Analysis and verification on second-order nonlinearity in radio frequency bulk acoustic wave devices employing temperature compensation films

This paper discusses the impact of SiO 2 /SiOF on second harmonic (H2) generation in temperature-compensated (TC) film bulk acoustic resonators (FBARs). First, two types of TC-FBARs are fabricated and their H2 behavior is compared with that of the standard FBAR. Next, the H2 characteristics of the TC layer are investigated by the use of a series of TC-FBARs where SiOF and Cr layers are placed on the outside of electrodes. The simulations agree very well with the measurements and can explain well how the H2 response changes with Cr thickness. Not only AlN but also SiOF contributes to the generation of H2 response, and H2 becomes very small at an appropriate Cr thickness. Finally, the TC-FBAR filter operating at 5.9 GHz is fabricated and its H2 response is compared with the simulation. The simulation agrees well with the experiment. It is also demonstrated that the insertion of the TC layer is effective in suppressing H2 generation.