Fabrication of curved PDMS microstructures on silica glass by proton beam writing aimed for micro-lens arrays on transparent substrates

Polydimethylsiloxane (PDMS), a type of silicone rubber, has excellent material properties such as flexibility, optical transparency and biocompatibility. Therefore, it can offer possible applications in the field of microfluidics as flexible micro-optical components, when they can be formed on transparent materials such as silica glass. We performed proton beam writing (PBW) (with 1.0 MeV beam) on PDMS microstructures with curved surface on silica glass. We found that 13-μm thick PDMS films on silica glass are sensitive only for proton fluences above 600 nC/mm² in contrast with the sensitivity of 4.0 nC/mm² when using a silicon substrate. Based on the hypothesis that the effective sensitivity was lower due to the electric charging of silica glass surface during PBW, we coated the silica glass surface by Au sputtering. As a result, we were able to observe the formation of PDMS on the Au-coated silica glass at a much lower fluence of 2.0 nC/mm². Arrays of curved PDMS structures with a height of 13 μm and diameter of 40 μm have been fabricated on a semi-transparent Au-coated silica glass.