High piezoelectric properties in LiNbO3 transferred layer by the Smart Cut™ technology for ultra wide band BAW filter applications

For the first time, high overtone bulk acoustic resonators (HBAR) based on thin homogeneous and single crystalline films (below 1mum) of lithium niobate (LiNbO₃) have been processed and characterized between 1 and 4 GHz. k_t ² greater than 30% are extracted from the frequency response envelope, by far superior to k_t ² usually obtained with traditional deposited AlN material (limited to 7%). This result confirms the interest of this technology for ultra wide band BAW (bulk acoustic wave) filters. The thin single crystalline LiNbO₃ films together with an embedded metal electrode were fabricated using the Smart Cuttrade technology. The crystalline quality of the transferred layer (characterized by XRD and HRTEM) was found to be comparable to the single crystal bulk starting material.