Abnormal ferroelectric properties of compositionally graded Pb(Zr,Ti)O-3 thin films with LaNiO3 bottom electrodes

We report abnormal ferroelectric properties of compositionally graded Pb(Zr ,Ti)O-3 thin films on LaNiO3-coated SiO2/Si substrates, where Pb(Zr,Ti)O-3 and LaNiO3 films were prepared by a metalorganic decomposition technique an d a sol-gel technique, respectively. It was found that the hysteresis loops of the Pb(Zr,Ti)O-3 graded films measured by the conventional Sawyer-Tower method shifted along the polarization axis, i.e., they showed polarization offsets when applied by an alternating electric field. The polarization of fsets were 82.5 muC/cm(2) at 270 kV/cm and 62.5 muC/cm(2) at 185 kV/cm for the up-graded film and the down-graded film, respectively. The absolute mag nitude of the polarization offsets was closely related to the magnitude of the driving electric field, and the direction of the polarization offsets d epended on the direction of the composition gradient with respect to the su bstrate. Analysis indicated that the polarization offsets did not originate from asymmetric contact effects, oxygen vacancies, alignment of defect dip oles, and/or electron injection. These results showed that polarization off sets in hysteresis loops were the intrinsic characteristic of the compositi onally graded Pb(Zr,Ti)O-3 thin films. (C) 2001 American Institute of Physi cs.