The composition dependence and orientation anisotropy of the dielectric and ferroelectric properties of epitaxial Pb(ZrxTi1−x)O3 (PZT) thin films grown using metalorganic chemical vapor deposition were investigated. {100}-, {110}-, and {111}-oriented PZT films were ascertained to have been grown on (100)c, (110)c, and (111)cSrRuO3//SrTiO3 substrates, respectively. The relative dielectric constant reached a maximum near x=0.5, around the morphotropic phase boundary (MPB) composition, irrespective of film orientation, with the {111}-oriented film showing the largest value. Well-saturated hysteresis loops were observed for all films, and abrupt saturation of the remanent polarization (Pr) and coercive field (Ec) values were observed when the value of x was small, irrespective of film orientation. The Ec value reached a minimum around the composition for {110}- and {111}-oriented films but not for {100}-oriented ones. The saturated polarization (Psat) and Pr values for the {111}-oriented film reached a maximum around the MPB composition, while attaining a minimum for films with other orientations. The ratio of Pr to Psat decreased near the MPB composition regardless of film orientation. These results suggest that the electrical properties of epitaxial PZT thin films strongly depend on both of the composition and orientation of the films.

Pb(Zr, Ti)O3 (PZT) thin films with Zr/(Zr+Ti) of 0.42 were prepared on (111)Pt/Ti/SiO2/Si substrates at 620°C by metalorganic chemical vapor deposition (MOCVD). We attempted the pulse introduction of a mixture of source gases into the reaction chamber and succeeded in simultaneous improvements of the crystallinity, surface roughness and electrical properties of the PZT film by this preparation method. The (111)-orientation increased and the surface roughness decreased. Moreover, the leakage decreased and well-saturated symmetrical polarization-electric field (P-E) hysteresis loop were obtained. Remanent polarization (P r) and the coercive field (E c) values of this pulse-MOCVD film were 44 µC/cm2 and 85 kV/cm, respectively.

Epitaxial Pb(ZrxTi1−x)O3 films with (001) and (100), (101) and (110), and (111) orientations were grown on (100)SrRuO3//(100)SrTiO3, (110)SrRuO3//(110)SrTiO3, and (111)SrRuO3//(111)SrTiO3 substrates, respectively. The two composition films with Zr/(Zr+Ti) ratios of 0.42 and 0.68 were prepared with the Pb/(Pb+Zr+Ti) ratio of 0.5. Well saturated and good square shape hysteresis loops with large remanent polarization (Pr) above 40 μC/cm2 were observed for all films. The Pr increased in the following order: (101), (111), and (001) orientations for the film with the Zr/(Zr+Ti) ratio of 0.42 and (100), (110), and (111) orientations for the Zr/(Zr+Ti) ratio of 0.68. On the other hand, the Ec value mainly depended on the Zr/(Zr+Ti) ratio and not on the orientation of the film; the Ec value of the film with a Zr/(Zr+Ti) ratio of 0.42 was larger than that of 0.68. The saturation behavior did not strongly depend on the orientation, especially for the films with the Zr/(Zr+Ti) ratio of 0.42. The frequency dependence of the dielectric constant was small regardless of the orientation of the films with a Zr/(Zr+Ti) ratio of 0.42. On the other hand, for 0.68, it was also small for the (100) and (110) orientations, but increased by about 15% from 103 to 106 Hz for the (111) orientation due to the relative large leakage. The (101)-oriented film with the Zr/(Zr+Ti) ratio of 0.42 and the (100)- and (111)-oriented films with 0.68 did not show deterioration up to 1010 switching cycles.

We prepared Pb(Zr x , Ti1-x )O3 [PZT] thin films on (111)Pt/Ti/SiO2/Si substrates at 620°C by metalorganic chemical vapor deposition (MOCVD). PZT [Zr/(Zr+Ti)=0.68] thin films of different thicknesses prepared by the conventional continuous source gas introduction MOCVD (continuous-MOCVD) and by pulsed gas introduction MOCVD (pulse-MOCVD) were compared to investigate the growth mechanism of these films. Stoichiometric PZT films were obtained for a wider range of Pb source input gas flow rates under fixed Zr and Ti sources for pulse-MOCVD compared with that for continuous-MOCVD. Highly (111)-oriented films were obtained for pulse-MOCVD regardless of their thickness, while the (111)-orientation decreased with film thickness for continuous-MOCVD. This suggests that the orientation homogeneity along the film thickness is higher for pulse-MOCVD films than for continuous-MOCVD films. The surface roughness of the pulse-MOCVD films was smaller than that of the continuous-MOCVD films and this result corresponds to the decrease of the leakage current density of the film. Well-saturated hysteresis loops with good square shapes were obtained, and the remanent polarization (P r) and the coercive field (E c) values of 100-nm-thick films prepared by pulse-MOCVD were 37 µC/cm2 and 82 kV/cm, respectively.

