Microwave FBAR Structures Fabricated using Micromachined GaN Membranes

This paper reports on microwave characteristics of micromachined GaN-based thin-film bulk acoustic resonator devices. The 2.2 micron active piezoelectric layer was epitaxially grown on (111)-oriented high-resistivity silicon substrate. Bulk micromachining techniques were used for the release of the resonating GaN membrane structure. S-parameter measurements have shown a fundamental mode resonance around 1.3 GHz. Extracted material parameters such as an acoustic velocity of 5700 m/s and an effective coupling coefficient of about 2% are in good agreement with those reported in the literature using other fabrication methods.