Deposition of preferred-orientation ZnO films on the lead-free ceramic substrates and its effects on the properties of surface acoustic wave devices

A study of the structure based on the ZnO layers and NKN-SrTiO ₃(NKN-ST) ceramic substrates 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 NKN-ST ceramic substrates by RF magnetron sputtering technique. The deposited films were characterized as a function of oxygen-argon gas flow ratio, RF power, sputtering pressure, and depositing time. The ZnO films with strong (002) orientation are obtained under a base pressure of 20 mTorr, containing 40% oxygen and 60% argon at RF power of 60 W. Crystalline structures and surface roughness characteristics of the films were investigated by using XRD analysis, SEM, and AFM measurements. It shows that the preferred oriented ZnO film is beneficial for improving the electromechanical coupling coefficient (k ²) of Surface Acoustic Wave (SAW) device. The velocity, k ², and temperature coefficient of frequency of the ZnO/IDT/NKN-ST SAW device properties are 3120 m/s, 4.20%, and -320, respectively.