| This thesis reports the results of investigations on the surface-tension-related phenomena and microdevices. Aiming at liquid microactuators, we studied mercury droplet actuations induced by the electrocapillary and electrowetting effects. The vertical displacement of the electrocapillary droplet actuation is as high as 200 mum with the voltage as low as 2 V. For the electrowetting droplet, we report the largest contact angle change of 74° and the lowest driving voltage of 25 V (for 30° contact angle change). The electrowetting hysteresis is as low as 1--2° on oil-soaked or Teflon AF-coated surfaces. The rough surfaces by plasma treatment of micropatterning are found to have high contact angle and very low lateral hysteresis. However, due to the big electrostatic pressure, the liquid is pulled into the air space in the microstructures, which results in large electrowetting hysteresis. To approve the effectiveness of these two actuation mechanisms, four MEMS devices have been developed: an electrocapillary piston micromirror, an electrowetting piston micromirror, an area-tunable micromirror, and a capacitive RF MEMS switch. The piston micromirrors supported and driven by the mercury droplets are able to move vertically more than 50 mum and have merits of moving freedom, simple fabrication process, compact design, and easy scalability. The micromirrors are able to restore very quickly from a very large tilting disturbance up to 60°. The area-tunable micromirror is promising for reflective display applications and has advantages of fast time response (as short as 0.1 ms), high reflectance and high contrast compared to other technologies. This technology has potentials of forming a large-size, ultraflat, and stressless mirror surface. The capacitive RF switch is aimed at achieving a new type of RF switch with a liquid-solid contact and thus avoiding the problems associated with a solid-solid hard contact. The preliminary tests show good RF performance of low insertion loss and high isolation with switch time of ∼ 2 ms. |
