Device effects of various Zr/Ti ratios of PZT thin-films prepared by sol-gel method

Abstract

PZT, PbZr_xTI_1−xO₃, thin-films with various Zr/Ti ratios, 100/0 (lead zirconate) to 0/100 (lead titanate), were prepared by the sol-gel method. Basic electric properties, dielectric constant, tan σ, P-E hysteresis curve, switching properties were measured respectively as a function of composition. Dielectric constant indicated a specific peak value (∼1100) around the morphotropic phase boundary between tetragonal and rhombohedral phase. Satisfactory low-voltage saturated hysteresis curves were observed for the compositions of PZT(90/10) through PZT(20/80). The remanent polarization and the coercive field increased as the titanium content decreased. The result of X-ray measurement showed that the lattice constants of thin-Film PZT are different from bulk ceramics for compatible compositionsS. The boundary, on which the c/a ratio must be 1 (rhombohedral phase), was slightly shifted to PbTiO₃ side. This distortion in crystal structure is considered to be due to the thin-film effect, which the lattice mismatch between the platinum substrate and the PZT layer, restricted the ions to position into proper cites.