Novel SOI inertial sensors with optical readout based on transparent metals

A novel optical microsensor has been fabricated using a SOI-based technology. The basic device is a symmetric flexure in which the central plate is used both as seismic mass and as optical target for displacement measurements. The device includes a multilayer, metal-dielectric Photonic Band Gap (PBG) structure, deposited on a flat substrate and bonded topside at a fixed distance from the movable plate. The reflection intensity of a light beam, pointed to the overall optical structure (top PBG, air gap, the moving plate), will depend on the air gap thickness whose value is determined by the displacement of the proof mass induced by the measurand, the external force. In particular, the realization of highly sensitive accelerometers is addressed here, the structure presented allows for detecting accelerations of the order of a few mG that produce displacements of the plate of few nanometers. Experimental prototypes have been realized and some results are shown here.