Preparation and Characterization of Pb(Zr,Ti)O₃ Films Deposited on Pt/RuO₂ Hybrid Electrode for Ferroelectric Random Access Memory Devices

Polycrystalline Pb(Zr,Ti)O₃ (PZT) films were fabricated at a low temperature of 450°C by the electron cyclotron resonance plasma-enhanced chemical vapor deposition (ECR PECVD) method. Stoichiometric PZT films with the pure perovskite phase could be obtained over a wider range of deposition conditions on Pt/RuO₂ hybrid electrodes than on RuO₂ electrodes. PZT capacitors fabricated on Pt/RuO₂ hybrid electrodes showed low leakage current and superior polarization characteristics compared with those on RuO₂ electrodes. PZT capacitors fabricated on Pt/RuO₂ were not as fatigue-free as those on RuO₂ but had higher resistance to fatigue than those on Pt. The introduction of a PbTiO₃ buffer layer prior to PZT film deposition on Pt/RuO₂ improved the fatigue characteristics by suppressing the formation of nonstoichiometric interfacial layers. Good leakage current property (J: 5.8 ×10^-7 A/cm² at 200 kV/cm) and fatigue characteristic (P^* - P^∧: 9% drop after 4 ×10⁹ fatigue cycles) could be obtained for the 110-nm-thick PZT film using Pt/RuO₂ hybrid top and bottom electrodes. This electrode structure is thought to be promising for use as a capacitor of high-density ferroelectric random access memory (FRAM) devices. The fatigue model that can explain the fatigue characteristics of PECVD-PZT capacitors with various hybrid electrode configurations is also suggested.