Direct current-induced breakdown to enhance reproducibility and performance of carbon-based interdigitated electrode arrays for AC electroosmotic micropumps
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© 2017 Elsevier B.V.The conventional fabrication process of carbon-based microelectromechanical systems (C-MEMS) often yields undesired carbon residues that reduce the reproducibility and performance of final structures by establishing unwanted electrical connections. In this work, we present a new and straightforward method based on the application of a low direct current (DC) to effectively remove the undesired electrical connections. The DC bias causes the breakdown and removal of the short-circuiting carbon residue due to Joule heating, resulting in significantly enhanced performance and reproducibility of the final structures. We fabricated carbon-based asymmetric coplanar interdigitated electrode arrays (IDEAs) for alternating current electroosmotic (ACEO) micropumps using the conventional Carbon-MEMS process. By scanning electron microscopy (SEM); Raman, energy dispersive X-ray (EDX) spectroscopies; four-point probe resistance measurements; and the combination of ion-beam etching and X-ray photoelectron spectroscopy (XPS), we confirmed the presence of residual carbon in the gaps of the IDEAs and established its deleterious effect on electrical properties of the structures and their performance as electrodes in micropumps. A computational study was also conducted to estimate the temperature increase due to the DC bias applied across a thin residual carbon. Experimentally, we found that the DC-treated IDEAs exhibited more than double the fluid velocity in ACEO pumping compared to untreated devices; and also, the coefficient of variation of the fluid velocity for the DC-treated ACEO micropumps was significantly smaller than that for the untreated ones. This simple and easy-to-implement method can substantially improve the yield of Carbon-MEMS manufacturing, leading to a highly reproducible production of high performance carbon electronic circuits and microstructures.