Lamb plate modes and surface acoustic wave resonator microwave filters

For sufficiently thin piezoelectric (PZ) wafers, Lamb wave plate modes can interfere with the response of the SAW resonator by introducing spurious modes in the vicinity of the resonant and anti-resonant frequencies of the IDT. We present data taken on individual SAW resonators constructed on thin wafers of LiTaO₃ bonded to silicon. Finite element methods are employed to simulate the effects of bulk acoustic excitations. From these simulations, a model is developed to account for these plate modes and their effect on a SAW resonator. Finally, a Band 3 (uplink frequencies 1710-1785 MHz, downlink frequencies 1805-1880 MHz) duplexer was constructed, and good agreement is found between the measured filter response and the simulation incorporating plate modes.