Carbon nanotube computer about equal to the Intel 4004

For the first time, researchers have built a computer whose central processor is based entirely on carbon nanotubes.

The carbon nanotube computers, created by Stanford University engineers, show that carbon nanotube electronics are a viable potential replacement for silicon when it reaches its limits in ever-smaller electronic circuits.

The carbon nanotube processor is comparable in capabilities to the Intel 4004, that company’s first microprocessor, which was released in 1971, says Subhasish Mitra, an electrical engineer at Stanford and one of the project’s co-leaders. The computer runs a simple software instruction set called MIPS. It can switch between multiple tasks (counting and sorting numbers) and keep track of them, and it can fetch data from and send it back to an external memory.

The nanotube processor is made up of 142 transistors, each of which contains carbon nanotubes that are about 10 to 200 nanometer long. The Stanford group says it has made six versions of carbon nanotube computers, including one that can be connected to external hardware—a numerical keypad that can be used to input numbers for addition.

Nature – Carbon nanotube computer

Franklin’s group has demonstrated that individual carbon nanotube transistors—smaller than 10 nanometers—are faster and more energy efficient than those made of any other material, including silicon. Theoretical work has also suggested that a carbon nanotube computer would be an order of magnitude more energy efficient than the best silicon computers. And the nanomaterial’s ability to dissipate heat suggests that carbon nanotube computers might run blisteringly fast without heating up—a problem that sets speed limits on the silicon processors in today’s computers.

Still, some people doubt that carbon nanotubes will replace silicon. Working with carbon nanotubes is a big challenge.

Of all the emerging materials and new ideas held up as possible saviors—nanowires, spintronics, graphene, biological computers—no one has made a central processing unit based on any of them, says Mitra. In that context, catching up to silicon’s performance circa 1970, though it leaves a lot of work to be done, is exciting.

Victor Zhirnov, a specialist in nanoelectronics at the Semiconductor Research Corporation in Durham, North Carolina, is much more cautiously optimistic. The nanotube processor has 10 million times fewer transistors on it than today’s typical microprocessors, runs much more slowly, and operates at five times the voltage, meaning it uses about 25 times as much power, he notes.

ABSTRACT

The miniaturization of electronic devices has been the principal driving force behind the semiconductor industry, and has brought about major improvements in computational power and energy efficiency. Although advances with silicon-based electronics continue to be made, alternative technologies are being explored. Digital circuits based on transistors fabricated from carbon nanotubes (CNTs) have the potential to outperform silicon by improving the energy–delay product, a metric of energy efficiency, by more than an order of magnitude. Hence, CNTs are an exciting complement to existing semiconductor technologies. Owing to substantial fundamental imperfections inherent in CNTs, however, only very basic circuit blocks have been demonstrated. Here we show how these imperfections can be overcome, and demonstrate the first computer built entirely using CNT-based transistors. The CNT computer runs an operating system that is capable of multitasking: as a demonstration, we perform counting and integer-sorting simultaneously. In addition, we implement 20 different instructions from the commercial MIPS instruction set to demonstrate the generality of our CNT computer. This experimental demonstration is the most complex carbon-based electronic system yet realized. It is a considerable advance because CNTs are prominent among a variety of emerging technologies that are being considered for the next generation of highly energy-efficient electronic systems.

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