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 (kteff2) 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.