Crystallographic characteristics and effective electromechanical coupling coefficients of AlN thin films for FNAR applications

In this study, AlN thin films for film bulk acoustic wave resonator (FBAR) device applications were investigated using facing targets sputtering system (FTS) and a DC power supply. The crystallographic characteristics, c-axis preferred orientations, and effective electromechanical coupling coefficients (K₂^eff) of such AlN thin films were characterized by varying N₂ gas flow ratio [N₂/(N₂+Ar)] from 0.6 to 0.9 and a substrate temperature from room temperature to 300°C. The optimal processing conditions for AlN thin films were found to be an N₂ gas flow ratio of 0.6 and a substrate temperature of 200°C at a sputtering power of 200 W and a working pressure of 1mTorr. In these conditions, we obtained the c-axis preferred orientation of AlN/Al/SiO₂/Si thin film about 4 degree.