Film bulk acoustic resonator fabrication for radio frequency filter applications

In this paper, a two-step radio frequency (RF) sputtering deposition technique for piezoelectric ZnO film formation and its successful application for film bulk acoustic resonator (FBAR) devices are presented. Several critical parameters of the RF sputtering process such as deposition pressure, RF power and O(2) concentration were studied to clarify their effects on the material characteristics of the ZnO films. The ZnO films deposited by the proposed two-step deposition are shown to have the growth characteristic of strongly preferred orientation toward the c-axis. The FBAR devices with the ZnO films showed a large return loss of similar to 50 dB at the center frequency of 1.49 GHz. It was also found that the impedance matching of the FBAR could be easily achieved simply by controlling the resonance area of the resonator.