Effect of bottom electrodes on microstructures and electrical properties of sol-gel derived Pb(Zr_0.53 Ti_0.47)O₃ thin films

Lead zirconate titanate (PZT) thin films were fabricated by adding 15 mol.% excess of Pb to the starting solution and spin coating onto Pt/Ti/SiO₂/Si and Ir/IrO₂/SiO₂/Si substrates. The effect of bottom electrodes on the microstructures, crystalline phases and electrical properties of the PZT thin films was investigated. It was found that the films deposited on Pt/Ti bottom electrode consisted of perovskite phase without pyrochlore phase, whereas the films deposited on the Ir/IrO₂ bottom electrode consisted of mainly perovskite phase with a small amount of pyrochlore phase. Bottom electrodes were also found to influence the preferred orientation and microstructure as well as the surface morphology of the PZT films. The Pt/Ti bottom electrode favored a (100) orientation and fine-grained structure as well as a smooth surface, whereas the Ir/IrO₂ bottom electrode favored a random orientation, non-uniform structure and rough surface. High-resolution electron microscopy observation reveals that there is an intermediate layer of IrO₂ at the PZT/Ir interface. This indicates that the intermediate layer of IrO₂ influenced the orientation and microstructure of the PZT films on the Ir/IrO₂ bottom electrode. Ferroelectricity was investigated by observing the polarization hysteresis loops. The remanent polarization and saturation polarization of the PZT films on the Ir/IrO₂ bottom electrode were smaller than those of the PZT films on the Pt/Ti bottom electrode. The difference between the dielectric and the ferroelectric properties in these PZT films was correlated to their crystalline phases and microstructure.