Characterization of Mechanical and Piezoelectric Properties of the AlN Thin Film in a Composite Resonator Stuctrue

Piezoelectric AlN thin film has been considered for fabricating the thin film bulk acoustic wave resonator (FBAR) for over years. Characterization of thin film material properties including density, elastic modulus, and piezoelectric coefficient are essential in processing study and for predicting the performance of the acoustic wave devices. In this paper, the authors present our results on the fabrication of highly c-axis oriented AlN thin films on Pt/Ti/Si (100) and Pt/Ti/sapphire (002) substrates by DC reactive magnetron sputtering method. The crystalline structure and the surface morphology of AlN films were characterized by scanning electron microscopy (SEM). The effective piezoelectric coefficient d_33eff of the AlN films on the sapphire substrate were measured by the laser interferometer method and the piezoelectric coefficient d₃₃ was calculated. In addition, a more detailed characterization on the mechanical properties was performed by using a recently developed resonance spectrum method. Based on the impedance spectrum, the density and elastic constant of the piezoelectric AlN thin film in the four-layer composite resonator structure were evaluated. The calculated results reveal that the piezoelectric coefficient d₃₃, density and velocity of the AlN thin film are 4.19pm/V, 3187.3kg/m³, and 10631m/s respectively