[Anonymous]

Silicon circuits made ink-jet printable
SAN
FRANCISCO, Calif. — Silicon ink for printing electronic circuitry atop
flexible foil substrates was unveiled today at the Printed Electronics
conference  Kovio, Inc. (Sunnyvale, Calif.) described its “green”
silicon ink for thin-film transistors (TFTs) that achieve the
performance of polysilicon transistors, but at a third their price and
consuming only 5 percent of the chemicals and 25 percent of the energy
of single-crystal silicon. Kovio claimed that radio-frequency
identification tags using its silicon ink will drop Kovio’s price from
15 cents today to 5 cents by 2008, when Kovio begins volume production
of its inkjet-printed RFID tags.”We have the world’s first all-printed
silicon transistor,” said Amir Mashkoori, CEO and chairman of Kovio.
“Our thin-film silicon transistors have very high mobilities for a
printed device and we can make both p-type and n-type devices for CMOS
circuits. Right now our design rules are 20 micron, but we have 10
micron working in the lab, which is where Intel started in 1971.
Intel’s first microprocessor used just over two thousand transistors:
similarly, our first devices for RFID tags will use less than about a
thousand transistors when we go into mass production by the end of next
year [2008].”

Kovio is building its own fab, which uses
temperatures too high for plastic substrates (which is why Kovio uses a
stainless steel foil substrate), but which does not require the
expensive processing equipment and clean-room environment of
single-crystal silicon fabs. Silicon ink devices can be fabricated on
roll-to-roll printing equipment, which is how Kovio plans to
dramatically drop the price of RFID tags and similar applications using
all types of flexible electronics.”From a capital viewpoint, we can
build a printable silicon fab for about $10 million, compared with $1
billion for a traditional silicon fab,” said Mashkoori. “Of course, we
will need more of them as volume ramps up, but the point is that it is
a much smaller incremental cost. Plus we need only about five percent
of the materials (one percent of substrate cost and three percent of
the cycle time) to create new devices.”

By way of comparison,
single crystal silicon transistors today can achieve mobilities as high
as 600 centimeters squared per volt second (sq cm/Vs), and polysilicon
transistors, like those that drive LCD displays, have mobilities of
about 100 sq cm/Vs. Unfortunately, there is a big gap between
single-crystal silicon and the printable organic transistors that are
being demonstrated at dozens of labs worldwide. Organic transistors
have dismal electron mobilities of less than 1 sq cm/Vs in contrast
with Kovio’s silicon ink, which rivals polysilicon with its 80 sq cm/Vs
electron mobilities. Most important, silicon ink can produce
transistors that are fast enough for RFID and most other electronic
interface protocols.Kovio’s only reported rival for silicon ink today
is a research project reported by Seiko Epson Corp. last year that used
a silane compound of hydrogen and silicon, called polysilane, which was
inkjet-printed in a nitrogenous atmosphere, followed by baking at 500
degrees Celsius and excimer-laser annealing. Unfortunately, the Seiko
Epson formulation only achieved electron mobilities 6.8 sq cm/Vs when
inkjet-printing transistors: too slow for RFID applications and almost
12 times slower than Kovio’s 80 sq cm/Vs process.”Single-crystal
silicon is faster than us, but we are faster than all the organics and
printable silicon circuits reported today,” said Vik Pavate, vice
president of business development at Kovio. “Most importantly, our
printable silicon is fast enough for RFID applications; in fact, the
speed of our RFID tags exceeds the specifications for both HF
[high-frequency, or 13.56 MHz] and UHF [ultra-high frequency, or 900
MHz] bands.”

Silicon ink was the brainchild of Professor Joe
Jacobson and his student Colin Bulthaup at the Massachusetts Institute
of Technology, who co-founded Kovio when it spun off from MIT in 2001.
Besides being speedy enough for easy integration into the existing RFID
infrastructure, Kovio’s silicon ink is greener than single-crystal
silicon chips. Silicon ink uses an additive approach, whereby the only
materials consumed go into the makeup of the circuitry. Traditional
silicon fabrication uses the opposite, or subtractive, approach, which
grows wafer-wide layers of materials, then etches away what is unwanted
the way a sculptor chips away at a block of marble: leaving most of the
material as waste.”We are taking an additive approach to making silicon
circuits, which is more economical in its both its price and its
conservation of resources,” Pavate said.Since with Kovio’s process the
circuitry is already on a flexible substrate, it can be attached to an
RFID tag’s antenna by means of roll-to-roll printing equipment instead
of with the more expensive pick-and-place semiconductor-chip-handling
equipment used to make single-crystal silicon RFID tags.Kovio has filed
more than 86 patents and has had about a dozen granted so far,
protecting the processes by which it achieves polysilicon transistor
performance from its silicon-ink-printed transistors. Kovio is also
reserving as trade secrets certain parts of its process, which it
believes give it a proprietary advantage and make reverse engineering
very difficult for other companies.So far Kovio has signed as customers
Toppan Forms Co. Ltd. (Tokyo), a Japanese business-form printer, and
Cubic Transportation Systems, Inc. (San Diego, Calif.), producer of
automated fare-collection systems for public transport, both of which
have joint development and supply agreements with Kovio.Kovio employs
31 people, 22 of whom are engineers, and has a dozen investors, ranging
from major venture capitalists, such as Kleiner Perkins Caufield &
Byers, to industrial giants, such as Panasonic

[Author]

November 28, 2007 at 11:58 AM