Illuminating the connection between contact angle saturation and dielectric breakdown in electrowetting through leakage current measurements

Recent findings on the connection between the dielectric breakdown strength and the contact angle saturation in electrowetting triggered further investigation of the underlying mechanisms towards reporting the consequences of the proposed relation. High sensitivity current measurements are conducted to monitor the dielectric leakage current during a standard electrowetting experiment by testing thin (15-500 nm) dielectric films of materials widely used in microelectronics industry (SiO2, tetra-ethoxy-silane, Si3N4). The measurements confirmed that the current is negligible as long as the applied, direct current, voltage is kept below a critical value at saturation onset. This current, however, exhibits a sharp increase at higher voltages. By exploiting the increased breakdown strength of stacked oxide-nitride-oxide dielectrics, the appearance of the contact angle saturation is inhibited, suggesting the use of such composites for the design of efficient electrowetting devices. (c) 2008 American Institute of Physics.