Electrothermal Pumping With Thin Film Resistive Heaters

The ability to manipulate small amounts of fluid is important for a variety of lab-on-a-chip applications. Electrokinetic microfluidic actuation methods, such as electrothermal pumping, are popular due to their simple implementation and reliability from no moving parts. Electrothermal motion in aqueous solutions results from the electric field acting upon dielectric inhomogeneities in the liquid induced by temperature gradients. The most traditional method of inducing temperature gradients is through direct Joule heating of the fluid itself, which is a function of the electrical conductivity of the liquid. In this case, the microelectrode geometry controls both the location of the Joule heating and the nature of the electric field. Therefore, it is impossible to independently control temperature and electric field with a single set of electrodes. A novel electrothermal microfluidic pump is demonstrated herein. The distinguishing feature of this electrothermal pump is an independent heating source using resistive heating of microfabricated metal traces. A second set of electrodes for electrothermal pumping have been layered on top of the electrically isolated heating elements. An arrangement of coplanar electrode strips with an additional resistive heating electrode was used to demonstrate electrothermal pumping. Fluid motion results were compared to established theory.