NASA's Ames Research Center could be bringing the vacuum tube back, at least spiritually, with vacuum-channel transistors. Two researchers there accidentally built this new kind of transistor when working on a single nanowire, and they wrote a description of what they built for IEEE Spectrum. Vacuum-channel transistors are built on the same idea as the vacuum tube of old: two electrodes (using transistor-style terminology, "source" for the cathode, "drain" for the anode) are placed in close proximity, separated by a vacuum. The flow of electrons from the source to the drain is governed by the voltage applied to what is called the gate. Unlike the tubes of old, however, NASA's vacuum-channel transistors measure the gap between electrodes, not in millimeters but in nanometers. Making them nanoscale has a couple of key advantages. First, it means that the vacuum-channel transistors don't actually need a vacuum. Vacuum tubes use a vacuum because without it, electrons collide with air molecules, ionizing the gas, which both damages the cathode and lets uncontrolled currents flow. When the gap is small enough, the chance of an electron colliding with a gas molecule is so low that this problem no longer arises. NASA's vacuum-channel transistor uses helium at atmospheric pressure in its gap. Second, the small scale means that thermionic emission isn't needed any more. Instead, a process called field emission can be used—electrons can be emitted by a cathode simply by placing the cathode in a strong static electric field. This removes the need for the heaters and corresponding power usage. More via Ars Technica.
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