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 (kt2) 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 (SiO2) passivation layer. It is shown that a 400-nm-thick SiO2layer reduces the temperature coefficient of frequency (TCF) of the GaN-based resonator by 50%, while improving Q and kt2of the fundamental thickness-mode resonance. The effect of SiO2passivation layer is studied on kt2, Q, and TCF of the device. Furthermore, the effects of temperature and input RF power on the resonator performance are characterized.