'Silicon Velcro' could make sticky chips

New Scientist Tech ^ | 19 June 2006 | Tom Simonite

[annie laurie]

An exotic form of silicon that can be stuck together and then peeled apart has been developed by German researchers.

The material, dubbed "silicon Velcro", could be used to manufacture microprocessors and devices that manipulate fluids on microscopic scales.

Researchers at the Technical University of Ilmenau in Germany created the material from "black silicon". This is generated when normal silicon is hit with a powerful laser beam or bombarded with high-energy ions, producing a dense, microscopic array of needle-like structures on its surface. Light bounces around between the needles without escaping to give the material its black appearance.

The German team used high-energy ions to generate black silicon bristling with around 1 million needles per square millimetre. Each needle is about 15 to 25 micrometres in length. They found that two surfaces covered with the material adhere when pressed together. Microscope analysis shows this is because the needles on each surface jam in between one another under pressure.

Mike Stubenrauch, a member of the research team, says silicon Velcro could prove useful for microchip manufacturers. It could help engineers manipulate very thin layers of silicon without using heat or adhesives, which can damage components.

"The Velcro could be used as a carrier system," Stubenrauch told New Scientist. "A carrier wafer could be used to pick up the thin wafer and hold it for processing."

Stubenrauch and colleagues also used the material to create devices that control the flow of fluids on microscopic scales, for chemical sensing and analysis. These devices are made by sticking together a layer covered with tiny grooves and another, smooth layer.

The layers of silicon Velcro can be unstuck afterwards, Stubenrauch says, "to retrieve a valuable substance or examine what has happened inside".

Silicon Velcro can be used more than once, but not indefinitely, Stubenrauch adds. "Some of the needles break, so you can't do it very often," he says. "Maybe three or four times, depending on how careful you are."

Until now, research involving black silicon has focused on its light-absorbing properties, explains Darren Bagnall, a microelectronics researcher at Southampton University, UK, who is using the material to make efficient solar cells. But he says the new technique sounds promising.

"This is a nice idea," Bagnall told New Scientist. "It's a simple and robust process that is easy to implement and then reverse."

Being able to stick silicon components together quickly could be useful for making complex microchips, he says: "If you want to quickly bolt together chips made using different processing technologies, this Velcro would be good."

[randog]

Kewl. Now I can build a Lego transistor!