Improved piezoelectric properties of zno films obtained by magnetron sputtering power stacking process

Piezoelectric ZnO thin films have good stability, binding force, and high electromechanical coupling coefficient, making them suitable for piezoelectric devices like sensors. However, the piezoelectric coefficient d₃₃ of ZnO films is still not high enough for applications, such as smart bolts in the structural health monitoring field. Herein, a novel method of power stacking of 3-μm-thick ZnO thin films pre-deposited onto nickel-based alloy substrates via RF magnetron sputtering was proposed. Compared to single power samples, the ZnO thin films formed through the sputtering power stacking at 300 W\200 W\100 W showed a clearly distinguishable preferred orientation (002). Meanwhile, the films exhibited relatively fine and uniform grains, coarse columnar crystals, and small roughness. More importantly, the piezoelectric coefficients d₃₃ of ZnO thin films obtained by the power stacking were improved to 1976.92 pm/V, being 7 times higher than those obtained at a single power and reported in the literature. Thus, this work provides a simple method of piezoelectric performance improvement for future development of advanced devices.