Piston-motion micromirror based on electrowetting of liquid metals

This paper reports a new actuating method of a micromirror with piston motion by the electrowetting effect. Liquid metals drops (LMD), gallium and mercury, instead of conventional electrolyte solution, are used in the electrowetting experiments to reduce the vapor pressure and to increase the conductivity. An approximate formula of LMD height changes versus actuated voltage is deduced and the electrowetting setup is improved for actuating the mirror. The actuating performance of the LMD as a pivot is investigated. The hysteresis of contact angle is effectively minimized with argon sputtering the surface of the insulating layer, which makes the deformation of the LMD highly repeatable. The frequency response (0.01 Hz-3 kHz) and 6 vibration modes of the mercury drop are observed. The maximum acceleration of the drop during the actuation is 300 g (g=9·8 m/s²). We fabricated a 1000 μm×1000 μm×20 μm, 50 μg micromirror and an actuating circuit based on the electrowetting of liquid metal. With the LMD confine spot, a mercury drop of 500 μm in diameter is placed between the mirror and the actuating electrodes. A 440-Hz sinusoidal voltage of 75 V actuates the micromirror, with a maximum of 60 μm displacement.