AlN coatings on silicon field emitters and oxidised gates to enhance reliability for space applications

This paper describes the development of coatings for silicon field emission arrays used as an electron source to maintain spacecraft charge neutrality. The neutraliser specification includes 6 mA emission current at 0.2 W/mA and the instrument is required to operate for a lifetime of >6000 hours. To make the field emission device more resistant to ion bombardment and thermal failure, the effects of adding a layer of aluminium nitride (AlN), and thermal oxidation of the chromium gate electrode have been investigated. Different thicknesses of AlN film have been sputter coated onto the emitters under a variety of chamber pressure conditions. The thermally oxidised samples have been analysed by ESCA (Electron Spectroscopy for Chemical Analysis) and ERDA (Elastic Recoil Detection Analysis). For the oxidised chromium the composition is Cr = 0.31 and O = 0.69.