Solidly mounted resonators operated in thickness shear mode based on c-axis oriented AlN films

We fabricated the solidly mounted resonators operated in thickness shear mode using lateral field excitation. The resonators are consisted of the electrodes parallel to the film surface, the c-axis oriented AlN film and the Bragg reflector of SiO2/AlN. In order to design the electrode frame, the electric field characteristic was calculated by finite element modeling. More than 20 finished devices were tested. The results show that the thickness shear mode wave can be excited by the lateral electric field in the c-axis oriented AlN film. There no obvious longitudinal resonance was found in the frequency responses due to the weak vertical electric field component generated by the parallel electrodes and the high frequency selectivity of the acoustic reflector. The resonators operated in thickness shear mode have resonance frequencies near 2 GHz with the average Q-factor of 520 in air. Importantly for sensors, the immersion into de-ionized water and glycerol liquids still allow for a high Q-factor of 408 and 313, respectively. This resonator shows the potential as mass loading sensors for biochemical application.