title: Experimental investigation of acoustic substrate losses in 1850-MHz thin film BAW resonators.
abstract: After optimizing for electromechanical coupling coefficient K(2), the main performance improvement in the thin film bulk acoustic wave resonators and filters can be achieved by improving the Q value, i.e., minimizing the losses. In Bragg-reflector-based solidly mounted resonator technology, a significant improvement of Q has been achieved by optimizing the reflector not only for longitudinal wave, the intended operation mode, but also for shear waves. We have investigated the remaining acoustic radiation losses to the substrate in so-optimized 1850-MHz AlN resonators by removing the substrate underneath the resonators and comparing the devices with and without substrate by electrical characterization before and after the substrate removal. Several methods to extract Q-values of the resonators are compared. Changes caused by substrate removal are observed in resonator behavior, but no significant improvement in Q-values can be confirmed. Loss mechanisms other than substrate leakage are concluded to dominate the resonator Q-value. Difficulties of detecting small changes in the Q-values of the resonators are also discussed.
authors: VTT Technical Research Centre of Finland, Espoo, Finland. tuomas.pensala@vtt.fi
authors: Tuomas
authors: T
authors: Pensala
authors: Robert
authors: R
authors: Thalhammer
authors: James
authors: J
authors: Dekker
authors: Jyrki
authors: J
authors: Kaitila
mesh_terms: D000162:Acoustics / Q000295:instrumentation*; D017076:Computer-Aided Design; D004735:Energy Transfer; D004867:Equipment Design; D019544:Equipment Failure Analysis; D008567:Membranes, Artificial; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014159:Transducers
chemical_list: D008567:Membranes, Artificial