Ferroelectric phase transitions in films with depletion charge

Bratkovsky, A. M.; Levanyuk, A. P.

doi:10.1103/physrevb.61.15042

Cited by 65 publications

(41 citation statements)

References 13 publications

(27 reference statements)

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“…This non-local behavior is due to long range Coulomb interaction, which makes the response rigid even when the FE itself would have a negative "dielectric constant" (for analogous situation in FE films with depletion charge see Ref. [10], Fig. 1).…”

Section: (Inset)mentioning

confidence: 99%

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

2001

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We study the dielectric response of ferroelectric (FE) thin films with "dead" dielectric layer at the interface with electrodes. The domain structure inevitably forms in the FE film in presence of the dead layer. As a result, the effective dielectric constant of the capacitor ǫ ef f increases abruptly when the dead layer is thin and, consequently, the pattern of 180-degree domains becomes "soft". We compare the exact results for this problem with the description in terms of a popular "capacitor" model, which is shown to give qualitatively incorrect results. We relate the present results to fatigue observed in thin ferroelectric films. 77.22.Ch, 77.80.Dj, 84.32.Tt, 85.50.+k We have shown recently that the dead layer forming at the interface between ferroelectric (FE) thin film and electrodes has drastic effect on the electric response of a capacitor [1]. 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]. We have shown that when the thickness of the dead layer d is not very small, the apparent (net) polarization P a of the ferroelectric with 180−degree domain walls follows an approximate relation dP a /dE ∝ ǫ g /d, which is in good correspondence with available experimental data (see e.g. [6,7] and references therein). Importantly, the response of this structure to an external bias voltage becomes more rigid when d increases, i.e. when the dead layer grows, even in the absence of pinning by defects.The implication for real systems is that with the growth of the passive layer the hysteresis loop very quickly deteriorates and looses its squareness, as observed. The approximate 1/d dependence of the response suggests that the effective dielectric constant of the capacitormay become very large when the layer is thin. Here C is the capacitance of the electroded FE film of area A, with L the separation between electrodes. Indeed, when the dead layer is thin, the domain width a becomes very large, it grows exponentially with 1/d 2 [1]. The response of this domain structure is very soft, and this should translate into very abrupt increase of the dielectric constant ǫ ef f of the capacitor. It is easy to show that in the present case (180 o domains) the linear response is not changed by electromechanical effect, the change in ǫ ef f only appearing in quadratic terms in external field, but here we are interested in zero-field value of ǫ ef f only. We have assumed a quadratic coupling between the elastic strains and the polarization (as in perovskites). In this case the linear response of 180 0 domain structure without pinning is not affected by intimate contact between th...

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Section: (Inset)mentioning

confidence: 99%

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

2001

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“…Moreover, there are regions where both the electric field and polarization always remain in negative values at the top electrode, and positive values at the bottom electrode, regardless of the sign of the external driving voltage. These regions have been designated dead layers, 27 or nonswitching layer, 28 within which the dipoles are not switchable. The size effect of different ferroelectric properties has been attributed to the presence of these layers.…”

Section: Effect Of Space Chargementioning

confidence: 99%

Modeling the role of oxygen vacancy on ferroelectric properties in thin films

2002

Journal of Applied Physics

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The presence of oxygen vacancies is considered to be the cause of various phenomena in ferroelectric thin films. In this work, the role of oxygen vacancies is theoretically modeled. Various properties are numerically simulated using the two-dimensional Ising model. In the presence of an oxygen vacancy in a perovskite cell, the octahedral cage formed by oxygen ions is distorted so that the potential energy profile for the displacement of the titanium ion becomes asymmetric. It requires additional energy to move from the lower minimum position to the higher one. Moreover, space charges are also developed by trapping charge carriers into these vacancies. The combination of the pinning effect induced by the distorted octahedral cage and the screening of the electric field in the presence of space charges results in phenomena such as fatigue and imprint.

