Vacuum tubes formed the core of computing right up to the 60s but then died a quick death thanks to the availability of the silicon transistor, which both sized and priced the vacuum tube out of the market. Was this then, the limit of where vacuum transistor technology could take us? Certainly one look at a tube of the time, its size and complexity would suggest so, however, researchers at NASA have rekindled the concept of such a device, applying modern, nano-scale concepts to its design.
Why bother rekindle an old technology? Silicon transistors are cheap, but also, believe it or not, slow and, as we already know, susceptible to radiation. Originally, the performance of silicon transistors sped away from their vacuum tube predecessors due to their compact size, reducing the time it took for electrons to travel, however, like-for-like in size, electrons travel much slower through a solid material than a vacuum, around 10 times slower in fact and, it's this solid material that can change state or generate erroneous charges when hit by radiation, something which NASA isn't very fond of.
NASA's new nano vacuum tubes are created by spacing a source, a gate and a drain around a phosphorous-doped 150nm silicon cavity. At 150nm in size, the cavity is so small that there is minimum interaction between electrons and the air, avoiding the need to form a true vacuum, pulling down the cost and complexity of manufacture.
The technology does have immediate potential for consumer use too; with switching speeds of up to 0.46 terahertz achieved, this could be the enabler for terahertz communication that is a current hot topic.