Fabricating a Dielectric Coating for an Improved Electrokinetic Micropump
Keywords:strontium titanate, rf-sputtering, dielectric thin-film, AC electrothermal, electrokinetic
This research proposes a method of fabricating a dielectric coating over the microelectrodes of an alternating current electrothermal (ACET) device to create a barrier between the biofluid and microelectrodes, eliminating the risk of electrolysis and creating a more effective device. Strontium titanate (STO) is proposed as a potential dielectric material for ACET devices, as it has a high dielectric constant compared to other materials, allowing for a higher device flow rate. This work examines various parameters used for the radio-frequency sputtering (rf-sputtering) of STO, and how these parameters affect the deposited film properties and the microelectrodes being coated. It was found during initial experimentation that the rf-sputtering technique used to deposit STO thin-films tends to etch away at the electrodes due to high energy oxygen ions. Literature is scarce on the topic but provides some guidance on modifications to the initial sputtering parameters. Through additional experiments, the following observations were made: a high oxygen injection (~30%) is required to ensure the STO film is nonconductive, sputtering the slides at 90° significantly reduces etching, a lower RF power reduces etching (but has not been found to eliminate it) and decreasing the bias power appears to reduce both etching and deposition rates. This work shows that a dielectric coating could be deposited over ACET electrodes with further work to optimize the parameters.