Electronic Design

Paint-on Laser Promises Speedier Interconnects

Armed with a brush and a hairdryer, Ted Sargent believes that the unique paint-on laser he has developed could eventually revolutionize semiconductor technology (see the figure).

The new laser is based on colloidal quantum dots—nanometer-sized semiconductor materials that are suspended in a solvent like particles in a paint. "The laser can literally be brushed onto another material, including a silicon chip," says Sargent, a professor of electrical and computer engineering at the University of Toronto.

Sargent and co-researcher Sjoerd Hoogland, a post-doctoral fellow at the University of Toronto, developed the technology to address the looming interconnect bottleneck that threatens to derail chip evolution as soon as 2010. As chips get increasingly dense, ever tinier and tighter wiring is leading to increased parasitic capacitance and signal propagation delay. In fact, sluggish communication between various chip parts is beginning to rival computational delays. Optical interconnects promise relief, but creating a cheap and practical optical-based chip communications technology has so far proven elusive.

Developing an optical interconnect is a two-stage process. Sargent notes that while a great deal of progress has been made by various research teams toward developing waveguides that can direct light around a chip, creating an efficient, nanoscale light source has proven to be a much more difficult task. He feels that his paint-on laser could solve the problem of creating light within a chip by allowing designers to simply dab-in lasers at critical circuit locations. Unlike a conventional laser, Sargent's creation requires no physical housing or dedicated power source. "We can generate light on a chip at exactly the right colors to allow it to travel freely across the chip," he says.

Optical data transmission requires infrared light. That's because light generated at the infrared wavelength of 1.5 µm travels farthest in glass. The new laser, which is stored in a vial and looks kind of like diluted ink, was engineered with particles that are just the right size to create 1.5-µm light.

Besides providing speedy interconnects within chips, the laser could also be used to bridge silicon chips and optical fibers. "You could bring together the technologies that make computers work with the technologies that make Internet communications work—and do it all on one chip," says Sargent. "That would be great for speed and it would also be great for cost."

Sargent says the biggest problem he faced was developing the concept and precisely crystallizing the nanoparticles that tune the laser's light. "The laser itself was created rather easily in about five minutes by dipping a miniature glass tube in the solution and drying it with a hairdryer," he says.

The prototype paint-on laser is excited by light that's emitted by another laser. A practical version will have to draw electricity from a circuit. "That's a challenge that still has to be solved," says Sargent, who already sees a light at the end of the waveguide.

University of Toronto

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