The $200-billion computer chip industry, famous for pushing at the boundaries of physics, faces a problem that is both very small, and very big. By 2010, microprocessors' tiny transistors will be operating at speeds faster than they will be able to talk to one another. Electronic signals will no longer be enough. It's a problem known as the interconnect bottleneck.
The solution may be just that — a solution: a tiny vial of watery brown fluid that is the result of some two years of research at the University of Toronto. The liquid is, in fact, a laser, that could enable transistors to communicate at the speed of light. It produces the specific wavelength of invisible light that could one day be used to carry information within microprocessors and between them. “Optical interconnects [such as this one] have been on the table for a long time, it's just that we didn't have a source of light that we can put onto a chip easily,” says Ted Sargent, the U of T nanotechnology professor who led the research. “What could be easier than painting it on?”
The paint contains nanometre-sized particles of lead sulfide, a synthetic semiconductor material that, unlike silicon, is able to produce the precise colour of infared light used in fibre optics. “There's an entire physical infrastructure of optical communications components that have been built to work at exactly that wavelength,” says Sargent. “We showed that we can make a paint-on laser that produces that precise colour of infrared light.”
The size of the nanoparticles determines the wavelength of infrared light they produce, which means they can be “tuned” to specific wavelengths. It only takes a couple of hours to produce the paint, though. “Then it's just a matter of coating it on whatever you're trying to make,” says Sargent. To make a laser-on-a-chip, a droplet of paint would be spin-coated into a film one-micron (1/1000th of a millimetre) thick on the surface of a chip.
Challenges remain, however. For instance, researchers still need to learn how to energize the laser with an electrical current, so that it can be integrated into silicon electronics. Also, the laser only works right now at about 0ûC, well below the temperatures inside a computer. With 2010 approaching fast, the heat is on.