Nanotube circuit from IBM
For some 50 years, the semiconductor industry has made circuits increasingly smaller to make chips faster and less expensive (Moore's law). The conventional silicon circuitry is expected to reach fundamental limits in the next 10 to 15 years - bringing the industry to a standstill. An important step would be the construction of integrated circuits along a single carbon nanotube. This is the most promising candidate for creating transistors on a scale smaller than can be achieved with silicon.
Researchers at IBM's Watson Lab have achieved this by demonstrating that carbon nanotubes can be used as a basis for electronics, similar to the way silicon wafers are currently used. The researchers have built the first complete electronic integrated circuit around a single "carbon nanotube" molecule, a new material that shows promise for providing enhanced performance over today's standard silicon semiconductors.
The achievement is significant because the circuit was built using standard semiconductor processes and used a single molecule as the base for all components in the circuit, rather than linking together individually-constructed components. This can simplify manufacturing and provide the consistency needed to more thoroughly test and adjust the material for use in these applications. The work was reported in an IBM paper appearing in the journal Science.
"Carbon nanotube transistors have the potential to outperform state-of-the-art silicon devices," said Dr. T.C. Chen, vice president, Science & Technology, IBM Research. "However, scientists have focused so far on fabricating and optimizing individual carbon nanotube transistors. Now, we can evaluate the potential of carbon nanotube electronics in complete circuits — a critical step towards the integration of the technology with existing chip-making techniques."
The semiconductor industry has relied on the ability to pack increasing numbers of electronic circuits on a single silicon chip to make these chips more powerful. This was achieved largely by finding ways to build circuits smaller. With scientists seeing an end to that capability looming, the use of nanotechnology is being explored as a means to keep the industry moving forward.
Looking like a microscopic roll of chicken wire, carbon nanotubes measure 50,000 times thinner than a human hair. Yet they have unique properties that may allow them to carry higher current densities than the "pipes" presently used in today's transistor and, with their smaller size, might allow for further miniaturization.
The circuit built by the IBM team was a ring oscillator — a circuit, chip makers typically build to evaluate new manufacturing processes or materials. The circuit stresses certain properties that can give a good indication of how new technologies will perform when used to build complete chips.
By integrating the complete circuit around a single nanotube, the IBM team observed circuit speeds nearly a million times faster than previously demonstrated circuits with multiple nanotubes. While this is still slower than the speeds obtained by today's silicon chips, the IBM team believes that new nanofabrication processes will eventually unlock the superior performance potential of carbon nanotube electronics.
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