Chips that communicate with pulses of light instead of electrical signals could lead to computers that are more power-efficient than today’s best machines and up to 1,000 times as fast. IBM researcher Solomon Assefa has brought this prospect a critical step closer.
Assefa has developed a new way to make a photodetector, a very sensitive device that amplifies optical signals and converts them into electrical signals that can be shuttled around in a microprocessor. Ordinarily, photodetectors are made using a process called chemical vapor deposition. But sticking with this process for chip-to-chip connections would make microprocessor manufacturing prohibitively expensive. Instead, Assefa seeds germanium onto a silicon wafer, and then melts it to achieve the regular crystal structure that makes for a good photodetector material. He has also determined when in the chip manufacturing process the photodetector should be added in order to get the best performance possible without degrading the surrounding electronics.
Assefa can demonstrate the performance of his photodetector in the lab. But before a chip incorporating his creation can be commercialized, he will have to figure out how all the rest of its elements can be integrated efficiently. Making today’s integrated circuits requires hundreds of steps and dozens of lithographic masks, the stencils used to pattern features on chips. “We don’t want to change any of these processes or it really increases the costs,” he says. —Katherine Bourzac