NEC Corp. has developed a method of positioning tiny tubes of carbon in a way that, 10 years from now, will make circuits run faster and consume less power than the fastest and most powerful silicon chips, the company said on Thursday.
The process is an important step toward NEC's goal of developing chips that run at 15GHz to 20GHz while consuming about the same power as today's Pentium 4 processors made by Intel Corp.
The company says it made a breakthrough in the way it makes carbon nanotubes, bringing them closer to being used in transistors in LSI (large-scale integrated circuit) chips.
"Before we developed this process, we could not control the position or the diameter of carbon nanotubes simultaneously. Now we can," said Yukinori Ochiai, principal researcher at NEC's nanotechology group at the company's fundamental and environmental research laboratories at Tsukuba, north of Tokyo. "We think, frankly, it's a major step forward and a breakthrough ... nobody else can do both position and diameter," he said.
Carbon nanotubes are made when carbon atoms form hollow, open-ended cylinders that have diameters between 0.4 nanometers and 1.8 nanometers. Carbon nanotubes vary in length up to several hundred nanometers long, depending on how they are made. A nanometer is one-billionth of a meter.
Ever since their discovery by NEC researcher Sumio Iijima in 1991, carbon nanotubes have held promise as the building blocks for transistors and circuit wiring that are much more efficient than those with conventional materials.
Electrons can flow through carbon nanotubes 10 times faster than they can in circuits made using silicon, and carbon nanotubes can carry 100 times the current and dissipate 20 times the heat of circuits made with silicon. Carbon nanotubes in transistors can also amplify about 20 times more current than conventional silicon-based transistors, Ochiai said.
For example, Pentium 4 chips contain about 54 million transistors and these transistors are embedded in lines on the chip's silicon wafer that are 90 nanometers across. Next year, Intel will introduce chips built in 65 nanometer lines. The transistors have gates, the switches that turn off and on, measuring 35 nanometers across, according to Intel.
According to the International Technology Roadmap for Semiconductors, an organization that helps standardize how companies advance chip technologies, processors will be built in lines as small as 22 nanometers by approximately 2016, and chips will contain billions of transistors.
It is at this bleeding edge that carbon nanotubes will be useful, Ochiai said. As circuits get smaller, silicon's comparative lack of efficiency means chips have to use more power and generate more heat. In addition, ever stronger yet thinner insulators are needed to stop electrons straying or leaking between the gate and other parts of the transistor. Placed in the circuits, as well as carrying more current faster, carbon nanotubes can also act as great insulators. Carbon nanotubes will solve many of the technical issues faced by transistors built on silicon alone, Ochiai said.
"With carbon nanotubes, the chips will run faster, but with the same power as today's chips," he said.
Presently, carbon nanotubes have one major drawback. Their size makes them difficult to manipulate, and unlike semiconductor technology, carbon nanotubes have not benefited from more than 50 years of technical development.
