Abstract
Pb(Zr,Ti)O3 (PZT) films having 2.0 µm in thickness with the Zr/(Zr+Ti) ratio ranging from 0.20 to 0.75 were prepared on (111)Pt/TiO2/SiO2/(100)Si substrates at 600°C by metalorganic chemical vapor deposition (MOCVD). Highly (100)-/(001)-oriented PZT films were successfully prepared with a deposition rate of 1.5 µm/h. Effects of the film composition on the crystal structure, ferroelectricity and electric field-induced strain of these films were investigated. It was ascertained by θ-2θ scans of X-ray diffraction that a tetragonal single phase and a rhombohedral single phase were obtained for the films with the Zr/(Zr+Ti) ratio below 0.40 and above 0.60, respectively. On the other hand, the mixed phases with tetragonal and rhombohedral phases were observed for the Zr/(Zr+Ti) ratio ranging from 0.43 to 0.57. This composition is similar to the morphotropic phase boundary (MPB) for the bulk ceramics. Remanent polarization (Pr) and coercive field (Ec) were almost constant and monotonically decreased, respectively, when the Zr/(Zr+Ti) ratio increased. This change of Ec value with the Zr/(Zr+Ti) ratio was in good agreement with the reported one for the sintered body, but not for the Pr value. On the other hand, the relative dielectric constant and the field-induced strain took maximum values around this composition which was in good agreement with the reported data for the sintered body. Field-induced strain was in good agreement with the estimation from the phenomenological equation, and the large change of polarizations is found to cause large field-induced strain. These results show that the highly (100)-/(001)-oriented films showed behavior similar to that of a PZT sintered body in terms of field-induced strain, coercive field and the dielectric constant together with the coexistence of the tetragonal and rhombohedral phases around the MPB composition.
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