Amorphous hydrogenated silicon carbonitride as low refractive index material in optical MEMS applications

Abstract

Microelectromechanical systems (MEMS) currently see a trend towards inclusion of optical functionalities, i.e., towards microoptoelectromechanical systems (MOEMS). However, typical MEMS materials such as silicon, silicon oxide and silicon nitride limit the choice of available refractive indices and spectral operating regions. Particularly, a low refractive index material is highly desirable which is usable in conjunction with high refractive index silicon, e.g., in distributed Bragg reflectors (DBRs) and which is not etched in an HF release step for releasing movable structures. Furthermore, MEMS applications typically need a careful control of the residual mechanical stress in free-standing structures. For this purpose, we present hydrogenated amorphous silicon carbonitride (a-SiCN:H) thin-films deposited by plasma-enhanced chemical vapour deposition (PECVD) from SiH 4 , CH 4 and NH 3 and show its beneficial properties for optical layers in mOeMS.