ABSTRACT
Fabrication techniques for preparing ferroelectric thin films for memory use have recently shown a great progress. In application of ferroelectrics for memory1 it is important to understand phenomena related to polarization reversals, i.e., switch ing, and analyses of the switching processes, observed mostly as switching currents, have been reported by many researchers. 2 One of the most familiar models used in such analyses is the Kolmogorov-Avrami model, 3 which Ishibashi and Takagi have rewritten in a way convenient for a use in ferroelectricity. 4
With respect to switching phenomena, it has been reported that the switching time decreases with decreasing electrode area. 5 It is quite puzzling as will be men tioned in what follows. Suppose that the ferroelectric sample is two dimensional and of the area S, and the switched domains expand two-dimensionally with a velocity v. Considering first the case of category II4 (the latent nucleus case), which is usually the case of ferroelectric polarization reversals, let us denote the density of latent nuclei as N. Then, the switching time will be proportional to 1/vVN, which is independent of the sample size in contradiction to experimental obser vations. Next, let us consider the case of category I (the constant nucleation case). If the domain caused by a single nucleus covers all the system, the switching time is estimated as the time required for a single nucleation, i.e., 1/75, where 7 is the nucleation probablity (per unit area per unit time). This obviously shows the ten dency opposite to the observed fact with respect to the size dependence.
