The ability to transport species and handling fluids in microchannels with ease and precision is central concept to the μTAS devices. Much attention has been focused on micropump research, not only for their use in μTAS systems, but also for a large variety of applications such as: aerospace and aircraft engineering, medical, pharmaceutical devices, cosmetics, paints and inks, food and beverage, environmental, energy and fuel, electronics smart devices applications, clinical and analytical lab.
Advances in microelectronics fabrication processes have allowed the miniaturization of mechanical pumps, however non-mechanical pumps have several advantages in handling flow rates in the range of nanolitre or picolitre per minute. In biomedical technology, pumps for handling extremely small fluid amounts become more and more important.
Microsystems for biological analysis routinely use solid-state electrokinetic micropumps which play an important role in microfluidic pumping. AC Electrokinetic micropumps in particular AC electroosmosis pump can be used to pump fluids using planar electrodes which induce electrical forces on the fluid. However, planar electrodes do not provide sufficient back pressure which limits the pumping capability of the micropump.
In this project a new design for the AC electroosmotic is introduced. The new AC electroosmotic desig presents the transition from planar microelectrode arrays to planar with High Aspect Ratio (HAR) pillars in order to increase the conductive surface area for the microchannel. The physical mechanism of AC electrosmosis is the motion of induced Electrical Double Layers on microelectrodes driven into motion by the electric field generated by the electrodes. Since AC-electrosmosis is a surface driven effect, increasing the surface area increases the power coupled into the fluid movement. By taking the channel volume and filling it with conductive pillars, the surface area therefore increases, but the volume remains the same, increasing the drive per unit volume. This will have the effect of increasing the pressure generated by the pump. One possible side effect is that the internal resistance of the pump will rise, reducing the maximum flow rate. However, it is expected that the increase in driving surface area will offset this to a degree.
To explore and realize the proposed pumping principle we benifited from available expertise of Professor Mark. J. Madou who specialises in Bio-MEMS field and microfabrication techniques. Prof. Madou and his team at UC Irvine have been able to construct HAR pillars made out of pyrolyzed SU-8 (conductive polymer). The current planar electrodes are made out of gold and it is desired to make the pillars out of gold as well. However we assume that the pillars made by gold undergo chemical reactions involving dissolution and redeposition. In contrast the pyrolyzed SU-8 pillars will be less conductive than the gold ones but they are perfectly polarisable, which is ideal for AC electroosmosis. was processed.
In this work a novel version of AC-electroosmosis micropump was designed, in a way it incorporates 3D high-aspect-ratio electrodes, the idea behind the implementation of the 3D electrodes is to increase the surface of the electrodes as the AC electroosmosis is a surface driven effect phenomenon. However the fabrication of high-aspect-ratio electrodes is very difficult using standard electroplating techniques. In this work a new technology using Carbon-MEMS technology was adopted. The fabrication process of the new AC-electroosmosis micropump was developed. A good results of the new device has shown a successful functionality and improvement to previous design.