Optimization of electromechanical coupling for a thin-film PZT membrane: II. Experiment

The optimization of the electromechanical coupling coefficient for thin-film piezoelectric membranes is investigated experimentally. The membranes are a two-dimensional laminate structure consisting of a lead zirconate titanate (PbZrxTi1-xO3, PZT) stack on a silicon substrate. PZT thickness, substrate thickness, residual stress, side length and electrode coverage are varied. The results show that the residual stress has a dominant effect on the magnitude of the electromechanical coupling coefficient. The PZT to silicon thickness ratio is important and may be tailored to optimize the electromechanical coupling coefficient. An electrode coverage of 60% produces the optimum coupling. Application of a dc bias also leads to increased coupling. In general, the results are in good agreement with the trends predicted by the model developed in part I. The results can be used to form a set of design guidelines for the performance optimization of micromachined piezoelectric membrane generators.