Measuring frequency response of surface-micromachined resonators

Resonator structures offer a unique mechanism for characterizing MEMS materials, but measuring the resonant frequency of microstructures is challenging. In this effort: a network analyzer system was used to electrically characterize surface-micromachined resonator structures in a carefully controlled pressure and temperature environment. A microscope laser interferometer was used to confirm actual device deflections. Cantilever, comb, and piston resonators fabricated in the DARPA-sponsored MUMPs process were extensively tested. Measured resonant frequency results show reasonable agreement with analytic predictions computed using manufacturer measured film thickness and residual material stress. Alternatively the measured resonant frequency data can be used to extract material data. Tuning of resonant frequency with DC bias was also investigated. Because the tested devices vary widely in complexity, from a simple cantilever beam to a comb resonator, the data collected is especially well suited for validation testing of MEMS modeling codes.