Effect of high temperature annealing on structure and properties of ZnO piezoelectric coating

Abstract

ZnO is currently the main coating material for piezoelectric bolt sensors, which exhibits excellent acoustic-electric signal conversion because of its unique piezoelectric effect, but its high-temperature structure and performance stability have been less studied. In this paper, ZnO piezoelectric coating that could generate ultrasonic longitudinal waves was prepared on （100）Si and industrial titanium bolts by RF magnetron sputtering, and annealed at different temperatures and different time durations to investigate the effects of high-temperature annealing treatment on the structure and properties of the coating. The results of scanning electron microscopy show that the annealing treatment below 600 °C does not affect the microscopic morphology of the coating surface, and the cross-sectional morphology of the coating shows a columnar crystal structure, and the columnar crystals tend to merge with the temperature increased. The results of atomic force microscopy show that the surface roughness of the coating varies by ±4 nm, and the X-ray diffraction results show that different annealing temperatures do not affect the crystal structure of the coating significantly. The acoustic signals of the bolt samples after annealing treatment at different temperatures and durations are examined, and the results show that the coating surface is intact after annealing treatment at 500 °C and below, and the bolt coating is completely peeled off after annealing treatment at 600 °C. The ultrasonic signals characterize that the structure of coating is stable after annealing at 500 °C or below; at 300 °C, after a long annealing treatment, none of the excitable ultrasonic properties of the bolt samples are destroyed, indicating that the ZnO coating can serve in the temperature range of 300 ℃ for a long time.

Keywords

• zno piezoelectric coating
• magnetron sputtering
• high temperature annealing
• smart bolt