4 and 7 GHz solidly mounted thickness extension mode bulk acoustic wave resonators using 36°Y LiNbO<sub>3</sub>
Michio Kadota, Fuyuko Yamashita, Shuji Tanaka
Abstract
Abstract This paper describes 4 and 7 GHz solidly-mounted structure bulk acoustic wave resonators (SM-BAWRs) using LiNbO 3 (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 μ m thick 36°Y LNs. The Bragg reflector is made of Al or SiO 2 , and Ta films. The 0.81 μ m 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 0.12 λ much thinner than the optimum thickness, SM-BAWR using the 0.5 μ m 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.