A novel polymer-based fluid-actuated variable focal length microlens system with a wide field-of-view (FOV) and large numerical aperture is designed and fabricated using standard photolithographic and silicon micromachining techniques. A flexible polydimethylsiloxane (PDMS) membrane is used to form the lens surface and is actuated by fluidic pressure applied by an external syringe pump. This lens system is capable of working in dual mode, forming either a double convex (DCX) or a double concave (DCV) lens. The relationship between the focal length (f) and FOV of the fabricated dynamic lens system as a function of the volume of the fluid pumped into or out of the lens chamber is investigated. The focal length of the dynamic lens system demonstrated in this paper could be tuned in the range of 75.9 to 3.1 mm and −75.9 to −3.3 mm for the DCX and DCV lens configurations, respectively. The FOV for this lens system was found to be in the range of 0.12 to 61° for DCX lens and 7 to 69° for DCV lens. The smallest F-number (f/#) that could be achieved using this dynamic lens is 0.61, which corresponds to the numerical aperture value of 0.64.

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A simple approach is developed to obtain scum-free pattern transfer in SU-8 resist by UV-lithography for electroforming applications. SU-8 is an epoxy-based negative resist used in the fabrication of high-aspect ratio microstructures. SU-8 resist poses considerable processing difficulties and tends to leave organic residues of undeveloped resist on the surface of the exposed metallic seed layer. Scum-free pattern transfer in SU-8 resist is important for the subsequent electroplating process used to fabricate the high-aspect ratio metallic microstructures. Dry plasma etching processes are commonly used to remove the SU-8 residue prior to electroplating. However, these processes are complex and not cost-effective. In this work, it is shown that scum-free SU-8 patterns could be achieved by proper selection of process parameters such as soft-bake temperature, exposure time, post-exposure-bake temperature, developing time and rinsing in solvents. The success of this particular process is due to controlled rinsing of the patterned sample in acetone to remove the resist scum. The results of our method for patterning the SU-8 resist to fabricate nickel microstructures using this mold are reported.

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