Effects of sputtering process and annealing on the microstructure, crystallization orientation and piezoelectric properties of ZnO films

Ceramic piezoelectric films play a crucial role in sensors, acoustic wave devices, and micro-electromechanical systems (MEMS) due to their superior piezoelectric properties. This study focuses on optimizing ZnO piezoelectric films through radio frequency (RF) magnetron sputtering under a combination of varied deposition parameters such as tuning the target-substrate distance, sputtering power, and pressure effectively to control the atomic bombardment, collisions, and surface diffusion of sputtered particles, thereby influencing the surface morphology, grain size, thickness and chemical composition of the ZnO films. Furthermore, annealing heat treatment enhances the crystallization quality and piezoelectric properties of the ZnO films. Results show that annealing the films sputtered at a magnetron power of 50 W at 300 °C maximizes a favorable c-axis (002) orientation. Piezoelectric performance confirms that the annealed ZnO films exhibits enhanced piezoelectric amplitude, mechanical-electrical signal response, stable linear piezoelectric behavior, and a 180° phase flip under voltage excitation. This work is promising to lay a foundational solution for the development of advanced sensors with excellent piezoelectric properties.