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 LiNbO3multilayer 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 (LiNbO3) 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 mm2, 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.