Anti-symmetric shear-extensional AlN lamb-wave resonators with kt2 > 4%

This paper presents a waveguide-based aluminum nitride resonator that simultaneously exploit transverse (d
₃₁
) and shear (d
₁₅
) piezoelectric constants to realize a large electromechanical coupling factor (k
_t
²
), while having a frequency defined by lateral dimensions. An anti-symmetric Lamb wave with co-existing in-plane extensional and thickness-shear elastic energy distribution is used along with proper dispersive energy trapping to simultaneously exploit transverse and shear electromechanical coupling of AlN film. Specifically, the shear transduction (k
_t,15
²
) benefits from the large d
₁₅
constant (due to the columnar single crystallinity) as well as low in-plane relative permittivity (due to the in-plane poly crystallinity) of the AlN film, and hence significantly improves the overall k
_t
²
. A proof-of-concept device operating at 733MHz with a Q of ~1400 and k
_t
²
of ~4.4% is demonstrated.