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

Abstract

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.

Ultra-wideband longitudinally coupled-resonator filters on lithium niobate using periodically slotted SiO2 as an acoustic coupler

“…The authors showed that transverse modes experiencing propagation toward the crystal x direction can be suppressed by the use of free side boundaries (±x surfaces) in LN-based TSFBARs. 15,16,32) Thus, here we discuss only the plate wave propagation toward the y direction [see Fig. 1(a)].…”

“…Thus, for the composition of LCRFs using an AlN-based BAW with a k 2 less than 7%, 12,13) coupler materials should possess extremely high or extremely low acoustic impedance Z a to make the coupling weak. [2][3][4][5][6] In contrast, LiNbO 3 (LN)-based thickness shear BAW resonators (TSBARs) [14][15][16] seem attractive for use in LCRFs because of an extremely large k 2 close to 40%, i.e. not so small Z a is required for the coupling layer.…”

Field analyses of thickness shear bulk acoustic resonators with different electrode edge ratio using full three dimensional finite element method simulation

“…The author's group reported 13) complete suppression of transverse mode resonances in TSBARs by applying the standard piston mode design to the Y side boundaries normal to the X-side boundaries in addition to the BPM to the X-side boundaries.…”