EMITTED CURRENT INSTABILITY FROM SILICON FIELD-EMISSION EMITTERS DUE TO SPUTTERING BY RESIDUAL-GAS IONS

We have fabricated arrays of silicon field emitters using semiconducto r lithography techniques. The density of the tips was 10(5)/CM2. The m aximum current that can be extracted from each emitter is limited by r esistive heating. We have investigated how the electron current emitte d changes under constant applied voltage. We found that the current is very sensitive to the vacuum conditions. We attribute this to sputter ing of the emitters due to ionized residual gas molecules. The poorer the vacuum, the higher the instability in the current. We studied this phenomenon at 10(-6) and 10(-8) Torr. The model of two concentric sph erical shells is used to obtain the ion energy distribution. This is t hen used to calculate the rate of ion bombardment and the rate of atom s sputtered. A lifetime of the tip can be deduced from these calculati ons.