Improvement by surface modification of Ir electrode-barrier for Pb(Zr,Ti)O3-based high-density nonvolatile ferroelectric memories

We have tried to improve the Ir electrode-barrier for Pb(Zr,Ti)O3 (PZT)-based non-volatile ferroelectric memories (NvFRAMs). Ir layer of 150-nm thickness was deposited on poly-Si substrates by means of the rf-sputtering method. Although Ir in itself acted as an oxygen barrier and a IrO2/PZT/Ir/poly-Si capacitor showed device-worth ferroelectric properties, whose remanent polarization, coercive field, fatigue loss after 1011 switching repetitions were 25 μC/cm2, 48 kV/cm and 12%, respectively, the high leakage current at the field of larger than 80 kV/cm was found, which might be caused by the reaction of PbO with bottom-Ir. Such poor leakage current behaviors could be successively improved by the insertion of vacuum-annealed thin IrO2 (or IrOx) layer of 20-nm thickness between PZT/Ir. We suggest that such improvements in the microstructures and the ferroelectric properties including the leakage current behaviors are attributed to the reduction of the reaction between PbO and Ir in bottom electrode by inserting the IrOx interlayer.