Twymann Green interferometry in study of A1N material as an actuation layer in MEMS

摘要

In this study we focus on the aluminium nitride (A1N). This material shows a large number of advantages associated with good piezoelectric properties. Therefore, A1N is an excellent candidate for MEMS actuation where low dielectric loss, low thermal drift and high signal-to-noise ratios are required. In this paper, the case of A1N driven cantilevers composed of three thin layers deposited on the silicon substrate will be considered. Precise knowledge of physical and material parameters of A1N applied in these simple elements are necessary for their further applications. However, up to now, A1N still represents a technological challenge and many of its micromechanical and piezoelectric properties are not precisely described. That is why, our study has been concentrated on determination of such parameters like the residual thin film stresses, thermal expansion coefficient a and piezoelectric coefficient d_(31). In this paper the interactions between the theoretical solution, the numerical FEM simulations and experimental results were performed. This hybrid methodology allows to identify the main source of behaviors discrepancy between the physical and numerical model of tested cantilevers. Obtained knowledge leads to optimization of the technological process and required parameters of actuator functionality achievement by better understanding of the tested microdevices properties. In experimental procedure, it was used nanoindentation tests for obtaining an elastic properties of A1N, interferometric techniques for performing the static and dynamic measurements of cantilevers and scanning electron microscope for measuring topography.