Improving the voltage holdoff performance of alumina insulators in vacuum by quasimetallizing or doping

The high voltage holdoff capability of insulators may be improved by changing the material of the insulator or by a proper choice of geometry for the device using the insulator. Treatment of the surface of an alumina insulator with coatings incorporating varying amounts of Cr, Mn, and Ti are found to significantly increase the vacuum voltage holdoff capability of the insulator (up to 25 percent). During processing (quasimetallizing) the coating penetrates into the alumina, so it is insensitive to mechanical damage. This quasimetallize treatment is also compatible with subsequent metallizing and brazing of the alumina insulator.