Characterization of PZT thin film transducers obtained by pulsed laser deposition

Oriented lead zirconate-titanate (PZT) thin films have been deposited on silicon substrates by pulsed laser technique and tested in transducer structures. The deposition has been performed in a vacuum chamber in oxygen atmosphere, by using a pulsed Nd-YAG laser of wavelength 1064 nm. The targets have been PZT sintered samples and the substrates Si wafers covered with thin Au electrodes. Highly oriented PZT thin films with smooth surface have been obtained in our experiments at low substrate temperature by optimising different parameters involved in the deposition, like target-substrate distance, laser fluence, oxygen pressure etc. This fact could be of particular relevance for silicon-integrated piezoelectric devices where processing at high temperatures should be avoided. PZT thin films have been characterised by energy dispersive spectroscopy (EDS), X-ray diffraction and scanning electron microscopy (SEM) in order to determine their composition, crystallographic structure and morphology. The samples presented perovskite structures with preferential alignment of the (111) planes parallel to the film surface. Piezoelectric properties of PZT films have been evaluated through a direct method. The measurements revealed good piezoelectric properties of PZT films in the absence of any poling, due to the intrinsic orientation of the films. In order to evaluate transducer properties thin Au top electrodes have been deposited over PZT layer and metallic films confined in a small square area. Electrical measurements have been performed by using a network analyzer and piezoelectric and dielectric coefficients as well as electromechanical coupling factors have been evaluated for different transducer configurations.