Experimental Investigation of Acoustic Substrate Losses in 1850-MHz Thin Film BAW Resonators

Tuomas Pensala, Robert Thalhammer, James Dekker, Jyrki Kaitila

    Research output: Contribution to journalArticleScientificpeer-review

    12 Citations (Scopus)


    After optimizing for electromechanical coupling coefficient K2, 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.
    Original languageEnglish
    Pages (from-to)2544-2552
    Number of pages9
    JournalIEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control
    Issue number11
    Publication statusPublished - 2009
    MoE publication typeA1 Journal article-refereed


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