Preparation of SrRuO 3 and CaRuO 3 Films by Mocvd and Its Application to Electrodes for Ferroelectric Thin Films
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vapor
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INTRODUCTION Ferroelectric materials based on the perovskite structure, such as (Pb,La)(Zr,Ti)0 3 and SrBi 2Ta 2O9 , have been widely investigated for application to ferroelectric random access memories (FERAM). Properties of FERAM are widely known to strongly depend on the electrode materials.
Oxide electrodes such as SrRuO,, IrO2 and LaSrCoO3 , are known to
decrease fatigue by the switching cycle and H2 degradation. SrRuO 3 has low resistivity with ptype conduction and has small lattice mismatch with the various kinds of ferroelectric materials. Preparation of SrRuO 3 films has been reported by sputtering [1-31 and laser ablation [59J. However, the preparation by A metalorganic chemical vapor deposition (MOCVD) has been hardly reported [10-121. In the present study, we report the epitaxial N 2 gas growth of SrRuO 3 films by MOCVD together with CaRuO 3 films. EXPERIMENTAL SrRuO3 and CaRuO. thin films were successfully prepared by MOCVD. This apparatus had a cold-wall vertical type reactor [12]. Sr(C, H19 0 2),(C 8H,,N5 ), Ru(C,,H 1 90 2 )3
-
02
and
Sr(CIH, 902)2(CH,3N5), - Ru[(C 5H 4)(CH 5)]2 - 02 systems, and Ca(C,,H,90_)4(C 8 H2N.), Ru(C,,H, 9O2)3 01 and Ca(C ,IH,90 2),(C 8H2N 5 ) -
CgH 23N5
Sr(C,,H 1 90 2) 2(C8 H23N5 ). Ca(Ci1 H1 9O2)2(CiH 23N5)x
Container Figure 1 Schematic diagram of the delivery system of Sr and Ca vapors.
79 Mat. Res. Soc. Symp. Proc. Vol. 596 © 2000 Materials Research Society
Ru[(C5H 4)(C2 Hs)12 - 02 systems were used as source materials for SrRuO3 and CaRuO3 thin Path line (1) Path line (2) film preparation, respectively[ 11, 13]. 427.4 Sr and Ca source vapors were in Fig.2 inFig.2 obtained by bubbling N2 gas including . 27.2 C8 I,3N 5 vapor through liquid sources. Sr and Ca sources were liquid at the operating • 27 temperature, so that those vapors were easily 0 prepared by bubbling method. However, 026.8 when these sources are kept at high temperature in the containers, the CH2 N, a 26.6 10 20 30 40 50 60 70 u0 ligand is easily dissociated and C8H•N 5 vapor Run time / min having high vapor pressure was carried out from the container of Sr and Ca sources. As Figure 2 Change of the pressure of gauge "A" in Fig. 1 with the run time. a result, the fraction of Sr(C,,H1 90 2)2 and Ca (C1 Hg 0O2)2 increased in the Sr and Ca containers, respectively. These are solid at operating temperature, so that the bubbling operation becomes unstable. To improve this problem we added tetraethylenepentamine, C8H2,N,, vapor into the N 2 carrier gas. Fig.1 shows the schematic diagram of the delivery systems of Sr and Ca sources. CH42N 5 vapor was generated by bubbling liquid C8 H-,N5 arrived at the Sr and Ca source bottles. The vapors of Ru(C,,H1 90,) 3 and Ru[(C5 H4 )(C2 H,)] 2 were generated by passing N2 gas over a heated solid source and bubbling by N2 gas, respectively. (100), (110) and (11l)SrTiO3, (100)LaAIO 3 and (100)MgO single crystals were used as substrates. The theoretical input gas concentration was defined as R[source][141. Composition and the deposition rates of t
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