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

This paper discusses impact of SiO2/SiOF on the 2nd 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, H2 characteristics of TC-layer are investigated by the use of series of TC-FBARs where SiOF and Cr layers are placed on the outside of electrodes. Simulations agree very well with measurements, and can explain well how the H2 response changes with the Cr thickness. Not only AlN but also SiOF contribute generation of the H2 response is shown, and H2 becomes very small at an appropriate Cr thickness. Finally, 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 insertion of the TC-layer is effective to suppress the H2 generation.