Crystallographic characteristics and effective electromechanical coupling coefficients of AlN thin films for FBAR 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 2 electromechanical coupling coefficients (K-eff(2)) of such AlN thin films were characterized by varying N-2 gas flow ratio [N-2/(N-2+Ar)] from 0.6 to 0.9 and a substrate temperature from room temperature to 300degreesC. The optimal processing conditions for AlN thin films were found to be an N-2 gas flow ratio of 0.6 and a substrate temperature of 200degreesC at a sputtering power of 200 W and a working pressure of 1 mTorr. In these conditions, we obtained the c-axis preferred orientation of AlN/Al/SiO2/Si thin film about 4 degree.