Improvement of droplet speed and stability in electrowetting on dielectric devices by surface polishing

This paper reports on a technique that significantly improves the performance of open-plate electrowetting on dielectric (EWOD) devices by using chemical mechanical polishing (CMP) to achieve surface planarization. In EWOD devices, trenches are inevitably generated during fabrication, and these can have a considerable effect on droplet manipulation. Such artefacts lead to a local intensification in the electric field that not only hinders the droplet movement due to a partially increased adhesion force, but also limits the maximum applicable potential by increasing the likelihood of a dielectric breakdown. We conducted theoretical and experimental studies on the effect of trenches on the performance of both unpolished and polished EWOD devices. Various combinations of the droplet volume and electrode size were tested, and our proposed technique resulted in a notable improvement for all cases. For instance, when operating at 100 V, a 3.5 μL droplet could be translated at 70 mm/s on the polished EWOD device, which is twice as fast as that for its unpolished counterpart at the same voltage. Also, the maximum applicable potential resulting in a dielectric breakdown of the polished EWOD device was measured to be 27% higher than that of a conventional device.