Shape of things to comeDay of plastic electronics nears

Published 28 June 2007

Chemical process could soon be adopted to produce the next generation of small switches for transistors in RFID tags, flexible screen displays, and debit or key cards

Carnegie Mellon University chemists have found that grease can make some innovative plastics much better electrical conductors. The discovery was reported in the 25 June 2007 issue of Advanced Materials, and it outlines a chemical process which could soon be adopted to produce the next generation of tiny switches for transistors in radio frequency identification (RFID) tags, flexible screen displays, and debit or key cards. “This research brings us closer to developing organic semiconductors with electrical and physical properties far superior to those that exist today,” said Richard McCullough, professor of chemistry and dean of the Mellon College of Science at Carnegie Mellon and a principal investigator in the project. The new process involves adding a little grease in two ways. The first step involves chemically combining an inherently conducting polymer (ICP) with a grease-like chemical. The second step involves depositing this hybrid material — called a block copolymer — onto a greased platform.

On the surface layer of a transistor, ICPs make good electrical conductors which provide the switch element for a transistor to turn on and off. ICPs, however, are by nature brittle. To address this brittleness, scientists chemically link ICPs with grease-like, elastic polymers to make block copolymers.

Elastic polymers provide much-needed flexibility, but they insulate rather than conduct electricity. Block copolymers which contain grease-like polymers are typically less effective electrical conductors than pure ICPs — but in the right processing setting, the opposite can hold true, the Carnegie Mellon scientists report. It just depends how you treat a transistor’s silicon dioxide base layer. “This is the first report that copolymers are good organic semiconductors,” McCullough said. “These results mean that we could soon design devices that are both flexible and highly functional.” Geneviève Sauvé, co-author of the Advanced Material report, says that eventually polymer chemists could replace a silicon dioxide base with a flexible plastic so consumers could roll up plastic displays.

-read more in Geneviève Sauvé and Richard McCullough’s, “High Field-Effect Mobilities for Diblock Copolymers of Poly(3-hexylthiophene) and Poly(methyl acrylate),” Advanced Materials(25 June 2007) (sub. req.)