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 (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${Q}_{s}$ </tex-math></inline-formula>) and maximum (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${Q}_{\max }$ </tex-math></inline-formula>) 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 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${Q}_{\max }$ </tex-math></inline-formula> of 531 (with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${Q}_{s}$ </tex-math></inline-formula> of 348 and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${Q}_{p}$ </tex-math></inline-formula> of 264) and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\text {FoM}}_{{os}}$ </tex-math></inline-formula> (defined as <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\text {FoM}}_{{os}} = {{f}_{{s},{p}} {Q}}_{{s},{p}} \times {{10}}^{-{9}}$ </tex-math></inline-formula>, where <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${Q}_{{s},{p}}$ </tex-math></inline-formula> is the quality factor at series (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${f}_{s}$ </tex-math></inline-formula>) or parallel (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${f}_{p}$ </tex-math></inline-formula>) 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.