A High Quality Factor, 19-GHz Periodically Poled AlScN BAW Resonator Fabricated in a Commercial XBAW Process

This article presents 19-GHz bulk acoustic wave (BAW) resonators realized in a periodically poled piezoelectric film (P3F) microfabricated in a commercial XBAW process. The polarization of the three layers comprising the P3F film are realized via a combination of as-grown (two-layer) and electrically poled (one-layer) aluminum scandium nitride (AlScN). To improve the series ( ${Q}_{s}$ ) and maximum ( ${Q}_{\max }$ ) quality factors, the device is constructed by connecting two-BAW resonators in series, which lowers the effect of the via resistance when compared with a traditional single BAW. Resonators achieved ${Q}_{\max }$ of 531 (with ${Q}_{s}$ of 348 and ${Q}_{p}$ of 264) and ${\text {FoM}}_{{os}}$ (defined as ${\text {FoM}}_{{os}} = {{f}_{{s},{p}} {Q}}_{{s},{p}} \times {{10}}^{-{9}}$ , where ${Q}_{{s},{p}}$ is the quality factor at series ( ${f}_{s}$ ) or parallel ( ${f}_{p}$ ) resonance frequency) of 6542 at 18.8-GHz frequency, which is higher than most of the state-of-the-art piezoelectric BAW resonators operating at similar and higher frequencies. The experimental results indicate that the P3F BAW resonators are promising for applications in emerging RF communication systems.