Printed electronics promise scalability, low cost, and flexibility. "Printing allows you to achieve scalability and low cost, but the field has been dominated by organic semiconductors whose performance is low," says Mark Hersam, professor of materials science and engineering at Northwestern University. Carbon nanotubes, on the other hand, offer a high-performance alternative in flexible electronics. But the printed nanotube circuits made so far require a lot of power to switch at high speeds--in a display driver, for example, this would mean a trade-off between the refresh rate of the picture and device battery life.
Working with researchers led by University of Minnesota chemical engineering professor Daniel Frisbie, Hersam has overcome the two main challenges to printing high-performance nanotube circuits. First, researchers don't know how to make batches of purely semiconducting nanotubes; metallic nanotubes in a printed circuit act like tiny copper wires, shorting out the circuit. The new devices get a performance boost because they're printed from pure solutions of semiconducting tubes separated using a technique Hersam developed in 2006. The pure nanotubes offer a boost in switching speed.