Development of an X-band filter using air-gap-type film bulk acoustic resonators

Masanori Ueda, Motoaki Hara, Shinji Taniguchi, Tsuyoshi Yokoyama, Tokihiro Nishlhara, Ken Ya Hashimoto, Yoshio Satoh

    Research output: Contribution to journalArticlepeer-review

    54 Citations (Scopus)


    We have developed an X-band filter utilizing air-gap-type film bulk acoustic resonators (FBARs). The air-gap structure is simple and cost-effective. Results from both simulations and experiments demonstrate that a dome-shaped air gap was formed between the substrate surface and the bottom electrode and that an air-gap-type FBAR structure was possible. The air gap can be formed on the flat substrate using stress control of piezoelectric and metal films without using a thick sacrificial layer. As a result, the fabricated X-band FBAR operated successfully with a keff2 of 6.30%, a resonance Q of 246, and an antiresonance Q of 462. The fabricated filter had a center frequency of 9.07 GHz, a fractional bandwidth of 3.1% and a minimum insertion loss of 1.7 dB.

    Original languageEnglish
    Pages (from-to)4007-4010
    Number of pages4
    JournalJapanese journal of applied physics
    Issue number5 PART 2
    Publication statusPublished - 2008 May 23


    • Air-gap
    • Bulk acoustic wave (BAW)
    • Coupling factor (K )
    • Film bulk acoustic resonator (FBAR)
    • Mobile communication
    • Piezoelectric thin-film resonator
    • Q factor
    • Solidly mounted resonator (SMR)
    • Surface acoustic wave (SAW)

    ASJC Scopus subject areas

    • Engineering(all)
    • Physics and Astronomy(all)


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