Laterally coupled solidly mounted BAW resonators at 1.9 GHz

Laterally coupled bulk acoustic wave resonators fabricated onto an acoustic mirror are studied. The acoustic mirror comprises two W-SiO₂ pairs. Thin-film AlN is used as the piezoelectric material with a Mo bottom electrode and an Al top electrode. Structures consist of laterally acoustically coupled electrodes 2.5 ¿m wide and 300 ¿m long, with gaps of 4 ¿m in-between. Acoustical coupling between the electrodes results in two resonances forming an electrical bandpass response at 1.9 GHz. A device with two coupled electrodes features a 1.5% relative to center frequency bandwidth, 10 dB insertion loss in 50-¿ environment and 3.9 dB insertion loss after matching. Electrical frequency responses are presented and compared to simulations. Mechanical vibration fields in the devices are studied with a laser interferometer.