ScAlN Lamb wave resonator in GHz range released by XeF2 etching

Recently, it was reported that the piezoelectric characteristic of AlN was enhanced by doping Sc, and that 40% Sc-doped AlN (Sc_0.4Al_0.6N) had approximately 5 times higher piezoelectricity than pure AlN. In this study, we designed, fabricated and evaluated Lamb wave resonators using a Sc_0.4Al_0.6N thin film. First, we examined elastic constants c₄₄^E and c₄₄^D of Sc_0.4Al_0.6N using a thickness-shear wave resonator excited by parallel electric field, and then designed Lamb wave resonators using revised material constants. The Lamb wave resonators were fabricated by electron beam lithography, reactive ion etching, XeF₂ release etching etc. The maximum and average electromechanical coupling coefficients were 8.3% and 6.8%, respectively, for 2.6 GHz devices working in S₀ mode.