Microwave Analysis and Electrical Properties of ZnO thin Films Prepared by RF Magnetron Sputtering

A piezoelectric thin film sandwiched between two metal electrodes is basic structure for high frequency bulk acoustic wave device have been investigated. The films used for acoustic wave devices require high dielectric properties, piezoelectric coefficients and high electromechanical coupling coefficients, because the piezoelectric films launch and receive the acoustic wave. We fabricated ZnO films by RF magnetron sputtering. For that propose, the RF magnetron sputtering deposition for piezoelectric ZnO films 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 3.8m 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.