@tubetime the Vacuum Transistor allows fabrication of chip-scale vacuum tubes on normal CMOS process. These devices switch in the terrahertz range and require neither a heated filament nor a vacuum, since the source-to-drain distance is shorter than the mean free path (which means electrons won't hit any other atoms along the way): https://spectrum.ieee.org/introducing-the-vacuum-transistor-a-device-made-of-nothing