Design, Microfabrication and Characterization of Capillary Force Actuators

Capillary Force Actuators (CFAs) are a new type of MEMS (Micro Electro Mechanical Systems) microactuator. They are capable of delivering significantly greater forces and larger actuation strokes than current technology. CFAs operate on a novel principle by employing a conducting liquid bridge between two surface electrodes covered with a thin dielectric layer. When the voltage is applied to the electrodes, the contact angle of the liquid changes, a process known as Electrowetting on Dielectric (EWOD). The contact angle change results in a change in the capillary pressure the droplet exerts on the surfaces, causing them to move in the direction normal to the surface. It has potential applications in microvalves of micro-total-analysis systems, optical switches, digital optics, and in variable capacitors for telecommunication systems.

This dissertation focuses on the design, microfabrication and experimental characterization of a CFA. We developed a CFA design based on the actuator physics and simulations using finite element analysis. The microfabrication process was optimized through several experimental iterations. A test platform for measuring the actuator displacement was configured using interferometric techniques, while the actuator mechanical characteristics were measured with a nanoindenter instrument. In parallel, we conducted EWOD experiments using the candidate materials to be employed in the actuator to characterize the CFA physics. A measurement platform was configured to make simultaneous measurements of contact angle and device current in response to various electrical signals.

After studying the influence of various dielectric and hydrophobic materials, conductive liquids, and semiconductor wafers on the electrowetting behavior, we identified suitable materials and conductive liquid solutions to guide the construction of a CFA prototype. Through the design, microfabrication, and experimental testing of prototype devices, we have verified the CFA actuation principle.