Field emission from carbide film cathodes

Abstract

We report here on experiments with the deposition of ZrC onto individual prefabricated W and Mo emitters and on field emission arrays using Mo and Si emitters. With observed field emission current densities greater than 1×108 A/cm2 and work functions approximately 1 eV lower than Mo or W, carbides make good candidates for low voltage microelectronic field emitter arrays. In addition, evaporation of ZrC films onto Mo and W single field emitter cathodes improves their emission stability and greatly improves beam confinement. Mo and W field emitters were individually fabricated and an appropriate quantity of ZrC was evaporated onto the emitter surface from a high-purity ZrC evaporation source. Several emitters prepared by this method have been tested. The uniformity of the emission pattern was checked by in situ field emission microscopy, both before and after carbide deposition, in order to verify that the surface of the emitter had been cleaned and smoothed. The deposited film was subjected to a variety of heating treatments, each of which was followed by examination of the emission pattern 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 by the deposition of ZrC films onto W or Mo field emitters. The observed emission patterns indicate that the lowest film work functions occur on and around the (100) planes of the underlying Mo or W emitter. Beam confinement is therefore possible with carbide film deposition on Mo or W field emission cathodes. We also report on experiments with ZrC film deposition onto field emitter arrays with Mo and Si emitters. In the case of ZrC on a Spindt array of Mo cathodes we observed a decrease of operating voltage from 122 to 68 V for 100 μA emission current following ZrC deposition. The ratio of the Fowler–Nordheim slope for the ZrC layer to that for the cathode before deposition was approximately 0.68. These results seem consistent and very promising for the use of ZrC film on field emitters and field emitter arrays.