Small carbon nanotube cold field emission source for microwave device

We developed a new method to manufacture discrete miniature cold cathodes for microwave devices by hot bonding CVD grown CNT with Ball Grid Array (BGA) Tin alloy spheres to form a small cathode. First the CNT is grown on a Si wafer with CVD method, next a BGA Tin alloy sphere is placed on top of the CNT, and a hollow metal tube is pressed on the BGA sphere, then the whole set up is heated for several minutes. The heat causes the BGA sphere to melt and weld the CNT with the metal tube. When the metal tube is removed from the wafer, the CNT is detached from the wafer surface and transferred to the melted BGA sphere, thus a miniature CNT filed emission source is formed. The cathode diameter is 0.5 mm, and the turn-on field (defined as the field when field emission current density reaches 1 mA/cm²) is less than 3 μV/m, with good field enhancement factor β around 2200. The introduction of the alloy between the CNT and the metal tube together with the pressured melting process greatly enhances the field emission capability because the Schottky barrier between these two is lowered while the mechanical strength is enhanced.