Nanotubes debut as "last mile" interconnect in 1GHz chip

Researchers at Stanford and Toshiba have unveiled a 1GHz CMOS circuit that uses carbon nanotubes as an interconnect. The 11,000-transistor chip has 256 ring oscillators and was fabbed at Taiwan Semiconductor Manufacturing Company, or TSMC for short. According to electrical engineering professor Phillip Wong, this particular chip is the first to demonstrate a commercial speed of 1GHz.

While the chip in question is an impressive accomplishment, it's not a "true" carbon nanotube design. The core is an array of ring oscillators. Each oscillator (all built on standard copper) is missing a connection. The nanotubes in question were inserted to bridge that gap and complete the chip's various circuits. The tubes in question are rather large, at 5 microns long and 50-100nm in diameter—researchers eventually hope to to build single-wall nanotubes as small as 1nm in diameter.

One of the challenges of working with nanotubes has been assembling them into appropriate structures. The team working on the project got around the issue with a bit of ingenuity. The circuit itself was designed with multiplexing circuity that allowed each individual oscillator to be charged separately. A solution of nanotubes was then floated over the oscillators, and an AC signal was applied. Once a nanotube snapped into place to bridge a particular oscillator gap, the AC charge was shut off for that particular oscillator until all the individual circuits were completed with their nanotube components.