Micromechanical structures for thin film characterization

Micromechanical structures designed for material characterization through analysis of their lateral vibrations are reported. The structures are made of doped LPCVD (low-pressure chemical vapor deposited) polycrystalline silicon and consist of beams supporting a rigid mass which is used to drive as well as sense the oscillatory motion. Amplitude and phase responses with respect to frequency are measured by an amplitude modulation technique and are used with the corresponding mechanical model to estimate various electromechanical properties. Young´s modulus for this material is estimated to be 174+or-10 GPa, with the film supporting a tensile residual stress of 10+or-2 MPa. It is shown that some structures exhibit significant nonlinearities for moderate lateral displacements. The observed response curves are well modeled by Duffing´s equation for a stiffening spring.<>