach-and perhaps its introduction into
mass manufacturing.
Gate-all-around devices can be made by orienting
a nanowire made of semiconducting material in one
of two ways: laterally, as today's transistor channels
are arranged, or vertically, so that the nanowire
stands on end, perpendicular to the plane of the chip.
The Imec team, which presented its findings at
the Symposia on VLSI Technology and Circuits,
held in June in Honolulu, took the lateral approach.
They began by growing alternating layers of silicon and a silicon germanium mix. The team then
etched away parallel trenches, leaving behind fins
containing these alternating layers-a bit like pillars of rock with different sedimentary strata. In
a later step, the team etched away the remaining
silicon germanium, leaving behind two silicon
nanowires in each erstwhile fin.
To create a transistor, insulating material and
then metal gates were added around each nanowire
to form the gate structure. And for each vertical
pair of nanowires, the source and drain regions-
the places where current originates and winds up-

Five years ago, Intel introduced today's highperformance transistor to the world. Dubbed the
FinFET, the device takes its name from its appearance: The
transistor's current-carrying channel sticks up vertically in
the shape of a fin, and the gate that controls it drapes over
the sides. The result is a much tighter control over the flow of
current, which in modern microprocessors can fairly easily
sneak across the transistor when it's supposed to be shut off.
But well before the FinFET exploded onto the scene in 2011,
engineers and device physicists had already
been looking at the possibility of taking that
Fin evolution:
transistor geometry to its logical conclusion,
Transistors made
with stacks
with a gate that completely surrounds the
of horizontal
current-carrying channel. Shifting to such a
nanowires take a
"gate-all-around" geometry would, in theory,
page from the finlike
devices used today.
allow chip companies to produce shorter tranThe gate material
sistors that don't leak copious amounts of curwraps around each
rent, improving speed or power consumption
channel to provide
better control.
in the process.
Stacking the
Now, Hans Mertens and colleagues from
nanowires boosts
the nanoelectronics research firm Imec,
current density.

Gate

Nanowires

Insulator
Silicon

NEwS

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NORTh AMERICAN

OCT 2016

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Table of Contents for the Digital Edition of IEEE Spectrum October, 2016