Laterally Excited Bulk Acoustic Resonators With Grooves Between Interdigital Electrodes

Laterally excited bulk acoustic resonators (XBARs) with adjustable piezoelectric coupling coefficient ( $K^{2}$ ) are a hot spot in radio frequency (RF) filters for the flexible adjustment of bandwidth. In this letter, the XBARs with grooves (G-XBARs) achieve adjustable $K^{2}$ by changing the groove size. The equivalent series capacitor ( $C_{\text {r}}$ ) is introduced due to the etched grooves, and consequently, $K^{2}$ is adjusted. The designed G-XBAR is fabricated using a 300-nm Z-cut LiNbO3 on an insulator (LNOI) wafer, where the grooves in LiNbO3 thin films are formed by ion beam etching (IBE) at an etch rate of 15.7 nm/min. The measured $K^{2}$ of G-XBAR is adjusted from 7.54% to 33.69%, with a wide range of 77.6% over 6 GHz. Furthermore, the power-handling capability of G-XBAR is measured over +19 dBm. The G-XBAR demonstrated in this work exhibits a wide adjusting range, showing great potential for high-performance RF filters with tunable bandwidth in multiband applications.