Boundary characterization of MEMS structures through electro-mechanical testing

Abstract

Micro-electro-mechanical-systems (MEMS) are coupled electro-mechanical microsystems used in many different sensing and actuation applications. The mechanical characteristics of the microsystem depend in large part to the choice of material and microfabrication process. In microsystems where there are suspended structures, as in the case of atomic force microscope (AFM) microcantilever probes, the boundary supports are uniquely defined by the microfabrication process implemented. In practice, AFM microcantilever probes suffer from large variations in natural frequencies due to the inherent microfabrication limitations, such as, material non-uniformity, geometrical non-uniformity and non-classical boundary support conditions. Out of these influences, non-classical boundary support conditions are difficult to estimate and are also very important for design and modeling considerations. Hence, this paper presents a testing method in which most of the influences were quantified or made variant while the support condition was kept invariant. This approach will help to identify the influence of microfabrication to the support boundary condition. This paper presents the results on the characterization of non-classical support boundary conditions of microcantilevers through electro-mechanical testing. A laser based non-contact optical testing approach is employed for the dynamic testing of the microstructure. The theoretical formulation is based on the Rayleigh-Ritz energy method using boundary characteristic orthogonal polynomials.