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Materials and Cost Benchmarking

CVD Process Used to 'Solder' Carbon Nanotube Arrays

26 November 2013

Researchers at the University of Illinois have developed a simple and self-regulating chemical reaction process for applying to hot spots in carbon nanotube arrays to "solder" the gaps in its nanowires.

Creating single nanotubes suitable to serve as transistors is very difficult. Arrays of nanotubes are much easier to make, but the current has to hop through junctions from one nanotube to the next, slowing it down.

In standard electrical wires, such junctions would be soldered, but these tiny gaps cannot be bridged on the nanoscale using solder.

"It occurred to me that these nanotube junctions will get hot when you pass current through them," said Joseph Lyding, an electrical and computing engineering professor at the University of Illinois. "We use these hot spots to trigger a local chemical reaction that deposits metal that nano-solders the junctions."

Lyding's research team includes experts in materials engineering and chemistry. Chemistry professor Greg Girolami, an expert in chemical vapor deposition (CVD) placed a carbon nanotube array in a chamber pumped full of the metal-containing gas molecules.

When a current passes through the transistor, the junctions heat because of resistance as electrons flow from one nanotube to the next. The molecules react to the heat, depositing the metal at the hot spots and effectively "soldering" the junctions.

Then the resistance drops, as well as the temperature, so the reaction stops (as seen in the accompanying video).

The nano-soldering takes only seconds and improves the device performance by an order of magnitude—almost to the level of devices made from single nanotubes, but much easier to manufacture on a large scale, according to the researchers.

"It would be easy to insert the CVD process in existing process flows," Lyding said. "Ultimately it would be a low-cost procedure."

The National Science Foundation and the Office of Naval Research supported this work.

The Illinois team has published its results in the journal Nano Letters.

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