A 10 GHz Single-Crystalline Scandium-Doped Aluminum Nitride Lamb-Wave Resonator

This work reports on the first demonstration of Lamb-wave resonators based on single-crystalline Scandium (Sc)-doped Aluminum Nitride (AlN) films operating at 8-10 GHz. Sc-AlN and AlN films are grown on Silicon substrates using molecular beam epitaxy (MBE). The electrodes are defined using electron beam lithography with sub-micron feature sizes to maximize the electromechanical coupling coefficient$(k_t^2)$. A high $k_t^2$ value of 4.8 % is reported at 9.9 GHz, with unloaded Quality factor (Qm) of 185, yielding $f \times {Q_m} \times k_t^2$ values of 74 GHz. The high $k_t^2$ is attributed to enhanced piezoelectric coefficients achieved due to single crystallinity, as well as Sc-doping. This work demonstrates higher performance resonators achieved by using single-crystalline Sc-AlN thin films compared to sputter-deposited films with sub-micron thicknesses, required for 5G filter applications.