Characteristics of c-axis oriented GeAlN films and applications to higher-order mode BAW resonators

Abstract

AlN film bulk acoustic wave (BAW) resonators and filters that operate at frequencies above 5 GHz are required for 5G and beyond 5G communication applications. However, the power-handling capability, Q factor, and electromechanical coupling in high-frequency AlN film BAW resonators will be degraded as a result of the significantly reduced thickness and volume of the devices. Higher-order mode BAW resonators with polarity inverted (PI) multilayered films can operate at high frequencies while maintaining the thickness and volume of the devices. In this study, we fabricated an eight-layered PI GeAlN/AlN film BAW resonator by alternately growing Al-polar AlN layers and N-polar GeAlN layers. The PI GeAlN/AlN film BAW resonator resonated in the 8th-order mode. The film thickness of the PI GeAlN/AlN film BAW resonator was approximately thirteen times larger than that of a single-layer AlN film BAW resonator operating in the same frequency range.