FBAR using LiNbO3 thin film deposited by CVD

The authors have realized a film bulk acoustic wave resonator (FBAR) using a thin LiNbO₃ film deposited by a chemical vapor deposition (CVD) for the first time. As a result, a 2.9GHz FBAR, which is higher than 2.1GHz of the BAW using a LiNbO₃ single crystal thin plate, with an impedance ratio of 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 a scanning non-linear dielectric microscope (SNDM) measurement, -c domains and +c domains occupy 82% and 18%, respectively. A quality factor is small because it is considered that the film has the mixed polarity, the thickness is not flat and the structure of electrode is not optimum. A transverse mode was not excited on the fabricated FABR According to a calculation, the transverse wave mode is observed when the thickness of electrodes is thin. On the other hand, the transverse wave mode isn´t observed when the thickness of electrodes is thick. The main responses of longitudinal mode wave are not different by the thicknesses of electrodes. Therefore it is found that the transverse wave mode can be suppressed by selecting the thickness of electrodes. Further, the effect that LiNbO₃ film is twinned crystalline epitaxial one is evaluated by calculation. The transverse wave mode is excited even if the film is twinned epitaxial one. It is important to deposit another oriented LiNbO₃ film with larger coupling factor to realize a wider band resonator.