Development of ultrafast electronic oscillator by exploiting advantage of cold cathodes

Origin of the upper frequency limit in vacuum devices was investigated. New analytical theory was developed for a simple vacuum diode in which electrons are launched on a cathode surface and are accelerated or decelerated toward an anode by a DC-biased AC electric field. We found electrons or charge carriers collectively arrives on the anode surface regardless of the frequency of the AC electric field if a diode configuration and the electric field are manipulated with some parameter values given by our theoretical calculations. The extraordinary collective behavior of electrons exceeds the transittime limit which has given the upper frequency barrier in transitional electronic devices. For the novel electron devices, cold cathodes which emit electrons by the field emission is preferable to conventional thermionic cathodes because of the high nonlinearity between the current and the applied voltage. We are expanding the principle to develop a novel electronic oscillator that can operate in the terahertz frequency regime which demands ultrafast physical phenomenon.