A 36 GHz Trilayer AlN/ScAlN/AlN Periodically Poled FBAR

Communication bands at mm-wave frequencies with large bandwidths call for innovative solutions in frontend filter design for 5G and beyond. Bulk acoustic wave (BAW) resonators have already become a mature technology in sub-8 GHz filters, but face a number of challenges at mm-wave frequencies. A periodically poled resonator is capable of achieving high quality factors while maintaining its electromechanical coupling coefficient at mm-waves. In this work, the results for a new MBE grown trilayer AlN/ScAlN/AlN mm-wave thin film bulk acoustic resonator (FBAR) is presented. The trilayer FBAR has been polarization switched electronically to reverse the piezoelectric coefficient in the ScAlN layer. The resonator achieves the highest reported coupling coefficient and quality factor for FBARs at similar frequencies, exhibiting a measured coupling coefficient of 6.7% and a quality factor of 252 at 36GHz.