Field emission triode amplifier utilizing aligned carbon nanotubes

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 (Ia) as a function of anode voltage (Va) for different gate voltages (Vg) 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/cm2 was achieved at Vg = 46 V and Va = 300 V. Saturation of the anode currents at Va > 80 V was also observed. The AC performance of the CNT triode amplifier was characterized by input voltage (vin) vs. output voltage (vout). The voltage gain of the triode amplifier, Av, is given by the ratio of vout/vin. The estimated Av is calculated to be ∼ 3.13 with a phase shift of ∼ 180°, as expected. A larger Av could be attained if larger RL 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.