How carbon nanotubes will power future gadgets
For most of the last five decades,
the processing hearts of all our computers, game consoles, smartphones, cars, media players and even alarm clocks have been
made of silicon. No surprise: The namesake of Silicon Valley is cheap, readily
available, and easily manipulated during manufacturing processes.
But scientists and researchers now
believe silicon-based processors are reaching their limits. Physical laws
limit how small silicon transistors can get before the signals they process
just become a random electrical haze. That’s why new research from scientists
at IBM seems to hold so much promise for the future of computing: They may have
found a realistic way to ditch silicon in favor of carbon nanotubes.
Carbo-nano-what
do you think of this one...?
Carbon is one of the most versatile
elements in nature, taking the form of everything from coal to pencil lead and
diamonds. One of the forms it can take is graphene
You can think of graphene as a bit like molecular chicken wire:
individual carbon atoms bond together in a hexagonal pattern, forming a sheet
that can be just one atom thick. At a very basic level, a carbon nanotube
is a sheet of graphene that’s rolled up and joined with itself to form a
cylinder: The hexagonal structure of the carbon bonds means that tube can
ideally be seamless no point is weaker
than any other and the tubes can be
very, very long ... molecularly speaking, anyway. Carbon nanotubes have been
constructed that are more than 100 million times longer than they are wide.
Sure, that’s still tiny to you and me, but carbon nanotubes can be far larger
than any other known cylindrical nanostructure and that’s a tremendously useful
characteristic if you’re trying to design very tiny things like processor
chips.
Like silicon, carbon nanotubes are
also semiconducting, and (in some cases, in theory) can be more than 1,000
times more conductive than copper. This makes them one of the very few
nano-materials that could feasibly be used to replace silicon in chip design.
Creating
order from chaos
Chip designers looking to use carbon
nanotubes for processors face one major problem: how to manipulate them and lay
them out in the kinds of tiny, very precise patterns needed for processors.
Current chip manufacturers essentially create wafers of silicon embedded
between layers of non-conductive material, then use chemicals or lasers and
particle beam etching to trace out paths and individual transistors.
Transistors are the absolute heart
of digital processors, acting at the gates that control the individual
ones and zeros (or bits) that define digital technology. A single character in
the most basic email message or text takes seven bits (or transistors) to
represent; a single pixel in a digital photograph requires over 500 bits.
Transistors are responsible for both memory (like RAM and flash storage), but
(by switching on and off again to transform and manipulate data) for all
execution and code running on a device.
The old-school etching approaches to
making transistors wouldn’t work with nanotubes, but researchers at IBM came up
with a new technique, reported in Nature
Nanotechnology. First, the researchers made a
traditional wafer, but with a layer of hafnium deposited on silicon. Next, they
put the carbon nanotubes in a chemical that made them soluble in water.
Finally, they dipped the hafnium wafer in the solution of nanotubes, then
dipped the wafer in a second chemical that sticks to the hafnium and
acts as a two-part epoxy to bind the nanotubes — but only to the areas of the
wafer with exposed hafnium. The result? Carbon nanotubes neatly lined up on
paths etched in a wafer — just the sort of thing you’d want for a chip. The IBM
team was able to make both memory and microprocessor chips with more than
10,000 working transistors.
How tightly packed are the
nanotubes? About one billion nanotubes per square centimeter. According to IBM
materials scientist (and study co-author) James Hannon, the technique deposited
one nanotube roughly every 150 to 200 nanometers. That’s not small enough for a
realistic microprocessor, and it’s a far cry from 22 nanometer distances that
have been used by memory manufacturers since 2008 (and which are currently mainstream
in Intel’s Ivy Bridge
processors), but Hannon told the BBC
that represents a 100-fold improvement over previous efforts to pack nanotubes
into chip-like configurations — and puts the technology within striking
distance of silicon.
Nanotubes
might power your future
Processors built using carbon
nanotubes could be the breakthrough that enables digital technology to continue
advancing at a steady pace. Since the development of the first integrated
circuit in 1958, the number of transistors chipmakers have been able to cram
into the same are has been doubled roughly every two years — a maxim known as
Moore’s Law, named for Intel co-founder Gordon Moore. When Moore first
articulated the idea back in 1965, nobody really thought the industry would be
able to sustain that pace for long. Yet despite a few hiccups, engineers and
researchers have largely been able to maintain that pace through innovations in
chip manufacturing processes (like Intel’s “3D” tri-gate transistors and exotic new materials). The first integrated circuits
contained only a few transistors; today, mainstream chips like Intel’s Ivy
Bridge line carry as many as 1.4 billion.
Silicon hasn’t reached the end of
the road yet; chipmakers already have the next generation or two of silicon
chips planned out. After the current 22nm process, expect to see 14nm chips —
switches are getting so small they can be meaningfully measured in individual
atoms. That sets a startlingly high bar for the plants that make them, which
would have to execute near atom-accurate operations billions of times for every
single processor they produce. On the other hand, the techniques outlined by IBM’s
nanotube research point toward self-assembling solutions where molecules wind
up in the proper placed through chemical reactions.
In theory, processors built around
carbon nanotubes could be considerably smaller than today’s transistor
technology. Just like today’s processors, smaller means they consume less
power. That means less heat and far longer battery life for mobile devices.
Furthermore, the electrical properties of carbon nanotubes also means they can
switch on and off faster than silicon-based transistors, meaning they could
operate at significantly higher clock speeds than today’s chips. That’s a good
thing: While Moore’s Law is still in force for transistor density, processor
clock speeds have started to plateau in recent years, with chipmakers getting
more performance out of chips by adding additional processor cores rather than
making those cores run faster. Carbon nanotube processors could theoretically
handle speeds as high as 8GHz or 9GHz and run at half or one third the power of
today’s chips – at least in rough calculations.
So nanotube processors would be
smaller, faster — and since they’re made of carbon, they’d be greener, right?
Probably not. Although carbon nanotubes are certainly less damaging to the
environment than many compounds and materials used in high-tech products, the
process of manufacturing carbon nanotube processors isn’t likely to be
inherently greener than making silicon wafers — and don’t expect the devices
they power to be magically biodegradable.
Similarly, the chips will still be
difficult to make and expensive. Just like today’s chips, the newest, fastest
versions will only power the newest, flashiest, high-end devices — but those
devices could be much smaller than today’s gizmos. For instance, with
the iPhone 5 Apple has packed more processing power into a handset
than it ever put into a PowerPC-based notebook. Extend trends like that, and you start to see tablets that
only a few millimeters thick, technology that might be able to support things
like bendable and flexible portable devices and wearable computing technology like Google Project Glass - with enough processing power to handle speech
recognition, augmented reality, multitasking and high-end graphics — and
batteries that last for days or even weeks.
When
will they be on sale?
Carbon nanotube processors might
prove to be the future of computing … but it’s going to be a long while before
they appear retailer’s shelves. The process outlined by IBM still has to be
considerably refined to make it practical in the real world. Assuming that can
be done, existing chip manufacturing facilities will have to be converted to
use the new processors, or (as likely) whole new chip fabrication facilities
will have to be built. All in all, we’re probably looking at at least another
decade before the technology is commercially viable. But, conveniently, that’s
just about when silicon will probably hit the end of its feasible development.
