Aligned carbon nanotubes/fibers for applications in vacuum microwave amplifiers

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 30-100 GHz with output power in the region of a few tens of watts. Carbon nanotubes ͑CNTs͒, 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 ϳ1 A/cm 2 , under direct current and 1.5 GHz 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, radar͒.

Degradation of a CNT-Based Field Emission Cathode due to Ion Sputtering

“…Such a possibility is caused by the effect of the enhancement of the electrical field (6) due to which the electrical field strength in a vicinity of the nanotube's tip can exceed hundreds times that in the inter-electrode gap. The array of CNT-based cathodes and prospects of their usage in flat displays (7)(8)(9), X-ray and lighting tubes (10) as well as in MW generators and amplifiers engaged into space communication systems (11,12) make the problem of establishing the physical factors limiting the lifetime of the abovelisted devices and mechanisms of degradation of CNT-based cathodes topical. The present work studies one of the main mechanisms of degradation of such a cathode related to the sputtering of the CNT surface with residual gas ions.…”

Field emission characteristics of carbon nanotube films fabricated on a metal mesh by filtration

“…CNT emitters have been extensively explored not only for large area applications such as backlight units (BLUs) of liquid crystal displays (LCD) [4,5] and field emission lamps (FELs) [6,7] but also for small area but high current applications such as X-ray tubes [8][9][10][11] and microwave amplifiers [12,13]. For the latter applications, in particular, emission of high current from the small area CNT emitters may cause failure to them in a short period of time mainly due to Joule heating [14], field evaporation [15], or electrostatic interaction [16].…”

Carbon Nanotube Based Magnetic Tunnel Junctions (MTJs) for Spintronics Application

“…The orientation of CNTs is highly important in achieving the maximum benefit of its property. The ability to pattern or position carbon nanotubes (CNTs) with a vertical orientation in controlled arrays has been demonstrated by many researchers [104][105][106]. Conventional plasma enhanced (PE) CVD is an established technique for the synthesis of vertically aligned CNTs [107][108][109][110].…”