STUDY ON STIFFNESS AND RESONANT FREQUENCY OF A PARYLENE SUSPENDED STRUCTURE

摘要

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 f_r. 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.