Improving Performance of FBARs by Advanced Low-Temperature High-Pressure Technology

In this study, a unique supercritical fluid (SCF) treatment is utilized to improve the resonance properties of thin film bulk acoustic resonators (FBARs) composed of a piezoelectric material of AlN. In an etching process of the sacrificial oxide, FBARs suffered from severe surface tension of etching acid solvent, resulting in structural bonding and residues generation. These impact on FABR’s structural integrity would influence its resonance properties. Therefore, a SCF treatment with low surface tension and high penetrability can effectively carry out residues from the release gap in a FBAR, observed from SEM images. The results show that the reflection coefficient, the quality factor, and the effective coupling coefficient are all improved in FABRs.