title: Long thickness-extensional waves in thin film bulk acoustic wave filters affected by interdigital electrodes.
abstract: We studied free vibrations of thin-film bulk acoustic wave filters with interdigital electrodes theoretically using the scalar differential equations by Tiersten and Stevens. The filters are made from AlN or ZnO films on Si substrates with ground and driving electrodes. They operate with thickness-extensional modes. The basic vibration characteristics including resonant frequencies and mode shapes were obtained. Their dependence on various geometric parameters was examined. It was found that for properly design filters there exist trapped modes whose vibrations are strong in regions with a driving electrode and decay away from the electrode edges. These trapped modes are essentially long plate thickness-extensional modes modulated by the electrode fingers. The number of trapped modes is sensitive to the geometric parameters.
authors.affiliation: Piezoelectric Device Laboratory, School of Mechanical Engineering and Mechanics, Ningbo University, Ningbo, Zhejiang 315211, China; School of Mechanical and Electrical Engineering, Ningbo Dahongying University, Ningbo, Zhejiang 315175, China.
authors.forename: Jing
authors.initials: J
authors.lastname: Liu
authors.affiliation: Piezoelectric Device Laboratory, School of Mechanical Engineering and Mechanics, Ningbo University, Ningbo, Zhejiang 315211, China. Electronic address: dujiangke@nbu.edu.cn.
authors.forename: Jianke
authors.initials: J
authors.lastname: Du
authors.affiliation: Piezoelectric Device Laboratory, School of Mechanical Engineering and Mechanics, Ningbo University, Ningbo, Zhejiang 315211, China.
authors.forename: Ji
authors.initials: J
authors.lastname: Wang
authors.affiliation: Piezoelectric Device Laboratory, School of Mechanical Engineering and Mechanics, Ningbo University, Ningbo, Zhejiang 315211, China; Department of Mechanical and Materials Engineering, The University of Nebraska-Lincoln, Lincoln, NE 68588-0526, USA. Electronic address: jyang1@unl.edu.
authors.forename: Jiashi
authors.initials: J
authors.lastname: Yang
keywords: Piezoelectric; Vibration; Wave