Use of nano-dimensional hydrophobic coatings for obtaining electrets based on silicon dioxide

Abstract

The article considers the physical-technological foundations of formation of the silicon dioxide (SiO₂) based electret for use in devices of MEMS technology. Studies have shown that the best electret properties are in SiO₂ obtained in «wet» oxygen medium as compared to samples obtained by other oxidation methods. This is probably due to the large number of Si-OH groups on the surface of the oxide in the «wet» SiO₂, which increases the effectiveness of the hydrophobic coatings during the modification of the SiO₂ surface. It has been found that other methods of obtaining oxide, for example, electrochemical or plasmachemical, do not make it possible to obtain SiO₂ with good electret properties. The decrease of the charge injected into an electret can occur due to the presence of volume or surface conductivity, as well as the screening of this charge by opposite charges from the medium, leading to significant decrease of electret surface potential at high ambient humidity. To increase the stability of the electret effect, it is necessary to perform water-repellency treatment of SiO₂ surface by applying thin (nanosized) water-repellent coatings. Experimental results on the stability of the electret surface potential are presented for usage of various water repellents. The most promising water repellents are high-temperature photoresist FPT-1-40 and polyimide nanolayer compositions – Langmuir-Blodgett films.