Graphene flash memory cells perform better because of the material’s unusual chemical structure and electrical properties, says Kang Wang, professor of electrical engineering at UCLA, who led the work. Part of the problem with silicon-based flash is that as memory cells get smaller, the transistor gates have to be thicker relative to the rest of the circuit in order to store sufficient charge, and these thick-gated cells tend to interfere with their neighbors. Because gates made from graphene are ultrathin, says Wang, they do not interfere with one another. Graphene can also hold much more charge than silicon without its leaking out—another problem with conventional flash as the cells are miniaturized.
So far, the graphene flash memory cells the researchers have made are relatively large—on the order of ten micrometers. But graphene, unlike silicon, has no known physical properties that would cause a dip in performance as the devices are miniaturized. “Their simulation results suggest that graphene-made devices can be scaled down to about ten nanometers,” says Barbaros Özyilmaz, assistant professor of physics at the National University of Singapore, who was not involved with the research. Conventional flash is expected to become unstable below about 22 nanometers.
Wang says the researchers are now building smaller graphene cells to test. His group collaborated with researchers from Samsung on the project and is talking with Micron about commercialization.
“One question is when to get started with putting graphene on a commercial process line,” says Wang. Semiconductor manufacturing is an extremely well controlled process—defects at the scale of single atoms can turn a high-performance chip into trash—so introducing a new material takes much time and care.
Wang says that in theory, it should not be difficult to add graphene to chips, because the material is relatively stable and can be grown on wafers using processes that are already common in chip manufacturing plants.