High $k_{t}^{2}\cdot Q$ Waveguide-Based ScAlN-on-Si UHF and SHF Resonators

This paper reports, for the first time, on waveguide-based resonators implemented in scandium-doped aluminum nitride-on-silicon (ScAlN-on-Si) stack to simultaneously benefit from large piezoelectric constants of ScAlN and low acoustic dissipation in single crystal silicon. 1μm-thick ScAlN film with Sc content of 7% is reactively sputtered on silicon substrates using ac-powered dual-target S-gun magnetron with Al targets containing embedded pure Sc pellets. A Cl
₂
/H
₂
based low-power plasma etching recipe is developed to pattern resonators with smooth vertical sidewalls. In-and out-of-plane waveguide-based resonator prototypes with large electromechanical coupling coefficient (kt
²
) and high quality-factor (Q) are implemented over 80 MHz-3.5 GHz demonstrating kt
²
of 0.7
^%
-2.9
^%
and Q of 2000-6400. Specifically, a high f0×Q of 4.3×10
¹²
is measured for a resonator at 3.5 GHz, and a high kt
²
×Q of 51 is measured at 108 MHz. The large kt
²
×Q of ScAlN-on-Si waveguide-based resonators along with lithographical frequency tailorability demonstrate their potential for realization of highly integrated front-end filters for multi-band 5G systems.