Studies on the interaction between thin film materials and Mo field emitter arrays

Abstract

A simple method for the evaluation of materials suitable for the fabrication of field emission vacuum microelectronic devices is presented. Since there can be a wide range of electron and ion interactions with the device, it is important to be able to quickly assess if a material may have a particular adverse effect on emission performance under operational conditions. The technique is based on the sensitivity of a large field emitter array to the outgassing or desorption of gas species from thin films under electron beam excitation. We found that Mo field emitter arrays degraded rapidly with stainless steel anodes coated with various oxide materials. The extent of degradation was found to be the most rapid with SiO2, Si3N4, and MoO3 thin films. Stainless steel anodes with Mo and Nb thin films show a faster degradation rate than stainless steel anodes, most likely because of native oxides grown during processing and handling. The emission behavior in the presence of Ir, Pd, Al, Zn, and Ti metal films and barrier materials like C and TaN is similar to stainless steel reference data. We find that once the oxide films are covered with barrier layers like C and TaN, emission decay rates approach the values obtained with stainless steel reference anodes. The observed emission current degradation is consistent with a model based on the liberation of oxygen from the surface of electron beam bombarded materials. Using controlled oxygen exposure experiments, we have determined the equivalent local oxygen pressures in the presence of various thin films. We found that with thin films of Nb, ZrO2, Ta2O5, MgO, Nb2O5, and Al2O3, the emission degradation is akin to having a local O2 partial pressure in the 1×10−7–1×10−6 Torr range and with Mo, MoO3, Si3N4, and SiO2, this is equivalent to having local O2 pressures of 1×10−5 Torr.