Piezoelectric Thin Films for High Frequency Electroacoustic Devices

Abstract

Development of SAW (Surface Acoustic Wave) and BAW (Bulk Acoustic Wave) devices operating at microwave frequencies, as well as transducers for micromechanical devices, is strictly connected with the performances of the piezoelectric layer employed for the transduction. The more interesting materials for these applications are ZnO, A1N and PZT. Regardless of the particular material considered, the goal is to obtain a film with physical and electrical characteristics very close to that of the corresponding bulk material. This can be reached by a proper choice of the deposition method and parameters. Common requirements for the deposition methods are the repeatability and the compatibility of the deposition environment with the substrate. Another important requirement is the possibility to deposit sequentially on the same chamber a metallic layer between the substrate and the piezoelectric film.

Between the various technologies proposed for this purpose, the most widely used is the sputtering (DC or RF Magnetron). More recently PLD (Pulsed Laser Deposition) has been successfully introduced and the results are very promising. With both of them, the required deposited compound can be obtained starting from a target of the same composition or better from a target of a pure element reacting with a specific ambient gas before the condensation phase ( reactive deposition).

In this study we present the results of our experience on piezoelectric thin film deposition with this two techniques in order to put in evidence and compare their peculiarities.