A K-Band Bulk Acoustic Wave Resonator Using Periodically Poled Al0.72Sc0.28N

This letter presents a K-band bulk acoustic wave (BAW) resonator constructed from an Al 0.72 Sc 0.28 N periodically poled piezoelectric film. The resonators exhibited dominant resonance responses around 20 GHz, approximately four times higher than the resonance frequencies of similar unpoled devices fabricated on the same wafer. Resonators with a quality factor ( $ {Q}_{ {p}}$ ) of 160 and an electromechanical coupling ( $ {k}_{ {t}}^{ {{2}}}$ ) of 8.23% were achieved. The figure of merits (defined as ${{ {\textit {Fo}{M}}}_{ {I}}= {k}}_{ {t}}^{ {{2}}} {Q}_{ {p}}$ and ${ {\textit {Fo}{M}}}_{ {\textit {II}}}= {f}_{ {p}}{ {\textit {Fo}{M}}}_{ {I}} \boldsymbol {\times }{ {{10}}}^{ {-{9}}}$ ) of the resonator are 13.2 and 274 which are higher than most reported acoustic resonators operating at K-band (18 GHz to 27 GHz) or higher frequency. The experimental results suggest that periodically poled BAW resonators are promising for emerging RF filter and oscillator applications at K-band frequencies.