Bidirectional Electrothermal Electromagnetic Torsional Microactuators

This paper presents a novel design of bidirectional torsional micromirror utilizing vertically driven electrothermal electromagnetic silicon beam actuators to generate large static angular motion. The microactuators are fabricated on silicon-on-insulator (SOI) wafer using three photo masks in order to form two different thicknesses of single crystal silicon (SCS) device layer and backside cavities. When the driving bias is applied to the device, four buckle beams placed alongside of the torsion bars are subjected to thermal expansion and buckle in vertical direction generating torsional displacement of the micromirror with respect to two torsion bars placed at the center. The direction of buckle is controlled by Lorentz force caused by the magnetic field applied and the amount of current flowing through the micro beam to be buckled, enabling the bidirectional motion of the torsional micromirror. The maximum static angular displacement of the torsional actuator is up to 14.35deg (28.7deg, optical angle) under driving DC voltage of 7.5 V. For resonance mode operation, the measured angular displacement is 8.46deg (16.92deg, optical angle) at 10.94 kHz under sinusoidal driving voltage of 0 to 3 V.