Micromachined GaN-based FBAR structures for microwave applications

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 1.2 GHz. Extracted material parameters such as acoustic velocity and effective coupling coefficient are in good agreement with those reported in the literature using other methods. These are, to our knowledge, the first FBAR results with GaN-based active layers.