Tungsten Oxide Layers of High Acoustic Impedance for Fully Insulating Acoustic Reflectors

• Published in: IEEE transactions on ultrasonics, ferroelectrics, and frequency control Vol. 63; no. 7; pp. 938 - 944
• Main Authors: DeMiguel-Ramos, M., Diaz-Duran, Barbara, Munir, Junaid, Clement, Marta, Mirea, Teona, Olivares, Jimena, Iborra, Enrique
• Format: Journal Article
• Language: English
• Published: United States IEEE 01-07-2016; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Acoustic impedance; Acoustic insulation; Acoustic reflector; Acoustics; AlN; Aluminum nitride; High impedance; III-V semiconductor materials; Impedance; Liquids; Reflectors; Resonators; Shear; solidly mounted resonator; Sputtering; Substrates; tungsten oxide; Tungsten oxides
• ISSN: 0885-3010; 1525-8955
• DOI: 10.1109/TUFFC.2015.2498968

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 (WO 3 ), for acoustic reflectors. We have optimized the sputtering conditions of WO 3 to obtain nonconductive layers with mass density around 6700 kg/m 3 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, WO 3 films display several manufacture advantages, such as high deposition rates, great reproducibility, and good adhesion to underlying substrates. We have demonstrated the applicability of WO 3 in practical shear mode bulk acoustic wave resonators that display good performance in liquid environments.