Abstract: In this paper,the influence of chemical surfaee modification on charge Storage stability in the thermally grown SiO₂ film electret is studied.A hydrophobic protective layer is formed on the surface of the SiO₂ film electret by an appropri-ate chemical surface modification (using HMDS or DCDMS).Generally,this hydrophobic layer prevents water absorption on the surface of SiO₂ and makes the SiO₂ electret an excellent electret.During the permanent charge captue and storage in the SiO₂ film electret,an electrochemical reaetion takes place and water is produced.The hydrophobic layer formed after chemical surface modification sometimes obstructs the excess water from diffusing out of the electret.In this condition,an unusual phenomenon occurs:the charges stored in the SiO₂ electret modified by HMDS or DCDMS decay faster than surface.

Key words: charge storage, stability, silicon dioxide, surface, modification