Pb(Zr,Ti)O3 (PZT) has been studied widely as a material for ferroelectric random access memory (FeRAM), microelectronics materials (MEMS) and so on. In the FeRAM application, we need the PZT thin films with higher ferroelectricity and reliability. Controlling the crystal orientation of PZT, so called ﾒDomain Engineeringﾓ is one of important ways to improve the ferroelectricity of PZT. The residual stress from the substrate by thermal-expansion-coefficient differences affects the degree of the domain switching and the distortion of the crystal structure. In this work, epitaxial PZT thin films deposited on Si and YSZ substrate with appropriate buffer layers to investigate the relationship between crystal orientation and ferroelectricity. To control the crystal orientation of PZT thin films, we controlled the orientation of SrRuO3 (SRO) by introducing atomic buffer layers of MgO and TiO2 on (CeO2)/YSZ/Si and (CeO2)/YSZ substrate. Epitaxial SRO (001) orientation can grow on MgO(0.43nm)/CeO2/YSZ/Si. Depositing 0.25 nm of TiO2 layer on YSZ/Si substrate, we can obtain more than three times higher crystallinity of SRO (110) thin film than without TiO2 layer. As TiO2 thickness increases over 1nm, SRO become (111) orientation due to the mismatch with (200) oriented rutile structure of TiO2. We investigated the orientation dependency of PZT thin films deposited upon (001), (110), (111) oriented SRO/buffer/Si and SRO/buffer/YSZ substrates by chemical solution deposition processing. PZT thin films showed identical orientations to those of the bottom SRO electrode. The relationship between orientation and Pr values of Rhombohedral PZT is (111)R>(110)R>(010)R, which agrees with predicted values from crystallographic considerations. By the existence of a-domain which does not contribute to polarization of tetragonal PZT, the order of the Pr values is (111)>(101)>(001). Furthermore, the Pr values of the ferroelectrics on single crystal substrates have higher than that of ferroelectrics on Si substrate, because of the high thermal expansion coefficient of single crystal substrate makes larger c-domain ratio and higher Perpendicular/Parallel values.
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