Planarization of the surface of electrowetting on dielectric device for droplet speed improvement

The surface roughness aggravates droplet manipulation speed by increasing contact angle hysteresis (CAH) and pinning force between droplet and an electrowetting on dielectric (EWOD) device. Because spacing between electrodes in the EWOD device cannot be filled up by thin film deposition process for an insulation and hydrophobic layer fabrication, trenches as deep as metal electrode layer are generated on the surface. The trenches increase the surface roughness of EWOD device, especially at the edge. In this work, polishing technique (chemical mechanical polishing, CMP) was appplied to EWOD fabrication to remove the trenches on the surface of the EWOD device. To verify the effect of the surface polishing on droplet speed improvement, we fabricated both unpolished and polished EWOD devices that comprised of 0.5 × 0.5, 1 × 1, and 1.5 × 1.5 mm² electrodes array to manipulate 1 to 10 μL droplets. Droplet speed on the polished devices was improved by 21 to 100 % compared to that of the unpolished one.