Charging efficiencies and heat resistance in three types of SiO2/Si3N4 electrets

Charging efficiencies and heat resistance of three types of silicon dioxide/silicon nitride double-layer electrets were investigated. These electrets were fabricated with SiO
₂
films deposited from SiH
₄
via plasma-enhanced chemical vapor deposition (PECVD SiO
₂
) or with tetraethylorthosilicate (TEOS) using PECVD (TEOS SiO
₂
) or were thermally grown SiO
₂
. Electrets with thicker SiO
₂
films were found to have higher charging efficiencies and heat resistance than those with thinner SiO
₂
layers. Moreover, the expected lifetimes of the SiO
₂
electrets were significantly longer than that of a fluorinated ethylene propylene copolymer electret.