Dependence of electrical properties of epitaxial Pb(Zr,Ti)O3 thick films on crystal orientation and Zr∕(Zr+Ti) ratio

Abstract

Epitaxial Pb(Zr,Ti)O3(PZT) films, 1.5–2.0μm in thickness, with a Zr∕(Zr+Ti) ratio ranging from 0.20 to 0.75 were grown on (100)c-,(110)c-, and (111)c-oriented SrRuO3∕∕SrTiO3 substrates at 600 °C by metal-organic chemical vapor deposition (MOCVD). The effects the Zr∕(Zr+Ti) ratio had on the crystal structure, dielectric and ferroelectric properties, and piezoelectric response of these films with different crystal orientations were systematically investigated. We ascertained from x-ray-diffraction reciprocal-space-mapping analysis that (001)T-∕(100)T-∕(100)R-,(101)T-∕(110)T-∕(110)R-∕(101¯)R-, and (111)T-∕(111)R-∕(111¯)R-oriented films had epitaxially grown on the respective (100)c-,(110)c-, and (111)c-oriented SrRuO3∕∕SrTiO3 substrates. The constituent phase changed from a tetragonal single phase, a mixture phase of a tetragonal and rhombohedral, to a rhombohedral single phase with increasing Zr∕(Zr+Ti) ratio irrespective of the orientation of the substrates. However, the range of the Zr∕(Zr+Ti) ratio of the film with the mixture phase differed depending on crystal orientation. This suggests that the stress relaxation process applied from the substrates changed due to crystal orientation. The relative dielectric constant was maximum for films with the mixture phase regardless of the crystal orientation. Remanent polarization was also maximum for these films on the (111)cSrRuO3∕∕SrTiO3 substrates, while it was minimum on the (100)c- and (110)c-oriented SrRuO3∕∕SrTiO3 substrates. Films with two phases coexisting had larger electric-field-induced strain than films with a single tetragonal or rhombohedral phase for the (111)-oriented films, but there were no remarkable changes in the (100)- and (110)-oriented films. Small ac signal measurements suggested that domain-wall motions easily occurred in the (111)-oriented films with the mixture phase compared with other orientations. These results indicated that the larger field-induced strain of the (111)-oriented PZT films consisting of a mixture of tetragonal and rhombohedral phases largely contributed to extrinsic factors such as domain-wall motions and phase transformation due to the applied electric field.