Reliability of potassium ion electret in silicon oxide for vibrational energy harvester applications

In this paper, we report on the long-term reliability of potassium ion electret included in a thermally grown silicon oxide. The electret in this work is used in a microelectromechanical systems (MEMS) energy harvester to generate electrical current from mechanical vibration. A spring-mass system similar to a comb-drive electrostatic actuator is developed by silicon micromachining, and the surface is oxidized by wet-oxidation through a potassium hydroxide bubbler, thereby including potassium atoms at a high concentration. The potassium is then electrically polarized by an applied voltage of 150 V at 650 ?C for 5 min. Degradation of the stored polarization potential is monitored in a vacuum of 1 ? 10?3 Pa at elevated temperatures of 350, 400, and 450 ?C. The time needed to cause a ?1 dB decay of the potential is used as the lifetime of the electret, and the Arrhenius extrapolation plot suggested a life time of more than 400 years at 25 ?C.