Abstract: This paper reports SiO₂/Si₃N₄ double layer electrets both prepared by PECVD on glass substrates with Cr/Au lower electrode.A process was developed to expose part of lower metal electrode,which is connected to the ground during corona charge process.Different charging temperatures,time and other factors were investigated for improving performance of PECVD prepared SiO₂/Si₃N₄ double layers electrets.This paper has proved high performance of PECVD prepared SiO₂/Si₃N₄ double layers electrets,which can thus be expected a wide application in micro devices.