Characterization of micromachined silicon nitride membrane using resonant ultrasound spectroscopy

Resonant ultrasound spectroscopy (RUS) is used by scientists to determine the elastic constants of materials. In this paper we extend RUS into the MEMS field, to characterize the micromachined silicon nitride membrane. The central idea of RUS is the comparison of measured and computed natural frequencies of the samples. For measurement, RUS can easily excite the vibration of the micromachined silicon nitride membrane structure and measure a large number of its natural frequencies. For computation, finite element method (FEM) is used to calculate the natural frequencies and obtain normal mode shapes of sample. Furthermore, we used FEM to directly set up the linear relationships between the natural frequencies and mechanical properties and dimensions of the micromachined silicon nitride membrane sample, so RUS can be used for fast characterization in industrial application. The accuracy of structural dimensions determined by this technique has been verified within 0.35~4.62% and Young´s modulus of the LPCVD silicon nitride thin film is 195±9 GPa verified by the load-deflection measurement