Unconventional hysteresis behavior in compositionally graded Pb(Zr,Ti)O3 thin films

Abstract

Thin-film lead–zirconate–titanate (PZT) capacitors with composition gradients normal to the substrate were fabricated via a novel technique using pulsed laser deposition. These capacitors exhibited large polarization offsets when driven by an alternating electric field. The direction of the offsets depended on the direction of the gradient with respect to the substrate. The largest offset, greater than 400 μC/cm2 when driven with a 50 V/μm field, was nearly an order of magnitude greater than any reported for other graded ferroelectric films. This difference is attributed to both the high spontaneous polarization of PZT and the high-quality films obtained by pulsed laser deposition.

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

“…A composite possesses effective dielectric and ferroelectric properties, and we imagine this ''effective'' sample is placed in the Sawyer-Tower circuit. Figure 5 ϩ (sat) generally obeys a power law, 30,34,35 i.e., D o f f (sat)ϰE A ϩ (sat) n , 2ՇnՇ5, which differ from the present results. The possible reason is that, in our calculation, f ϩ and f Ϫ are assumed to be constants independent of E A ϩ (sat).…”

“…However, the drift magnitude might be surprisingly large and was reported to be an order larger than the spontaneous polarization. [33][34][35] Although our model assumes a single ferroelectric sample, our analysis is thought to be roughly valid for a graded ferroelectric, which is a multilayered composite. A composite possesses effective dielectric and ferroelectric properties, and we imagine this ''effective'' sample is placed in the Sawyer-Tower circuit.…”

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

“…This is also the range of experimental measurements where notable vertical shifts of the hysteresis loop are reported in the literature. [12][13][14][15] In our previous study of compositionally graded ferroelectric films, we have already demonstrated that the polarization gradient across a ferroelectric film can lead to asymmetric conduction, which we believe provides a mechanism for the polarization offset phenomenon. Now it is worth further examining the asymmetric conduction current.…”

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

“…Indeed, many large polarization offsets observed in graded ferroelectrics possessed unequal shift magnitudes for downgraded and upgraded films. 29 Concerning the origin of asymmetric f , Bouregba et al suggested that the compositional gradient in a graded ferroelectric might induce some change in the free-carrier concentration and the magnitude of the band gap along the growth direction. 17 Those could lead to asymmetric conductivity within the film.…”