Effect of hydrogen on true leakage current characteristics of (Pb,La)(Zr,Ti)O 3 thin-film capacitors with Pt- or Ir-base
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Dwi Wicaksana and Dong-Joo Kim Department of Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina 27695
Seung-Hyun Kim Inostek Inc., 356-1 Gasan-Dong, Keumcheon-Gu, Seoul 153-023, Korea
A.I. Kingon Department of Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina 27695 (Received 24 August 2000; accepted 1 February 2001)
The degradation behavior of polarization and leakage current characteristics of sol-gel-derived (Pb,La)(Zr,Ti)O3 (PLZT) thin films, with Pt, Ir, and IrO2 top electrodes, by annealing under a 4% H2/96% N2 atmosphere were investigated. The leakage current behaviors of Pt/PLZT/Pt and IrO2/PLZT/Pt capacitors annealed at 300 °C for 20 min in 4% H2 were well consistent with the space-charge-influenced injection model proposed. However, IrO2/PLZT/Pt capacitors recovered at 700 °C for 10 min in Ar ambient after hydrogen anneal were not consistent with the proposed model because a conducting phase of IrPb was formed between the top electrode and PLZT during the recovery anneal at 700 °C in Ar ambient and modified the Schottky barrier height. The true leakage current behavior of IrO2/PLZT/Pt capacitors recovered after hydrogen forming are similar to those of Ir/PLZT/Pt capacitors without the hydrogen-forming gas anneal. The P–E loops of Pt/PLZT/Pt and Ir/PLZT/Pt capacitors showed good recovery through recovery anneal after H2 treatment. However, IrO2/PLZT/Pt capacitors depended on the recovery anneal atmosphere (Ar or O2).
I. INTRODUCTION
The choice of electrode materials used in conjunction with Pb-based ferroelectric thin films strongly influences the structural and electrical properties. Recently, Ir and IrO2 have attracted attention as electrode materials for PZT and (Pb,La)(Zr,Ti)O3 (PLZT) thin-film capacitors since they showed higher quality ferroelectric properties than Pt/PZT/Pt capacitors. In addition, PZT capacitors with hybrid bottom electrode structures, such as Pt/IrO2 and Ir/IrO2, have been reported.1–4 However, problems still remain concerning integration that may occur during the etching process of the ferroelectric capacitor and electrode materials.5 Degradation of Pr by the incorporation of hydrogen in the film by passivation or intermetallic dielectric (IMD) processing is still a problem that should be overcome for successful integration of ferroelectric memory devices. It has been reported that J. Mater. Res., Vol. 16, No. 4, Apr 2001
dissociative adsorption of the hydrogen atoms or protons by the catalytic activity of Pt play critical roles in degrading the ferroelectric properties6–8 and leakage current densities9 of SBT and PZT thin films. On the other hand, the use of IrO2 as the top electrode in PZT capacitors offers an opportunity to suppress the degradation because it does not have a catalytic effect. However, an as-grown IrO2 top electrode was easily reduced to Ir metal by a hydrogen annealing at 300 °C which simulates a process condition of interlayer-dielectric deposition.10 Therefore, in this st
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