Experimental and theoretical investigation on the relationship between AlN properties and AlN-based FBAR characteristics

Film bulk acoustic resonators (FBARs) with an Al/AlN/Mo/Si (111) configuration are fabricated. In particular, the effects of deposition conditions on material properties of AlN films grown on Mo/Si substrate as well as the performance of FBARs are studied. Piezoelectric AlN films are deposited using RF magnetron sputtering at RF power=250 W∼600 W, N₂/Ar ratio=5/25∼25/5, working pressure=5 mTorr, substrate temperature=250°C. For all the deposited AlN films, the X-ray diffraction (XRD) spectra and full width at half maximum (FWHM) of rocking curves are measured in terms of the deposition conditions, to characterize the c-axis preferred orientation and crystal quality. The frequency response characteristics (S₁₁) of the fabricated FBARs are also measured. The experimental results indicate that the characteristics of FBARs can be determined by the material properties of the AlN films. Furthermore, the theoretical relation ship between the impedance parameters (R_m) of the BVD model and the AlN properties has been established.