We prepared Pb(Zr,Ti)O 3 [PZT] thin films on (111)Pt/Ti/SiO 2 /Si substrates at 395 to 580 • C by metalorganic chemical vapor deposition (MOCVD). PZT thin films with Zr/(Zr + Ti) = 0.62 prepared by conventional continuous source gas introduction (continuous-MOCVD) and pulse introduction (pulse-MOCVD) were compared. Film with higher crystallinity and smoother surfaces were obtained by pulse-MOCVD compared with continuous-MOCVD. Moreover, the leakage current density of the film decreased and ferroelectricity increased with pulse-MOCVD. Ferroelectricity decreased with decreasing the deposition temperature, but the remanent polarization (Pr) value was 22.5 µC/cm 2 for the film with a 5 nm-thick PbTiO 3 buffer layer deposited at 395 • C by pulse-MOCVD, while ferroelectricity was not obtained for the film deposited by continuous-MOCVD at the same deposition temperature.

Epitaxial-grade polycrystalline Pb(Zr,Ti)O3 (PZT) films were deposited at 415 °C by source- gas-pulsed-introduced metalorganic chemical vapor deposition. The polycrystalline PZT film with Zr/(Zr+Ti)=0.35 which was prepared on (111)Pt/Ti/SiO2/Si substrate showed highly (100)- and (001)-preferred orientations. Well-saturated ferroelectricity with a remanent polarization (Pr) and coercive field of 41.4 μC/cm2 and 78.5 kV/cm, respectively, was obtained. This Pr value is almost the same as that of epitaxially grown films at 580 °C with the same composition and orientations taking into account of the volume fraction of (100) and (001) orientations.

(100)- and/or (001)-preferred-oriented and (111)-preferred-oriented polycrystalline Pb(Zr,Ti)O3 (PZT) films with Zr/(Zr+Ti) ratios of 0.35 and 0.62, corresponding to tetragonal and rhombohedral PZT, respectively, were compared with that of epitaxially grown ones with the same composition and similar orientation from the viewpoint of crystal structure and ferroelectricity. (100)- and/or (001)-preferred-oriented and (111)-preferred-oriented polycrystalline PZT films were deposited on (111) Pt/Ti/SiO2/Si substrates at 580 and 415 °C, respectively, by pulsed-metalorganic chemical vapor deposition (pulsed MOCVD). On the other hand, epitaxially grown PZT films with the same composition and similar orientation were deposited on SrRuO3‖SrTiO3 substrates at 580 °C also by pulsed MOCVD. The difference in ferroelectricity between the polycrystalline and epitaxial films was found to be mainly due to the film composition rather than to the film orientation. Polycrystalline tetragonal PZT films deposited by pulsed MOCVD showed almost the same remanent and saturation polarizations (Pr and Ps) as the epitaxially grown ones corrected for film orientation even though the films were deposited at a low temperature of 415 °C. Moreover, the coercive field (Ec) values were almost the same. On the other hand, the polycrystalline rhombohedral films showed almost the same Ps value as the epitaxially grown ones, but their Pr value was smaller than that of the epitaxial ones. Moreover, the Ec value of the polycrystalline films was smaller than that of epitaxially grown ones. The difference in ferroelectricity between tetragonal and rhombohedral PZT is strongly related to the film composition’s dependence on the domain wall stability when the electric field is released.

The crystal structure and the electrical properties were systematically compared for tetragonal and rhombohedral Pb(Zr,Ti)O3 [PZT] films prepared at various deposition temperatures from 580 °C to 395 °C on (111)Pt/Ti/SiO2/Si substrates by pulsed-metalorganic chemical vapor deposition (pulsed MOCVD). Film orientation changed from (111) to (100) and/or (001) with the decrease in the deposition temperature, but the well-crystallized PZT phase was obtained down to 395 °C. The lattice parameter was almost constant with decreasing deposition temperature, suggesting that the Zr and Ti elements in the films were incorporated into the PZT phase. When the deposition temperature decreased, the leakage current density decreased together with a decrease in surface roughness, especially for tetragonal PZT films. Remanent polarization (Pr) continuously decreased with decreasing deposition temperature down to 395 °C, but was above 20 μC/cm2 even at 395 °C. Specifically, the tetragonal film shows good squareness down to 415 °C. These results show that PZT films with low leakage current density and a large Pr were obtained even at 395 °C by pulsed MOCVD irrespective of the film composition.