Highly c-axis oriented thin AlN films deposited on gold seed layer for FBAR devices

Abstract

In this study, highly c-axis oriented aluminum nitride (AlN) films are deposited on gold (Au) seed layer using a rf reactive sputtering method under various rf power and sputtering pressures. The evolution of preferred orientation and surface morphologies of the deposited films was studied by x-ray diffraction, scanning electron microscope, and atomic force microscope. It was found that the AlN films prepared using the higher rf power of 400 W and sputtering pressure of 7 mTorr were shown to have the stronger c-axis orientation and exhibit smoother morphologies. The fabricated film bulk acoustic-wave resonator (FBAR) devices considered here with AlN film thickness are 2.25μm, Au and Al are used as bottom electrode and top electrode with the thickness of 0.1 and 0.18μm, respectively. The effective electromechanical coupling coefficient (keff2), quality factor (Qfx) and resonant frequency of the fabricated FBAR device were about 1.47%, 535 and 2.172 GHz, respectively. Moreover, the effect of the top electrode materials, AlN and Al top electrode film thickness on the frequency response characteristics of FBAR devices is also investigated.