Silicon circuits made ink-jet printable

Fast enough for RFID
"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.