An 18GHz Alscn Film Bulk Acoustic Wave Resonator with Epitaxial Metal Electrodes

This work presents an 18 GHz thin-film bulk acoustic wave resonator (FBAR) based on epitaxial Aluminum Scandium Nitride (Al
1-x
Sc
x
N), and epitaxial metal electrodes, optimized for simultaneously achieving high electromechanical coupling coefficient $\left( {{k_t}^2} \right)$ and high conductor quality factor (Q). Here, we utilize 40 nm-thick epi-metal electrodes to obtain the highest ${k_t}^2$ achievable for 120 nm-thick Al
0.8
Sc
0.2
N piezo films. Our 40 nm-thick epi-Molybdenum (Mo) exhibits sheet resistance (R
sh
) 25 times smaller than sputtered-Mo films of similar thickness, thus increasing the conductor Q by 25×. We report on the first demonstration of an 18 GHz all-epi Mo/AlScN/Al FBAR, with a Q
Bode
of 110 and ${k_t}^2$ of 6%.