Field emitter arrays for high-current, high-current density, and high frequency operation

Common issues of interest when considering a cathode for microwave tube applications are total current, current density, emittance, and parasitic capacitance if beam pre-bunching is planned. Single SRI Spindt-type emitter tips have been shown to be capable of producing over 1 mA of emission when properly processed. However, when working with large arrays of tips, achieving an average emission per tip greater than about 10 muA/tip has been elusive due primarily to insufficient uniformity from tip to tip in the as-fabricated arrays. Recent work in addressing this issue has shown that it is possible to improve tip-to-tip emission uniformity with a pulse-conditioning technique currently under development. Using recently developed lithography techniques, emitter arrays are now fabricated with gate aperture diameters of 0.35 mum and a 1-mum aperture or tip pitch (1-mum space between apertures and tips, or 10⁸ tips/cm²). This configuration would have approximately 785,000 tips in a 1-mm-diameter area, and an average tip loading of less than 1.5 muA/tip would produce 1 amp of total peak emission with a current density of about 130 A/cm², exceeding most vacuum tube requirements