Design, fabrication, and applications of silicon electroosmotic micropumps

A new class of micropumps based on electroosmotic flow has been developed. These micropumps are fabricated through silicon micromachining and incorporate electroosmotic flow elements consisting of parallel arrays of hundreds of narrow, deep trenches designed to enhance the transfer of momentum into the fluid phase. A comprehensive model of silicon electroosmotic micropump operation has been developed by adapting and extending the Burgreen-Nakache model of electroosmotic flow in slit capillaries. The newly developed model takes into account deviations from the ideal slit capillary geometry arising from silicon etch and thin film processes, as well as factors such as pressure losses and potential gradients within the micropump but external to the electroosmotic flow element.; Over sixty prototype silicon electroosmotic micropumps have been fabricated and tested. Prototype silicon electroosmotic micropumps with 1.5 cm 3 package sizes generate flow rates up to 170 muL min-1 and pressures of nearly 10 kPa. Using the newly developed micropump model to compare data for micropumps with different electroosmotic flow element geometries and for a range of operating voltages, micropump flow rate is seen to scale in proportion to the magnitude of the electric field in the electroosmotic flow element, while pressure scales in proportion to the total voltage drop across the electroosmotic flow element---findings consistent with established models of electroosmotic flow and electric double layers. The effect on micropump performance of dielectric thin film composition has been characterized, with zeta potentials found to be approximately -20 mV for nitride films and -40 mV for oxide-on-nitride films.; Critical processing steps in the silicon electroosmotic micropump fabrication process have been characterized in detail. Dielectric thin film deposition processes have been developed which mitigate substrate current sufficiently to permit micropump operation at up to 500 V. Trap-controlled hole conduction in the silicon nitride layer is proposed as the current-limiting mechanism in these films. Transient pressure response data has been obtained by laser vibrometry measurement of the deflection of integrated pressure-sensing diaphragms. Silicon electroosmotic micropumps have been evaluated for applications in integrated circuit thermal management and biological fluids analysis.