Parylene has intrinsic tensile stress on account of mismatch of thermal coefficient of expansion (TCE) between the substrate and the deposited film. Therefore, the stiffness k of the Parylene suspended structure under tensile stress is much higher than that under no stress, which also leads to its higher resonant frequency fr. These mechanical characteristics are investigated in this study. First, FEM simulation is employed, and it is proved that k is decreased in proportional to the first power of the beam length l, while it is decreased in proportional to the third power of l under no stress according to the theory of strength of materials. Considering this, a structure with spiral shaped beams is proposed for lowering k. Second, practical Parylene suspended structures are fabricated. The vibrations of them are observed by LDV (Laser Doppler Vibrometer) and their experimental resonant frequencies obtained. They coincide well with simulated ones.

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