The effect of post-annealing on surface acoustic wave devices based on ZnO thin films prepared by magnetron sputtering

Zinc oxide (ZnO) thin films were deposited on unheated silicon substrates via radio frequency (RF) magnetron sputtering, and the post-deposition annealing of the ZnO thin films was performed at 400 degrees C, 600 degrees C, 800 degrees C, and 1000 degrees C. The characteristics of the thin films were investigated by X-ray diffractometry (XRD), scanning electron microscopy (SEM), and atomic force microscopy (AFM). The films were then used to fabricate surface acoustic wave (SAW) resonators. The effects of post-annealing on the SAW devices are discussed in this work. Resulting in the 600 degrees C is determined as optimal annealing temperature for SAW devices. At 400 degrees C, the microvoids exit between the grains yield large root mean square (RMS) surface roughness and higher insertion losses in SAW devices. The highest RMS surface roughness, crack and residual stress cause a reduction of surface velocity (about 40 m/s) and increase dramatically insertion loss at 1000 degrees C. The SAW devices response becomes very weak at this temperature, the electromechanical coupling coefficient (k(2)) of ZnO film decrease from 3.8% at 600 degrees C to 1.49% at 1000 degrees C. (c) 2010 Elsevier B. V. All rights reserved.