Study on PECVD SiO2/Si3N4 double-layer electrets with different thicknesses

In this paper, performance of PECVD SiO2/Si3N4 double layers electrets with different thicknesses were investigated detailedly in respect of chargeability, storage charge stability in high temperature and reliability in high humidity environment. Samples with different thicknesses of Si3N4 and SiO2 were prepared on Pyrex 7740 glass substrates and characterized by isothermal and high humidity charge decay. The results of experiment approved that the PECVD SiO2/Si(3)N4 double layers electrets on glass substrate has as good chargeability and charge stability in high temperature and high humidity environment as thermal oxidation or APCVD/LPCVD ones on silicon substrates. The experiment results indicated that a Si3N4 layer no less than 50 nm is necessary for good charge stability in high temperature and a Si3N4 layer thicker than 500 nm decreases the chargeability. Even a 2 nm Si3N4 layer is enough to significantly improve the charge stability in high humidity environment. Thick SiO2 layer can increase the surface potential of electrets under the same charging condition and its charge stability in high temperature. However, the electrets with high surface potential also exhibit poor uniformity of charge stability in high humidity environment.