Dominant Factor of Squareness in P-E Hsyteresis Loops of MOCVD-PZT Films
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0902-T04-04.1
DOMINANT FACTOR OF SQUARENESS IN P-E HSYTERESIS LOOPS OF MOCVD-PZT FILMS
. Hiroshi Funakubo, Akihiro Sumi, Hitoshi Morioka, Shoji Okamoto and Shintaro Yokoyama Department of Innovative and Engineered Materials, Tokyo Institute of Technology J2-43, 4259 Nagatsuta-cho, Midori-ku, Yokohama 226-8502, Japan
ABSTRACT The effects of the film thickness and temperature on the P-E properties for epitaxially grown rhombohedral Pb(Zr,Ti)O3 film were systematically investigated. (100)-oriented rhombohedral Pb(Zr0.65Ti0.35)O3 films with 50 - 3200 nm in thickness were grown on (100)cSrRuO3//(100)SrTiO3 substrates by metalorganic chemical vapor deposition (MOCVD). The ratio of the remanent polarization (Pr) to saturation polarization (Psat), the Pr/Psat ratio, at room temperature decreased with decreasing the film thickness at room temperature. Moreover, the Pr/Psat ratio at 10 K of 180-nm-thick films was smaller than that of 3200-nm-thick film and dropped at lower temperature with increasing the film thickness. These results suggest that the small Pr/Psat ratio of thin film at room temperature is originated to both of small Pr/Psat ratio even at 10K and their drop starting at lower temperature when the temperature increased.
INTRODUCTION Present ferroelectric random access memory (FeRAM) mainly used tetragonal Pb(Zr,Ti)O3 film due to its large remanent polarization (Pr) and its good squarness, designated as the ratio of the Pr to the saturation polarization (Psat), the Pr/Psat ratio, in polarization-electric filed (P-E) characteristics [1]. For high-density FeRAM applications, low voltage operation by the decrease of the film thickness is highly required [2,3]. Rhombohedral Pb(Zr,Ti)O3 film have various advantages for these requirements due to the lower coercive field (Ec) together with the relative low leakage current density [4]. However, the serious drawback of rhombohedral Pb(Zr,Ti)O3 films is the worse squarness in P-E hyteresis loops. This worse squarness is known to be improved by increasing the film thickness [5] and for making epitaxial films [6]. However, the detailed analysis of the squareness of rhombohedral Pb(Zr,Ti)O3 has been hardly reported due to the lack of the practical application, such as FeRAM. In the present study, we tried to grow epitaxial rhombohedral Pb(Zr0.65Ti0.365)O3 films with various film thicknesses by metalorganic chemical vapor deposition (MOCVD) and systematically investigated the change of the squereness in P-E hysteresis loops at room temperature together with the temperature dependency of the electrical properties. Based on these results, we discuss the origin of the decrease of the Pr/Psat ratio with decreasing film thickness for epitaxial rhombohedral Pb(Zr,Ti)O3 films.
0902-T04-04.2
EXPERIMENTAL Pb(Zr0.65Ti0.35)O3 [PZT] films were grown at 540 °C by pulsed-MOCVD using Pb(C11H19O2)2, Zr(O·t-C4H9)4, Ti(O·i-C3H7)4 and O2 gas as the source materials. In pulsed-MOCVD, a mixture of the source gases was introduced in a pulse sequence for 10 seconds with a 5 seconds interval,
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