Ferroelectric Aging Research Articles

Aging behavior in single-domain Mn-dopedBaTiO3crystals: Implication for a unified microscopic explanation of ferroelectric aging

The change of ferroelectric, dielectric, and piezoelectric properties with time, the ferroelectric aging phenomena, has been observed in most ferroelectrics. Phenomenologically, aging can be attributed to the gradual stabilization of ferroelectric domains by defects, but the microscopic origin of the domain stabilization has remained controversial. It is unclear whether the domain stabilization is a boundary effect (caused by domain-wall-pinning) or a volume effect (stabilization of the whole domain). In the present paper, we made a single-domain (domain-wall-free) Mn-doped ${\mathrm{BaTiO}}_{3}$ single crystal and studied the aging behavior of its hysteresis loop. We found that after aging, the single-domain sample shows a significant increase in the coercive field, clearly indicating a strong stabilization of the single domain. Furthermore, the sample exhibits an abnormal double hysteresis loop, which corresponds to an interesting reversible domain switching process. These are direct evidence for the stabilization of single domain by aging. Our results preclude any explanation by the domain-wall-pinning effect and strongly suggest that the volume effect is the governing mechanism for the aging in hysteresis loop. We further show that the microscopic origin of the volume effect comes naturally from a general symmetry-conforming property of point defects. Such a microscopic mechanism can explain not only the aging in hysteresis loop (large signal aging) but also the aging in dielectric and piezoelectric constants (small signal aging), thus providing a unified microscopic explanation for all kinds of ferroelectric aging.

Aging in Ferroelectrics

The reorientation of defect dipoles and the drift of free charge carriers are the most prominent microscopic mechanisms under discussion to provoke the aging effect in ferroelectrics. These two mechanisms are contrasted taking into account the influence of grain boundaries in a polycrystalline material. For the drift model, clamping pressures on domain walls only depend on geometry and on the transport properties of the mobile defect charge carrier independent of its electronic or ionic nature. For a numerical example clamping pressures as a result of drift of oxygen vacancies are determined in BaTiO3. They range from 106 to 107 Pa corresponding to experimental values.

An investigation into the spectral analysis of dielectric aging in ferroelectrics.

Aging and degradation indicate the time-dependent change of physical and electrical properties. Most studies neglect to report the effects of aging on the electromechanical properties of an electroactive material and subsequent deterioration of performance. Recent work has shown that the strain and polarization response of an electroactive device can be transformed into its harmonic spectrum (transformation from the time domain to the frequency domain) through the implementation of Fourier analysis. The ability to create this harmonic spectrum provides a new way to characterize the effects of aging by revealing subtle changes in the fundamental components that comprise the response. This study shows how Fourier analysis can be applied to an aged PMN-PT-BT composition to characterize and quantify the effects of aging. The average weak-field permittivity is measured as a function of time, temperature, and frequency. A typical "saddle" in the permittivity and dielectric loss is apparent, and the magnitude decays logarithmically with time. Harmonic analysis of the strain response reveals a slight time-dependent amplitude variation and logarithmic dependence of the phase of the 6th order harmonic. Similar analysis of the polarization response, as a function of time, fully characterizes the development of constriction or wasting seen in a typical aged electrostrictive material. Variations in the amplitudes of the 5th and higher order harmonics of polarization, logarithmic in nature, and the phase of the 5th order harmonic combine to define aging on the harmonic level.

Interface-related decrease of the permittivity in PbZrxTi1−xO3 thin films

In ferroelectric thin films, a decrease of the permittivity is observed obeying a logarithmic time dependence. In the literature, a similar effect has been reported for ferroelectric single crystals and ceramics, which is referred to as ferroelectric aging, and different models have been proposed to explain this phenomenon. In this letter, ferroelectric aging of PbZrxTi1−xO3 thin films is studied as a function of dopant types and concentrations as well as the temperature. The results clearly show that the traditional models for the aging mechanism of ferroelectric single crystals and ceramics are not applicable. Based on these results, a mechanism is proposed which explains the decrease of the dielectric constant in ferroelectric thin films by the growth of a thin surface layer with suppressed ferroelectric properties in the course of aging.

A qualitative model for degradation of FRAM® products during plastic packaging

A model for plastic package degradation of FRAM products involving both the thermal budget of the assembly process and the hydrogen evolution from the mold compound is proposed. Qualitative verification of the model is presented by utilizing ferroelectric aging data and failed bit analysis of the defective parts along with the measured hydrogen evolution from the three mold compounds. The implications of the model on the choice of plastic mold compound are discussed.

