Transversely varying thickness-extensional modes in thin film bulk acoustic wave piezoelectric filters with interdigital electrodes

Abstract

Abstract We study free vibrations of thin-film bulk acoustic wave filters theoretically using the scalar differential equations by Tiersten and Stevens. The filters are made from piezoelectric crystal films of AlN or ZnO on Si substrates with interdigital ground and driving electrodes. They operate with thickness-extensional modes. Transversely varying modes with variations in both of the in-plane directions along and perpendicular to the electrodes are obtained, including both the device operating modes and unwanted modes which need to be predicted and avoided through design.