Characterization of Deformation Behaviors and Elastic Moduli of Multilayered Films in Piezoelectric Inkjet Head

A bulge testing system was developed to mechanically characterize the deformation behaviors and elastic moduli of multilayered films, mainly composed of polycrystalline silicon (polysilicon) and lead zirconate titanate (PZT), used in a multilayer actuator of a piezoelectric inkjet head. In the tests, commercial inkjet heads including a few tens of multilayer actuators were directly pressurized by air, and the corresponding deflections were measured via full-field optical measurement techniques. An analytic solution derived from a thin-plate theory and finite-element analysis were used to describe pressure-deflection behaviors of films, and the results were compared with the experimental data to evaluate the elastic modulus of individual film. The results showed that the elastic moduli of polysilicon and PZT films are ~110 and ~49 GPa, respectively. These values were consistent with the nanoindentation results. For polysilicon films, about 30% reduction in elastic modulus, compared with that calculated from single-crystal elastic constants, was observed, and this was most likely attributed to the presence of microdefects like voids and microcracks at grain boundaries between columnar grains.