Development of microminiature thermionic vacuum tube devices

Vacuum microelectronic devices called microminiature thermionic vacuum (MTV) tubes have been fabricated on silicon wafers. The operation of these MTV devices is based on the thermionic electron emission of low work function materials on a directly heated filament. There are many advantages and applications for MTV devices. MTV devices are very small in size (micron-scale) and are more reliable in rugged, harsh and radiation hard environments. Unlike semiconductor devices, MTV devices do not suffer from the mobility or velocity saturation problems of carriers; therefore they can be used in higher speed and frequency applications. Potentially, MTV technology can be widely used in flat panel displays, electron beam writing sources and some electron beam based tools (i.e., SEM, TEM, etc.). In this research work, the fabrication technology of MTV devices based on the vacuum tube technology combined with the thin-film deposition and photolithography delineation techniques of conventional silicon integrated circuits has been developed. Techniques for the coating and the activation of low work function materials (mixture of crystals of barium oxide, strontium oxide and calcium oxide) on the micron-scaled cathodes also have been developed. The fabricated MTV diodes and triodes are tested in a high vacuum chamber. The air-bridge structures and the choices of materials permit the MTV devices to have low power consumption. Both MTV diodes and triodes have achieved good performance. MTV diodes have been characterized and follow the Child's law as with conventional tubes. MTV coplanar-grid and barshaped-grid structure triodes using micro plating techniques were fabricated and tested. The improved characteristic of the bar-shaped-grid triode compared to the coplanar one has been shown. A finite difference simulation program has been written and the simulation results also have been compared to the experiment results of MTV triodes.;The choice of the substrate (silicon), the small feature size and the low power consumption characteristic (about one mW) provide much potential for the integration of MTV devices with conventional silicon VLSI circuits. The excellent performance of MTV devices also shows a very promising future in the vacuum microelectronics arena.