Characteristics of ZnO thin film for film bulk acoustic-wave resonators

Highly c-axis-oriented zinc oxide (ZnO) thin films were deposited on Au electrodes by reactive radio frequency (RF) magnetron sputtering and their sputtering pressure on thin film bulk acoustic-wave resonator (FBAR) characteristics are presented. The evolution of the preferred orientation and the surface morphologies of the deposited ZnO films are investigated using X-ray diffraction, scanning electron microscopy, and atomic force microscopy measurement techniques. The result obtained in this study show that the ZnO films prepared using a lower sputtering pressure of 2 × 10⁻³ Torr have a strong c-axis orientation, promote smoother surface and higher resonance frequency. The experimental results demonstrate that the fabricated two-port FBAR using the optimum process parameters yields an effective electromechanical coupling constant (\( k^{2}_{{{\text{eff}}}} \)) of 2.8%, series quality factor (Q _s) of 436, and a parallel quality factor (Q _p) of 600.