Date on Master's Thesis/Doctoral Dissertation

5-2012

Document Type

Doctoral Dissertation

Degree Name

Ph. D.

Department

Electrical and Computer Engineering

Committee Chair

Harnett, Cindy K.

Subject

Microfluidics; Fluid dynamics; Microelectrodes

Abstract

Most of the structures in submillimeter-scale engineering are created from thin films, making them essentially two-dimensional (2D). Significant work has been done to fabricate 3D structures using self-folding, a deterministic form of self-assembly, and three dimensional lithographic and non-lithographic patterning. The objective of this work is to propose different fabrication and patterning strategies of 3D structures used as pumping electrodes for micro fluidic applications. 3D electrodes drive flows over the whole channel height while 2D electrodes stay near one wall. The first application of the 3D electrodes is mixing chemical or biological samples with reagents for chemical analysis which is one of the most time consuming operations in microfluidic platforms. The mixer used is based on the electrokinetic phenomenon of induced charge electro-osmosis (ICEO). ICEO creates microvortices around polarized posts with gold coated sidewalls, connected to embedded electrodes, by application of alternating current (AC) electric fields. These microvortices around posts help in mixing the two reagents very quickly. These vertical sidewall gold coated posts and embedded electrodes are fabricated using 3D photolithographic patterning and an ion milling fabrication technique. The second application is fast ac electro-osmotic (ACEO) pumps using 3D electrodes. These 3D electrodes dramatically improve the flow rate and frequency range of ACEO pumps over the planar electrodes. A non-photolithographic electrode patterning method is proposed to fabricate such electrodes. The method is based on shadowed evaporation of metal on an insulating substrate. This method is considered to be simple and cost effective compared to others used to create these stepped 3D electrodes. Finally, a self-folding technique is proposed to create out-of plane three dimensional electrodes for ACEO tube pumps. The technique depends on the strain mismatch between two different layered sheets of material. One layer usually has compressive stress, i.e. thermally grown Si02, and the other has relatively tensile stress, i.e. metals. The design is similar to the planar electrodes design in the literature, except as a 3D electrode it interacts with a larger volume of fluid for a more efficient pump.

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