Tunable Fabry-Pérot cavities fabricated from PECVD silicon nitrideemploying zinc sulphide as the sacrificial layer

Abstract

The construction of self-supporting and suspended structures isone of the fundamental challenges of microelectromechanical systems(MEMS). Many technologies have been developed for the fabrication of suchstructures, which can be categorized into bulk or surface micromachining.Generally surface micromachining techniques rely on a high-temperaturedeposition process such as low pressure chemical vapour deposition toproduce high-quality films. Plasma enhanced chemical vapour deposition(PECVD) can be used to deposit films at temperatures less than300 °C. PECVD of silicon nitride has not been used extensively inMEMS structures due to the material limitations created via the depositiontechnique, primarily controllability of the intrinsic stress and etchselectivity of the deposited film. We show here that PECVD silicon nitridecan be used successfully in MEMS structures, and that the intrinsic stressis controllable through variations in the PECVD deposition parameters. AMEMS-based Fabry-Pérot cavity has been fabricated using PECVD siliconnitride as the membrane layer with ZnS as the sacrificial material.Devices with an initial 1 µm cavity length typically provide adisplacement of 240 nm across a 380 µm membrane span for an appliedbias of only 1.6 V.