Spatial variation of ferroelectric properties in Pb(Zr_0.3, Ti_0.7)O₃ thin films studied by atomic force microscopy

Imaging of the phase and magnitude of the piezoelectric strain in Pb(Zr_0.3, Ti_0.7)0₃ (PZT) capacitors is performed with an atomic force microscope. The imaging reveals a significant spatial dependence of the ferroelectric properties of both fatigued and unfatigued PZT films. We propose that the variation is related to the domain structure of the PZT. Through the measurement of local piezoelectric hysteresis loops and imaging of the piezoelectric strain, areas are observed in fatigued PZT that exhibit hysteresis loops shifted along the polarization axis. In some regions of fatigued samples, the hysteresis loops are shifted such that both remanent points of the hysteresis curve have the same polarization direction. These results have important implications for the scalability of nonvolatile ferroelectric random access memory to higher device densities.