4 and 7 GHz solidly mounted thickness extension mode bulk acoustic wave resonators using 36°Y LiNbO3

This paper describes 4 and 7 GHz solidly-mounted structure bulk acoustic wave resonators (SM-BAWRs) using LiNbO3 (LN) thin plates. A Bragg reflector solidly supports the LN thin plate. The two kinds of SM-BAWRs use thickness extension mode in 0.81 and 0.5 μm thick 36°Y LNs. The Bragg reflector is made of Al or SiO2, and Ta films. The 0.81 μm thick LN SM-BAWRs with each acoustic layer thickness 0.23 wavelength (λ), which is almost optimum thickness, exhibited resonance frequency (f r) of 3.84 GHz, antiresonance frequency (f a) of 4.17 GHz, a bandwidth of 8.4%, an impedance (Z) ratio of 54 dB, and coupling factor k t 2 of 17.7%. Despite using an acoustic film 0.12λ much thinner than the optimum thickness, SM-BAWR using the 0.5 μm thick LN exhibited f r of 6.86 GHz, f a of 7.15 GHz, and Z ratio of 37 dB. Those results suggest a high potential for this device.