Field emission triode amplifier utilizing aligned carbon nanotubes

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 a) as a function of anode voltage ( V a) for different gate voltages ( V g) 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 2 was achieved at V g = 46 V and V a = 300 V. Saturation of the anode currents at V a > 80 V was also observed. The AC performance of the CNT triode amplifier was characterized by input voltage ( v in) vs. output voltage ( v out). The voltage gain of the triode amplifier, A v, is given by the ratio of v out/ v in. The estimated A v is calculated to be ∼ 3.13 with a phase shift of ∼ 180°, as expected. A larger A v could be attained if larger R L 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.