Abstract
High frequency communication devices including thin film surface acoustic wave (SAW) filter, film bulk acoustic resonator (FBAR), as well as microelectromechanical systems (MEMS) use piezoelectric thin films (PZT, LiNbO_3, AlN, ZnO) as actuating elements. However, sound velocity of polycrystalline piezoelectric films is sometimes different from that calculated using published single-crystal elastic constants. There is reason to believe that that was caused by grain boundaries. In this work, elastic constants of thin films were calculated by using a composite model. In addition, because complex elastic constants were introduced in the calculation, propagation loss was evaluated, and a good result was obtained.
