Thermally driven torsional micromirrors using pre-bent torsion bar for large static angular displacement

Abstract

This paper presents one- and two-degree-of-freedom (DOF) torsional micromirrors driven by in-plane thermal actuators for large static angular motion at low operational voltage. The micromirror actuator is fabricated on a silicon-on-insulator (SOI) wafer using three photomasks to form two different thicknesses on the device layer and to define backside holes. The thin layer beam connected to the thick layer torsion bar is pulled by the in-plane thermal actuator, twisting the torsion bar and therefore inducing angular motion of the mirror. The proposed pre-bent torsion bar design enhances the angular motion significantly and suppresses unnecessary translational motion. The fabricated 1-DOF micromirror is driven to the maximum optical scan angle of 6.5° at 13 V dc. For a 2-DOF micromirror, optical scan angles of 5.4° and 5.2° are achieved in each direction of rotation at 11 V dc.