Fabrication of aligned convex CNT field emission triode by MPCVD

In this work, vertically aligned carbon nanotubes (CNTs) were used to form a gated microcathode with a convex surface profile, being selectively synthesized from Microwave Plasma Chemical Vapor Deposition (MPCVD) with nickel (Ni) as a catalyst. A single-mask microfabrication process achieved an array of 10 μm × 10 μm CNT microtriodes with self-aligned gate. The convex profile is important in preventing cathode-gate leakage without resorting to more complicated fabrication processes or utilizing a gate over-etching approach. The main mechanism for the formation of the convex-shaped CNT microcathodes was investigated and is proposed to be the result of plasma etching of CNTs near the gate opening region due to higher plasma density during the growth process, leading to slower growth rate or shorter CNTs at the circumferential area. Additionally, previous simulation work has predicted that this type of surface profile is beneficial for more quasi-uniform electric field distribution on CNT tips. Field emission characteristics of the triode device were investigated, whereby a gate turn-on voltage as low as 25 V was achieved. The low turn-on of the device is mainly due to the smaller gate aperture made possible by the convex-shaped CNT microcathodes.