Effects of H2O partial pressure on the crystallinity of ZnO thin film and electrical characteristics of film bulk acoustic wave resonators

We have improved electrical characteristics of a film bulk acoustic wave (BAW) resonator that features the injection of H₂O gas into a process chamber. The preferred crystallinity of piezoelectric ZnO film was obtained by RF sputtering at a high H₂O partial pressure 1.5×10⁻⁴ Pa. The effective electromechanical coupling coefficient () of the BAW resonator remarkably goes up from 1.8% to 4.7% for which the corresponding H₂O partial pressures are 2.7×10⁻⁵ and 1.5×10⁻⁴ Pa. Injection of H₂O during the deposition process contributes to the improvement of crystallinity of ZnO thin film and the electrical characteristics of the BAW resonator.     

Preparation and photoluminescence properties of ZnO/amorphous-BaTiO3 thin-films by sol–gel process

ZnO/amorphous-BaTiO₃ thin-films were prepared on glass substrates by a sol–gel process. DSC/TGA, XRD and AFM were used to analyze the thermolysis of the precursor and the crystal growth characteristics of ZnO, and IR spectroscopy was used to determine the presence of OH groups and CO impurities containing in the films. Violet emission centering at 418 and 438 nm was observed in room temperature PL spectra of the films annealed at 400–500 °C. The strongest violet emission was observed in the film annealed at 400 °C. The emission intensity reduces as the annealing temperature increases, and vanishes in the film annealed at 550 °C. All of the films contain OH and CO groups, and the films annealed at the temperature over 450 °C contain CO₂ impurities, indicating the enhancing oxidation of the films. The vanishing of the violet emission is probably due to the improvement of the oxygen deficient of ZnO crystals.