Development of environment controlled micro mechanical testing system for thin films

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In order to develop a reliable micro machine and MEMS in a service operation, much care must be taken into micro mechanical evaluation, i.e., mechanical properties of μm-sized microelements including fatigue behavior and effects of loading mode, e.g. tensile and bending loading. However, the evaluation method has not been well established yet. In this study, a bending testing system based on a Nano Indenter with knife-edge type indenter and a piezo stage were developed and the bending tests have been conducted for poly-Si thin microelements with 3.5μm thick, 5μm wide and 10μm long. Fracture stress obtained by the bending test was 3.9 ± 0.5GPa, which was higher than the strength under uni-axial tensile loading. To evaluate the effect of loading mode on the mechanical properties of a thin microelement, the uni-axial tensile testing system has also been developed. The system consists of a micromechanical tensile testing machine actuated by a PZT driven positioning stage, a micro manipulation system, a non-contact strain measurement system with a help of a double field of view microscope. By using this testing system, tension-tension fatigue tests for poly-Si thin microelements with 3.5μm thick and 10μm wide can be carried out up to 10 Hz of stress cycle frequency in various environments ; in wet environment, in dry air and in laboratory air. Moreover to evaluate the influence of the crystalline orientation, the number of grains and the grain size distribution on the elastic modulus of poly-Si thin film, finite element models were developed based on the Monte Carlo method. The analytical results were compared with the experimental ones.