100% polar-axis (c-axis)-oriented epitaxial Pb(Zr0.35Ti0.65)O3 (PZT) thin films were grown and their large remanent polarization (Pr) was directly measured. Perfectly c-axis-oriented epitaxial PZT thin films were obtained on (100)cSrRuO3//(100)SrTiO3 substrates when the deposition temperature increased to 540 °C together with a decrease in the film thickness down to 50 nm. Polarization–electric-field hysteresis loops were well saturated and had a square shape. The Pr of a 50 nm thick film saturated at 0.9 V, and its value was over 90 μC/cm2; almost independent of the measurement frequency within the range from 20 Hz to 1 kHz. This value was in good agreement with the estimated one from the a- and c-axes mixture-oriented epitaxial PZT film having the same composition taking into account the fact that only the c-axis-oriented domain contributed to the polarization. On the other hand, the coercive field value of a perfectly c-axis-oriented film was 140 kV/cm and almost the same as that of the mixture-oriented one having the same film thickness. These results show that PZT has a large Pr applicable for high-density ferroelectric random access memory.

(111)c- and (100)c-oriented SrRuO3 films were successfully grown on (111)Pt/TiO2/SiO2/(100)Si and (100)LaNiO3/(111)Pt/TiO2/SiO2/(100)Si substrates, respectively, by RF-magnetron sputtering method. On these (111)c- and (100)c-oriented SuRuO3 films, (111)- and (001)/(100)-oriented fiber-textured Pb(Zr0.35Ti0.65)O3 films with 2.0 µm in thickness were grown by metalorganic chemical vapor deposition (MOCVD). Well-saturated polarization-electric field (P-E) hysteresis loops were observed for both films. The remanent polarization (P r) values of (111)- and (001)/(100)-oriented 2.0 µm-thick Pb(Zr,Ti)O3 (PZT) films were almost the same at approximately 45 µC/cm2 at 200 kV/cm, while the coercive field (E c) values of these films were slight different at 61 kV/cm and 71 kV/cm, respectively. Moreover, the field-induced strains measured by scanning probe microscopy were also almost the same at approximately 0.2% up to 100 kV/cm. These data show the crystal orientation independence of the remanent polarization and field-induced strain of Pb(Zr0.35Ti0.65)O3 films.

We deposited an RuO2/Pb(Zr0.40Ti0.60)O3/RuO2 capacitor by metalorganic chemical vapor deposition. RuO2 and Pb(Zr0.40Ti0.60)O3 films were prepared at 350, 395, and 445 °C from respective Ru(C7H11)(C7H9)–O2 and Pb(C11H19O2)2–Zr(O⋅t-C4H9)4–Ti(O⋅i-C3H7)4–O2 systems. Good ferroelectricity was observed for PZT films deposited at 445 °C but not at 395 °C. However, we obtained ferroelectricity with a remanent polarization above 30 μC/cm2 by inserting a 10-nm-thick sputtered-Pt layer between the PZT and RuO2 bottom electrodes, which improved the crystallinity of PZT films even those deposited at 395 °C. This capacitor had hardly any fatigue after 1×1010 switching cycles. This demonstrates the possibility of preparing fatigue-free capacitor all deposited below 400 °C for high-density ferroelectric random-access memory applications.

We investigated the effect of a solvent on the metallorganic chemical vapor deposition ͑MOCVD͒ of Pb͑Zr, Ti͒O 3 ͑PZT͒ films by comparing conventional bubbling and sublimation delivery methods with one using liquid delivery where the source materials were dissolved in a solvent and vaporized in separate vaporizers. A Pb͑C 11 H 19 O 2 ) 2 -Zr͑O•t-C 4 H 9 ) 4 -Ti͑O•i-C 3 H 7 ) 4 -O 2 system was used as the source, while C 8 H 18 was used as the solvent together with C 4 H 8 O. The deposition rates of all constituent oxides decreased with the liquid-delivery method. Moreover, the process window to obtain stoichiometric PZT films ͓Pb/͑Pb ϩ Zr ϩ Ti) ϭ 0.5], irrespective of the supply rate of the Pb source, was diminished with the liquid delivery method, suggesting the contribution of the solvent on the deposition mechanism of PZT film. These phenomena were observed not only with C 8 H 18 but also when C 4 H 8 O was used as a solvent. Pb͑Zr, Ti͒O 3 ͓PZT͔ is a solid solution of PbTiO 3 and PbZrO 3 and has a perovskite structure. PZT films with thicknesses of less than 300 nm deposited on Si substrates have been used for nonvolatile memory ͑FeRAM, ferroelectric random access memory͒ applications. 1 Moreover, PZT thick films above 2 m in thickness have been investigated for use as optical waveguides 2 and in microelectromechanical system ͑MEMS͒ applications. 3 High-quality PZT films are essential in these applications and metallorganic chemical vapor deposition ͑MOCVD͒ is recognized as one of the most promising methods of deposition. This is because MOCVD-PZT films produce exceptional film quality together with good step conformability, a high deposition rate, and large areas of uniform film quality. 4 Two types of methods have been employed in PZT-MOCVD to obtain source gases that included Pb, Zr, and Ti elements. The first is the conventional bubbling and sublimation method where the vapor of the source gases, including the metal elements, is obtained by bubbling through an inert gas, or by sublimation where the vaporized elements are carried by the inert gas. [5][6][7] In this method of supply, only the carrier gas, such as Ar and N 2 , is supplied to the reaction chamber together with the source gases including the metal elements and the oxidant gas, such as O 2 . The other method, called the liquid-delivery source supply, is widely used to deposit PZT films by MOCVD,4,[8][9][10][11] where the source materials are dissolved into the solvent and vaporized at the vaporizer. The advantage of this is the increased deposition rate of films due to the increased rate of supply of the source gases to the reactor irrespective of their vapor pressure. Moreover, it is easy to precisely control the rate of supply of the source materials by measuring the solution, including the source materials, with a liquid mass-flow controller. In addition, the reliability of the precursor delivery is expected by alleviating the direct heating of the sources which usually degrades the source and diminishes the source vapor pressure with time. Ho...

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