Two-step deposition process of piezoelectric ZnO film and its application for film bulk acoustic resonators

In this article, a two-step deposition technique of piezoelectric zinc oxid e (ZnO) film formation using radio-frequency (rf) sputtering and its succes sful applications for film bulk acoustic resonators (FBAR) are presented. S everal critical sputtering process parameters such as deposition pressure, rf power, and O-2 concentration were investigated to understand their impac ts on the resulting crystal structures and surface morphologies of the ZnO films. The ZnO films formed by the two-step deposition have shown the growt h characteristic of the strongly preferred orientation toward c axis. The F EAR with the ZnO films showed a large return loss of similar to 50 dB at th e center frequency of 1.49 GHz. It was also found that the impedance matchi ng of the FEAR could be easily achieved by simply controlling the resonance area of the resonator. (C) 2000 American Vacuum Society. [S0734-2101(00)06 005-X].