Field emission from ZrC and ZrC films on Mo field emitters

We have been working for several years on field emission measurements from transition metal carl,ides. These studies have covered emission primarily from HfC and ZrC in the form of solid carl,ide emitters, thin film carbide overcoatings on single tip field emitters, and film coatings on field emitter arrays (FEAs). These carbide materials have work functions approximately 1 eV lower than Mo or Si, making them attractive candidates for low voltage microelectronic field emitter arrays. Uses for arrays or single emitters of these carbides include video displays, microwave applications, high current or small spot electron sources, and cold cathodes for operation in poor vacuums. Since Mo is one common FEA emitter material, we used it for an emitter substrate in this study. Our aim is to determine improvements in I(V) characteristics, emission stability, capability of emission at high currents and in poor vacuum or tube conditions, and the ability to withstand exposure to atmospheric pressure without degradation. Individually, fabricated Mo field emitters were dosed via plasma vapor deposition from a high-purity ZrC, source. The deposited film used for high currents were generally not heated but tested as deposited by field emission microscopy examination and determination of I(V) characteristics. The results of these experiments indicate that work function reductions of the order of 1 eV can be achieved along with the ability to emit at higher current levels. Stable high current emission has; also been obtained in the 0.5 mA range with ZrC films on Mo. This represents a tenfold increase in the obtainable emission levels compared to emission from a clean Mo substrate. These data are also compared to field emission data from bulk ZrC emitters. Some observations of high current emission in mu Torr vacuum levels are also presented. The mechanisms for these improvements are discussed along with the possible role of stoichiometry. (C) 1998 American Vacuum Society.