Abstract
Due to their nonlinear properties, ferroelectric materials are ideal candidates for smart materials. Degradation properties such as low voltage breakdown, fatigue, and aging have been major problems in commercial applications of these materials. Such degradations affect the lifetime of ferroelectric materials. Therefore, it is important to understand degradation for reliability improvement.
In this article, recent studies on fatigue and hysteresis of ferroelectric ceramics such as Lead Zir conate Titanate (PZT) thin films is reviewed. A new fatigue model is discussed in detail which is based on effective one-directional movement of defects by internal field difference, defect entrapment at the ferroelectrics-electrode interface, and resultant polarization loss at the interface. A fatigue equation derived from this model is presented. Fatigue parameters such as initial polarization, piling constant, and decay constant are defined from the fatigue equation and voltage and temperature de pendence of fatigue parameters are discussed. The jump distance of defect calculated from voltage dependence of the decay constant is close to the lattice constant of ferroelectric materials, which im plies that oxygen or lead vacancies migrate either parallel or antiparallel to the polarization direc tion. From the temperature dependence of the decay constant, it is shown that the activation energy for domain wall movement plays an important role in fatigue.
The hysteresis model of ferroelectrics is shown using polarization reversal. The hysteresis loop is made by four polarization stages: nucleation, growth, merging, and shrinkage of domains. The hysteresis equation confirms that dielectric viscosity controls hysteresis properties, and temperature dependence of the coefficient of dielectric viscosity is also discussed in conjunction with fatigue mechanism.
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