Growth and characterization of carbon nanotubes for improved field emission

Abstract

Carbon nanotube (CNT) based cold cathodes are considered to be the most promising material for fabrication of next generation high-performance flat panel displays and vacuum microelectronic devices. Various improvisations in the synthesizing techniques in order to improve the field emission properties of the CNTs like use of buffer layer, effect of thickness of the buffer layer used, control of the density of the CNTs produced by chemical vapor deposition (CVD) technique, growing CNTs on Inconel super alloy to increase the current density, decoration of the grown CNTs with aluminium (Al) and copper (Cu) to reduce the turn on and threshold field of emission and a simple, novel method for infiltrating iron (Fe) nanoparticle into the CNT forest with the help of a magnet have been presented. A detailed report on increase in the current density from 10 mA/cm2 to 30 mA/cm2 with the help of titanium (Ti) buffer layer have been presented. Moreover, improved adhesion of CNTs with the substrate due to the incorporation of Ti buffer layer have also been studied. Secondly, the effect of varying the thickness of the Ti buffer layer on the field emission properties of CNTs are discussed. This was followed by the investigation of a simple density control technique during the CNT synthesis with the help of Ti capping layer. This method not only improved the density of the CNTs grown by CVD but also increased the adhesion of the CNTs with the substrate and reduced the screening effect to a larger extent. The result of increasing the current density to around 100 mA/cm2 by growing CNTs on Inconel super alloy is discussed in detail. Further, the limitations of the CNTs grown on silicon (Si) like early arcing, rapid failure of the device is also discussed. This is followed by the development of new technique of decorating the CNTs with Al and Cu for enhanced field emission characteristics. The technique is shown to yield ultra low turn on and threshold voltages of 0.13 V/μm and 0.14 V/μm respectively for the Al decorated CNTs grown on Al coated Si. The excellent field emission properties of the metal decorated CNTs is shown to be due to the edge effect, reduced screening effect, lower contact resistance. A thorough investigation of the development of one step process of infiltrating Fe3O4 nanoparticles into the CNT forest by a novel and simple technique with the help of a magnet has been reported. The results presented here may be adopted for CNT based cold cathodes suitable for high power microwave vacuum devices and also for long-life low-power applications.