Carbon Nanotube Computers
IBM researchers have found a way to arrange nanotube transistors into complex circuits

SOURCE: “Field-Effect Transistors Assembled from Functionalized Carbon Nanotubes”
Christian Klinke et al. Nano Letters 6(5): 906-910

RESULTS: Researchers at IBM have selectively arranged carbon nanotubes on a surface to make transistors, an important step toward arranging them into complex circuits. To control the placement of the nanotubes, they attached them to molecules that bind to patterns of metal-oxide lines on a surface. They then demonstrated high-performance transistors assembled through this technique.

WHY IT MATTERS: Researchers estimate that transistors based on carbon nanotubes could run many times faster than anticipated future generations of silicon-based devices but would use less power. The IBM work overcomes one of the serious obstacles to nanotube-based computers: the difficulty of deliberately arranging the molecules so that they can form complex circuits.

METHODS: To make working transistors, the researchers first laid down aluminum wires using a lithographic technique. These wires served as the gates that turned the transistors on and off. They then oxidized the aluminum, creating a thin layer of aluminum oxide that acted as an insulator. The oxidized aluminum also served as a template for the carbon nanotubes. After arranging the nanotubes by allowing them to bind to the aluminum oxide, the researchers deposited palladium leads perpendicular to the aluminum wires. These leads crossed over the nanotubes, becoming the sources and drains of high-performance transistors.

NEXT STEPS: The speed of the transistors is currently limited by the large size of the leads and their poor contact with the nanotubes. One possible solution is to replace the palladium wires with metallic nanotubes. Because current fabrication techniques produce a mix of nanotubes with different sizes and electronic properties, not all of which will work well in integrated circuits, another challenge is to find reliable and inexpensive ways to isolate a preferred type of carbon nanotube.

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