Polarization inverted (0001) / (000-1) ScAIN film resonators operating in second overtone mode

Polarization-inverted multilayered structure can excite high overtone mode resonance. Resonant frequency of high order mode resonator is higher than that of 1st mode resonator even though entire film thickness is same. The film thickness of high order mode resonator is thicker in same operating frequency. Therefore, high order mode resonator is expected to have high power handling capability. Polarization are controlled by bottom surface properties in epitaxial films, but polarization inverted multilayer structure can not be fabricated. We obtained polarization inversion in ScAlN film by Al target sputtering with small amount of Al₂O₃ ingot. Thickness extensional mode electromechanical coupling coefficient k_t of the ScAlN film was estimated to be 0.21. Two layered polarization inverted ScAlN film resonator was prepared in this deposition process. Suppression of 1st mode resonance and excitation of 2nd overtone mode resonance were observed.