title: Influence of crystal quality on the excitation and propagation of surface and bulk acoustic waves in polycrystalline AlN films.
abstract: We investigate the excitation and propagation of acoustic waves in polycrystalline aluminum nitride films along the directions parallel and normal to the c-axis. Longitudinal and transverse propagations are assessed through the frequency response of surface acoustic wave and bulk acoustic wave devices fabricated on films of different crystal qualities. The crystalline properties significantly affect the electromechanical coupling factors and acoustic properties of the piezoelectric layers. The presence of misoriented grains produces an overall decrease of the piezoelectric activity, degrading more severely the excitation and propagation of waves traveling transversally to the c-axis. It is suggested that the presence of such crystalline defects in c-axis-oriented films reduces the mechanical coherence between grains and hinders the transverse deformation of the film when the electric field is applied parallel to the surface.
authors.affiliation: Grupo de Microsistemas y Materiales Electrónicos del Centro de Materiales y Dispositivos Avanzados para las TIC (GMME-CEMDA TIC), Universidad Politécnica de Madrid. mclement@etsit.upm.es
authors.forename: Marta
authors.initials: M
authors.lastname: Clement
authors.forename: Jimena
authors.initials: J
authors.lastname: Olivares
authors.forename: Jose
authors.initials: J
authors.lastname: Capilla
authors.forename: Jesús
authors.initials: J
authors.lastname: Sangrador
authors.forename: Enrique
authors.initials: E
authors.lastname: Iborra