Power amplification at high frequencies is one of many applications under investigation using vacuum microelectronics technology. The results of an ongoing program to develop a gigahertz amplifier using Spindt-type field-emitter arrays are reported. The maximum frequency at which a field-emission source in the form of a Spindt-type cathode array can be operated is determined by the capacitance of the structure and the transconductance of the array. It has been shown that by fabricating arrays with high emitter-tip packing densities and small total areas it should be possible to achieve operation in the gigahertz range. Structures having a capacitance in the range of 0.1 pF have been fabricated, and total emission currents of 25 mA with current densities of 1000 A/cm2 have been demonstrated with a 0.1 pF structure having 625 emitter tips (40 μA/tip). The transconductance under these operating conditions was 500 μs or 0.8 μS/tip. Simultaneous experiments with our standard low-frequency Spindt-type cathode geometry have shown that average emitter tip loadings of 200 μA/tip and transconductances of 5 μS/tip can be achieved. A 625-tip, 0.1-pF array with transconductance of 5 μS/tip would have a cutoff frequency of about 5 GHz. The factors determining the capacitance and transconductance of the device and methods for improving performance are discussed.
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Spindt et al. (1993) studied this question.