Micromachined sensors and actuators applied with electrostatic fields are getting widely developed. At the same time, "electrets," which are dielectrics carrying non-equilibrium permanent space charges or polarization distribution, are in demand because they improve the transducer characteristics. In this paper, we have reported on our successful fabrication of silicon dioxide electrets with extremely superior long-term charge stability by plasma chemical vapor deposition (PCVD). We have also reported on the correlation between the deposition conditions, the long-term charge stability and thermally stimulated current (TSC). Finally, the characterization of the long-term stable electrets will be described and discussed.

In order to improve the sensitivity of micromachined sensors applied with electrostatic fields and increase their actuated force of electrostatic micromachined actuators, "electrets," which are dielectrics carrying non equilibrium permanent space charges of polarization distribution, are very important. In this paper, positively corona charged silicon dioxide electrets, which are deposited by Plasma Chemical Vapor Deposition (PCVD) and thermally oxidized, are investigated. Physical studies will be described, in which the charge stability is correlated to Thermally Stimulated Current (TSC) measurements and to Electron Spin Resonance (ESR) analysis. Some intrinsic differences have been observed between materials. The electrets with superior long-term charge stability contain 10,000 times as much E' center (Si3 as the ones with inferior long-term charge stability. Finally, some investigations on the long-term charge storage mechanism of the positively charged silicon dioxide electret will be described.