Pretty much the only place you see vacuum tubes any more is inside a quality audio amp. But, once upon a time, they were the primary ingredient in any piece of electronic equipment, including computers. The glass tubes have since been replaced with the smaller, less fragile and cheaper to manufacture silicon transistor. There are, however, disadvantages, to transistors. For one, electrons tend to move more slowly though the semiconductors, and two, they're highly susceptible to radiation. The second of those problems doesn't affect us much here on Earth, but for NASA it poses a major obstacle. Engineers have finally managed to combine the advantages of both vacuum tubes and silicon transistors, though, in what has been dubbed "nano vacuum tubes." They're created by etching tiny cavities in phosphorous-doped silicon, bordered on three sides by electrodes that form the gate, source and drain. The term "vacuum tube" is slightly misleading however, since there is no true vacuum in play. Instead, the source and drain are separated by just 150 nanometers, making it highly unlikely that flowing electrons would run into stray atoms. In addition to their space-worthy hardiness, they can also potentially operate at frequencies ten-times as higher than silicon transistors, making them a candidate to push terahertz tech from experimental to mainstream. For more, check out the source link.
[Image credit: Shane Gorski]