The physics of vacuum microelectronic devices

Vacuum microelectronics combines solid-state fabrication and processing with vacuum ballistic electronic transport. The resultant technology promises terahertz power amplifiers and oscillators, radiation hardness, subpicosecond digital switching, and temperature insensitivity in a device as small as, or smaller than, standard solid-state devices. At present vacuum microelectronic devices are based on field-emitter arrays (FEAs), which do not depend on single-crystallinity, material purity, or PN junctions. They do, however, depend on highly controlled three-dimensional nanostructure fabrication and the physics of electron transport and tunneling in those structures. Classical electron field emission has been dominated by a single parameter: the work function. Although field-emitter work functions are important in vacuum microelectronic devices, bulk nonequilibrium electron transport in fields greater than the classical breakdown field may be more important. Furthermore, emission stability might be obtainable if velocity saturation and current crowding can be incorporated into FEAs properly. Monte Carlo scattering calculations suggest a possible cause of the well-known catastrophic FEA breakdown. The same calculations point to a fundamental frequency limit in semiconductor FEA-based vacuum microelectronic devices.