Thin film windows for use in a bulge tester and as a piezoelectric actuator

This paper reports the results of experimental studies using a bulge tester and accompanying computer models. The bulge tester applies a load on the backside of the thin film and measures the resulting deflection (the height of the bulge). The load-deformation data can then be used to establish a model that can be used to determine Young's modulus and the in-plane stress of the film. A variety of different films are tested under different conditions and the results are compared to theoretical values and to the results of a non-linear finite element model. The approach of the computer model is inverse to the tester. The determined values are used as input for the model and the load-deformation data is the output. The experimental results are found to be in excellent agreement with the numerical prediction. The applicability of using a thin piezoelectric film on top of another film in a window as an actuator is also investigated. The ultimate goal is to create a smart thin film window that can precisely sense and control stretching and/or deflection of the base film. This could be very useful in lithography procedures in order to align and control the mask or particular portions of the mask.