Abstract
This paper investigates electrostatic actuation of microscopic liquid-metal droplets, typically mercury, for MEMS applications. Theory concerning droplets on a plane solid surface is briefly exposed, followed by the contact angle characterization, experiment for electrostatic actuation, and FEM analysis. Being a major parameter in the modeling of sliding droplets the contact angle has been characterized in the case of mercury on oxidized silicon wafer. The method used involves both traditional optical microscope and confocal laser imaging. On a set of 30 samples, the contact angle is found to be around 130° with an associated standard deviation of 8°, mostly due to measurement uncertainties. The sample preparation is detailed, based on selective condensation of mercury vapor on gold dots acting as preferred nucleation sites. This technique provides control on droplet dimensions and locations and is suitable for batch fabrication. Experimental study of electrostatic actuation coupled with FEM analysis is described. Results confirm the proportionality between minimum driving force and the droplet dimension. Finally, a modeling methodology is discussed using traditional FEM simulator calibrated with an equivalent Young’s Modulus concept.
