| Nowadays, the aluminum films have wide application in micromechanical devices such as micro sensors and actuators, so that their mechanical properties come to be very important for reliability evaluation. However, there is no standardized method to evaluate the mechanical properties of material used in MEMS (micraelectromechanical system) device since the measured mechanical properties are influenced by many factors such as surface condition, friction force, etc. Hence, we intended to evaluate the mechanical properties of thin film in our study, which is important in mechanical operation. Because MEMS devices are usually operating in elastic range, the Young`s modules and yield strength were evaluated by using microcantilever beam technique. First, Al cantilever beams were fabricated using the silicon bulk micromachining technology to have various film thickness. And then, the load-displacement curve was obtained by nanoindentation method. The linear relation in elastic range was utilized in deriving the Young`s modulus of Al film, which gives us reproducible result regardless of film thickness. In high load range, the deviation from the linear relation was detected, so that the yield strength of Al film could be evaluated. It is found that the yield strength increases with decreasing film thickness. By applying the misfit dislocation theory and the Hall-Petch relation, the theoretical estimation could predict well the trend of yield strength. |
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