A Comparative Study on the Performance of Aluminum Nitride Thickness and quasi-Thickness Extensional Mode Resonators

This paper reports on a comparative study regarding the performance of three different Aluminum Nitride (AIN) acoustic resonant technologies, based on thickness extensional or quasi-thickness extensional modes of vibration. In the last decades, Film-Bulk-Acoustic-Resonators (FBARs) have been extensively used in radio frequency (RF) front-ends because of their high electromechanical coupling coefficient (kt
²
~7%). However, monolithic integrated FBARs with different resonance frequency (fres) can only be attained through an augmented fabrication complexity because their fresis set by the thickness of the forming layers. Just recently, Two-Dimensional-Mode-Resonators (2DMRs) and Two-Dimensional-Resonant-Rods (2DRRs) have been discovered. Both devices provide new means to achieve high-kt
²
and a lithographic tunability of fres. In this work, to evaluate the real potential of 2DMRs and 2DRRs in replacing FBARs in future RF applications, we compared, through Finite Element Methods (FEM), the electromechanical performances (quality factor (Q) and kt
²
) exhibited by a 2DMR and a 2DRR with those of an FBAR made of the same material stack. We show that the 2DRR exhibits the highest Figure of Merit (FoM=Qloaded·kt
²
), exceeding 81, among the analyzed devices.