Compositional dependence of electrical properties of highly (100)-/(001)-oriented Pb(Zr,Ti)O3 thick films prepared on Si-substrates by metalorganic chemical vapor deposition

Pb(Zr,Ti)O-3 (PZT) films having 2.0 mum 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 600degreesC by metalorganic chemical vapor deposition (MOCVD). Highly (100)-/(001)oriented PZT films were successfully prepared with a deposition rate of 1.5 mum/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 theta-2theta 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 (P-r) and coercive field (E-c) were almost constant and monotonically decreased, respectively, when the Zr/(Zr+Ti) ratio increased. This change of E-c value with the Zr/(Zr+Ti) ratio was in good agreement with the reported one for the sintered body, but not for the P-r 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 similat 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.