Uniform Electron Field Emission from a Carbon-nanotube-based Cold Cathode with Micro-imprinted Microstructures

Abstract

Carbon nanotube (CNT) is an excellent field emitter due to its small diameter (1-40 nm), high aspect ratio (>103), and high theoretical current limit (~1 muA/SWNT). The applications like CNT-FED or HPM require uniform distribution of field emission current, low turn-on field, and high current density. However, macroscopic cathodes made from CNTs for CNT-FED and microwave devices have been shown to exhibit low emission site density (103-104 sites/cm2) compared to CNT density (109-1010 /cm2 ), non-uniformity in emission sites distribution, and lower current density achievable than dispenser cathode. The non-uniformity of emission sites distribution is closely related to field screening effect at individual sites. Only the CNTs with the highest local electric field can emit current. The effect of field enhancement factor, which is a strong function of local microstructure and a result of manufacture method, is found to be the dominate factor in deciding field emission current characteristics, and its effects surpass the work function of CNT, or the types of CNTs. An artificial microstructure is designed to utilize electric field screening effect and enhance electric field penetration around every CNT site so that a similar level of enhanced local electric field can be assured in each pre-designated site. These microstructures can be made by FIB, photolithography, or a low-cost micro-imprint technique. CNTs are deposited onto the surface by electrophoresis method. MAGIC simulation indicates that an improved field uniformity and penetration can be achieved by such microstructures