Electrical properties of highly oriented Pb(Mg_(1/3)Nb_(2/3))O_3 Pb(Zr,Ti)O_3 thin films fabricated by the sol-gel method

摘要

Highly (100)- and (111)-oriented lead magnesium niobate-lead zirconate titanate (PMN-PZT) films were deposited on Pt(111)/Ti/SiO_2/Si substrates using a sol containing polyvinylpyrrolidone (PVP). The molar ratio of Zr/Ti in the PZT was fixed at 60/40, and the PMN content was changed in the range of 0-30 mol percent. The films had a dense and columnar microstructure with a thickness of about 1 mu m as a result of being spun four times. The crystallographic orientation of the films was controlled by adjusting the pyrolysis temperature; a (100) orientation was obtained by pyrolyzing at 300 deg C and a (111) orientation by pyrolyzing at 350 deg C. The electrical properties of the films were strongly dependent on the crystallographic orientation and PMN content. With increasing PMN content, the dielectric constant of all of the films increased. On the other hand, the remnant polarization of the (111)-oriented films decreased steadily with increasing PMN content, while that of the (100)-oriented films remained unchanged up to a PMN content of 20 percent. The piezoelectric coefficients of the (100)-oriented film were consistently higher than those of the (111)-oriented film with the same composition. The highest piezoelectric coefficient was observed for the (l00)-oriented film with a composition of 0.2PMN-0.8PZT, indicating the morphotropic phase boundary between the rhombohedral PZT phase and the pseudocubic PMN phase is in the vicinity of this composition.