Wideband 6 GHz RF Filters for Wi-Fi 6E Using a Unique BAW Process and Highly Sc-doped AlN Thin Film

A Wi-Fi 6E BAW filter with relative bandwidth of 12% (665 MHz at 5.5 GHz) and good rejection over the whole 6 GHz band (1200 MHz) is reported. The Wi-Fi 6E filters have much wider bandwidth than those of early Wi-Fi 5/6 filters. High coupling coefficient piezoelectric films, highly Sc-doped AlScN, are developed to realize such a wide bandwidth. A novel bulk acoustic wave device fabrication process that capable of utilizing wide variety of piezoelectric thin films is used to realize such a challenging filter. The resonators fabricated with the material show keff2 of 13.2% and maximum quality factor of 1789.