High frequency thickness expansion mode bulk acoustic wave resonator using LN single crystal thin plate

In this report, a thickness expansion mode film bulk acoustic resonator (FBAR) was fabricated using 4 m thick 36°Y-LiNbO3(LN) single crystal thin plate. The LN thin plate was made by polishing after bonded to a Si bare wafer. The LN FBAR showed a bandwidth of 10.3% and an impedance ratio of 45 dB at 800 MHz. The spurious response due to a thickness shear (TS) mode was much smaller than the main mode, because the optimal cut angle was chosen. The quality factor of anti-resonance is poor probably due to acoustic loss caused by a misalignment of the upper and lower electrodes, the series connection of two resonators etc. By minimizing the acoustic loss, the impedance ratio can be improved up to 60 dB.