Friday, December 14, 2007

Expandable Silicon

A new chip design could lead to cheaper solar panels, sensor networks, and flat-screen TVs.

By Kevin Bullis

Growing chips: Researchers have built chips (top) that can be expanded for large-area applications (bottom). Credit: Peter Peumans

A new design for silicon-based chips makes it possible to mechanically stretch them out to cover large areas. These expanded chips, which could be thousands of times the size of the original, could be used to make cheaper solar panels, sensor networks, and flat-screen TVs.

The chips, built by researchers at Stanford University, consist of free-floating islands of silicon surrounded by coils of silicon wire. Each island can be processed to include transistors, sensors, or materials for tiny solar cells. When the corners of the chip are pulled on, the coils around the silicon islands unwind. As they do, the islands, which start out nearly touching each other, spread apart. The end result is a netlike array of silicon devices.

So far the researchers have demonstrated arrays that are 50 times larger than the original chip, but they've been limited by the size of their laboratory equipment. Peter Peumans, the professor of electrical engineering at Stanford who led the work, says that the chips could be made to expand thousands, or even tens of thousands, of times. Peumans's work was presented this week at the International Electron Devices meeting in Washington, DC.

Silicon nets: Using conventional silicon-processing techniques, researchers at Stanford University have built chips that consist of islands of silicon surrounded by silicon coils. The top-left image shows one such silicon island, and the bottom-left image shows the entire chip composed of an array of these islands. When the corners of the chip are pulled, the coils unwind, and the islands spread apart. The finished network is shown at the bottom right. The top-right image shows the coils completely unwound.

The work is "taking the integrated circuit concept that has been so successful in microelectronics and adapting it to large-area applications," says Marc Baldo, a professor of electrical engineering at MIT. The semiconductor industry has excelled at packing more high-performance transistors into a given space, driving down the cost per transistor in the process. But many applications require that transistors and other silicon-based devices be more distributed.