Nanonets, tiny circuits made of semiconducting carbon nanotubes randomly overlapping in a fishnet-like fashion, have been plagued by a critical flaw: contamination with metallic nanotubes that cause short circuits. One solution is to cut the nanonet into strips, thereby breaking the path of metallic nanotubes and preventing short circuits. "This would be a fundamental advance in nanotube circuits," says Purdue University Professor of Electrical and Computer Engineering Ashraf Alam. He is working with Purdue Professor of Electrical and Computer Engineering Kaushik Roy and doctoral students Ninad Pimparkar and Jaydeep Kulkarni. Their idea could make it possible to print circuits on plastic sheets for applications such as, flexible displays for portable medical devices.

Metallic nanotubes make up about one-third of the nanotubes in the transistors. Because carbon nanotubes are twice as numerous as the metallic tubes, there are enough to form a complete circuit. Models and simulations tell researchers precisely how wide to make the strips to cut the pathway of metallic tubes yet still allow carbon nanotubes to complete their circuit.

The team created a flexible circuit containing more than 100 transistors, the largest nanonet ever made and the first demonstration of a working nanonet circuit, says Alam. "If you can make a flexible circuit with 100 transistors, you can make circuits with 10,000 or more transistors."

The advance may let researchers use carbon-nanotube transistors to create high-performance, shock-resistant, lightweight and flexible circuits at low cost, adds Alam. What’s more, nanonets can be made at relatively low temperatures. Shape-conforming electronics are not possible using conventional silicon-based circuits, which are manufactured on rigid wafers or glass plates. "Existing electronics are flat, which limits their use since most objects in real life are not flat," says Roy.

Flexible circuits in the accompanying image are made with carbon nanotubes at Purdue University and the University of Illinois at Urbana-Champaign.