Technische Hochschule Darmstadt, 61 Darmstadt, Merckstrasse 25, Germany
Electret microphones made with the methods of silicon technology require electret materials other than the conventional polymers. Up to now, amorphous SiO[sub 2] has proven its good electret characteristics, and SiO[sub 2]-electret microphones have already been developed as prototypes. In this paper, new manufacturing methods for SiO[sub 2], namely cold plasma deposition and the sol--gel process, are presented. The charge storage behavior, which could be improved by heat treatment or chemical surface modification, was investigated by isothermal and thermally stimulated discharge measurements and the results were compared to the discharge characteristic of thermally wet grown SiO[sub 2] electrets. In addition, the chemical composition of the electret surface was investigated by the ESCA method, which revealed the stoichiometry of the differently manufactured and treated SiO[sub 2].