Tunable Fabry-Perot cavities

The construction of self supporting or suspended structures is one of the fundamental challenges of MEMS, with many technologies existing for the fabrication of such structures, such as bulk micromachining and surface machining. Generally surface micromachining techniques rely on the high temperature deposition process such as LPCVD, which produce high quality films. Process technologies exist for the deposition of material at substantially reduced temperatures, in particular PECVD that can deposit films at temperatures <300 degree(s)C. Plasma Enhanced Chemical Vapor Deposition (PECVD) of silicon nitride has not been used extensively in MEMS structures due to the material limitations created via the deposition technique, primarily controllability of the intrinsic stress and etch selectivity of the deposited film. We show here that PECVD silicon nitride can be used successfully in MEMS structures, and that the intrinsic stress is controllable through variations in the PECVD deposition parameters. A MEMS based Fabry-Perot cavity was fabricated using PECVD silicon nitride as the membrane layer with ZnS as the sacrificial material. Devices with an initial 1-micron cavity length typically provide a displacement of 320 nm across a 300 micrometers membrane span for an applied bias of 2.4 V.