Experimental and Theoretical Dynamic Investigation of MEMS Polymer Mass-Spring Systems

This paper presents the experimental, analytical and numerical dynamic analysis of SU-8 polymer MEMS mass-spring systems using two different attachment beams, dual and quad. Beam thicknesses of $4.48~\mu \text{m}$ and $8.21~\mu \text{m}$ produce two different sets of prototypes using dual-beam attachments. Those using quad-beam are only $8.21~\mu \text{m}$ thick. Using Lazer Doppler Vibrometer (LDV), dynamic characterization is performed to measure respective resonance frequencies of 1325 Hz and 1813 Hz for dual and quad-beam attachments having a thickness of $8.21~\mu \text{m}$ . Numerical and analytical dynamic analysis are performed to investigate the frequency response of systems using both attachment structures. Using measured key geometric dimensions, numerical and analytical resonance frequencies are evaluated. Theoretical and experimental values are in good agreement with maximum errors of 16% and 12% for dual and quad-beam structures, respectively. The low-cost microfabrication process can be used to incorporate a piezoresistive material/nanomaterial in locations of maximum stress on the beams producing dual and quad-beam MEMS piezoresistive sensors. Numerical analysis is performed to show that the resonance frequency is not affected which proves that the developed dynamic analysis stays valid.