Bidirectional electrothermal electromagnetic torsional microactuators for large angular motion at dc mode and high frequency resonance mode operation

This paper presents a novel design of a bidirectional torsional micromirror utilizing vertically driven electrothermal electromagnetic silicon beam actuators to generate large angular motion in both static mode and high-frequency resonance mode with low operational voltages. The microactuators are fabricated on a 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 in the static mode operation, four buckle beams placed alongside the torsion bars are subjected to thermal expansion and buckle in the vertical direction generating torsional displacement of the micromirror with respect to two torsion bars, the center of rotation. The direction of buckle is controlled by the Lorentz force caused by the current flowing through the silicon beams to be buckled in the magnetic field applied, enabling the bidirectional motion of the torsional micromirror. At resonance, Lorentz force itself drives the actuator instead of thermal expansion force from the buckle beams. The maximum static angular displacement of the torsional actuator is 13.42 degrees (26.84 degrees, optical angle) under a driving dc voltage of 7.5 V. In the resonance mode operation, the measured angular displacement is 8.22 degrees (16.44 degrees, optical angle) at 10.64 kHz under sinusoidal driving voltages of 0 to 4.4 V.