Browsing by Author "Cenaiko, Stirling Autumn"

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    Dielectric Thin-Films for Improving the Durability of AC Electrothermal Microfluidic Devices
    (2024-08-21) Cenaiko, Stirling Autumn; Dalton, Colin; Birss, Viola Ingrid; Natale, Giovanniantonio
    Microfluidic devices such as lab-on-a-chip, organ-on-a-chip and micro-total analysis systems allow for fast and precise testing of biofluids but can be limited in their capacity to perform more complex tests with currently available particle and fluid manipulation methods. Electrokinetics offers a way to precisely control particles and fluids using electric fields without the use of moving parts such as valves and diaphragms. Electrokinetics mainly includes dielectrophoresis, electroosmosis and electrothermal phenomena. Devices using these phenomena are limited in the voltage that can be applied, as higher voltages, along with higher fluid conductivities, significantly increase the risk of electrolysis and electrode degradation due to electrochemical reactions. AC electrothermal (ACET) is the most effective electrokinetic technique for pumping and mixing high conductivity fluids (including many biofluids, such as blood and urine). This thesis investigates the simulation and fabrication of dielectric thin-films for improving the durability of ACET micropump electrodes. RF-sputtering was investigated as a means to produce high-permittivity thin-film dielectrics. RF-sputtering is a widely-available method to coat high purity thin-films. Sputtering parameters (including power, oxygen content and temperature) were investigated to determine their impact on the deposition of metal oxides. This work also uses simulations to investigate the influence of spatially variant electrical phases on ACET fluid velocity, as well as simulating the dielectric coating effectiveness. This work showed that RF-sputtering can cause significant damage to the materials used for the microelectrodes of ACET devices. However, utilising certain process parameters, RF-sputtering can successfully be used as a method to deposit high-permittivity dielectrics to decrease degradation of ACET electrodes at higher applied voltages. These dielectric coatings may be applied to other forms of electrokinetic devices to improve their longevity and electrochemical stability.