Abstract
Rotary electrostatic comb-drive actuator can achieve the 1 × N channels optical switching by actuating a single vertical micromirror. The first rotary comb-drive actuator presented by Tang et al. in 1989 uses the symmetric-gap comb fingers to generate the electrostatic torque. For the applications of optical switching, resonant frequency of the microactuators is an important specification of the dynamic response. This research proposes the actuator design which enhances the resonant frequency of the rotary actuator without scarifying the responding rotation angle via the asymmetric gap and the wedge-shaped bearing. Compared to classical symmetric-gap rotary comb-drive actuator, the asymmetric-gap rotary comb-drive actuator generates the larger electrostatic torque under the same actuating voltage. The asymmetric-gap rotary actuator can rotate itself without the pull-in behavior via the wedge-shaped bearing when the applied voltage is beyond the pull-in voltage in our design. The design of serpentine flexures with the middle beams is utilized in this study to support the restoring rotation of the asymmetric-gap rotary actuator, approach appropriate vibration modes as well as enhance the resonant frequency of desired rotational mode. A responding rotation angle of 5° at the DC applied voltage of 107 V beyond the pull-in voltage for a steady-state measurement and ±5° at the AC applied voltage of 77 V at the resonant frequency of 1.54 kHz were measured with our asymmetric-gap rotary actuators. We also propose the design and fabrication process to attach the vertical micromirror to our symmetric-gap and asymmetric-gap rotary comb-drive actuators. The vertical-micromirror actuations based on our symmetric-gap and asymmetric-gap rotary comb-drive actuators are demonstrated and characterized in this thesis.