The demonstration carbon nanotube circuit converts an analog signal from a capacitor—the same type of sensor found in many touch screens—into a digital signal that’s comprehensible by a microprocessor. The Stanford researchers rigged a wooden mannequin hand with the capacitive switch in its palm. When someone graspsed the hand, turning on the switch, the nanotube circuit sent its signal to the computer, which activated a motor on the robot hand, moving it up and down to shake the person’s hand.
The nanotube circuit is still relatively slow—its transistors are large and far apart compared to the latest silicon circuits. But the work is an important experimental demonstration of the potential of carbon nanotube computing technology.
“This shows that carbon nanotube transistors can be integrated into logic circuits that perform at low voltage,” says Aaron Franklin, who is developing nanotube electronics at the IBM Watson Research Center
Carbon complexity: This wafer is patterned with a complex carbon nanotube circuit that serves as a sensor interface
Working with carbon nanotubes presents many challenges—as many as 30 percent of them are metallic, rather than semiconducting, with the potential to burn out a circuit. Nanotubes also tend to grow in a spaghetti-like tangle, which can cause circuits to switch unpredictably. The approach taken by the Stanford group is to work with their imperfections, coming up with error-tolerant circuit design techniques that allow them to build circuits that work even when the starting materials are flawed. “We want to build up the circuit complexity, then go back to improving the building methods, then make more complex circuits,” says Wong.