Spurious free thickness shear bulk acoustic resonators on lithium niobate using standard and broadband piston mode designs

This paper describes design and fabrication of sprious-free thickness shear bulk acoustic resonators (TSBARs) using the lithium niobate (LN) plate. Previously, the authors conjected from the experiment on the TSBAR that cutoff edges with crystal LN X-plane serve as ideal reflectors for the piston mode operation, and complete suppression is possible by adding the standard piston mode design to the other edges normal to the X-axis. Following to this conjecture, the traditional piston mode structure is designed by the traditional two-dimensional finite element method, and the TSBAR is fabricated following to the design. The experiment showed complete suppression of the transverse mode resonances, and the conjecture was verified.