Effects of DC & AC bias on the dynamic performance of micro resonators

It has been observed in many MEMS devices that there is a shift in resonant frequency due to voltage bias. The voltage bias may include either AC or DC bias or both. This paper reports on the significant discrepancy between the analytical and experimental resonant frequencies of folded beam micro resonators. Experimental results for the resonant frequency showed a consistent 20% discrepancy over theoretical and finite element results for MUMPs fabricated resonators. This difference in frequency is also seen in SOI fabricated devices. Possible causes of the discrepancy from tapered cross section of the flexure beams, dimensional variations and electrostatic spring effects are discussed and shown to contribute to the significant difference between analytical and experimental values. IntelliCAD^TM electrostatic simulation was done to isolate the electrostatic spring effect and compared with the experimental observations. The compliance due to AC voltage has also been observed in SOI and MUMPs resonators and has been presented.