Xerox reports three-basic materials needed for printable circuits
Most semiconductor materials, including those that are polymer-based, require processing at high temperatures and under inert atmospheres. Beng Ong’s team at the Xerox Research Centre of Canada (XRCC) has also developed materials for printing conductor and dielectric components. Ong discussed the research findings in a presentation at the Materials Research Society spring conference.
Thus, all three elements necessary to make a plastic circuit - a semiconductor, a conductor and dielectric - may now be printed using inkjet techniques. The technology promises a low-cost alternative to silicon technology that could print flexible plastic transistors as easily as printing a newspaper.
"Having developed these three critical liquid-processable materials may make it possible to create low-cost, flexible plastic transistor circuits using common liquid-deposition techniques such as spin coating, screen or stencil printing, offset or inkjet printing," says Ong. He believes that products based on these or similar materials will be available commercially in the near future.
Xerox's advances build on the unique polythiophene semiconductor previously designed by Ong's team at XRCC, as well as on a method developed by the Palo Alto Research Center (PARC) for creating a plastic semiconductor transistor array using inkjet printing. PARC is a wholly owned subsidiary of Xerox.
Being able to print in open air is significant because the electrical properties of most liquid-processable organic semiconductors degrade when exposed to atmospheric oxygen. This makes it difficult to build functional transistors in air. However, the Xerox polythiophene semiconductor not only possesses better air stability, it also exhibits excellent self-assembly behaviour. Its unique molecular characteristics allow it to be readily processed into structurally ordered semiconductor nanoparticles. These nanoparticles, when dispersed in a liquid, form an environmentally-stable nanoparticle ink. The ink provides consistent properties and enables inkjet printing of high-performance organic transistor channel layers under ambient conditions.
Xerox is working with Motorola and Dow Chemical to develop plastic integrated circuits for various electronic applications under a National Institute of Standards and Technology (NIST) Advanced Technology Program grant. In addition to XRCC's materials and PARC’s inkjet printing of active-matrix addressed arrays for display backplane switching circuits, Motorola is fabricating plastic circuits for various applications using commercial printing technologies.
Last week, US company TDA Research announced development of a new conductive plastic - oligotron polymer possessing a conducting polyethylenedioxythiophene (PEDOT) centre and two non-conducting ends (Bulletin 526, April 14, 2004).
Caption: Beng Ong's research team at the Xerox Research Centre of Canada.
