Electron emission from a single Spindt-type field emitter structure: Correlation of theory and experiment

Abstract

The performance characteristics of rf power amplifiers will be significantly enhanced if a cathode source capable of producing current densities greater than 10 A/cm2 under gigahertz modulation can be created. Characterization of single- and multiple-tip arrays is imperative to determine performance characteristics in order to design and implement inductive output amplifiers (IOA): knowledge of the beam spread is paramount in the design of the helix or cavity power extraction region. Nevertheless, a simple analytic model for gated field emitters for understanding the spatial dispersion of the emitted electrons has not emerged. We provide such a model, approximating the tip by a smooth sphere and the gate by a ring of charge (Saturn model), and correlate it with experimental measurements made on a single Spindt-type molybdenum field emitter using a nanofabricated anode whose position from the emitter was determined using laser interferometry. Methods used to correlate theory with experiment are explained, and the dependence of the beam profile on tip sharpness, gate diameter, anode distance, and tip work function are examined. There is good agreement between theory and experiment. Measurement has shown that the rms spread angle is between 15° and 29°.