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Can Vacuum Tubes Solve the Moore's Law Problem?

A research group led by Hong Koo Kim at the University of Pittsburgh's Swanson School of Engineering is proposing a switch from the use of silicon electronics back to vacuums as a medium for electron transport. The University of Pittsburgh solution could help solve one of the difficulties chip designers will face in trying to extend “Moore's Law,” the name given to the ability of the number of transistors on integrated circuits to double every two years. “Moore's Law” has held for the past 40 years, but it will be hard to continue reducing transistor sizes. Hong Koo Kim said, “Physical barriers are blocking scientists from achieving more efficient electronics. We worked toward solving that road block by investigating transistors and its predecessor—the vacuum.”

Kim explained that the ultimate limit of transistor speed is determined by the “electron transit time,” or the time it takes an electron to travel from one device to the other. “Electrons traveling inside a semiconductor device frequently experience collisions or scattering in the solid-state medium.” He compared this to driving a vehicle on a bumpy road—cars cannot speed up very much. “The best way to avoid this scattering—or traffic jam—would be to use no medium at all, like vacuum or the air in a nanometer scale space, Think of it as an airplane in the sky creating an unobstructed journey to its destination.” 

Of course, one of the problems with conventional vacuum tubes is they require high voltages that aren't compatible with many applications or other circuits. The University of Pittsburgh news release explains Kim's solution to this problem:

“With the assistance of Siwapn Srisonphan, a University of Pittsburgh PhD candidate and Yun Suk Jung, a Pitt postdoctoral fellow in electrical and computer engineering, Kim and his team discovered that electrons trapped inside a semiconductor at the interface with an oxide or metal layer can be easily extracted out into the air. The electrons harbored at the interface form a sheet of charges, called two-dimensional electron gas. Kim found that the Coulombic repulsion—the interaction between electrically charged particles—in the electron layer enables the easy emission of electrons out of silicon. The team extracted electrons from the silicon structure efficiently by applying a negligible amount of voltage and then placed them in the air, allowing them to travel ballistically in a nanometer-scale channel without any collisions or scattering.”

Kim said, “The emission of this electron system into vacuum channels could enable a new class of low-power, high-speed transistors, and it’s also compatible with current silicon electronics, complementing those electronics by adding new functions that are faster and more energy efficient due to the low voltage.” 

This isn't the first research to propose use of a vacuum channel in a transistor. In May I wrote about work at the NASA Ames Research Center at Moffett Field, California on A New Take on Vacuum Tubes.