OXIDIZED AMORPHOUS-SILICON AS GATE INSULATOR FOR SILICON TIPS

Field emission cathode arrays of Betsui type [K. Betsui, Technical Dig est of the International Vacuum of Microelectronics Conference, Nagaha ma, Japan, 1991 (unpublished)] need an intermediate spacer layer with excellent insulator properties, i.e., ultrahigh resistivity, high brea kdown voltage, excellent adhesion both to substrate and gate layer, lo w roughness, low dielectric constant, and sufficient long term stabili ty. This study reports on an investigation of various fabrication meth ods for this insulating film in order to optimize its properties. Sili con and some compounds (a: Si, SiO, SiO2, SiO(x)N(y)) have been deposi ted by e-beam or thermal evaporation and plasma enhanced chemical vapo r deposition, respectively. These layers have been annealed or oxidize d before deposition of the extraction gate layer. The structures have been characterized by means of capacitance measurements. The best resu lts have been obtained with the deposition of pure silicon by e-beam e vaporation followed by an oxidization process. The method described in detail results in an insulator consisting of SiO2 which exhibits exce llent insulating properties (breakdown field strength 7 MV/cm). Field emission cathodes fabricated in this manner exhibit stable emission cu rrents up to 1 muA/tip.