Effect of AlN Film Thickness and Top Electrode Materials on Characteristics of Thin-Film Bulk Acoustic-Wave Resonator Devices

Abstract

Highly c-axis-oriented aluminum nitride (AlN) thin films were deposited on Mo electrodes by reactive RF magnetron sputtering and their thickness effects on thin-film bulk acoustic-wave resonator (FBAR) characteristics are presented. The results obtained in this study show that thick AlN films have a strong c-axis orientation and tend to promote a small rocking curve full-width at half-maximum (FWHM), but a high grain size and a high surface roughness, hence degrading the characteristics of FBARs. The characteristics of FBARs depend not only the thickness and quality of AlN films, but also the thickness of the top electrode and the type of material used. Specifically, an increase in either AlN film or top electrode thickness increases parallel resonant quality factor (QP), but reduces effective electromechanical coupling coefficient (keff2). However, the resonance provides a maximum keff2 when AlN film thickness approaches the fundamental one-half-wavelength. The effects of the type of top-electrode material and AlN film thickness on the keff2 and quality factor of the fabricated FBARs are also discussed.