| dc.description.abstract | Typical micro-thermal actuators are based on the thermal expansion-induced displacement. To generate large displacement, one can use hot-and-cold-arm structures for the in-plane motion, and bimorph cantilever structures for the out-of-plane motion. The later usually has larger displacement, lower operation voltage, and wider design range. Recently, polymer materials are used in micro-devices, due to their low Young’s modulus and high elongation rate. In this study, polydimethylsiloxane (PDMS) is used as one of the bimorph material due to its compliance and biocompatibility. Polymer film patterning is usually conducted by dry etch, bond-detach lithography, or lift-off processes. We propose a novel technique that pattern the PDMS film directly on the metal cantilever by localized heating and eventually form a bimorph structure with the cantilever. This method not only reduces the number of the mask, hence reduce the process steps, but also achieves self-alignment.
In the design, the metal micro-cantilever served as a heater is suspended above a cavity made by bulk-machining. This prevents the stepping problem at the anchor of the cantilever usually found in that made by surface micromachining. The micro heater properties are then characterized to precisely control the heating temperature when pattering PDMS. After the PDMS is patterned, we release the micro cantilever structure by wet etching and analyze the deformation and curved angle. The result shows that the thickness of cured PDMS film is a strong function of heating temperature and heating duration. When the heating temperature is at 120 ℃, it has less variability than at 150 ℃ and its variability will increased substantially with the temperature rising. Higher heating temperature and longer heating time result in thicker film, but the thickness variation between experiments also increases. This may be caused by the uncertainty of temperature control of micro-heater in high temperature.
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