Transversal Spurious Mode Suppression in Ultra-Large-Coupling SH0 Acoustic Resonators on YX36°-Cut Lithium Niobate

This work reports on the design and fabrication of fundamental shear horizontal (SH0) mode acoustic resonators based on a suspended lithium niobate (LNO) film at 1.04 GHz. Due to the large
$\boldsymbol {e}_{ \boldsymbol {16}}$
piezoelectric coefficient of YX36°-cut LNO, fabricated devices exhibit ultra-large effective electromechanical coupling (
$\boldsymbol {k}_{ \boldsymbol {eff}}^{ \boldsymbol {2}}$
) as high as 29% with a loaded quality factor of 500 at resonance. Moreover, improved device designs with suppressed spurious mode responses are developed based on analysis of the dispersion relation of the SH0 mode in the suspended film. By adding a low-velocity region at the transducer edge and perforations in the inactive area, a spurious-free response is obtained without any reduction in
$\boldsymbol {k}_{ \boldsymbol {eff}}^{ \boldsymbol {2}}$
. In combination with the ability to tune the resonance frequency lithographically, the demonstrated devices are promising for wide-band or tunable radio frequency (RF) filters. [2023-0008]