A Temperature-Compensated Gallium Nitride Micromechanical Resonator

A GaN bulk acoustic wave resonator is presented in this letter, showing fundamental thickness-mode resonance at 2.18 GHz, with a quality factor (Q) of 655 and a coupling coefficient (k
_t
²
) of 1%. The resonator is integrated with an AlGaN/GaN high electron mobility transistor (HEMT); the integrated resonator/HEMT structure is coated with a silicon dioxide (SiO
₂
) passivation layer. It is shown that a 400-nm-thick SiO
₂
layer reduces the temperature coefficient of frequency (TCF) of the GaN-based resonator by 50%, while improving Q and k
_t
²
of the fundamental thickness-mode resonance. The effect of SiO
₂
passivation layer is studied on k
_t
²
, Q, and TCF of the device. Furthermore, the effects of temperature and input RF power on the resonator performance are characterized.