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 user 2007-11-28 at 11:58:00 am Views: 56
  • #21340

    Silicon circuits made ink-jet printable
    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