If Rolltronics Corporation has its way, building integrated circuits will be as simple as printing a
newspaper.
by Wade Roush
What if creating transistors were as easy as printing the New York Times ? In that world, abundant,
cheap and flexible electronics could be embedded in countless every-day objects. Manufacturers would
use fewer pollutants, gadgets would contain more recyclable materials, and computers would cost less.
That's exactly what Silicon Valley startup Rolltronics Corporation and its partner, Iowa Thin
Film Technologies, envision. The two companies recently demonstrated the world's first working
silicon transistors made using a radical new "roll-to-roll" manufacturing technique. In this
process, a continuous sheet of flexible polymer is unrolled from one spool, covered with
circuit-board-like patterns of silicon, and collected on another spool.
The advance, its proponents say, could speed implementation of devices such as cheaper desktop
displays and flexible electronic paper. "We're working toward something that could be very beneficial
to people," says Frank Jeffrey, president of Ames, IA-based Iowa Thin Film. The company, which
receives funds from Rolltronics to pursue the development of its roll-to-roll processing technology,
has manufactured Rolltronics' first working transistor. "I consider it a great accomplishment,"
Jeffrey says.
Rolltronics, based in Menlo Park, CA, is planning new company divisions to incorporate flexible,
roll-to-roll electronics into radio-frequency ID tags, digital X-ray detector panels, biometric
sensors and backplanes, the layers of electronics that control the pixels in active-matrix displays.
"Each of these could be a multi-billion-dollar market," says Rolltronics CEO Michael Sauvante.
"Right now, we are an R&D company, but very shortly we could be a full-fledged production company."
The Role of Roll-to-Roll
Rolltronics' technology exploits an economic opening left by today's chip fabrication plants. In
these facilities, integrated circuits and memory chips are burned onto crystalline silicon one
wafer at a time.
Chipmakers can squeeze tens of billions of transistors onto each wafer. But the economies of
scale that come from such batch processing disappear with low-density applications such as the
drive electronics for liquid-crystal displays, where only one transistor is needed for each
widely-spaced pixel. "It costs the same amount to make this one transistor as it would to make
thousands," explains James Sheats, Rolltronics' chief technical advisor.
The alternative? Think newspaper. In the roll-to-roll system, amorphous (non-crystalline) silicon
transistors are deposited in precise patterns onto a continuously unwinding ribbon of plastic as
it rolls through a vacuum chamber. The final cost of four to eight cents per square centimeter is
"vastly lower" than that of crystalline silicon wafers, says Sheats, making it affordable to space
transistors as far apart as the pixels in a display.
Size Matters
So far, the smallest structure produced using this method is about 10 micrometers across. That's
50 times fatter than the finest features produced using conventional photolithography. But that's
okay, since these electronics are not designed for devices that require high density, like memory
chips or microprocessors.
"There are a lot of applications, like your cell phone or PDA, that need transistors that can be
spread over a large surface area, and that is what we can make cost-effectively," says Sauvante.
He proudly unpacks the company's demo unit: a plastic square bearing one of Rolltronics's
transistors, attached via alligator clips to a small, gray box. The box sends a periodic charge
to the transistor's "gate" layer, allowing current to flow from one of the transistor's terminals
to the other. When this current returns to the box, it's amplified and used to turn a red
light-emitting diode on and off.
As a display of computational power, it isn't exactly stunning, but it does prove that Rolltronics'
transistor can--like all transistors--act as a switch, clearing the way for the manufacture of more
complicated silicon-on-plastic structures. "Inside of two years from now we'll be shipping products
based on this technology," Sauvante predicts. The first of these will likely include backplanes for
organic light-emitting displays and electronic paper systems such as those under development at
Cambridge, MA-based E Ink and Palo Alto, CA-based Gyricon Media.
Rolltronics isn't the only company trying to bring flexible transistors to market. Bell Labs, for
example, has developed a system for printing multi-layered plastic
transistors on small sheets of flexible polymer using a finely patterned rubber stamp. And Lucent
has fused Bell Labs' printed transistors with sheets of electronic ink from E Ink to demonstrate a
working electronic paper prototype.
But Sauvante contends that because Bell Labs' transistors are themselves made of plastic, "they'll
never be capable of reaching the switching speeds of silicon." Rolltronics' silicon-on-plastic
circuits, he says, are "the only viable approach" for making integrated e-paper devices where the
display, the backplane, and high-speed drive electronicsÑsuch as analog-to-digital converters and
row- and column-driversÑare all flexible.
Sauvante's enthusiasm about Rolltronics' technology has begun to spread. "What they are doing
is very, very promising, and it looks to me like it has a very high probability of success,"
says Nicholas Sheridon, director of research at Gyricon Media. "And if it does succeed, it could
have a very big effect on making transistor arrays more available to people, for things like
displays."
People, Planet, Profits
At the same time as Rolltronics refines its technology, of course, the company will have to
attend to its bottom line. That may be tricky, given the still experimental nature of the
company's technology, investors' wariness toward new high-tech ventures, and the recent slump
in demand for electronics that's cutting into revenues at Intel, AMD, Hitachi and other major
electronics manufacturers.
Still, new flexible transistor technologies could bring payoffs for the whole industry. "Putting
transistors on organic substrates [like plastic] is another step in the electronics revolution
that puts more functions into the daily life of the consumer," says Jerry Marcyk, director of
Intel's Components Research Lab. Another key advantage: the roll-to-roll process is more
environmentally friendly than conventional semiconductor production technology. It uses fewer
toxic solvents and cleaners and can be carried out with many recyclable materials.
For now, Rolltronics can work without much fear of competition from semiconductor industry leaders,
most of whom still focus their R&D primarily on making faster, denser microchips on silicon.
Sauvante believes these chip-making giants "are essentially jostling around a pie that's getting
smaller and smaller, instead of going out to find the game-changing new paradigm. That's what
Rolltronics represents."
Wade Roush is a senior editor at Technology Review.
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