Electrostatic actuation without electrolysis in microfluidic MEMS

Electrostatic actuators exhibit fast response times and are easily integrated into microsystems because they can be fabricated with standard IC micromachining processes and materials. Although electrostatic actuators have been used extensively in "dry" MEMS, they have received little attention in microfluidic systems because of challenges such as electrolysis, anodization, and electrode polarization. Here we demonstrate that ac drive signals can be used to prevent electrode polarization, and thus enable electrostatic actuation in many liquids, at potentials low enough to avoid electrochemistry. We measure the frequency response of an interdigitated comb drive actuator in liquids spanning a decade of dielectric permittivities and four decades of conductivity. The results show that actuation is initiated at frequencies less than 1 MHz, in electrolytes of ionic strength up to 10 mmol/L.