Effects of IrO 2 /Pt Hybrid Electrodes on the Crystallization and Ferroelectric Performances of Sol-gel-derived Pb(Zr,Ti
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Cheol Song Hwangb) School of Materials Science and Engineering, Seoul National University, Seoul 151-743, Korea (Received 8 March 2001; accepted 18 April 2002)
The effects of IrO2/Pt layered hybrid bottom and/or top electrode structures on the leakage current density versus voltage (J–V), polarization versus voltage (P–V), ferroelectric imprint, and fatigue properties of chemical-solution-derived Pb(ZrxTi1-x)O3 (PZT, Zr/Ti ⳱ 35/65) thin films were investigated. The best P–V and J–V performances were obtained from a capacitor with nonhybrid electrodes (Pt/PZT/Pt capacitor). However, the poor fatigue performance of the capacitor required the adoption of hybrid electrode structures. A thin IrO2 layer, as thin as 6 nm, which was inserted between top Pt electrode and PZT layer was sufficient for improving the fatigue performance without any degradation of the other ferroelectric properties. However, the same layer adopted on the bottom Pt electrode was not effective in improving the fatigue performance with degradation in P–V and J–V properties. This was ascribed to IrO2 layer dissolution into the PZT layer during the crystallization annealing of the PZT thin film. A thicker IrO2 layer resulted in more serious degradation.
I. INTRODUCTION
Although a number of experimental and theoretical contributions have been made concerning issues of polarization fatigue, leakage current, imprint, and degradation by forming gas annealing of ferroelectric thin-film devices,1–3 no clear consensus has emerged regarding their origins or potential solutions. The purpose of this research was to investigate aspects of these degradations which were observed in recent experimental results and to define and suggest various phenomenological explanations and possible solutions. In an approach to address these issues, an extensive series of experiments on the effects of IrO2/Pt layered hybrid bottom and/or top electrode heterostructures on those degradations were performed. It is well known that the choice of electrode materials used for the lead zirconate titanate (PZT) film has an impact on ferroelectric film quality and device performance. In general, the use of conductive oxide electrodes such as RuO2, SrRuO3, IrO2, or La1-xSrxCoO3 helps to improve the resistance to polarization fatigue for
a) b)
e-mail: [email protected] e-mail: [email protected] J. Mater. Res., Vol. 17, No. 7, Jul 2002
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PZT.4 –7 However, these electrodes have generally resulted in larger leakage currents and greater susceptibility to dielectric breakdown than noble metal electrodes. In our early paper,2 it was demonstrated that when using such a hybrid electrode system, the film properties are influenced by the thickness/partial coverage of the oxide electrode layers. Therefore, optimization research on the thickness of the IrO2 electrode layer, which allows excellent fatigue and minimal leakage current values, was performed and the results are presented here. II. EXPERIMENTAL PROCEDURE
The choice of starti
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