Thin AlN Film Resonators utilizing the Lowest order Symmetric Lamb mode: Further Developments

Thin film plate acoustic wave resonators utilizing the lowest order symmetric lamb wave (SO) propagating in highly textured 2 mum thick aluminum nitride (AlN) membranes were successfully demonstrated for the first time. Further the utilization of fast lateral modes in thin films has recently being targeted independently by other groups as well. The unperturbed SO mode in thin film AlN has an acoustic wave velocity in excess of 10 000 m/s with a weak dispersion and sufficient coupling. Q factors of around 1800 were demonstrated for 890 MHz one-port synchronous resonators operating in the vicinity of the upper stopband edge. In this work an experimental study on the resonators' performance vs variety of design parameters is performed. Devices operating in the vicinity of the stopband center offering a Q of up to 3000 at a frequency of around 875 MHz are demonstrated. Further, micromachined 2-port longitudinally coupled thin film resonators utilizing the SO mode are demonstrated for the first time.