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“…In such an application, DC charge transport through the ferroelectric gate stack is inhibited. However, ferroelectric thin films also exhibit semiconducting properties, which could provide additional functionality in ferroelectric -semiconductor heterostructures [4][5][6][7]. In conjunction with the re-orientable polarization, the semiconducting properties of thin film ferroelectrics could potentially be utilized to control charge transport through ferroelectric-semiconductor heterojunctions.…”

Section: Introductionmentioning

confidence: 99%

“…It should be noted that a constant field within the BTO/BST dielectric stack is shown in Fig.3(b) and (c). A more rigorous description should consider gradients in polarization and fields due to the Sr alloying [5][6][7]. Finally, we note that the transport current effect observed in our heterostructures could potentially form the basis for a type of memory.…”

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confidence: 99%

Hysteretic electrical transport in BaTiO3/Ba1−xSrxTiO3/Ge heterostructures

Ngai

Kumah

Ahn

et al. 2014

Applied Physics Letters

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We present electrical transport measurements of heterostructures comprised of BaTiO 3 and Ba 1−x Sr x TiO 3 epitaxially grown on Ge. The Sr-alloying imparts compressive strain to the BaTiO 3 , which enables the thermal expansion mismatch between BaTiO 3 and Ge to be overcome to achieve c-axis oriented growth. The conduction bands of BaTiO 3 and Ba 1−x Sr x TiO 3 are nearly aligned with the conduction band of Ge, which facilitates electron transport. Electrical transport measurements through the dielectric stack exhibit rectifying behavior and hysteresis, where the latter is consistent with ferroelectric switching. PACS numbers: 74.50.+r, 74.72.Bk, 74.20.Rp, 74.25.Nf 1 Recent advancements in epitaxial growth have enabled single crystalline ferroelectrics to be integrated with conventional semiconductors, opening a pathway to exploit the polarization of the former in semiconducting based devices. Electrically coupling the re-orientable polarization of a ferroelectric to a semiconducting channel remains a long standing challenge in materials research. Single crystalline ferroelectrics on semiconductors are ideal for such applications, since they offer superior material characteristics in comparison to polycrystalline materials [1,2]. Ferroelectric -semiconductor heterojunctions were originally conceived to operate as capacitors, where the polarization could be utilized to maintain accumulation or depletion in the semiconducting electrode [3]. In such an application, DC charge transport through the ferroelectric gate stack is inhibited. However, ferroelectric thin films also exhibit semiconducting properties, which could provide additional functionality in ferroelectric -semiconductor heterostructures [4][5][6][7]. In conjunction with the re-orientable polarization, the semiconducting properties of thin film ferroelectrics could potentially be utilized to control charge transport through ferroelectric-semiconductor heterojunctions.In this letter, we introduce mobile carriers into a ferroelectric-semiconductor heterostructure and exploit the re-orientable polarization to modulate the Schottky barrier to a semiconductor. Our heterostructures are comprised of BaTiO 3 (BTO) and Ba 1−x Sr x TiO 3 (BST) grown epitaxially on a Ge wafer, with Pt serving as the counter electrode. X-ray photoemission spectroscopy measurements indicate that the conduction bands of Ge and BTO are nearly aligned, thus enabling charge transport through the heterojunction interface.Transport measurements of the current through the asymmetric capacitors reveals rectifying behavior and hysteresis. The former arises from the presence (absence) of a barrier at the metal-ferroelectric (ferroelectric-semiconductor) interface for charge transport, whereas the latter can be attributed to switching of the ferroelectric polarization.The BTO/BST heterostructures were grown using reactive molecular beam epitaxy (MBE) [8,9]. The (100)-oriented p-type (ρ ∼0.018 Ωcm) Ge wafers were cleaned by dipping in a 30:1 solution of H 2 O:HF for 60 s, followed by e...

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Ferroelectric phase transitions in films with depletion charge

Cited by 65 publications

References 13 publications

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

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

Modeling the role of oxygen vacancy on ferroelectric properties in thin films

Hysteretic electrical transport in BaTiO3/Ba1−xSrxTiO3/Ge heterostructures

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