A robust and inexpensive composite insulation layer for digital microfluidic devices

•A cheap way and materials for deposition of insulation of digital microfluidic devices were suggested.•The digital microfluidic chip we made demonstrated impressive robustness and sustainability with a broad actuation range between 30 and 350V and a long working life of 5000 consecutive runs.•The electromechanical force of our DMF chip was calculated and compared with other chips. The cause of broad actuation range was investigated theoretically. Digital microfluidics is a plausible platform for manipulation of discrete droplets, which are driven by electrowetting and dielectrophoretic forces. Increasing the sustainability of DMF chips while reducing their fabrication cost would be attractive to research on droplet-based micro-actuators. Here, we report a new robust composite layer, with which a broad range of its operation voltage of DMF chips was demonstrated, covering from 30V, which was 25V below the theoretical value predicted with scaling model that derived from d/ɛ, to at least 350V with a minimum dispensing voltage at 100V. Also, a lifetime of at least 5000 continuous cycles at 110 volts was achieved. Deposition of such a composite layer was solely accomplished with a low-cost spincoater, instead of expensive vapour deposition instruments. And the materials we used were cheap as well. The electromechanical force, which was expressed in separate terms of electrowetting force and dielectrophoretic force on a droplet, in six chips with different values of d/ɛ were calculated and compared. The result from our calculation showed that, differently from low-d/ɛ DMF chips, there was considerable electrowetting factor among the electromechanical force in the high-d/ɛ DMF chips and it may be the cause that the initial apparent actuation voltage was much lower than theoretical threshold actuation voltage.