Film Bulk Acoustic Resonator Based on Zinc Oxide Thin Film

Abstract

A piezoelectric thin film sandwiched between two metal electrodes is basic structure for high frequency bulk acoustic wave devices. For that propose, the RF magnetron sputtering deposition for piezoelectric ZnO film formation and its such application for film bulk acoustic resonator (FBAR) devices are presented. Several critical parameters of the RF magnetron sputtering process deposition pressure, RF power, substrate temperature, O₂ concentration and the target to substrate distance were determined to clarify their effects on the material characteristics of the ZnO. Highly c-axis oriented thin films as thick as 5.7 mm were grown and analyzed. Compressive stresses were observed. The FBAR devices with the ZnO films exhibited a pronounced resonance peak centred at 537 MHz with a k² coupling coefficient of 7 %. It found therefore that the impedance matching of the FBAR could be easily achieved simply by controlling the resonance the resonator.

Keywords: ZnO; FBAR; R.F sputtering magnetron; resonator.