Global Designer: Printed circuitry takes on a new meaning

Research organization QinetiQ will soon begin a research program focusing on printing complete electronic circuits, including both active and passive devices. With funding from both the United Kingdom's Ministry of Defense and Department of Trade and Industry, the program will explore the feasibility of applications in both consumer electronics and defense.

Earlier work in active-circuitry printing has focused largely on high-volume, low-cost applications, says project leader and QinetiQ Research Fellow Ian Sage, PhD. By contrast, his program will first develop materials and then examine ways of applying them to areas in which users might derive other benefits.

In the consumer area, a possible route is the development of production processes that could combine low manufacturing cost with the ability to produce short runs of products with different configurations and features. The research could also result in reductions in the size and cost of many electronic products and allow designers to add electronics in other ways, such as in fabrics or product packaging.

Possible defense applications include printing electronic circuitry onto substrates, including curved shapes, to add functions to an object without adding materially to its weight or volume. Examples might include adding features to a helmet or other items of clothing without impacting their primary functions.

Earlier work has also frequently centered on display technologies. For example, the ability to print the active transistors that every pixel of a TFT (thin-film-transistor) display requires, using deposited conductive polymers instead of etched amorphous silicon, could represent an economical route to mass-producing displays. Such an approach could also be more environmentally friendly than conventional technology, Sage points out. As an additive rather than subtractive process, it potentially dispenses with the need for large quantities of aggressive etching chemicals. For high-volume manufacturing, previous work envisaged production processes such as continuous printing on rolls of flexible substrates or on large sheets. The QinetiQ project will also look at the possibilities for large-screen displays for TV and advertising applications.

QinetiQ has demonstrated the ability to print fine metal lines with a feature size of approximately 1 micron, to build thin-film FETs. The process, "soft lithography," forms a relief mold of the required pattern in a polymer material, which in turn deposits the conductive elements by a pad-printing process. It deposits carefully engineered inks with high resolution. The ink then binds metal selectively onto the surface to form the complex structures that active devices need. In contrast, ink-jet techniques, which previous systems used, are limited to features no smaller than tens of microns. The QinetiQ process will use conventional digital printing techniques, such as ink jet, in the interconnect-deposited components.

Materials that designers can use to print semiconducting layers have typical electron mobilities of 0.1 cm²/V-sec, Sage notes—a fraction of that of silicon. Nevertheless, with continuing progress in materials technology, he anticipates that designs should be able to achieve switching speeds into the megahertz region.

Observing an impetus in organic electronics in general, Sage says, "A lot more work is needed, but the technology also offers a huge opportunity to quickly add electronics to defense equipment at low cost. And we can expect to see products using printed electronics beginning to appear in stores by the end of the decade."

QinetiQ, www.qinetiq.com.