Fabrication of double-gated Si field emitter arrays for focused electron beam generation

Abstract

Double-gated Si field emitter arrays (FEAs) capable of generating focused electron beams were fabricated and experimentally evaluated. The present field emitter array has a vertical triode structure consisting of a conical Si tip and two gate openings (upper and lower) surrounding the tip. The lower gate with a 2-μm-diam opening acts as an extraction electrode controlling the emission current, and the upper one with a 3-μm-diam opening acts as an electrostatic lens focusing the electron trajectories. The focusing property was evaluated by observing the spot size of a phosphor (ZnO:Zn) screen located about 20 mm apart from the field emitter array and biased to 1 kV. It was found from experimental results that decreasing the upper gate voltage (VF) down to a few volts was quite effective to generate focused electron beams. At VF of about 4 V, the electrons emitted from the tip were well collimated and a beam current of about 0.1 nA/tip was obtained.