High Q single-mode high-tone bulk acoustic resonator integrated with surface-micromachined FBAR filter

This paper describes a high-tone bulk acoustic resonator (HBAR) integrated with a surface micromachined FBAR (film bulk acoustic resonator) filter on sapphire substrate. The single-mode HBAR exhibited a quality factor (Q) of 3,580 at 2.5 GHz with total size (including the contact pads) of 0.8 × 0.4 × 0.4mm³. The integrated narrow band FBAR filter provides adequate suppression (>4dB) of the unwanted modes in the HBAR. This high Q and small size resonator is ideally suited for Pierce oscillator for voltage controlled oscillator (VCO) above 2 GHz.