Microgating carbon nanotube field emitters by in situ growth inside open aperture arrays

Abstract

Multiwalled carbon nanotubes were grown using chemical vapor deposition inside small apertures having a horizontal gate and a sidewall insulator spacer. Emission currents up to 140 nA per cell at 63 V have been obtained. These arrays have exhibited a gate current as low as 2.5% of the anode current throughout the entire gate voltage range, representing the lowest gate to anode current ratio of gated nanotube emitters reported to date. We attribute this feature to the emitter geometry and method of fabrication. The overall fabrication method required only a few and simple processing steps. ͓DOI: 10.1063/1.1472463͔One of the first applications of carbon nanotubes ͑cNTs͒ has been their use as field emitters on account of their natural material, structural, and electronic properties which satisfy many demanding requirements for field emission, including stability, robustness, low voltage, high current-carrying capacity, and mechanical strength. A key factor to their stability as field emitters is the lack of a nonvolatile surface oxide. Surface oxide formation ͑such as on metal or silicon emitters͒ increases the work function, impedes electron transport, and makes the effective work function variable during emission. Furthermore, surface oxides could be the main cause for field emitter array ͑FEA͒ catastrophic destruction by trapping charge which could lead to arcing.1 Carbon nanotubes are also less likely to form nanoprotrusions as metal and silicon cathodes do, thus reducing the probability of current runaway.2 Their small diameters ͑2-50 nm͒ and high aspect ratios enable the high electric field enhancement for lowvoltage operation, despite the relatively high work function (ϳ5.0 eV for graphite͒. They are resistant to blunting by residual back ion bombardment, especially when placed vertical to the substrate, since the nanotube diameter remains the same even when material has been removed from by sputtering.The most commonly studied cNT emitters involved a diode configuration in which the cNTs, grown or placed as dense mats on substrates, were positioned at a known separation from an anode, to which a positive potential was applied to induce field emission from the cNTs. Although very low turn-on voltages ͑as low as 1-2 V per m͒ were measured, the voltages used were still too high for most applications because the cNT-anode separations were usually large distances. In addition, many device applications, such as flat panel displays, require precise control of the array pixels, thus precluding a diode configuration. Hence, gating of the emission by the placement of a third electrode in close and precise proximity to a group of cNT emitters is necessary to lower the operating voltage as well as afford precise local control of emission. Gating is necessary to enable certain applications which include field emitter displays, highfrequency amplifiers, high-voltage switches, portable x-ray sources, multibeam electron-beam lithography, radiation and temperature-insensitive electronics, space craft propulsion, and electro...

Field emission triode amplifier utilizing aligned carbon nanotubes

“…3(b). As mentioned in [10], this convex profile is important in preventing cathode-gate ''shorting'' without resorting to more complicated fabrication processes such as sidewall protector [11,12] or gate over-etching method [8,13] that result in higher turn-on voltages. The cathode-gate spacing was¨2.0 Am, as estimated from the edge of the gate to the edge of the CNT cathode.…”

Approach for fabricating microgated field-emission arrays with individual carbon nanotube emitters

“…4 Hsu et al fabricated two types of gated CNT field-emission arrays ͑FEAs͒ with a number of randomly oriented CNTs: one with CNTs on Si posts and the other with CNTs inside open apertures. 5,6 Other integrated gate structures with multiple aligned CNTs in each aperture have been demonstrated. [7][8][9] We have also reported integrated gate structures with multiple CNT emitters.…”

Micro-gated-field emission arrays with single carbon nanotubes grown on Mo tips

“…Therefore, in recent years micro-gated CNT arrays gain much popularity as can be seen from some of the reports. These CNT cold cathodes include a buried gate cathode with CNTs inside open trenches [11], cathodes with CNTs on Si posts and inside open apertures [12][13], micro-gated cathodes with multiple CNT emitters [14][15][16][17] and those with single CNT emitters fabricated by using electron beam lithographic patterning [18]. In contrast to multiple CNT emitters, single CNT emitters in an integrated gate structure is desirable in terms of field emission properties in a number of fields, such as microwave amplifiers and electron beam lithography.…”