Polarization In Ferroelectric Films Research Articles

Enhancement of Polarization in Ferroelectric Films via the Incorporation of Gold Nanoparticles.

Ferroelectric thin films have been extremely studied for many applications such as nonvolatile memories, super capacitors, and solar cells. For these devices, improving the polarization properties of ferroelectric thin films is of great significance to their performance. Here, Au–lead zirconate titanate (PZT) nanocomposite thin films were prepared by a simple one-step chemical solution deposition (CSD) method on silicon substrates, and the effects of Au concentration on the ferroelectric properties were investigated. The experimental results show that the remanent polarization of the Au–PZT films with 1.2 mol % Au is about 80 μC/cm2, which is 50% higher than that of the pure PZT thin films. On the basis of the analysis of chemical valences, the enhanced polarization properties can be ascribed to the interaction between Au nanoparticles (Au NPs) and PZT at the Au–PZT interfaces. Our results demonstrate that the incorporation of an appropriate amount of Au NPs is an effective way to enhance the polarization properties of ferroelectric films. The Au–PZT nanocomposite thin films with excellent polarization properties on silicon substrates are expected to be widely used in integrated ferroelectric devices.

Polarization of ferroelectric films through electrolyte

A simplified model is developed to understand the field and potential distribution through devices based on a ferroelectric film in direct contact with an electrolyte. Devices based on the ferroelectric polymer polyvinylidenefluoride-trifluoroethylene (PVDF-TrFE) were produced—in metal–ferroelectric–metal, metal–ferroelectric–dielectric–metal, and metal–ferroelectric–electrolyte–metal architectures—and used to test the model, and simulations based on the model and these fabricated devices were performed. From these simulations we find indication of progressive polarization of the films. Furthermore, the model implies that there is a relation between the separation of charge within the devices and the observed open circuit voltage. This relation is confirmed experimentally. The ability to polarize ferroelectric polymer films through aqueous electrolytes, combined with the strong correlation between the properties of the electrolyte double layer and the device potential, opens the door to a variety of new applications for ferroelectric technologies, e.g. regulation of cell culture growth and release, steering molecular self-assembly, or other large area applications requiring aqueous environments.

Effect of out-of-plane misfit strain on phase diagrams and ferroelectric properties of ferroelectric films in vertical nanocomposite structures

A phenomenological thermodynamic Landau–Devonshire theory is developed to investigate phase diagrams of epitaxial ferroelectric films with out-of-plane misfit strain induced by vertical nanocomposites. The thermodynamic potential of ferroelectric films is obtained based on the boundary conditions of three-dimensional clamping induced by the vertical nanocomposites. Our calculated results indicate that the out-of-plane misfit strain modulates the transition temperature and spontaneous polarization of ferroelectric films in a wide range even the substrate does not provide an effective in-plane misfit strain control. An enhanced critical transition temperature up to 803 °C in BaTiO3 films under a tensile out-of-plane misfit strain is predicted, which is consistent with the experimental result very well. The polarization properties of BaTiO3 films can also be effectively modulated by the out-of-plane misfit strain which is controlled by the volume fraction of nanopillars in the vertical nanocomposites. Our method provides a theoretical guide for the out-of-plane strain engineering of ferroelectric films.

Piezo-Spectroscopic Stress Measurement near PZT-Microstructures on Silicon

Domain formation and polarization in ferroelectric films probably are strongly influenced by intrinsic stress. Raman microscopy offers the possibility to get informations about the stress state even in film structures with lateral dimensions of several ten microns. PZT (Pb[Zr,Ti]O 3 ) microstructures with Pt bottom electrodes sputtered on silicon wafers were investigated using the Raman peak of the single crystalline silicon. Near edges of Pt and PZT films Raman shifts |Δv| ≤ 1,5 cm -1 were measured corresponding to stresses in the silicon substrate near the interface in the order of several hundred MPa. The Raman shift profiles are dependent on the particular geometry of the investigated structures and specific microstructure defects near the edge. An estimate of the stress in the PZT film was obtained by modelling the stress in the silicon as a function of the distance from one edge using a finite element code.

Effects of disturbing pulses on the switchable polarization of Pb(ZrTi)O3 thin film capacitors

The effect of disturbing pulses on the switchable polarization in ferroelectric films of PbZrxTi1−xO3 with x=0.36 and 0.71 has been investigated. The two compositions were selected because of their different hysteresis shapes. Pulse measurements were carried out with a varying number of disturbing pulses at different amplitudes, interrupted by single shot read/write pulses. It was found that the composition with the squarer loop (x=0.36) showed less sensitivity to disturbing pulses, i.e., the switchable polarization did not significantly degrade with 109 disturbing pulses of amplitude 1.2 V. In addition, these results demonstrate that degradation of the stored polarization due to parasitic disturbing voltages in high density ferroelectric random access memories can be kept at an acceptable level.

Decay of remanent polarization in ferroelectric films using polarization-dependent photovoltages

Abstract Following polarization reversal, the strength of photovoltaic currents from lead-based perovskite film capacitors shows a dependence on time. An initial photovoltaic current decays rapidly to an almost steady-state current, which then decays slowly. We use a nonswitching surface layer model to explain remanent-polarization-dependent photovoltaic outputs in terms of photocarrier-generated screening of an incompletely compensated depolarization field within the film bulk. The rapid decrease in the initial photovoltaic current (photovoltaic transient) is explained as resulting from a change in the potential distribution within the film. The initial distribution results when charges compensating polarization are confined to the electrodes; the final distribution results when compensating charges occupy defect states within the volume of the surface layers. The slow decay in the steady photovoltaic current is explained as the result of changes in the potential distribution resulting from a slow decay in the remanent polarization. The log time rate of decay of the photovoltaic current is then equal to that of the remanent polarization, its determination serves as a measure of the log time decay rate of remanent polarization.

Retention in thin ferroelectric films

Rentention of polarization in ferroelectric films is defined asiR = [l-ΔPr/Pr(0)], where ΔPr is the decrease of remanent polarization due to depoling and Pr(0) is the remanent polarization at time zero. Results for measurements of retention as a function of time for films of composition Pb.92Bi.o7La.01(Fe.405Nb.325Z.27)03 are presented. When ferroelectric elements are poled with 10-V, 10-ms pulses, depoling disturb pulses of 0.5 V up to a total of 109pulses do not affect the retention. Retention is found to be a function of the heat treatment of the films and the electrodes. It decreases as temperature increases and decreases as the amount of charge initially switched becomes smaller. Also, definite improvement in retention is observed when a high series resistance is placed in the circuit.