50 GHz Piezoelectric Acoustic Filter

This paper presents significant frequency scaling of acoustic filter technology to 50 GHz. This achievement is enabled by the periodically poled piezoelectric film LiNbO<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> multilayer stack, in which piezoelectric thin-films of alternating orientations are transferred in sequence, thereby allowing efficient exploitation of high-order modes with high quality factor and coupling coefficient in a thicker piezoelectric stack. The demonstrated filter is comprised of twelfth-order symmetric mode lateral-field-excited bulk acoustic wave resonators (XBARs), built on a 4-layer periodically poled piezoelectric 128° Y-cut lithium niobate (LiNbO<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub>) stack. The filter exhibits 3.3 dB insertion loss and a fractional bandwidth of 2.9% . The miniature design, with a footprint of 0.36 mm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>, makes it promising for future wireless front-end applications. These results represent the highest frequency acoustic filters reported to date, setting a new benchmark in piezoelectric filter technology. Upon further development, the platform could enable filters further into the FR2 range, essential for next-generation communication systems.