| 초록 |
Carbon nanotubes (CNTs) are one of the most promising field emitter materials due to their excellent electrical conductivity and chemical and mechanical stability as well as their high aspect ratios. Although much effort has been made to commercialize CNT field emitter devices, several obstacles, in particular, emitter lifetime, still remain to be overcome. Even though there are many factors affecting the lifetime of emitters working in a vacuum, residual gases inside a panel would be one of the most crucial causes, especially when the CNT emitters are made from the paste. The residual gases can cause a catastrophic damage to the vacuum microelectronic devices by electrical arcing or ion bombardment onto the cathode plate. Since the residual gases are a mixture of several different gas species, an effect of individual gas species on the field emission characteristics of CNT emitters has to be separately investigated to solve the complex problems related to the residual gases. In this study, we first investigated by a residual gas analyzer (RGA) the composition of residual gases inside the vacuum-sealed panel which was composed of a CNT emitter cathode plate, a phosphor anode, and glass spacers, all kept in a vacuum. The RGA data were obtained from the panel electrically operated for 3 days. H2, CO, CO2, N2, CH4, H2O, C2H6, and Ar were detected. The CNT emitter cathode was prepared in a diode structure by screen printing and photolithography of the photosensitive CNT paste. The sample was electrically conditioned in an oxidative ambient to secure uniform emission over a large area by level the height of the protruding CNTs which would first participate in the electron emission. It is expected that such a electrical oxidative conditioning enhances their emission stability and lifetime. The electrical conditioning was carried out by applying the pulse voltages with the duty ratio of 3.3%, which varied to keeping the constant emission current of 28 μA. The conditioning was continued until the electric field reached 9 V/μm under the oxidative gas ambient of 5x10-4 torr. The chamber was then evacuated and maintained at a high vacuum of ~10-8 torr for 10 h while field emission of still 28 μA, which would level off an emission current. Thereafter, each gas species were introduced to a vacuum chamber up to three different pressures (5x10-7, 5x10-6, and 5x10-5 torr) each for 1 h while electron emission where three different pressure regions were separated by keeping a high vacuum of ~10-8 torr for a 1 h. Here we attempted to study the effect of individual gas species and their pressures on the emission properties at the same time. The emission was terminated 6 h after the third gas exposure was completed. |
