Electroosmotic pumps fabricated from porous silicon membranes

N-type porous silicon can be used to realize electroosmotic pumps with high flow rates per applied potential difference. The porosity and pore size of porous silicon membranes can be tuned, the pore geometry has near-unity tortuosity, and membranes can be made thin and with integrated support structures. The size of hexagonally packed pores is modified by low-pressure chemical vapor deposition (LPCVD) polysilicon deposition, followed by wet oxidation of the polysilicon layer, resulting in a pore radius varying from 1 to 3 μm. Pumping performance of these devices is experimentally studied as a function of pore size and compared with theory. These 350-μm-thick silicon membranes exhibit a maximum flow rate per applied field of 0.13 ml/min/cm²/V. This figure of merit is five times larger than previously demonstrated porous glass EO pumps.