title: Tungsten Oxide Layers of High Acoustic Impedance for Fully Insulating Acoustic Reflectors.
abstract: Gravimetric sensors based on solidly mounted resonators require fully insulating acoustic reflectors to avoid parasitics when operating in liquid media. In this work, we propose a new high-acoustic impedance material, tungsten oxide ([Formula: see text]), for acoustic reflectors. We have optimized the sputtering conditions of [Formula: see text] to obtain nonconductive layers with mass density around [Formula: see text] and acoustic velocities for the shear and the longitudinal modes up to 2700 and 4500 m/s, respectively. Compared to other conventionally used high impedance layers, [Formula: see text] films display several manufacture advantages, such as high deposition rates, great reproducibility, and good adhesion to underlying substrates. We have demonstrated the applicability of [Formula: see text] in practical shear mode bulk acoustic wave resonators that display good performance in liquid environments.
authors.forename: M
authors.initials: M
authors.lastname: DeMiguel-Ramos
authors.forename: Barbara
authors.initials: B
authors.lastname: Diaz-Duran
authors.forename: Junaid
authors.initials: J
authors.lastname: Munir
authors.forename: Marta
authors.initials: M
authors.lastname: Clement
authors.forename: Teona
authors.initials: T
authors.lastname: Mirea
authors.forename: Jimena
authors.initials: J
authors.lastname: Olivares
authors.forename: Enrique
authors.initials: E
authors.lastname: Iborra