ELECTROSTATICALLY DEFLECTABLE POLYSILICON TORSIONAL MIRRORS

This paper describes the fabrication of electrostatically deflectable structures using surface micromachining with chemical vapour deposition (CVD) polysilicon. Particular attention has been paid to the realization of torsional mirrors. Free-standing structures with a thickness of 1 mum are produced by lateral etching of a 2 mum sacrificial silicon dioxide layer deposited between the substrate and the CVD polysilicon layer. In order to avoid sticking of completely under-etched structures to the substrate, the polysilicon microstructures are fixed by a frozen solvent after etching of the sacrificial layer and rinsing; subsequently a sublimation process under vacuum is applied. The torsional mirrors are deflectable with voltages of about 20 V. The maximum deflection is approximately 2-degrees. Several mirrors with different dimensions have been made. For comparing and optimizing their mechanical properties and behaviour during deformation, mirror designs are modelled using the finite-element program ANSYS.