COMPUTATIONAL ANALYSIS OF THE SURFACE PERMITTIVITY AND CHARGING OF DIELECTRICS WITH THE SEMI-MIRROR TECHNIQUE

Computational analysis, based on the charge simulation method (CSM), is used to predict the electric potential distribution produced by charges implanted within the surface layer of a solid dielectric. The potential distribution thus obtained is used to match the experimental distribution using the scanning electron microscope (SEM) mirror technique. Using an optimization iteration process, a comparison is obtained for quartz, alumina, and yttria. The computational analysis assumes a surface layer with a permittivity higher than that of the bulk. The justification for this assumption is based on the experimental observations that, for a given material, the surface breakdown strength decreases by increasing the density of surface defects by mechanical abrasion. An increase in the surface defect density implies a decrease in surface permittivity. The electric potential distribution produced by a surface with increased surface defects, as determined by the SEM mirror technique, indicates a surface with a higher permittivity. It is also shown that the ability of such a surface to store charges is decreased. The results are consistent with physical models based on band structure (or trapping energy) considerations.