Frozen water for MEMS fabrication and packaging applications

A frozen water process, which is clean, low temperature and biocompatible, is successfully demonstrated. The working principle is based on that frozen water can be processed as a solid thin film before it melts. In order to pattern the frozen water, hydrophobic and hydrophilic regions should be defined to allow water to be selectively attached to the hydrophilic area under the ambient environment. After water is frozen, a polymer layer can be spun on top of this solid layer to form the final structure. The frozen water can melt and evaporate gradually afterwards and function as the sacrificial layer. This frozen water process can also serve as a packaging procedure to encapsulate working liquids with an impermeable layer over the polymer. Two possible applications are envisioned and realized, including capillary-driven micropumps and micro optical lenses. Experimental results show that micropumps have flow rate from about 3nL/min at the beginning and reduce to about 0.2nL/min after 10 minutes with microchannel widths of 20 to 40 μm. The fabricated microlenses have measured focal lengths from 433 μm to 5660 μm when the frozen water patterns are from 500 μm to 2000 μm.