Thickness dependence of ferroelectric and piezoelectric properties in epitaxial PZT thin films

Epitaxial (110)-oriented Pb(Zr0.52,Ti0.48)O3 (PZT) thin films were fabricated on SrRuO3-coated (001) YSZ/Si and SrRuO3-coated (110) SrTiO3 (STO) substrates with various thicknesses ranging from 0.1 μm to 1.0 μm by pulsed laser deposition. The effects of the film thickness on the structure, ferroelectric and piezoelectric properties were systematically investigated as a function of the film thickness. On the STO substrate the remnant polarization of the films increased from 36.6 to 45.5 μC/cm2 with the increasing film thickness, while in the films on the silicon substrate the remnant polarization was in the range of 12.4 - 20.2μC/cm2. The improvement of the remnant polarization with increasing film thickness was due to the reduction of the film/electrode interface effect which leads to improve the switching of domains. The films on the STO substrate were in a compressive stress, while in the films on the silicon substrate a higher tensile stress was found. Compressive stress causes the ferroelectric domains to orient along the longitudinal direction (c-domain orientation), which in turn can result in an increase of the polarization. Moreover, the effective piezoelectric coefficient of the PZT thin films increased steady with increasing thickness. This effect is likely related to a mechanism of elastic domains that can move more easily in thicker film, and that give rise to out-ofplane piezoelectric displacement.