Ferroelectric Switching Dynamics Research Articles

Dynamics of ferroelectric switching of [H3CNH3]5[Bi2Br11

The switching behavior of the organic, order-disorder ferroelectric [H3CNH3]5[Bi2Br11] has been studied. It exhibits a complex behavior that arises from the different ferroelectric domain structures that dominate in different time scales. An analysis of the dynamics of the switching of [H3CNH3]5[Bi2Br11] using the theory of rates of reactions has shown that the activation volumes and energies associated with the switching nuclei of critical size are very different at low (10 Hz) and high (100 Hz) frequencies. In both cases, it was found that the contribution from the thermal fluctuations to the formation of the switching nuclei is much larger than the contribution from the work done by the applied electric field.

Switching Dynamics in Ferroelectric Vinylidene Fluoride–Trifluoroethylene Copolymer Thin Film with α,ω-Dihexylsexithiophene Semiconductor Layer

Ferroelectric switching dynamics in thin vinylidene fluoride–trifluoroethylene copolymer films with an organic semiconductor α,ω-dihexylsexithiophene layer have been investigated on the basis of the measurements of the electrical properties including D–E hysteresis loop, switching characteristics, and capacitance changes. The authors elucidate that the full polarization reversal can be accomplished and the depletion is maintained at zero bias field. The time domain measurement together with capacitance measurements enables the evaluation of the close relationship between polarization reversal and carrier behavior in semiconductor layer. Polarization reversal toward the negative side under negative voltage progresses rapidly owing to the accumulation of majority carriers. Polarization reversal toward the positive side proceeds through two-step reversals. The mechanism of the two-step switching is explained by the depolarization field induced by the uncompensated polarization charge due to the formation of the depletion layer.

Ferroelectric switching dynamics in VDF-TrFE copolymer thin films spin coated on Si substrate

Simultaneous measurements of the charge Q and the capacitance C were performed for an MFS capacitor with Au-(vinylidene fluoride-trifluoroethylene copolymer)-(n-Si) structure using a double-frequency voltage consisting of a low-frequency high voltage and a high-frequency sinusoidal low voltage. The use of a triangular high voltage yields asymmetrical Q-V and C-V hysteresis loops that support the full ferroelectric polarization reversal occurring in close relation to charge compensation in the n-Si layer. The use of a rectangular high voltage reveals the details of asymmetric switching dynamics. Polarization switching toward the positive side starts with the loss of the depletion layer and progresses rapidly owing to the accumulation of majority carriers to be completed at a time analogous to that for the case of a metal-ferroelectric-metal capacitor. On the other hand, that toward the negative side is markedly impeded by depletion layer formation but is eventually completed via a constant-current process at a time given by the ratio of switched polarization and constant current. On the basis of a linear relationship between the constant current and the depletion layer width, we conclude that the switching dynamics under a negative voltage is controlled by the rate of minority carrier generation in the depletion layer.

Switching time dispersion and retention of bistable states in Langmuir-Blodgett ferroelectric films

Polarization switching and retention of each of the two polarized states in Langmuir—Blodgett (LB) ferroelectric films are studied using nonlinear dielectric spectroscopy. It is found that polarized states can be preserved for a long time, but the polarization dynamics in 10–40-nm-thick LB films is characterized by a considerable switching-time dispersion. In addition, ferroelectric LB films exhibit clearly manifested asymmetry of switching to states with opposite directions of polarization. To explain the experimental results, a polarization-switching model is proposed that takes into account the energy of interaction of a ferroelectric polymer with boundary surfaces. The effect of inhomogeneity of the LB film structure on the ferroelectric switching dynamics is also discussed.

Temperature anomaly of ferroelectric polarization reversal of β-LiNH4SO4

Abstract The dynamics of ferroelectric switching in β-LiNH4SO4 was studied using NLC decoration technique in the temperature range from 293 K to 367 K. An anomalous change in activation field α with temperature was found. Differences in values of α for the samples “as grown” and heated above Tc can be related to various ferroelectric domain patterns. The anomaly of α(T) is discussed in terms of the dynamics of Li-SO4 framework, responsible for ferroelectric properties of β-LiNH4SO4.