By using light beams in place of metal wires, engineers at Johns Hopkins have devised a cost-effective way to speed up the way microchips "talk" to each other. The method, created by a team in the Whiting School's Department of Electrical and Computer Engineering, takes advantage of unusual characteristics associated with silicon on sapphire technology, a new way to manufacture microchips.
"We've developed a very fast and cost-effective way of getting data on and off a chip without using wire," says Andreas G. Andreou, a professor in the department and director of the lab in which the work was done. "It really promises to revolutionize how computer systems for homes and businesses are put together."
Andreou's team relies on the same fiber optics technology that is used to carry phone conversations across great distances. These components are incorporated into a new type of microchip technology. The microchips inside most modern computers are assembled on thin slices of silicon, a material that is a semiconductor. The Hopkins engineers use microchips in which silicon is layered onto thin slices of synthetic sapphire, a material that is an insulator and also allows light to pass through it.
In the microsystem devised by Andreou's team, a signal that originates in a wire is transformed into light and beamed through the transparent sapphire substrate via a laser that is only slightly larger than a human hair. Microlenses and other optical components, manufactured at the same time as the electronic circuits on the microchip, collect the light beam and guide it to another place on the microchip or, using an optical fiber, move it to another chip.
At its destination, the light enters a high-speed optical receiver circuit that transforms the stream of photons into a stream of electrons that continue their journey through electrical wiring connected to other computer components. By using optical signals, or simply an unhindered laser beam, the Hopkins researchers believe a signal could move 100 times faster than it does along a metal wire. Also, the optoelectric interface circuits require much less power because the sapphire substrate is an insulating material, not a semiconductor. This property of the substrate reduces the power dissipation that commonly occurs in modern microprocessors when signals travel through wires that have capacitances, which are parasitic components that not only degrade the signals but also increase the power consumption of the system.
The new design is expected to significantly speed the movement of data between electronic components across a single chip and from one chip to another for a simple reason: "Without the parasitic capacitances, it's much faster to send signals at the speed of light," says Alyssa Apsel, a doctoral student in the Anderou lab who helped develop the system.
Andreou and Apsel wrote about the breakthrough in an article published in the November 2001 issue of IEEE Circuits and Systems Magazine. Their co-authors were Zaven K Kalayjian, a former Johns Hopkins doctoral student; Phillippe O. Pouliquen, a Johns Hopkins postdoctoral fellow; Ravi A. Athale, formerly of George Mason University and now at the Defense Advanced Research Projects Agency; George Simonis of the Army Research Laboratories; and Ron Reedy of the Peregrine Semiconductor Corp. Also, in the Sept. 13, 2001, issue of the journal Electronics Letters, Apsel and Andreou reported on this new design and described a high-speed, very low-power optical receiver that uses this new technology.
The project was supported by grants from the Army Research Laboratories and the National Science Foundation.