Crystallographic Texture of Submicron Thin Aluminum Nitride Films on Molybdenum Electrode for Suspended Micro and Nanosystems

The structural properties of piezoelectric AlN/Mo/AlN stacks have been investigated for obtaining an improved c-axis oriented, piezoelectric AlN thin film on Mo electrodes to be employed in suspended nano- and micromechanical devices. With increasing thickness of the AlN interlayer up to 80 nm, the texture of the overgrown Mo layer improves significantly, marked by a significant reduction in full-width-at-half-maximum of the rocking curve obtained around 220 Bragg reflections. The improved orientation of Mo crystallites promotes the growth of preferentially c-axis oriented columns in the overgrown AlN film as evidenced by analyzes of crystal orientation determined by scanning nano-beam transmission electron diffraction. Atomic-Force Microscopy revealed only a slight deterioration of the surface roughness of AlN films upon introduction of the interlayer. The whole film stack has a total thickness of less than 1 μm and is, thus, promising for suspended piezoelectric active RF devices. © 2013 The Electrochemical Society. [DOI: 10.1149/2.001305jss] All rights reserved. Aluminum nitride (AlN) thinfilms are being used as active materials in many devices that take advantage of the piezoelectric properties of the films. Compared to other piezoelectric materials, such as, zinc oxide (ZnO), cadmium sulfide (CdS), lead zirconate titanate (PZT), and lithium niobate (LiNbO3), AlN films can be easily integrated in conventional silicon and III-V technologies. This is mainly because the piezoelectric films can be grown by low temperature deposition processes. Additionally, compared to ZnO and CdS, the acoustic velocity of AlN film is almost two-fold, and thus, the central frequency in acoustic devices can be enhanced twice without decreasing the inter-digital electrode width. 1 Piezoelectric AlN films are either predominantly used or are promising for active films in Microelectromechanical systems (MEMS), 2‐4 such as film bulk acoustic resonators (FBAR) for mobile communications operating at high frequencies from 0.5 to 10 GHz, 5‐7 and radio-frequency (RF) switches. 8‐10 Recently, attention has been attracted for application of AlN films in