THE LONG-TERM CHARGE STORAGE MECHANISM OF SILICON DIOXIDE ELECTRETS FOR MICROSYSTEMS

In order to improve the sensitivity of micromachined sensors applied w ith electrostatic fields and increase their actuated force of electros tatic micromachined actuators, ''electrets.'' which are dielectrics ca rrying non equilibrium permanent space charges or polarization distrib ution, are very important. In this paper, positively corona charged si licon dioxide electrets, which are deposited by Plasma Chemical Vapor Deposition (PCVD) and thermally oxidized, are investigated. Physical s tudies will be described, in which the charge stability is correlated to Thermally Stimulated Current (TSC) measurements and to Electron Spi n Resonance (ESR) analysis. Some intrinsic differences have been obser ved between materials. The electrets with superior long-term charge st ability contain 10,000 times as much E' center ( . Si=O-3),) as the on es with inferior long-term charge stability. Finally, some investigati ons on the long-term charge storage mechanism of the positively charge d silicon dioxide electret will be described.