Prebreakdown investigations of vacuum discharge between nano gaps

The electrical breakdown behavior between nano vacuum gaps is vital with the miniaturization of electronic and electromechanical devices, which is mainly determined by the prebreakdown process. Therefore, the prebreakdown characteristics of different electrode configurations in vacuum gap were investigated in this paper using an in-situ scanning electron microscopy (SEM) and piezoelectric displacement approach. The measurement of current between the sphere-sphere electrodes revealed two distinct stages: (a) a low leakage current of 1×10^-11 A during the prebreakdown process; (b) the occurrence of a current pulse of 10^-3 A and the breakdown took place at a critical voltage. In contrast, the current showed three stages for the needle-sphere electrodes: (a) a low leakage current of 1×10^-11 A the same as the sphere-sphere configuration; (b) an exponential field emission current; (c) a current pulse of 10^-7 A was detected and the breakdown took place. The difference of prebreakdown current implied that for the quasi uniform field gap the field emission turned on simultaneously from the whole area of the cathode surface and the threshold field was nearly equal to the dielectric strength.