Piezoelectric properties and micro structures of lead titanate thin films for GHz-band bulk acoustic wave filters

Abstract The bulk acoustic wave filters at GHz bands were fabricated using lead titanate, PbTiO3 (PT) piezoelectric films which were deposited by RF magnetron sputtering and were oriented along crystal direction. To improve the quality of PT films, the bottom electrodes which had the Ti-diffusion suppressible layers were designed and prepared. X-ray diffraction intensity of the PT(111) became 5 times larger and degree of crystal orientation became 2 times stronger in comparison with those of the former PT films. The filters using the improved PT films had the insertion loss of -14dB. The PT film had effective electromechanical coupling coefficient (k) of 31% and electrical Q of 50. This k value was superior to those of well-known ZnO and AlN piezoelectric films.