FIELD-EMITTER-ARRAY DEVELOPMENT FOR HIGH-FREQUENCY OPERATION

Power amplification at high frequencies is one of many applications un der investigation using vacuum microelectronics technology. The result s 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 ca n be operated is determined by the capacitance of the structure and th e 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. Str uctures having a capacitance in the range of 0.1 pF have been fabricat ed, and total emission currents of 25 mA with current densities of 100 0 A/cm2 have been demonstrated with a 0.1 pF structure having 625 emit ter tips (40 muA/tip). The transconductance under these operating cond itions was 500 mus or 0.8 muS/tip. Simultaneous experiments with our s tandard low-frequency Spindt-type cathode geometry have shown that ave rage emitter tip loadings of 200 muA/tip and transconductances of 5 mu S/tip can be achieved. A 625-tip, 0.1-pF array with transconductance o f 5 muS/tip would have a cutoff frequency of about 5 GHz. The factors determining the capacitance and transconductance of the device and met hods for improving performance are discussed.