Recovery Characteristics of Hydrogen-Damaged  ( Pb , La )  ( Zr , Ti )  O ₃ Capacitors with Pt and IrO₂ Top Electrodes

Abstract

The effect of hydrogen on ferroelectric properties was investigated for ͑Pb, La͒͑Zr, Ti͒O 3 ͑PLZT͒ films with Pt and IrO 2 top electrodes. The P-E hysteresis loop and fatigue properties of the Pt/PLZT/Pt capacitor are completely recovered by recovery anneal at 700°C in O 2 ambient after a hydrogen-forming gas anneal. On the other hand, IrO 2 /PLZT/Pt capacitor after recovery anneal does not show a complete recovery for ferroelectric properties. The IrO 2 top electrode in the IrO 2 /PLZT/Pt capacitor is completely reduced to Ir metal in 4% H 2 at 300°C and then change to the IrO 2 /Ir complex phase after recovery anneal at 700°C in O 2 ambient. The ferroelectric properties of PLZT capacitors greatly depend on the residual hydrogen near the film/top electrode interface after recovery anneal.The choice of electrode materials used in conjunction with Pbbased ferroelectric thin films strongly influences the structural and electrical properties. Recently, Ir and IrO 2 have attracted attention as electrode materials for Pb͑Zr, Ti͒O 3 ͑PZT͒ and ͑Pb, La͒͑Zr, Ti͒O 3 ͑PLZT͒ thin film capacitors since they showed ferroelectric properties with higher quality than Pt/PZT/Pt capacitors. In addition, PZT capacitors with hybrid bottom electrode structures, such as Pt/IrO 2 and Ir/IrO 2 have been reported. 1-4 One of the processing issues that is receiving considerable attention in the integration of ferroelectric capacitors on Si is a low temperature forming gas anneal. Unfortunately, both PZT and SrBi 2 Ta 2 O 9 ͑SBT͒ ferroelectric thin film capacitors with Pt top electrodes lose their polarization hysteresis characteristics as a result of such an anneal. 5 It has been reported that dissociative adsorption of the hydrogen atoms or protons by the catalytic activity of Pt play critical roles in degrading the ferroelectric properties 6-8 and leakage current densities 9 of SBT and PZT thin films. On the other hand, the use of IrO 2 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 IrO 2 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 Ramesh et al. reported that even a bare La 0.5 Sr 0.5 CoO 3 ͑LSCO͒ top electrode can prevent the complete loss of ferroelectricity during forming gas treatment. 11 Therefore, in this study, the impact of Pt and IrO 2 top electrodes on capacitor properties annealed in H 2 and recovered in O 2 ambients is reported, with particular emphasis on P-E hysteresis and fatigue properties. The Pt͑top͒/PLZT/Pt and IrO 2 ͑top͒/PLZT/Pt capacitors are annealed in H 2 at 300°C and recovered at 700°C in O 2 ambients. ExperimentalPLZT (Zr:Ti ratio ϭ 30:70) thin films with 3% La dopant concentration were prepared using a chemical solution deposition ͑CSD͒ method. Approximately 12% excess lead was added to the precursor solution to compensate for the loss of lead oxide during the final annealing process. Films were ...

Structural Stability of Hydrogen Forming Gas Annealed ( Ba , Sr ) RuO3 Oxide Electrodes

“…However, an as-grown IrO 2 top electrode was easily reduced to Ir metal by hydrogen annealing at 300°C which simulates the process conditions for interlayer-dielectric deposition. 12 Aggarwal et al reported that even a bare La 0.5 Sr 0.5 CoO 3 ͑LSCO͒ top electrode can prevent the complete loss of ferroelectricity during forming gas treatment. 13 The conducting oxide, ͑Ba,Sr͒RuO 3 ͑BSR͒, 14,15 which has many advantages for BST due to their similarity in crystal structure and chemical composition, was evaluated as an electrode for high dielectric capacitors.…”