droplet actuator, reliable electrowetting, electrochemical diodes, high speed droplet actuation


We demonstrate bi-directional continuous electrowetting by embedding metal-semiconductor diodes in the electrowetting substrate. Unlike conventional electrowetting on dielectric (EWOD), bi-directional continuous electrowetting uses a single electrode pair to actuate a droplet through long distances. As long as the voltage potential is maintained between two end electrodes, the droplet moves toward the electrode with the higher potential. However, previously reported material systems had limited success in repeated actuation. In this work, diodes based on Schottky barriers were fabricated by forming metal-semiconductor junctions between titanium and high resistivity n-type silicon. The performance enhancements were evaluated using current-voltage measurements of interface pairs. When the titanium is coated with gold to limit electrochemical reactions, the Schottky diodes achieved superior performance compared to electrochemical diodes previously studied. Droplet speed range from 8 mm/s to 240 mm/s is reported. Under repeated actuation, the speed of the droplet showed no degradation for up to 2000 cycles (experiment duration).

Original Publication Citation

Q. Ni, D. Capecci, M. Schlafly, and N. B. Crane, “Robust Bi-directional Continuous Electrowetting Based on Metal-semiconductor (M-S) Diodes,” Microfluidics and Nanofluidics, August 2016, DOI: 10.1007/s10404-016-1788-0.

Document Type

Peer-Reviewed Article

Publication Date


Permanent URL


Microfluidics and Nanofluidics




Ira A. Fulton College of Engineering and Technology


Mechanical Engineering

University Standing at Time of Publication

Full Professor