Integration of bottom electrode in Y-cut lithium niobate thin films for high electromechanical coupling and high capacitance per unit area MEMS resonators

This paper reports the integration of a bottom electrode in thin films of Y-cut lithium niobate (LN) on silicon to demonstrate high performance lamb-wave (S0 mode) and thickness-shear-mode (TSM) resonators. The LN resonator is sandwiched between top and bottom electrodes and attained high coupling (kt²) > 6% when excited in S0 mode and > 30% when excited in TSM. The reported devices possess capacitance per unit area of 0.4 fF/um², which is 30 times that of X-cut LN and 5 times that of AlN resonators. This demonstration enables MEMS designers to fully harness the high coupling of thin LN films, which can have a transformative impact on reconfigurable and ultra-low-power communication systems.