Effects of Erbium alloying on the structural and piezoelectric properties of Aluminum Nitride thin films annealed under
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Effects of Erbium alloying on the structural and piezoelectric properties of Aluminum Nitride thin films annealed under extreme thermal conditions. V. Narang1 and D. Korakakis2 1
Department of Physics, West Virginia University, Morgantown, WV 26506-6315, U.S.A
2
Lane Department of Computer Science and Electrical Engineering, West Virginia University, Morgantown, WV 26506, USA ABSTRACT Effects of adding Erbium(Er) to Aluminum Nitride thin films on their structural and piezoelectric are reported along with stability of the films after annealing them at temperatures up to 600° C. The thin films samples were deposited on the (001) p-type silicon substrates by reactive magnetron sputtering, using the Er alloyed Aluminum targets with Er atomic concentrations of 0, 1, 3 and 4% and the magnetron sputtering power of 200 W. The samples were characterized by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). XPS analysis was used to confirm the stoichiometry of AlN phase, Er atomic content and its possible chemical state in the films. Results show that alloying with Er results in higher piezoelectric coefficient d33 as compared to that in Er-free AlN thin films. Structural analysis of the films by XRD shows the shift of (0002) AlN peak to lower 2θ values upon Er doping, indicating the presence of uniform internal compressive stress. INTRODUCTION Aluminum Nitride is a robust material which maintains its piezoelectric properties at high temperatures and in harsh environments where most commonly used piezoelectrics such as Lead Zirconate Titanate (PZT) cannot be used [1]. However, the piezoelectric response of AlN is lower than that of other commonly used piezoelectrics. In order to achieve the higher piezoelectric response from films capable of sustaining extreme thermal conditions, the properties of AlN films alloyed with Er are investigated. Rare earth doping is widely reported to enhance the piezoelectric properties of materials such as PZT [2,3]. Inclusion of rare earths in PZT increases the polarization and results in the existence of combinatory soft and hard piezoelectrics, leading to the higher piezoelectric coefficient [3]. Increase in piezoelectric coefficient of AlN films alloyed with Er has been reported earlier [4] as shown in Figure 1. However, since AlN is not a ferroelectric, the mechanism behind the increased piezoelectric coefficient of Er alloyed films could be different from that in PZT. It is also reported that the piezoelectric response of AlN films is related to the structural properties and increases with the increased preferential c-axis film depositions [5]. In light of these results, the effect of Er alloying of AlN films on its structural properties needs to be investigated. Also as the piezoelectric properties are related to the structural properties of the AlN films, the structural properties are investigated after annealing the films in air at 600 °C.
Figure 1: d33 vs. thickness for AlN:Er(3%) film PERTINENT EXPERIMENTAL DETAILS AlN and AlN:Er films of approximate 600 nm thick
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