Photosensitive poly(dimethylsiloxane) materials for microfluidic applications

Poly(dimethylsiloxane) (PDMS) is used as a thermally crosslinked material in microfluidics and Bio-MEMS. Recently photo-patternable materials show increasing interest, as the demand for easy alignment arises for multilayered structures. We present a photopatterning process for PDMS in microfluidics, for two main uses: (a) as a thin (approximately 10 μm) structural layer, and (b) as a very thin (approximately 1 μm) hard mask for oxygen plasma etching of microfluidic polymeric substrates down to several tens of microns. We study the deep-UV and I-line photocrosslinking properties of siloxane copolymers containing vinyl-methyl-siloxane groups as polymerizable units. These materials are sensitive to DUV and can be sensitized to 300–400 nm using free radical initiators. We prove that even thermally curable PDMS (Sylgard 184, base) can become photosensitive in DUV, although its practical use is limited to very thin films, due to its small molecular weight.