An asymmetric electrode for directional droplet motion on digital microfluidic platforms

Abstract The development of large-scale electrowetting-on-dielectric (EWOD) platforms with numerous integrated functions requires a large number of electrodes. While this challenge has traditionally been addressed by pin-count minimization strategies and circuit-routing schemes, we propose heart-shape electrodes that allow using even fewer pins when the droplet motion is unidirectional. This electrode geometry ensures that the droplet overlaps more with the front electrode than with the rear one, resulting in a net capillary force that pulls the droplet forward. Droplets with a footprint diameter between 0.8 and 1 times the electrode width can be driven reliably over long distances using only two alternately applied actuation signals. The maximum signal switching frequency that enables the reliable movement of droplets is proportional to the square of the applied voltage and the gap height, but inversely proportional to the electrode diameter. Each segment of the interconnection circuit spans only two electrode-lengths, which simplifies the circuit routing and avoids the possible trace overlap in large-scale electrode arrays. By minimizing the pin number, this asymmetric design provides a promising strategy for electrode arrangement in multifunctional, large-scale EWOD platforms.