Investigation of Negative Charge Storage Mechanism in the Potassium Ion Electret by First-Principle Calculations

Abstract

A potassium-ion electret, which is a key element of vibration-powered microelectromechanical generators, is a material that permanently stores negative charge. However, the charge storing mechanism of a potassium-ion electret is still unclear. In this study, we theoretically study the atomic and electronic structures of amorphous SiO₂ with and without potassium atoms using first-principles molecular-dynamics calculations. As a result of calculations, we confirmed the existence of a fivefold-coordinated Si atom with five Si-O bonds as a characteristic local structure in a-SiO₂ with potassium atoms, which is negatively charged. This result indicates that the fivefold-coordinated Si structure is the physical origin of the negative charge observed in potassium-ion electret. Furthermore, we show the guidelines for the experimental observation of the fivefold-coordinated structure and the fabrication of high-reliability potassium-ion electret.