SIMPLE ELECTRODE-BARRIER STRUCTURE USING Ir FOR INTEGRATION OF PZT-BASED HIGH-DENSITY NONVOLATILE MEMORIES

摘要

We have investigated the electrode-barrier properties of Ir for PZT-based nonvolatile memories. Ir layer was rf-sputtered onto a poly-Si coated Si wafer. PZT thin films were deposited on Ir/poly-Si/SiO_2/Si by means of sol-gel spin coating. Highly c-axis oriented perovskite PZT thin films were obtained, which might be due to the interface-controlled growth. We found that Ir in itself acted as an oxygen barrier, which was confirmed from the measurement of P-E hysteresis loops with the electrical contact between top-electrode and bottom-poly-Si. Remanent polarization and coercive field of IrO_2/PZT/Ir/poly-Si capacitor were 20 μC/cm~2 and 30 kV/cm, respectively and the capacitor showed negligible polarization fatigue up to 10~(11) switching repetitions. However, the leakage current density at the field of larger than 80 kV/cm was high, which was believed to be related to the unknown phase in PZT caused by the reaction of PbO with bottom-Ir. Such high leakage current behavior could be successively improved by the insertion of vacuum-annealed IrO_x buffer layer between PZT/Ir. The electrical properties of IrO_2/PZT/annealed-IrO_2/Ir/poly-Si capacitors are also discussed.