An investigation of preferred orientation of doped ZnO films on the 36° YX-LiTaO₃ substrates and fabrications of Love-mode devices

Love-mode surface acoustic wave (SAW) devices are very promising for liquid and gas media sensing applications because of high sensitivity. In this paper, an experimental study of the structures based on zinc oxide (ZnO) guiding layer and 36° YX-lithium tantalate (LiTaO₃) substrate with different sputtering conditions to deposit ZnO films is presented. Poly-crystal ZnO films with c-axis (002) orientation have been successfully grown on the 36° YX-LiTaO₃ substrate by RF magnetron sputtering technique. The deposited films were characterized as a function of argon-oxygen gas flow ratio, RF power, deposition pressure, and annealing temperature. Crystalline structures, stress, and surface roughness characteristics of the films were investigated by X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), and atomic force microscopy (AFM) measurements. Highly orientated (002) films were obtained under a base pressure of 10 mTorr, containing 40% oxygen and 60% argon at RF power of 60 W and a substrate temperature around 120 °C. The films were then annealed at 600 °C. Love-mode devices based on this structure (ZnO/ IDT/36° YX-LiTaO₃) are presented.