Novel carbon-doped oxide-FBAR structure and its simulation verification

Low acoustic impedance support layer with a certain thickness between film bulik acoustic resonator (FBAR) and the substrate can form an acoustic isolation layer to prevent sound leakage to the substrate. Carbon-doped oxide(CDO) is a kind of low acoustic impedance material with good temperature compensation for FBAR, and it can be used as acoustic isolation layer between FBAR and the substrate which results in a novel FBAR structure named as CDO-FBAR. In order to analyze whether the properties of CDO-FBAR is degenerated compared with via-hole type FBAR and the required thickness of CDO as acoustic isolation layer, we used multi-physics coupled simulation software to analyze the resonant frequency, the Q (quality factor) value, the effective electromechanical coupling coefficient and S -parameter of the two kinds of FBARs, and to extract longitudinal vibration displacement of CDO-FBAR. The results indicate: the overall resonant frequency of CDO-FBAR is downshift; CDO isolation layer induced parasitic disturbance in S -parameter; because of the increasing acoustic loss, the Q value decreased slightly, and more reduction happened at parallel resonant frequency; and the effective electromechanical coupling coefficient has also reduced slightly; acoustic wave did not completely attenuate until sound wave propagating in the acoustic isolation layer for 9 m, i.e. it needs only 9 m thick CDO material to form an effective acoustic isolation layer between FBAR and the substrate. Thus, the feasibility of the novel CDO-FBAR structure is verified by simulation.