Abstract
A vacuum field emission transistor utilizing aligned carbon nanotubes (CNTs) to form a triode configured as a common emitter amplifier is investigated. DC and AC performances of this triode amplifier are reported. The vertically aligned CNT emitters for the microtriodes with a convex surface profile were selectively synthesized utilizing microwave plasma chemical vapor deposition (MPCVD) with Ni or Co as catalysts. The single-mask micro-fabrication process achieved a CNT microtriode array (array size: 34 × 84, element dimension: 10 μm × 10 μm square, element spacing: 20 μm) with self-aligned gate. Transistor curves for the CNT triode with anode current (I <sub>a</sub> ) as a function of anode voltage (V <sub>a</sub> ) for different gate voltages (V <sub>g</sub> ) was measured, followed by AC characterization. The triode amplifier demonstrated gate-controlled modulation of the emission current with distinct cutoff, linear and saturation regions of operation. A large DC gain or amplification factor of ∼ 350, transconductance of ∼ 2 μS, and a computed anode resistance of 182 MΩ are obtained. A large anode current of ∼ 3.5 μA or current density of ∼ 1.2 mA/cm <sup>2</sup> was achieved at V <sub>g</sub> = 46 V and V <sub>a</sub> = 300 V. Saturation of the anode currents at V <sub>a</sub> > 80 V was also observed. The AC performance of the CNT triode amplifier was characterized by input voltage (v <sub>in</sub> ) vs. output voltage (v <sub>out</sub> ). The voltage gain of the triode amplifier, A <sub>v</sub> , is given by the ratio of v <sub>out</sub> /v <sub>in</sub> . The estimated A <sub>v</sub> is calculated to be ∼ 3.13 with a phase shift of ∼ 180°, as expected. A larger A <sub>v</sub> could be attained if larger R <sub>L</sub> is applied. Preliminary frequency response of the triode amplifier is presented. The results obtained thus far demonstrate that the CNT triode amplifier can be a promising amplifier candidate. © 2005 Elsevier B.V. All rights reserved.