Qing Cao, Ph.D

Scientists use carbon nanotubes to make the world’s smallest transistors

As computing has moved into the nanoscopic realm, it’s getting harder and harder for engineers to follow Moore’s Law, which says, essentially, that the processing speed of computer chips should double every year or two. But IBM researchers have just reported a new way to keep Silicon Valley on the right side of at least this law, using a delicate material to make microchips’ basic processing elements—transistors—smaller and faster than ever before. For decades, computing speed has increased as silicon transistors have shrunk, but they’re currently near their size limits. So scientists have been experimenting with carbon nanotubes, rolled-up sheets of carbon atoms just 1 nanometer, or a billionth of a meter, in diameter. But difficulties working with the material have meant that, for optimal performance, nanotube transistors have to be even larger than current silicon transistors, which are about 100 nanometers across. To cut that number down, a team of scientists used a new technique to build the contacts that draw current into and out of the carbon nanotube transistor. They constructed the contacts out of molybdenum, which can bond directly to the ends of the nanotubes, making them smaller. They also added cobalt so the bonding could take place at a lower temperature, allowing them to shrink the gap between the contacts. Another advance allowed for practical transistors. Carrying enough electrical current from one contact to another requires several nanotube “wires.” The researchers managed to lay several parallel nanotubes close together in each transistor. The total footprint of the transistor: just 40 nanometers, they report today in Science. Electrical tests showed their new transistors to be faster and more efficient than ones made of silicon. Silicon Valley may soon have to make way for Carbon Valley.