High-performance silicon field emitter arrays for microwave power tube cathodes

Summary form only given. Microwave power tube cathodes set the most demanding performance standards for any application of field emitter arrays. Hundreds of milliamperes of total emission current is required for useable output power. For gated cathode tubes operating in the gigahertz frequency range, the arrays must have low capacitance, and the materials used in fabricating the arrays must have low microwave losses. The relatively high current density required in an amplifier tube produces heating in the collector and a high probability of ion generation in the beam tunnel. These conditions conspire to produce a poor vacuum environment when compared to the ultra-clean, 10/sup -11/ torr UHV systems used in most field emitter research to date. MCNC has fabricated gated field emission cathodes for microwave power tube applications from single-crystal low resistivity silicon. The emitter tips are fabricated on silicon posts, increasing the distance between the cathode and the gate electrode and so lowering the parallel-plate capacitance of the device. The devices have uniform sharp tips and small gate aperture diameters, resulting in low turn-on voltage and good transconductance. In electrical testing done both at MCNC and the Naval Research Laboratory, the devices have yielded emission currents in the milliampere range at vacuum levels as high as 2/spl times/10/sup -8/ torr, comparable to the environment in an operating vacuum tube. A power gain of approximately 10 dB can be expected when these arrays are used as cathodes in an inductive output amplifier tube.