High current density nanofilament cathodes for microwave amplifiers

We study high current density nanofilament cathodes for microwave amplifiers. Two different types of aligned nanofilament array have been studied: first, metallic nanowires grown by electrodeposition into nanoporous templates at very low temperature (T<100°C) on a silicon wafer; second, carbon nanotubes/nanofibers (CNs) grown by catalytic plasma enhanced chemical vapour deposition. The fabrication process and the field emission properties of these two types of cathodes will be presented. Presently, the best results are obtained with CN cathodes. Arrays of 5.8 μm height and 50 nm diameter CNs exhibit geometrical enhancement factor (h/r) of 240±7.5%. Moreover, currents close to 100 μA per emitter have been measured using a scanning anode field emission microscope. Due to these properties, 0.5 × 0.5 mm² arrays emit a 2 mA current corresponding to 0.8 A/cm², in DC mode. The use of these cold cathodes in microwave triodes delivering 10 to 50 W at 30 GHz will be discussed for future telecommunication applications.