Electron movements in silicon transistors are limited by collisions and scattering. What if the bumps are removed and the electrons can travel freely in empty space? Such a phenomenon is possible in vacuum transistors to achieve the ultimate in transistor speed and efficiency.
Researchers in Pittsburgh University’s Swanson School of Engineering led by Hong Koo Kim proposed a return to vacuum transistors in their study published in the July 1 issue of Nature Nanotechnology. This is a dramatic shift from silicon electronics back to vacuum electronics.
It is to be recalled that the invention of semiconductor transistors in the 1940s paved the way for the replacement of bulky vacuum tubes that require high voltage inputs to operate. Since then, the number of silicon transistors placed inside integrated circuit boards have doubled every two years, a phenomenon called Moore’s Law.
Moore’s Law is due to advancements in the fabrication of silicon transistors that have steadily shrink in size. This allowed the design of increasingly small electronic devices such as computers and smart phones. However, as the size of a transistor device approaches the nanometer scale, it is more difficult to apply Moore’s Law.
Physical limitations in solid-state transistor devices hinder the fabrication of better electronics, according to Kim. The limit of transistor speed is dictated by the electron transit time from one device to another. In solid-state medium, this speed is hindered by electron collisions and scattering. That is why Kim’s group looked back to the re-use of vacuum transistors where electrons can theoretically achieve the ultimate speed for a more efficient functionality.
Kim’s research group discovered that electrons trapped inside a semiconductor at the interface with an oxide or a metal layer form a sheet of charges called an electron gas. The coulombic repulsion between electrons in this sheet makes it easy to displace these electrons with a minimum application of voltage. The displaced or emitted electrons can then be routed to a nanometer-scale vacuum channel where they can travel ballistically without hindrance.
Kim reported that their findings could pave the way for a new class of low power, high-speed transistors with nanoscale vacuum channels that are compatible with current silicon electronics. These transistors could complement the existing electronic technology with faster and more energy-efficient functionality due to their low voltage requirements.
In any case, the potential is open for the comeback of vacuum tubes in a different and improved design.