These initial results are impressive, says Milton Feng, professor of electrical and computer engineering at University of Illinois at Urbana-Champaign. “Professor del Alamo has provided the first experimental evidence that a 60-nanometer indium-gallium-arsenide [transistor] can outperform a 65-nanometer silicon [device].” He adds that the work has “significant implications,” and he indicates that compound semiconductors could be a good solution to some of the problems the chip industry faces as device dimensions shrink.
But this speedy transistor is still just a demonstration of the potential of compound semiconductors, and it’s far from overtaking silicon on the manufacturing line. While faster than today’s transistors, compound semiconductor transistors will only be economically feasible when silicon gate lengths are roughly 20 nanometers, near its physical limit. Therefore, to really extend Moore’s Law, the compound semiconductors need to be fabricated with gate lengths of at least 20 nanometers. One of the hurdles is to find an appropriate gate material that works well at the smaller dimensions, as indium aluminum arsenide may not be the best choice.
Additionally, the microprocessor industry has spent decades and billions of dollars perfecting silicon manufacturing. A complete materials transition would be horrifically costly. Some researchers are investigating ways to smoothly integrate compound semiconductors into this process by using standard silicon wafers as a substrate and building the new chips on top of them. But silicon and compound semiconductors don’t easily stack on top of each other, so the challenge is to find a buffer material to go in between them.
More and more researchers are beginning to seriously look at these problems, says del Alamo, whose research is funded in part by Intel (see “Beyond Silicon”). He expects that as the ranks grow, many issues will be resolved. Del Alamo estimates that he could have a working prototype for a 20-nanometer device in two to three years. When this happens, he says, it will show that materials other than silicon could have merit in the microprocessor fabrication plants. “If the promise is there, and there’s a chance to continue Moore’s Law, then the industry will be able to work on these [manufacturing] problems and solve them.”