Emission fluctuation and slope–intercept plot characterization of Pt and transition metal carbide field-emission cathodes in limited current regimes

Abstract

Our objective was to identify optimum emitter materials for block arrays and individually addressable tip arrays where emission stability and operation in a moderate vacuum is required. In general, transition metal carbide emitters are robust at high current and moderate vacuum levels due to their hard nature. Physical vapor deposition of composite emitters consisting of a carbide cone on a truncated niobium cone was used throughout. Four carbides (HfC, NbC, TiC, and ZrC) and platinum were deposited for the emitter materials in this study. All data were taken in the classically unstable pressures region of 10−7 Torr. Brief current stability measurements were collected along with current–voltage data. HfC, ZrC, and Pt demonstrated good initial stability, though all five materials were similar in emission performance. After a proprietary processing algorithm, TiC gave variations as low as ±1.5% ΔI/I at a 240 nA current level and 7.6×10−8 Torr pressure. An extensive discussion and analysis is given of Fowler–Nordheim slope–intercept plots that reveal information on noise and emitter apex behavior.