Property Improvement of PLZT Capacitor Using CaRuO 3 Top Electrode
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Property Improvement of PLZT Capacitor Using CaRuO3 Top Electrode HIROSHI FUNAKUBO, NORIYUKI HIGASHI, AND NORIKAZU OKUDA
Department of Innovative and Engineered Materials, Interdisciplinary Graduate school of Science and Engineering, Tokyo Institute of Technology G1-405, 4259, Nagatsuta-cho, Midori-ku Yokohama, 226-8502, Japan ABSTRACT SrRuO3 and CaRuO3 films prepared by MOCVD were compared not only in term of their own properties but for their characteristics as the top electrodes of (Pb, La)(Zr, Ti)O3[PLZT] capacitor, especially for H2 degradation. Resistivity of CaRuO3 and SrRuO3 films increased after heat treatment in H2-containing atmosphere, but was recovered by a heat treatment at 600 oC under O2 atmosphere. When SrRuO3 and CaRuO3 films deposited at 600 o C were used as top electrodes, the remanent polarization(Pr) value of SrRuO3/PLZT/Pt and CaRuO3/PLZT/Pt capacitors were almost the same as the values for capacitors with a Pt top electrode. After a heat treatment in a 3 % H2 atmosphere at 200 oC, followed by one in O2 atmosphere at 450 oC, Pr value was perfectly recovered for both of SrRuO3 and CaRuO3 films. The leakage current become the smallest when using 50 nm-thick CaRuO3 film as a top electrode. Moreover, no degradation was observed for fatigue test up to 1010 cycles when MOCVD-CaRuO3 films were used as top electrodes. These data show that MOCVD-CaRuO3 film with thin thickness is a useful top electrode for PLZT capacitor.
INTRODUCTION Pb(Zr,Ti)O3[PZT] film has been widely investigated for an application to nonvolatile ferroelectric random access memory (NVFeRAM). Strongly dependence of ferroelectric property of PZT film on the electrode material is widely known. Especially, oxide electrodes are known to improve the H2 and fatigue degradations. Among them, SrRuO3 and CaRuO3 are one of the most promising materials because it has the same perovskite structure as PZT and high conductivity. For high density NVFeRAM, high step coverage is essential for not only PZT but also electrode. Therefore, MOCVD preparation of SrRuO3 and CaRuO3 films is the most important preparation technique because of its high step coverage. One big problem with a SrRuO3 electrode material is the large current leakage relative to Pt electrode. J.Cross et al.[1] reported the formation of SrPbO3 at the grain boundary of PZT film by the diffusion of Sr element from SrRuO3 to PZT and increased the leakage of PZT film. On the contrary, Yamamoto et al.[2] reported that the resistivity of CaPbO3 is more than three order higher than that of SrPbO3. Therefore, CaRuO3 top electrode is expect to lowering the leakage character of PZT capacitor because of the low conductivity of CaRuO3 even if this compound formed at the grain boundaries. We have succeed for the first time in preparing SrRuO3 and CaRuO3 film by MOCVD[3-7]. In the previous study, we investigated the composition effect of SrRuO3 top electrode on the ferroelectric property of SrRuO3/(Pb, La)(Zr, Ti)O3[PLZT] /Pt capacitor[7]. In the present study, we compared MOCVD-SrRuO3 and Ca
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