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 (SiO2) passivation layer. It is shown that a 400-nm-thick SiO2 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 SiO2 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.