9.5 GHz Solidly Mounted Bulk Acoustic Wave Resonator using Third Overtone of Thickness Extension Mode in LiNbO3

This paper reports a new method to preferentially excite the third overtone response for a solidly-mounted-BAW resonator (SM-BAWR). By FEM simulation, it was found that lambda/20 layer thickness of a Bragg reflector was suitable for the excitation of the third overtone (lambda is the wavelength of the fundamental mode in a piezoelectric layer). The SM-BAWR was fabricated using a 1 mu m thick 36 degrees Y LiNbO3 plate and 4 pairs of SiO2 and T a as the Bragg reflector. A 9.5 GHz third overtone response was more strongly observed than the fundamental mode, and the impedance ratio was as high as 31 dB.