Graded ferroelectric thin films: Possible origin of the shift along the polarization axis

We model the dynamic polarization behavior of ferroelectric films by an analytical approach. Using a parallelogramlike P-E hysteresis model, explicit expressions were obtained for describing the D-E loops of ferroelectric films as would be measured from a Sawyer-Tower circuit. By introducing the consideration of electrical conduction, resistive losses inflate the ferroelectric loop to some extent. In addition, an asymmetric conduction will result in polarization offsets with the magnitude and direction depending on the asymmetric conductivities of the materials. The inflated loop, as well as the offset phenomena, which have been observed experimentally ͓e.g., L. Zheng, C. Lin, W.-P. Xu, and M. Okuyama, J. Appl. Phys. 79, 8634 ͑1996͔͒, will be discussed by means of our modeled results. Some simple exact formulas have been derived and the effects of electric, dielectric, and ferroelectric parameters, as well as the applied field on the ''apparent'' polarization were also examined.

Section: B Polarization Offsets In Ferroelectrics With Asymmetric Cosupporting

confidence: 79%

Section: Introductionmentioning

confidence: 99%

Explicit expressions for the dynamic polarization behavior in ferroelectrics with symmetric/asymmetric electrical conductivity

Wong

Tsang

Shin

2004

“…Actually, approaches involving asymmetric conductivity have been applied to study the vertical shift observed in graded ferroelectrics. [16][17][18] This mechanism leading to asymmetric leakage current has long been observed and discussed in literature. [7][8][9]19,20 The accumulated interfacial charge will allow the buildup of an internal bias field to displace the hysteresis loop from the origin.…”

Section: Introductionmentioning

confidence: 99%

Modeling of anomalous shift and asymmetric hysteresis behavior of ferroelectric thin films

Wong

Shin

2004

Surface acoustic wave micromotor with arbitrary axis rotational capability Appl. Phys. Lett. 99, 214101 (2011) Dielectric model of point charge defects in insulating paraelectric perovskites J. Appl. Phys. 110, 094110 (2011) A correlated electron diffraction, in situ neutron diffraction and dielectric properties investigation of poled (1-x)Bi0.5Na0.5TiO3-xBaTiO3 ceramics J. Appl. Phys. 110, 084114 (2011) Domain size engineering in tetragonal Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 crystals J. Appl. Phys. 110, 084110 (2011) Influence of the critical point on the electrocaloric response of relaxor ferroelectrics J. Appl. Phys. 110, 064118 (2011) Additional information on J. Appl. Phys. An analytical bilayer model has been developed to consider the effect of the existence of a dead layer (e.g., due to polarization degradation) at the film-electrode interface in an otherwise homogeneous ferroelectric thin film. By introducing asymmetric conductivity in the dead layer, the anomalous horizontal (along the field axis) shift behavior of hysteresis loops in ferroelectric thin films is successfully reproduced. Assuming that the ferroelectric P-E hysteresis loops of the layers are parallelogramlike, explicit expressions are derived for calculating the internal fields in the film, as well as the "apparent" D-E loop as measured from a Sawyer-Tower circuit. The general switching sequence for the ferroelectric phases will be considered. Using the ferroelectric-ferroelectric bilayer model, other anomalous phenomena, including vertical shift and deformed loop shape are also modeled.

“…On the other hand, recent results have shown the polarization offsets in graded PZT to be sensitive to the ambient oxygen concentration, giving rise to possible oxygen sensor applications. 5 Theoretical models have played key roles in providing deeper insight, and different approaches have been proposed. The offset has been interpreted as a static polarization developed across the ferroelectric film under the application of an alternating voltage.…”

Section: Introductionmentioning

confidence: 99%

Effects of polarization and permittivity gradients and other parameters on the anomalous vertical shift behavior of graded ferroelectric thin films

Zhou

Chan

Lam

et al. 2005

We studied theoretically the dependence of the "polarization offset" on various parameters in compositionally graded ferroelectric thin films. Our model adopts the Landau-Khalatnikov equation to describe hysteresis behavior and takes the time-dependent space-charge-limited conductivity into account to investigate the effects of polarization and permittivity gradients, charge mobilities, and thickness in graded ferroelectric thin films. We found that both polarization and permittivity gradients are requisite for the occurrence of offset phenomena. It is also found that larger gradients of remanent polarization and permittivity, a smaller thickness, and a larger charge mobility can generally enhance the effect of vertical offsets. The qualitative agreement between simulation and experiment further supports our previous notion that the asymmetric conduction current arising as a result of the composition gradient is an important factor leading to the polarization offset phenomenon.