Fabrication and characterization of hydrogel mems resonators via dynamic mask lithography

This paper reports a new fabrication method for various hydrogel MEMS resonators by employing dynamic mask lithography on a drilled polymethylmethacrylate (PMMA), of which through hole and boundaries are molded with polydimethylsiloxane (PDMS), PMMA-PDMS composite substrate. Polyethyleneglycol diacrylate (PEG-DA) mixed with a photoinitiator is introduced between a PMMA-PDMS substrate and a PDMS cover with a predefined recess. Then, the PEG-DA prepolymer is cured into an intended shape by a dynamic mask, an image projected from a digital micro-mirror device connected to a PC. After selective curing by the dynamic mask, the PDMS cover is removed and the uncured PEG-DA is gently washed with isopropyl alcohol to leave cured PEG-DA exclusively attached on the PMMA. Finally, the PMMA piece with the cured PEG-DA is simply separated from the surrounding PDMS to obtain a free-standing microstructure. This separation leaves no damage on photocured structures due to the relatively strong adhesion between the PMMA and the PEG-DA and the oxygen inhibition layer above the PDMS facilitating the demolding process.