Aligned carbon nanotubes/fibers for applications in vacuum microwave amplifiers

TLDR

Long‑range telecommunication relies on microwave links, and future amplifiers will need to operate at 30–100 GHz with tens of watts, making the high‑conductivity, high‑aspect‑ratio, thermally stable carbon nanotubes attractive emitters. The study describes plasma‑enhanced CVD growth of vertically aligned CNTs and demonstrates that well‑controlled arrays can deliver ~1 A cm⁻² under DC and 1.5 GHz modulation. CNTs are grown by plasma‑enhanced CVD to form vertically aligned arrays, which are then operated as cold cathodes under direct current and 1.5 GHz direct modulation to achieve high current densities. These CNT cold cathodes offer considerable weight and size savings over conventional hot cathodes used in microwave applications such as SATCOM and radar.

Abstract

Most long-range telecommunication systems are based upon microwave links. The transmitters use microwave amplifiers which in the very near future will be required to work at up to 30–100GHz with output power in the region of a few tens of watts. Carbon nanotubes (CNTs), which exhibit extraordinary field emission properties because of their high electrical conductivity, ideal high aspect ratio whisker-like shape for geometrical field enhancement, and remarkable thermal stability, can be used as the emitter in such applications. This article will describe the plasma enhanced chemical vapor deposition growth of vertically aligned carbon nanotubes, and how well controlled arrays of such structures can be grown. We will also describe how high current densities of ∼1A∕cm2, under direct current and 1.5GHz direct modulation, can be obtained from CNT cathodes. These CNT cold cathodes offer considerable weight and size savings over conventional hot cathodes used in microwave applications (e.g., SATCOM, radar).