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Insulation breaks could pave way to nanoscale ICs

Posted: 04 Feb 2002 ?? ?Print Version ?Bookmark and Share

Keywords:nanoscale ic? hp labs? fpga? complex circuit?

Scientists at HP Labs and UCLA have patented a technique to construct ICs from a grid template that could lead to a simple means of constructing circuits on the nanoscale100 times smaller than circuits today.

The patent was issued to Philip Kuekes and Stanley Williams of HP and James Heath of UCLA, and is an advance on previous patents which have emerged from work partly supported by the US Defense Advanced Research Projects Agency.

A previous patent described how metals such as aluminium and titanium form nanoscopic parallel wires in a reaction with a silicon substrate.

By placing two sets of parallel wires perpendicular to each other, a grid array is formed. The key breakthrough the new patent describes is the ability to introduce insulation breaks within the grid, allowing the construction of complex circuits.

"It is very much like an FPGA," said Keukes. "The essential strategy is to make something very regular at the nanoscale and then introduce complexity chemically.

"To make a chip you need both long and short wires. The crosswire design has the benefit of simplicity, but the vice that all the wires are the same length. If we can cut wires at arbitrary lengths, we should be able to design chips on this scale using cad."

The insulating breaks occur through the oxidation of specific points where two crosswires meet. The technique, which is potentially far simpler than the current chip manufacturing process, can only work on the nanoscale because the chemical reaction which oxidises the wires takes too longsecondsat the scale of CMOS ICs today.

"The process is electrochemical," said Williams. "You select a junction where you want a break. By applying a voltage across those two wires and grounding all the others, a chemical reaction occurs at that point only."

By subdividing the grid into smaller areas, different functions can be integrated on to a single circuit. But the logic functions also have to be introduced.

In order to do this, Kuekes, Williams and Fraser Stoddard of UCLA are working on introducing electrically switchable single molecules of the chemical rotaxane into the array. A one-molecule layer of rotaxane, which can act as a diode, is placed between the two wire layers. Careful design of the insulation points then defines the circuit's functionality.

"The molecules only become active when they connect with two wires," said Kuekes. "That means it does not matter if the two parallel arrays slip a bit, which should make it a very cheap process."

Kuekes and Williams see the technology as a potential solution to the problem of the physical limit to CMOS construction, likely to be reached in a little over a decade.

"The first simple devices should appear in about five years," said Keukes. "And in 10 to 15 years, molecular systems should be ready to allow us to push Moore's Law for another 40 or 50 years."

Nolan Fell

EE Times

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