Benedikt Stein

Large-aperture Fabry-Perot filters based on silicon/silicon carbonitride distributed Bragg reflectors for the near-infrared

This contribution presents silicon carbonitride as a new low refractive index material for integration together with silicon in suspended distributed Bragg reflector membranes. We show how its benign mechanical stress properties can be used to fabricate inherently flat mirror membranes of up to 5 mm diameter. Due to the large refractive index contrast to silicon such mirror membranes exhibit high reflectance over a wide spectral range. Using these mirrors, we demonstrate a proof of concept for a large aperture Fabry-Perot filter with narrow bandwidth that could help miniaturize hyperspectral imaging sensors.

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

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 SiH4, CH4 and NH3 and show its beneficial properties for optical layers in mOeMS.