Bottom Electrode Effects in Controlling Orientation of Lead Zirconate Titanate Films Deposited by Chemical Solution Depo
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IBM, T.J. Watson Research Center, P.O. Box 218, Yorktown Heights, NY 10598 ABSTRACT The microstructure and electrical properties of lead zirconate titanate Pb(Zr,Ti)0 3 (PZT) films prepared by chemical solution deposition (CSD) with and without lead titanate (PT) seed layers were examined as a function of Ir/lr oxide electrode type. The novel PZT CSD solution was prepared from a mixture of zirconium and titanium butoxyethoxides and lead ethylhexanoate dissolved in butoxyethanol. The use of excess-lead (PbhxTi) and stoichiometric PT seed layers was found to promote PZT(l 11) orientation on Ir but not on Ir oxide. Ir substrate thickness was observed to influence orientation of PZT deposited on stoichiometric PT with greater PZT(1 11) texturing on thinner Ir(l 11) substrates. PZT with greater PZT(1 11) texturing tended to have greater remanent polarization (2Pr, gtC/cm2 ). PZT deposited on stoichiometric PT seed layers on Ir(l 11) was of higher film quality than PZT deposited on PbxsTi seed layers on Ir(I 11). The PZT films deposited on stoichiometric PT on Ir(1 11) had enhanced PZT(1 11) orientation, a reduced pyrochlore content, and tended to saturate at lower coercive fields, have higher remanent polarization, squarer hysteresis loops with less tilt and greater fatigue endurance. The use of iridium oxide top electrode was demonstrated to significantly improve fatigue endurance compared to use of an iridium top electrode. INTRODUCTION Because of its high remanent polarization and relatively low processing temperature, PZT is a
prime candidate for use as ferroelectric in a nonvolatile random access memory (NVRAM). However, because of the poor fatigue endurance
of Pt/PZT/Pt ferroelectric
capacitors,
development of an alternative capacitor structure with alternate electrode materials, such as iridium/iridium oxide, is necessary [1]. Proper control of PZT orientation through electrode selection and use of seed layers to control PZT nucleation can lead to enhanced 2Pr and improved fatigue endurance. Lead titanate seed layers have been demonstrated to influence the orientation of PZT deposited on Pt by chemical vapor deposition [2], sputtering [3], and chemical solution deposition (CSD) [4,5]. In this study we looked at the influence of lead titanate seed layers on PZT deposited by CSD on iridium and iridium oxide electrodes. EXPERIMENTAL Chemical Solution Deposition of PZT The CSD solutions were prepared from a mixture of zirconium and titanium butoxyethoxides
and lead ethylhexanoate dissolved in butoxyethanol [6]. The films were deposited by spin casting on Ir and Ir oxide bottom electrodes sputter deposited at 250 'C on SiO 2 /Si substrates. Before spinning PZT, two parts PZT CSD solution (0.6M, Pbl lZr.4Ti.6, exceptions noted in paper), were 253 Mat. Res. Soc. Symp. Proc. Vol. 596 © 2000 Materials Research Society
diluted with one part butoxyethanol. The spinning solution was loaded into a syringe and 0.45 and 0.1 .tm syringe filters were attached. The solution was syringed on the substrate until completely wet
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