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Frozen Lightning: NIST's New Nanoelectronic Switch

Date:
March 5, 2007
Source:
National Institute of Standards and Technology
Summary:
Researchers at NIST have demonstrated a prototype nanoscale electronic switch that can be built from self-assembled layers of organic molecules on silver wires. Potential applications range from a replacement technology for magnetic data storage to integrated circuit memory devices.
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Researchers at the National Institute of Standards and Technology (NIST) have demonstrated a prototype nanoscale electronic switch that works like lightning--except for the speed. Their proof-of-concept experiments reported last week* demonstrate that nanoscale electrical switches can be built from self-assembled layers of organic molecules on silver wires. Potential applications range from a replacement technology for magnetic data storage to integrated circuit memory devices.

Silver would be a natural choice for nanoscale and microscale electrical contacts because of its high conductivity, but it has one notorious drawback. In an electric field, silver ions readily form silver "whiskers," tree-like branching growths of crystals that can short-out microelectronic devices.

Two NIST researchers have demonstrated that this can be a feature, not a bug, in an elegant experiment that uses this growth to make a nanoscale binary switch. In the experiment, an extremely fine silver wire is coated with a molecule that forms a self-assembled monolayer on the wire, typically some organic molecule with a sulfur group on one end to bond to the silver. An equally fine gold wire is laid crosswise to the silver wire and a small voltage is applied across the two wires.

When the voltage is increased to a critical level, silver ions form and quickly branch through the organic monolayer to the gold wire just like a lightning bolt--except solid. When a silver filament reaches the gold, it forms a short circuit, causing a dramatic change in conductance, which is easily detectable. Reversing the voltage retracts the filament and "opens" the switch.

As a candidate logic switch for nanoscale memory circuits and similar devices, the silver whisker switch has several attractive features:

  • The chemistry of the organic monolayer is not critical; the switch works with many different molecules and so can be used with many different self-assembled molecular electronics systems.
  • The crossed-wire structure is very simple to engineer and lends itself to large arrays of switches.
  • The difference between "on" and "off" is huge--electrical resistance ratios of a million or more. This makes it easier to reliably scale up the technology to very large arrays.

Problems to be overcome, according to the researchers, include volatility--the voltage has to be kept on to retain the switch state; slow switching speeds--about 10 kilohertz in the prototype; and a tendency of the switch to freeze permanently closed after a large number of cycles.

NIST has applied for a patent on the switch.

*J.M. Beebe and J.G. Kushmerick. Nanoscale switch elements from self-assembled monolayers on silver. Applied Physics Letters 90, 083117 (2007). Posted online Feb. 23, 2007.


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National Institute of Standards and Technology. "Frozen Lightning: NIST's New Nanoelectronic Switch." ScienceDaily. ScienceDaily, 5 March 2007. <www.sciencedaily.com/releases/2007/03/070302110927.htm>.
National Institute of Standards and Technology. (2007, March 5). Frozen Lightning: NIST's New Nanoelectronic Switch. ScienceDaily. Retrieved September 2, 2015 from www.sciencedaily.com/releases/2007/03/070302110927.htm
National Institute of Standards and Technology. "Frozen Lightning: NIST's New Nanoelectronic Switch." ScienceDaily. www.sciencedaily.com/releases/2007/03/070302110927.htm (accessed September 2, 2015).

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