Rhombohedral PZT Thin Films Prepared by Sputtering

Abstract

PZT thin films with a rhombohedral perovskite structure were successfully grown on (111) PLT/Pt/Ti/SiO₂/Si and (111) Ir/SiO₂/Si substrates. The crystal structures of the films were sensitive to the substrate temperature T _s . PZT films with a completely rhombohedral structure were obtained at a T _s of 630 °C to 660 °C on PLT/Pt/Ti/SiO₂/Si substrates, a wider T _s range than on Ir/SiO₂/Si substrates. The composition of the PZT film can be easily adjusted by changing the area ratio of the PbO/Zr/Ti target. Films deposited on both PLT/Pt/Ti/SiO₂/Si and Ir/SiO₂/Si substrates yielded the same electrical-property results. When the Zr content was increased from 0.8 to 0.97, the dielectric constant, remanent polarization and Curie temperature of the rhombohedral PZT films monotonically decreased, and were similar to those of PZT ceramics. A phase transition between two rhombohedral ferroelectric phases was observed in some highly (111)-oriented PZT films. The fatigue characteristics were also measured. The PZT films maintained their initial switching-charge value over 10¹2 switching cycles. The possibility of an engineered domain configuration was examined in (100)-oriented rhombohedral PZT single-crystal films. Highly (111)- and (100)-oriented rhombohedral PZT (Zr/Ti = 80/20) single-crystal films were obtained by RF magnetron sputtering on (111) Ir/(111) SrTiO₃ and (100) Ir/(100) SrTiO₃ substrates. The ferroelectric hysteresis curve of the (100)-oriented rhombohedral PZT film showed a square-like shape, and the (111)-oriented film showed a slanted loop. The coercivity E _c of the (100)-oriented film was smaller than that of the (111)-oriented film. These results show the possibility of an engineered domain configuration in [001]-oriented rhombohedral PZT single-crystal films. This structure may be advantageous for improvement of the fatigue properties of FeRAMs.