Theoretical simulation and optimization on material parameters of thin film bulk acoustic resonator

Abstract

The resonance frequency, f s, and the effective electromechanical coupling factor, k e f f 2, of thin film bulk acoustic resonators (FBARs) are derived by transfer matrix method. The effects of thickness and density of electrode on f s and k e f f 2 with different piezoelectric layers are investigated by numerical calculation method. The results show that thickness and density of electrode affect f s obviously, especially in large thickness and density area. Moreover, the effects of thickness, density, and acoustic velocity of electrode on k e f f 2 of FBAR were also studied. The results show that there is a maximum k e f f 2 corresponding to the composition of thickness and density of electrode which is about 20% over the original electromechanical factor of piezoelectric film. k e f f 2 is in the direct proportion to the density ρ e and v e of electrode, respectively. The electrode thickness affects k e f f 2 small with high v e; moreover, when v e is high enough, then k e f f 2 has almost nothing to do with d e. k e f f 2 always rises with electrode thickness first and then descends with its rising, and the thickness corresponding to the maximum k e f f 2 is different with different electrode, but it always locates in the special area. All above results indicate that the thickness, density, and acoustic velocity of electrode are so important that these results can be applied to design FBAR.