Serially Connected Strip-type Bulk Acoustic Resonator Using X40°Y-LiNbO₃ (XSAR) with Bandwidth of 33%

Acoustic wave devices with ultra-wide bandwidth in high frequency is required by 5G and new frequency bands due to the increased volume of data. Bulk acoustic wave (BAW) device using LiNbO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> (LN) single crystal is one of the suitable candidates, but the BW is still not wide enough for some bands like n77. In this work, we proposed a new serially connected strip-type bulk acoustic resonator using X40°Y-LN (XSAR). The Euler angles were optimized to (90°, 90°, 40°) to obtain the best performances. Two features, narrow strip and penetrated structure were proposed to suppress the spurious responses. The penetrated structure was realized for the first time by the developed fabrication process. The measured resonator showed excellent BW of 33% with Z-ratio of 32 dB. Smaller spurious response was demonstrated when strip width was narrow. Additionally, several approaches were introduced to enhance the performances of XSAR.