March/April 2008

Expandable Silicon

A new chip design could lead to far cheaper large-area electronics.

By Kevin Bullis

An array of silicon discs is expanded in a laboratory setup. Such arrays can expand to as much as 50 times their original area and be molded to curved surfaces for applications such as structural sensing. Credit: Jonathan Sprague

Multimedia •  View images of the silicon discs and see how they are designed. •  Watch videos of the arrays expanding.

The semiconductor industry is great at miniaturizing silicon devices and packing huge numbers of them into very small spaces. But for some applications, such as big-screen displays, it's helpful if transistors and other silicon-based devices are distributed relatively sparsely across many centimeters or even meters. Traditionally, cheap methods for distributing electronics over large areas have produced low-­performance devices; improving performance has required lots of expensive silicon.

Now Peter Peumans, a professor of electrical engineering at Stanford University, and his colleagues have developed small silicon chips that can be mechanically expanded to cover large areas, including curved surfaces such as the one pictured above. The chips consist of discs of sili­­con with silicon wire spooled around them. Each disc can incorporate transistors, pressure sensors, or tiny solar cells. When the corners of the chip are pulled, the wires coiled around the silicon discs unwind. As they do, the discs, which start out nearly touching each other, spread apart. The result is a netlike array of silicon devices.

Peumans is working with Boeing to put crack-­detecting sensors between layers of structural composite materials on aircraft. And he founded NetCrystal in Mountain View, CA, to make photovoltaic panels that spread out islands of photovoltaic chips in a way that exposes them to more sunlight, without the need for focusing lenses or mirrors. What's more, distributed high-performance transistors could control pixels in next-generation displays, such as those based on organic light-­emitting diodes.