Effect of Surface Morphology of NiCr-Bottom Electrode on Preparation of Ferroelectric PZT Thin Film Capacitor

We have studied the optimum conditions of the deposition of NiCr-bottom electrode for preparing the ferroelectric PZT(50/50) thin film capacitor. The NiCr(80/20) layer of about 300nm in thickness was deposited on bare Si(111) wafer by rf magnetron sputtering. The surface morphology and crystallinity were investigated by using Atomic force microscope (AFM) and X-ray diffractormeter (XRD). It is found that the size and crystallinity of grains of NiCr or Ni-silicide depend mainly on the rf power. The PZT(50/50) thin films were prepared on NiCr/Si substates by spin-casting of PZT coating sol and then annealing at 520°C in air for crystallization. The undesirable Pb-silicate is found to be grown during post-annealing in case that substrates having NiCr layer deposited by high power above 80 W are used. We suggest that the formation of Pb-silicate is due to the thermal diffusion of Pb or PbO through crystalline NiCr-grain boundaries. The ferroelectric PZT thin films having the perovskite structure can be obtained by using the NiCr-bottom electrodes whose morphologies are in the amorphous-crystalline boundaries, in which the surface roughness and grain size of NiCr layer is minimum. The values of the dielectric constant, εn, were measured in the range 300˜500, the remanent polarization, Pr, in the range 10˜13 C/cm2 and the coercive field, Ec, around 160 kV/cm, depending on the deposition conditions of NiCr layers.