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^■ 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‐μm 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/cm² and emitter‐tip loadings of 10 μA/tip can be routinely achieved with G_m≊1 μS/tip. Calculations based on these results show that an array having 0.4‐μm‐diam gate apertures on 1‐μm centers, a 600‐μm outer diameter, and a 560‐μm 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 μA/tip. The power dissipated in driving the gate at 10‐GHz rates would be between 0.1 and 1.0 W.