A 56 GHz Trilayer AlN/ScAlN/AlN Higher Order Mode FBAR with Alternating Polarization Excited Harmonic Resonance

Emerging wireless communication standards call for higher carrier frequencies, presenting challenges to frontend filter design for 5G and beyond. A multilayer structure with alternating polarization can be employed in a bulk acoustic wave (BAW) resonator to coherently excite a higher order mode, providing a promising pathway towards mm-Wave operating frequencies while maintaining fractional bandwidths. An AlN/ScAlN/AlN trilayer thin film bulk acoustic resonator (FBAR) can be polarization switched to reverse the piezoelectric orientation in ScAlN in order to operate at a higher order mode without a reduction in the coupling factor. In this work, a new trilayer design has been fabricated and polarization switched. The resonator operates at 56 GHz with a coupling factor of 4.2% and a quality factor of 60.