Anodic Metal Oxides for Electrowetting Systems

We discuss the electrochemical formation of metal oxide films as candidate materials for the primary dielectric layer in electrowetting-on-dielectric (EWOD) systems. The ability to produce significant contact angle reduction at low voltage requires thin (<100nm), high dielectric strength films that also exhibit a high breakdown field; these requirements are met in a wide variety of metal oxides. A detailed understanding of materials as well as electronic and ionic transport in dielectrics are essential for the development and performance enhancement of these devices; we describe the process of oxides in film formation, the peculiar defect structure, electrical transport processes, as well as degradation and breakdown. Additionally, examples of low-voltage EWOD systems based on oxide/hydrophobic bilayers are discussed along with current efforts to improve performance of the metal oxide layers.