Device modeling of ferroelectric capacitors

Abstract

A physically based methodology is developed for modeling the behavior of electrical circuits containing nonideal ferroelectric capacitors. The methodology is illustrated by modeling the discrete ferroelectric capacitor as a stacked dielectric structure, with switching ferroelectric and nonswitching dielectric layers. Electrical properties of a modified Sawyer–Tower circuit are predicted by the model. Distortions of hysteresis loops due to resistive losses as a function of input signal frequency are accurately predicted by the model. The effect of signal amplitude variations predicted by the model also agree with experimental data. The model is used as a diagnostic tool to demonstrate that cycling degradation, at least for the sample investigated, cannot be modeled by the formation of nonswitching dielectric layer(s) or the formation of conductive regions near the electrodes, but is consistent with a spatially uniform reduction in the number of switching dipoles.

Very large dielectric response of thin ferroelectric films with the dead layers

“…The "capacitor" model (incorrectly) presumes that the dielectric response of the dielectric layer is not affected by the presence of the dead layer, so the system looks like capacitances in series. We show that the effective "dielectric constant" of the FE layer, ǫ f , as found in the "capacitor" model [3,4,6], is actually negative. In spite of this the system remains stable (stiffness of the domain pattern is positive).…”

“…Here we address the anomalous behavior of the dielectric constant ǫ ef f in detail. We also discuss the important issue regarding the relation of the present results to socalled "capacitor" model [3,4,6]. The "capacitor" model (incorrectly) presumes that the dielectric response of the dielectric layer is not affected by the presence of the dead layer, so the system looks like capacitances in series.…”

“…It has direct bearing on fatigue observed in FE capacitors since in many cases the deterioration of the switching behavior, like the loss of the coercive force and of the squareness of hysteresis loop, were attributed to the growth of a "passive layer" at the ferroelectricelectrode interface [2][3][4][5]. It is of principal importance that the presence of a dead layer, no matter how thin in comparison with thickness of the ferroelectric layer, triggers a formation of the domain structure in FE film [1].…”

Microstructure and dielectric relaxor properties for Ba0.5Sr0.5TiO3/La0.67Sr0.33MnO3 heterostructure

“…Furthermore, it is found that the vs E characteristics exhibit a butterfly-shaped behavior with temperature below 200 K, and show a relatively weak hysteresis behavior above 200 K. This phenomenon is explained as follows: as temperature decreases, the ferroelectric domain wall movement in BST film becomes more difficult and the amount of switchable polarizations increase. Miller et al 17 pointed out that the peak ͑maximum of permittivity͒ in the vs E characteristics of ferroelectric capacitors corresponds to a reversal of the polarizations, and the amplitude corresponds to the amount of switchable polarizations. Therefore, with decreasing temperature below T C , the amount of switchable polarization in BST films was increased, which led to the higher magnitude of peaks.…”

Device physics and simulation of Metal/Ferroelectric-Film/p-type silicon capacitors

“…Studies of ferroelectric capacitors [1] and ferroelectric nonvolatile-memory field-effect transistors [2] have focused mainly on the analysis of the behavior of these devices in the SawyerTower circuit which is commonly used to measure their ferroelectric properties, and in circuits with asymmetric nonperiodic input signals with arbitrary intitial conditions [3]. In this paper, however, we model the device physics of ferroelectric capacitors fabricated on p-type silicon substrates using a simple electrostatic model, with the goal of predicting their lowand high-frequency capacitance-voltage characteristics, and relate their Cgb(VGB) hysterisis to the properties of the ferroelectric film.…”