Design, fabrication, and characterization of BESOI-accelerometer exploiting photonic bandgap materials

This paper reports the numerical and experimental investigation of a bulk and etch silicon on insulator optoelectromechanical system realized using a multilayer metal-dielectric photonic bandgap (PBG) structure. A specific optical structure is designed, which embeds an air gap; the acceleration to be measured induces displacements into a proof mass that in turn are transduced as variations in the optical reflectance spectrum of the PBG stack. The PBG optical stack is made of metals and dielectrics. Because of the large difference in the refractive indexes between these two classes of materials, the resulting optical properties of PBG transparent metals allow for obtaining a sharp change in the output signal even for very small changes of the air gap and therefore of the relative positions of the proof mass. The microelectromechanical system consists of a suspended square-shaped mass supported by four crab-leg beams; the central part is used as active optical area where the light beam is to be focused. The advantages of silicon micromachining combined with PBG properties have been addressed. The sensor proposed has been initially analytically modeled and numerically studied using CoventorWare. Then the device has been fabricated and an extensive experimental campaign has been performed.