Room-Temperature Fabrication of Anodic Tantalum Pentoxide for Low-Voltage Electrowetting on Dielectric (EWOD)

This paper presents a robust anodic Ta₂O₅ dielectric as an alternative insulator for fabricating low-voltage electrowetting on dielectric (EWOD) systems. Previously reported low-voltage EWOD technologies require high-temperature processes ( > 435degC), which unlike this room temperature technology, are not compatible with standard copper and aluminum integrated circuit interconnect technology as well as polymer-based substrates. The anodized Ta₂O₅ forms a uniform pinhole free layer with a surface roughness (R _a) of 0.6 nm. This robust film enables an ultrathin amorphous FluoroPolymer layer to be employed to reduce the EWOD driving voltage to 13 V. Both sub-20-nm Teflon-AF and CYTOP layers have been successfully coated on top of Ta₂O₅ with good adhesion. Applying voltages of 6-15 V significantly modified the contact angles of droplets in air on these samples (121deg to 81deg on Teflon-AF at 13 V and 114deg to 95deg on CYTOP at 6 V). Successful 14-V EWOD manipulation involving droplets being dispensed from a reservoir, their movement, followed by merging them together has been demonstrated using devices using a Teflon-AF + Ta₂O₅ dielectric.