Planar microfluidics: Toward large-scale integration of channels, pumps, valves, and fluid mixers in microelectromechanical systems (MEMS)

A cost effective, manufacturable technology for the large scale integration of microfluidic processing components would find wide application in drug delivery, drug development, micro-biology, genetics, printing and associated fields. This dissertation outlines a design paradigm which allows for such large scale integration using components which rely solely upon planar laminar flows. Concepts, analysis and prototypes are developed for components capable of handling picoliter, nanoliter and microliter volumes, including micro-channels, micro-pumps, micro-valves, and micro-mixing/reaction chambers. Specifically, the author demonstrates: fabrication of complex channel arrays in a silicon wafer; fabrication of electrical components on a quartz substrate; a technique for bonding a quartz wafer with electrical components to a silicon wafer using a patterned bonding layer; integration of electronic components onto the inside of fluidic channels; packaging of a fluidic device allowing for more than sixty electrical connections and more than ten fluidic connections; visualization of flow within a microfluidic device; the creation of thermally generated bubbles within closed fluid chambers; the “gettering” of dissolved gasses from fluid to form stable gas bubbles using thermally generated bubbles; the fabrication of released structures which move within plane of the device using Silicon-on-Insulator (SOI) wafers; an operational mechanical check valve which controls the motion of fluid within the plane of the device; the use of thermally generated bubbles to move mechanical structures within the plane of the device; a bi-stable actuation cycle which uses bubbles to move a mechanical structure in excess of sixty micrometers and which does not require that bubbles be collapsed to complete the actuation cycle; a bi-stable actuated mechanical micro-valve which controls the motion of fluid within the plane of the substrate; an operational thermally driven bubble piston chamber which may be incorporated into positive displacement bubble-pumps; a pumping effect caused by steady operation of a thermally generated bubble; and analysis, numerical simulations, and prototypes suggesting a method for mixing fluids in a planar laminar environment using chaotic advection.