Electrowetting-on-dielectric system based on polydimethylsiloxane

In this paper we present a detailed characterization of an electro-wetting on dielectric (EWOD) system able to move drop of liquid and to detect its position over an array of electrodes covered with a 1μm thick polydimethylsiloxane (PDMS) layer. In the presented system, the PDMS layer acts as both insulation and hydrophobic material. An electronic board controls all the signals needed for the actuation and sensing functionalities of the EWOD system. Sessile drop experiments show the saturation of the contact angle at negative bias voltage applied to the droplet. This behavior is ascribed to trapped carrier in the PDMS layer and explains the movement of the droplet toward the grounded electrode found in EWOD experiment. The procedure chosen for the drop movement achieves speed around 5cm/s with applied voltages around 200V. Detection of drop position is successfully achieved implementing the time-constant method, which evaluates the variation of electrode capacitance induced by the droplet presence on the PDMS surface corresponding to the metal electrode.