In situ characterization of PDMS in SOI-MEMS

This paper presents the in situ characterization of microscale poly(dimethylsiloxane) (PDMS) springs using silicon-on-insulator-microelectromechanical systems (SOI-MEMS). PDMS samples that were 30 mu m long, 20 mu m thick, and 6 mu m wide were fabricated on-chip along with a test mechanism that included electrostatic comb drive actuators and silicon flexures. The test mechanism allowed for applying strains up to 65%. The in situ test results were compared with results of tests on macroscale samples performed using a dynamic mechanical analyzer. The results imply that the process steps during fabrication initially led to increased crosslinking of the PDMS but that the final release of the structure in buffered hydrofluoric acid decreased the crosslink density, thereby decreasing the stiffness of the PDMS. Several implications of the results on processing PDMS in MEMS are presented. The results of this work are important for the design of MEMS devices which incorporate PDMS as a mechanical material.