Advanced lateral structures of BAW resonator for spurious mode suppression

To suppress spurious mode of the BAW (Bulk Acoustic Wave) resonator, advanced lateral structures are proposed. Three different techniques of apodization, air-edge reflector and border frame are integrated. Firstly, apodization is the method to design a proper shape of resonator which avoids parallel edges. By doing so, spurious mode is significantly improved at main resonances. Secondly, air-edge reflector is the method which creates lateral air interface to suppress the acoustic wave leakage. The Q_a (Q-factor at anti-resonance frequency) and kt² are improved from 420 to 640 and 6.0% to 6.7%, respectively. Thirdly, border frame is a specific thickened frame in which lateral acoustic wave cannot propagate. The Q_r (Q-factor at resonance frequency) and Q_a are increased from 850 to 1040 and 550 to 1670, respectively. After three techniques are integrated, the maximum value of Q_r and Q_a are achieved 1130 and 1920, respectively. Three practical techniques considerably improved the Q-factor and kt² of BAW resonator which are essential parameters for low loss and wide band of RF filter configuration.