Effect of carbon atoms on the reliability of potassium-ion electrets used in vibration-powered generators

• Published in: Japanese Journal of Applied Physics Vol. 61; no. SH; p. SH1013
• Main Authors: Ohata, Yoshiki, Araidai, Masaaki, Shibata, Yasushi, Hashiguchi, Gen, Shiraishi, Kenji
• Format: Journal Article
• Language: English
• Published: Tokyo IOP Publishing 01.07.2022; Japanese Journal of Applied Physics
• Subjects: Carbon; Contamination; density functional theory; Electrets; energy harvesting; First principles; first-principles calculation; Generators; Mathematical analysis; Molecular dynamics; Potassium; potassium-ion electret; Silicon dioxide; SiO; Vibration; vibration-powered generator
• ISSN: 0021-4922; 1347-4065
• DOI: 10.35848/1347-4065/ac6a3f

Abstract Potassium-ion electrets, which are key elements in vibration-powered microelectromechanical generators, can store negative charge almost permanently. However, our experiments show that the charge storing capability of potassium ion electrets is severely degraded when a SiC plate instead of the usual SiO 2 plate is used in the fabrication process, indicating the negative influence of carbon incorporation. We theoretically studied the atomic and electronic structures of amorphous silica (a-SiO 2 ) with and without potassium and carbon atoms using first-principles molecular-dynamics calculations. Our calculations show that negative charge accumulates in fivefold-coordinated Si atoms without carbon contamination. However, carbon contamination of the potassium-ion electret causes oxygen deficiencies in SiO 2 , hindering the formation of fivefold-coordinated Si atoms. As a result, carbon contamination causes degradation of the negative charge storing capability of potassium-ion electrets.