The effect of ferroelastic coupling in controlling the abnormal aging behavior in lead magnesium niobate-lead titanate relaxor ferroelectrics

The abnormal aging behavior, i.e., severe aging in the electric field induced piezoelectric coefficient while very weak dielectric aging, observed in the relaxor ferroelectric lead magnesium niobate-lead titanate (PMN-PT) ceramics under a dc electric bias field, can be significantly reduced by hot isostatic pressing (HIP) treatment on presintered samples. The aging can also be reduced by doping suitable amounts of either La (donor) or Mn (acceptor). We suggest that the reduction in the aging is due to the introduction of additional random fields into the material, which reduces the probability of the growth of micropolar regions into metastable and/or stable macropolar domains. The abnormal aging behavior and the effectiveness of HIP in reducing it indicate the importance of the elastic energy in controlling the aging and relaxor behavior in PMN-PT relaxor ferroelectrics.

Degradation Mechanisms in Ferroelectric and High-Permittivity Perovskites

Due to the importance of ferroelectric and high-permittivity perovskite thin films for a wide range of applications, there has been extensive research devoted to understanding the mechanisms responsible for the degradation observed with time, temperature, and/or external field stress. The three most important degradation phenomena for ferroelectric materials such as Pb(Zr, Ti)O3 (PZT) and BaTiO3 are ferroelectric fatigue, ferro-electric aging, and resistance degradation. Ferroelectric fatigue is the loss of switchable polarization by repeated polarization reversals. Ferroelectric aging is characterized by a spontaneous change with time in the polarization-voltage (P-V) response. Resistance degradation is a deterioration of the insulating properties of a dielectric under direct-current (dc) bias and elevated temperature.These degradation processes ultimately limit the lifetime and reliability of devices that use ferroelectric and high-permittivity perovskite dielectrics. Fatigue and aging lead to reliability concerns for electronic (nonvolatile memories), piezo-electric, electro-optic, and pyroelectric applications. Likewise resistance degradation typically limits the lifetime of ceramic capacitors and high-dielectric constant thin films such as (Ba, Sr)TiO3, which is the principal candidate material for very high-density dynamic random-access memories (DRAMs).Because of the importance of these degradation processes, it is critical to understand them and to develop methods of eliminating or mitigating their effects. By combining results from studies on thin films with ones on ceramics and single crystals, a consistent picture of the mechanisms involved in these degradation processes is emerging. In this article, we discuss these degradation mechanisms with particular emphasis on the interaction between ferroelectric domains and charge trapping and the role of oxygen vacancies and associated defect dipoles.

Aging Characteristics of Ferroelectric Epitaxial BaTiO3/YBa2Cu3O7 Heterostructures

AbstractThe nature of ferroelectric aging of epitaxial BaTiO3YBa2Cu3O7 heterostructures grown by laser deposition was investigated as a function of rricrostructure in the dielctric layer. Molar amounts of SrTiO3 were then substitutionally added to analyze the effect on the rnicrostructure and electrical properties. Corresponding shifts in c/a ratio and curie temperature were correlated to changes in aging rate (%δC/decade time). Microstructural analysis was provided by high-resolution x-ray diffraction (HRXRD), and Rutherford backscattering spectroscopy (RBS). Results indicate a moderate upward shift in c/a ratios from theoretical values due to increasing lattice strain across the bilayer interface. Minimum channel yields in RBS spectra were maintained between 6–8% for BaTiO3 purities above 60 %. Dielectric measurements were conducted using an impedance analyzer equipped with an isothermal chamber capable of maintaining ±1°C. The dielectric properies were consistent with c-axis oriented BaTiO3 values (k=120, D=.02)Minimum aging rates are observed at the lower c/a ratio compositions to be as low as .07%δC/decade.

A comparison of ferroelectric aging in bulk and thin-film materials

Thin-film ferroelectric device researchers have reported that hysteresis loop translation−a characteristic of bulk ferroelectric aging−does not occur in thin-film devices. This work examines ferroelectric aging in thin-film materials using a novel measurement procedure that combines the techniques used in bulk and thin-film testing. The results show that the aging characteristics of thin-film ferroelectric materials are the same as those exhibited by bulk materials. In addition, the primary and secondary waiting time effects are shown to be directly related to aging.

Aging mechanisms in Pb(Mg1/3Nb2/3)O3-based relaxor ferroelectrics

Abstract The complex perovskite Pb(Mg1/3Nb2/3)O3 [PMN] is just one of many relaxor ferroelectncs having the general formula Pb(B1B2)O3. PMN, and solid solutions thereof with PbTiO3 [PT] and Pb(Zn1/3Nb2/3)O3 [PZN], as well as other relaxor compositions, are excellent materials for use in a wide range of applications including electrostrictive actuators,1 multilayer capacitors,2 and pyroelectric bolometers.3 For any of these applications it is imperative that dielectric aging be minimal. Past studies4–13, on aging in relaxor ferroelectrics (primarily PLZT and PMN) have shown the aging rate depends on many variables including processing parameters, microstructure, dopant content, point defects, etc. Though great strides have been made with respect to modelling dielectric properties of relaxors, the lack of detailed information concerning defect structure, conduction, and ordering still hinders theoretical interpretation of aging results.