Ion Bombardment In Vacuum Microelectronic Devices

Compared with semiconductor devices, vacuum microelectronic devices can work with higher frequency and larger power at a wider range of temperature. In past years, the field-emission cold cathode of carbon nanotubes, which are made by screen printing and CVD, has attracted more and more attention.One problem of field-emission cold cathodes is the emission degradation of field emission array(FEA). This phenomenon is usually attributed to cathode oxidation,ion sputtering,ion implantation and so on. In these devices, the ionization of residual gas molecules produces many positive ions that will bombard the cathode, and results in cathode sputtering,dilapidation of emitter surface,gas de-adsorption,even discharge. As a result, this will increase the gas pressure of vacuum, deteriorate the stability of field-emission current and decrease the device's life. In this thesis, we develop an ionization model of energy electron colliding with residual Ar gas. The sputtering of metals under ion bombardment can be investigated by using LSS Theory,molecular dynamics method and Sigmund Model, et al. In this thesis, we simulate the ion bombardment to the field-emission cathode in a triode by developing a method similar to Sigmund Model. From our investigation of normal-gate CNT field emission triode model, we can have the following conclusions: the ions generated farther away from the cathode have less chances to bombard the cathode, and most of them are blocked by the gate electrode; the damage is about 3 times more serious at the cathode center than at the cathode edge; The ions produced far away from cathode have smaller effects on cathode, and their damage to the cathode does not concentrate on the center but is distributed everywhere; in the case of emission current density being distributed along a ring, the cathode damage caused by ion bombardment is smaller than uniformly distributed.After adding the additional gate electrode in the normal-gate CNT field emission triode, we have observed that it captures most of ions which are produced near the cathode, so the effect of the ion bombardment is greatly lightened with the structure of ion trap. In this thesis, we demonstrate that this method can decrease the cathode damage to a half degree of the structure without ion trap. We analyzed the residual gas's effect on the emission character in a field emission diode experiment. A transient instability of emission has been observed initially, then the emission gradually becomes relatively stable. In the whole period it shows a rising- declining-stable emission. From a quantitative analysis we think the reason for that phenomenon is that the ion bombardment destroys the cathode emission.