title: Shear mode coupling and tilted grain growth of A1N thin films in BAW resonators.
abstract: Polycrystalline A1N thin films were deposited by RF reactive magnetron sputtering on Pt(111)/Ti electrode films. The substrates were tilted by an angle ranging from 40 degrees to 70 degrees with respect to the target normal. A low deposition temperature and a high sputter gas pressure were found ideal for tilted growth. The resulting grain tilt angle amounts to about half the substrate tilt angle. For coupling evaluation, 5 GHz solidly mounted resonator structures have been realized. The tilted grain A1N films exhibited a permittivity in the 9.5-10.5 range and loss tangent of 0.3%. Two shear modes as well as the longitudinal mode could be clearly identified. The coupling coefficient k2(eff) of the fundamental thickness shear mode (TS0) was found to be about 0.5%, which is compatible with a c-axis tilt of about 6 degrees.
authors.affiliation: Ceramics Laboratory, Ecole Polytechnique Fédérale de Lausanne, Lausanne, Switzerland. Fabrice.Martin@csem.ch
authors.forename: Fabrice
authors.initials: F
authors.lastname: Martin
authors.forename: Marc-Etienne
authors.initials: ME
authors.lastname: Jan
authors.forename: Samuel
authors.initials: S
authors.lastname: Rey-Mermet
authors.forename: Brahim
authors.initials: B
authors.lastname: Belgacem
authors.forename: Dong
authors.initials: D
authors.lastname: Su
authors.forename: Marco
authors.initials: M
authors.lastname: Cantoni
authors.forename: Paul
authors.initials: P
authors.lastname: Muralt