Micro torsion mirror actuated by compound electrostatic driving structure

We report on a novel micro torsion mirror actuated by a compound electrostatic driving structure. The compound driving structure is made up of a planar plate drive and a vertical comb drive. The device is fabricated in SOI substrate by using a bulk-and-surface mixed silicon micromachining process. As demonstrated by experiment, the novel driving structure can actuate the mirror to achieve large-range continuous rotation as well as spontaneous 90 degrees rotation induced by the pull-in effect in a voltage control fashion. The continuous rotating range of the micro torsion mirror is increased to about 46 degrees at an increased threshold voltage. The measured threshold voltage ranges of the mirrors with torsion springs of 1 mu m and 0.5 mu m in thickness are 390-410 V and 140-160 V, respectively. Theoretical modeling is carried out to compare with the experiment. The optical insertion loss has also been measured to be - 1.98 dB when the mirrors serve as digital optical switches in a 2 x 2 array form. (c) 2006 Elsevier B.V. All fights reserved.