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.