Impact of metal electrodes on the figure of merit (kt2·Q) and spurious modes of contour mode AlN resonators

This paper presents an experimental study on the impact of the metal electrodes on the level of the first spurious mode, electromechanical coupling (k_t²) and quality factor (Q) of laterally vibrating AlN contour mode resonators (CMRs). Pt, Ni, and Al are selected for the fabrication of the device top electrode since they exhibit a broad range of values of Young´s modulus, density and resistivity, which are the most relevant parameters that have an impact on the electromechanical characteristics of the device. The results on the level of the first spurious mode, and k_t² suggest that the acoustic mismatch between electrode and nonelectroded regions affect mostly these parameters. The extracted Q (after subtracting the effect of the electrode resistance) exhibits a trend in line with the theory of interfacial dissipation.