Mechanical Properties Study And Testing Structures Design Of MEMS Multi-Layered Films

Micro-Electro-Mechanical Systems(MEMS), developed from microelectronic technology, is integrated microsystems which combine sensing, information processing, execution modules. As the essential component of micromechanical structure, thin film is widely used in MEMS devices. Apparently, The mechanical properties such as Young’s modulus, residual stress, Poisson’s ratio of thin films, are not only the essential parameters determing performance of microstructures, but also important reference factors used in microsystem design. However, affected by the restriction of process and size effect, the mechanical properties of MEMS thin films will be very different from bulk material. Besides, even the same material in the same process will show different properties under different manufacturing conditions, therefore, we should develop new technology which distinct with traditional ones to characterize the mechanical properties of MEMS thin films.In this paper, the research on mechanical characters of MEMS multi-layered thin films and relevant test structures are present. Theoretical models are built for multi-layed films to analyze mechanical properties and design test structures. The main work and innovations of this paper are described as following:First, the model of multi-layered cantilever is proposed and the radius of curvature formula is deduced. Further, we discussed the relationship between the thickness of film and radius of curvature.To solve the problem that the error of formular increases when width to length ratio increases, we modify the formular and verify it in FEM simulation. The results of FEM simulation are consistent with the theoretical analysis.Second, we study the transversal movement of multi-layed films drived by electrostatic power and introduce the extraction method of equivalent bending stiffness. By grouping several structures with different thickness, Young’s modulus of each layer can be calculated according to the model. In addition, the impact of geometry parameters on the model’s error is considered. We use FEM simulation to verify the accraunce and reliability of the theoretical analysis.Third, regarding the models and methods above as the foundation, test structures are designed and fabricated for bilayer films, which are intended to measure residual stress and equivalent bending stiffness. Experimental results and analysis on the structues are also present.The study of mechanical properties of MEMS multi-layered thin films and related test structures proposed in this paper are all verified by FEM simulation. Moreover, the impact of geometry parameters of structures are considered. On the basis of that, optimization of model and guidance on design are given, which shows great value in application.