A 43° rotated Y-cut LiNbO3 (LN) single-crystal thin film coated with a bottom electrode and a Mo/Ti Bragg reflector is successfully transferred onto the 4-in. LN wafer substrate by means of crystal-ion-slicing (CIS) technique and benzocyclobutene bonding method. The multilayer film is crack-free, and the Mo/Ti reflector shows good acoustic reflection efficiency. A thin film bulk acoustic wave resonator based on the Mo/Ti Bragg reflector and the LN thin film (LN-BAW) is prepared, and the properties are further analyzed. The results indicate that the LN-BAW provides a large Kt2 of ∼16.63% and the Q-factor and figure-of-merit of the LN-BAW reach 183 and 30.4, respectively.

43°Y-cut lithium niobate (LiNbO3, LN) single-crystalline thin films, which are integrated with two types of Bragg reflectors of W/SiO2 and Mo/SiO2, respectively, are fabricated by means of the crystal-ion-slicing technique. Crack-free LN thin films are obtained when the Mo/SiO2 reflector is adopted, while crumples take place when the LN thin film is combined with W/SiO2. Moreover, solidly-mounted-type thin film bulk acoustic wave resonators (LN-SMRs) based on the single-crystalline LN film and Bragg reflector layers of Mo/SiO2 are prepared and characterized. The results indicate that the LN thin film combined with the Mo/SiO2 reflector has good thin film quality, and keff2 of the LN-SMR reaches 20%.

The intrinsic electromechanical coupling coefficient (kt2) of the piezoelectric material is the decisive factor limiting the band width of the thin film bulk acoustic (FBAR) filters. In the present work, single crystalline LiNbO3 thin films are transferred by crystal ion slicing. Instead of the often used silicon dioxide, Benzocyclobutene is used as the bonding layer, which significantly increases the tolerance of wafer bonding for the surface flatness, thus a patterned bottom electrode is easily buried underneath the LiNbO3 thin film during the ions slicing process. More importantly, this single Benzocyclobutene layer also acts as an effective acoustic reflector, and a large kt2 exceeding 21% is obtained in the LN-based bulk acoustic wave resonator. The Mason model is built up according to the experimental results, and the fitting shows that the Benzocyclobutene has a low acoustic impedance, which effectively confines the acoustic energy within the piezoelectric layer and results in the high kt2.