Aluminum nitride films deposited under various sputtering parameters on molybdenum electrodes

In this study, highly c-axis-oriented fine polycrystalline aluminum nitride (AlN) films are deposited on molybdenum electrodes using the reactive RF magnetron sputtering method. Molybdenum is adopted as the electrode material rather than the conventional choice of Pt/Ti, Au/Cr or Al because it has low resistivity, large acoustic velocity, and provides a good adhesion between the thin AlN film and the low-stress Si₃N₄ membrane. The influences of the RF power and nitrogen flow rate ratio on the crystalline orientation and surface morphologies of the deposited AlN films are thoroughly investigated. It was found that the AlN films prepared using the RF power of 400 W and an elevated N₂ flow rate ratio of 75% exhibit a greater tendency towards the preferred c-axis-orientation and exhibit smoother morphologies. Furthermore, thicker AlN films and the use of a higher RF power (400 W) in the deposition process tend to promote a narrower full width at half maximum. The experimental results demonstrate that the fabricated FBAR devices, its piezoelectric-active area (24774 μm²) was polygonal shape with 5 sides of 120 μm, the thickness of low-stress Si₃N₄, AlN film, Mo (bottom) and Al (top) electrodes was consisted of 0.2 μm., 2.25 μm, 0.1 μm and 0.18 μm, respectively. The effective electromechanical coupling coefficient (k²_eff) and the quality factor (Q_fx) were about 1.5% and 312, respectively.