FBAR using LiNbO₃ thin film deposited by CVD

The authors have realized a film bulk acoustic wave resonator (FBAR) usinga thin LiNbO₃ film deposited by a chemical vapor deposition (CVD) forthe first time. As a result, a 2.9GHz FBAR, which is higher than 2.1GHz of theBAW using a LiNbO₃ single crystal thin plate, with an impedance ratioof 40dB at a resonant (fr) and an antiresonant (fa) frequencies was realized.The LiNbO₃ film has a mixture of the polarity. As a result of ascanning non-linear dielectric microscope (SNDM) measurement, c domains and cdomains occupy 82% and 18%, respectively. A quality factor is small because itis considered that the film has the mixed polarity, the thickness is not flatand the structure of electrode is not optimum. A transverse mode was not excitedon the fabricated FABR. According to a calculation, the transverse wave mode isobserved when the thickness of electrodes is thin. On the other hand, thetransverse wave mode isn't observed when the thickness of electrodes is thick.The main responses of longitudinal mode wave are not different by thethicknesses of electrodes. Therefore it is found that the transverse wave modecan be suppressed by selecting the thickness of electrodes. Further, the effectthat LiNbO₃ film is twinned crystalline epitaxial one is evaluated bycalculation. The transverse wave mode is excited even if the film is twinnedepitaxial one. It is important to deposit another oriented LiNbO ₃film with larger coupling factor to realize a wider band resonator.