Imagine being able to place a sheet of plastic in an ink-jet-like printer, and using an organic ink, printing the transistor-based circuits you need. Although seemingly a bit far-fetched, this capability is actually emerging from the research labs at Xerox Corp., Palo Alto, Calif. The laboratories have come up with a semiconductor ink based on a poly (alkylthiophene) compound that can be used to print electronic patterns. The ink can be dispensed using a variety of commercial or research tools that deliver small-drop payloads, similar to ink-jet print heads.
Although the ink-based transistors don't switch as fast as silicon transistors and currently can't be made as small as silicon structures, for applications like display driving, they can deliver adequate performance. The work on printed organic electronics isn't new, but Xerox's latest work demonstrated a field mobility in the transistors of 10−1 cm2/volt-second, which is within an order of magnitude of amorphous silicon. In addition, the organic transistors have an on-off resistance ratio of 108, which makes them a very viable alternative for electronic switches.
The organic material performs well over a wide temperature range, but it is sensitive to humidity. However, adding a moisture barrier layer resolves this problem. Also, early versions of the organic compound deteriorated when exposed to oxygen, but oxygen doesn't affect the latest compound combination.
Researchers estimate that the cost of producing ink-based circuits could be as low as about one-twentieth that of amorphous silicon deposited on glass and about one-fifth that of roll-to-roll amorphous silicon. The sizable cost reductions are largely due to the elimination of the costly vacuum deposition equipment required for amorphous devices. Once the technology reaches production, roll-up video displays, electronic "paper," and other low-cost displays could be mass produced. Other applications include RF identification tags and electronic smart cards.
Xerox Corp./Palo Alto Research Center