Field-emitter-array development for microwave applications

Microfabricated field-emitter arrays are being investigated as a means for gating or prebunching electrons in a microwave amplifier tube. The goals of the program are to demonstrate 10-dB gain at 50 W and 10 GHz in a gated klystrode(R) amplifier tube with 50% efficiency. The cathode specifications call for 160-mA peak emission at 10-GHz rates from an annular emitter array having a 600-mu m outer diameter and an inner diameter to be determined by cathode capacitance, emitter-tip loading, and transconductance (G(m)) considerations. We have shown that an average array capacitance of 6 nF/cm(2) and emitter-tip loadings of 10 mu A/tip can be routinely achieved with G(m) approximate to 1 mu S/tip. Calculations based on these results show that an array having 0.4-mu m-diam gate apertures on 1-mu m centers, a 600-mu m outer diameter, and a 560-mu m inner diameter would be a reasonable first design to meet the tube specifications. Such an array would have a predicted capacitance of 2.18 pF, a peak G(m) of 29.4 mS, and would produce a peak emission of 160 mA with a tip loading of 4.4 mu A/tip. The power dissipated in driving the gate at 10-GHz rates would be between 0.1 and 1.0 W. (C) 1996 American Vacuum Society.