A STUDY OF ABNORMAL ELECTRIC PROPERTIES OF LEAD LANTHANUM TITANATE THIN FILMS CAUSED BY EXCESS PbO

Abstract

Lead lanthanum titanate(PLT) thin films with excess PbO were prepared by metal organic decomposition (MOD) process.The C-V characteristics and ferroelectric properties of the PLT films were investigated as functions of amount of excess PbO.The normal P-E hysteresis loops and butterfly shape C-V curves were obtained for the PLT films with stoichiometric composition.While abnormal ferroelectric and C-V properties were observed in the PLT films with excess PbO.The P-E hysteresis loops were pinched before the polarization of the films reached the saturation.Instead of two peaks (butterfly-shape) in the normal C-V curves,the C-V curves had four peaks. The abnormal behavior of the hysteresis loops and C-V curves became more serious with increasing amount of excess PbO in the films.The results can be explained by the ferroelectric pinning effect.A part of excess PbO may be accumulated at boundaries of crystalline grains and clusters and the interface between the bottom electrode and the film during the annealing process of the films.PbO may act as the pinning centers and has a strong effect on the ferroelectric domains.If the biased voltage is not large enough,then part of the electric domains cannot overcome the force of the pinning,and abnormal ferroelectric and C-V properties will be observed.Excess PbO may be one of the main causes of fatigue and aging of ferroelectric thin films.