Evaluation of anodic TA2O5 as the dielectric layer for EWOD devices

We report that anodic tantalum pentoxide (Ta₂O₅) exhibits severe polarity and frequency dependencies that, when used as the dielectric material for electrowetting on dielectric (EWOD) devices, in many cases result in long-term performance that is worse than when conventional dielectrics (e.g., SiO₂) are used. This rather disappointing news is nevertheless relevant to the community and calls for critical assessment. Here, we find that under direct current (DC) actuation Ta₂O₅ is attractive for EWOD only if the droplet is negatively biased, and that under alternating current (AC) it is acceptable only for low frequencies.