Ferroelectric tunnel junctions with graphene electrodes

Lu, Haidong; Lipatov, Alexey; Ryu, Sangwoo; Kim, D. J.; Lee, H.; Zhuravlev, M. Ye.; Eom, C. B.; Tsymbal, Evgeny Y.; Sinitskii, Alexander; Gruverman, Alexei

doi:10.1038/ncomms6518

Cited by 111 publications

(120 citation statements)

References 36 publications

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“…12,13 Up to recently, most studies of FTJs have focused on improving device performance by modifying the electrode materials. [14][15][16][17][18][19][20] Typical examples include the use of lightly doped semiconductors, [14][15][16] For a thick barrier, these obstacles can be avoided, but the tunneling current becomes too small for realizing a practically useful device. As an alternative, several groups have theoretically proposed a new kind of FTJ using an FE/paraelectric (FE/PE) composite barrier.…”

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confidence: 99%

Overcoming the Fundamental Barrier Thickness Limits of Ferroelectric Tunnel Junctions through BaTiO₃/SrTiO₃ Composite Barriers

et al. 2016

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ABSTRACT:Ferroelectric tunnel junctions (FTJs) have attracted increasing research interest as a promising candidate for non-volatile memories. Recently, significant enhancements of tunneling electroresistance (TER) have been realized through modifications of electrode materials.However, direct control of the FTJ performance through modifying the tunneling barrier has not been adequately explored. Here, adding a new direction to FTJ research, we fabricated FTJs with Ferroelectric tunnel junctions (FTJs), composed of a thin ferroelectric (FE) layer sandwiched in between two metallic electrodes, have been intensively investigated in recent years. This device is considered to be a promising candidate for next-generation nonvolatile memories, because it combines the advantages of both ferroelectric random-access-memory and resistiveswitching memory. 1-3 The concept of FTJ was first proposed by Esaki in 1971, 4 but the research activities have not flourished untixl this decade. [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21] The operation of FTJs has been mainly explained in terms of interfacial screening of polarization charges. [5][6][7][8] In a metal 1(M1)/FE/metal 2 (M2) structured FTJ (Figure 1a), the two asymmetric electrodes lead to unequal screen lengths and potential changes at metal/FE interfaces. Depending on the polarizations, the electrostatic potential profile of tunneling barrier will be varied. As a result, the tunneling resistance can be switched between low (ON) and high (OFF) values by polarization reversal, leading to the socalled tunneling electroresistance (TER) effect.Extensive experimental works based on this asymmetric screening scenario have been reported during the last decade. In 2009, the TER effect was first demonstrated using conducting atomic force microscopy (CAFM). 9-11 Subsequently, FTJs with highly reproducible performance were realized in capacitor geometry, which will be useful for practical applications. 12,13 Up to recently, most studies of FTJs have focused on improving device performance by modifying the electrode materials. [14][15][16][17][18][19][20] Typical examples include the use of lightly doped semiconductors, [14][15][16] For a thick barrier, these obstacles can be avoided, but the tunneling current becomes too small for realizing a practically useful device. As an alternative, several groups have theoretically proposed a new kind of FTJ using an FE/paraelectric (FE/PE) composite barrier. 27,28 The PE layer provides a new route to control the tunneling barrier potentials, and thus the TER can be tuned and significantly enhanced. However, there have been few experimental efforts to systematically attest this theoretical prediction. 29 In this paper, we report experimental control of the TER effect by directly manipulating the tunneling barrier thickness and composition. For this purpose, we fabricated two types of FTJs: Figure S5), which further confirm good epitaxial film qualities.We estimated the lattice constants of the oxide layers from XRD reci...

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Overcoming the Fundamental Barrier Thickness Limits of Ferroelectric Tunnel Junctions through BaTiO₃/SrTiO₃ Composite Barriers

et al. 2016

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“…The tunneling resistance of a FTJ is modulated by electric field induced ferroelectric polarization switching-the effect known as tunneling electroresistance (TER). Following the theoretical predictions [9,10], there have been a number of successful experimental demonstrations of the TER effect in trilayer junctions [11][12][13][14][15][16], showing the potential of FTJs for nonvolatile memory applications [17,18]. The structural and/or electronic asymmetry of the FTJ plays a decisive role for the TER effect.…”

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confidence: 99%

Resonant tunneling across a ferroelectric domain wall

Tao

Velev

et al. 2018

Phys. Rev. B

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Li, M.; Tao, L. L.; Velev, J. P.; and Tsymbal, Evgeny Y., "Resonant tunneling across a ferroelectric domain wall" (2018 Motivated by recent experimental observations, we explore electron transport properties of a ferroelectric tunnel junction (FTJ) with an embedded head-to-head ferroelectric domain wall, using first-principles density-functional theory calculations. We consider a FTJ with La 0.5 Sr 0.5 MnO 3 electrodes separated by a BaTiO 3 barrier layer and show that an in-plane charged domain wall in the ferroelectric BaTiO 3 can be induced by polar interfaces. The resulting V-shaped electrostatic potential profile across the BaTiO 3 layer creates a quantum well and leads to the formation of a two-dimensional electron gas, which stabilizes the domain wall. The confined electronic states in the barrier are responsible for resonant tunneling as is evident from our quantum-transport calculations. We find that the resonant tunneling is an orbital selective process, which leads to sharp spikes in the momentum-and energy-resolved transmission spectra. Our results indicate that domain walls embedded in FTJs can be used to control the electron transport.

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“…[4][5][6] Furthermore, ferroelectric domains and their dynamics 7-10 offer additional degrees of freedom and give rise to an analog memristive response of the tunnel junction [11][12][13][14] that emulates the behavior of synapses in neuromorphic networks. 15,16 Large tunnel electroresistance values of more than 10 3 are now achievable at room temperature, [17][18][19][20][21] which makes ferroelectric tunnel junctions interesting candidates for resistive memories. 3 In addition, coupling ferroelectric materials to strongly correlated oxide electrodes can provide a local, permanent, and switchable electric field able to trigger electronic or magnetic phase transitions.…”

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Tunnel electroresistance in BiFeO3 junctions: size does matter

Boyn

Douglas

Blouzon

et al. 2016

Applied Physics Letters

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In ferroelectric tunnel junctions, the tunnel resistance depends on the polarization orientation of the ferroelectric tunnel barrier, giving rise to tunnel electroresistance. These devices are promising to be used as memristors in neuromorphic architectures and as non-volatile memory elements. For both applications device scalability is essential, which requires a clear understanding of the relationship between polarization reversal and resistance change as junction size shrinks. Here we show robust tunnel electroresistance in BiFeO 3 -based junctions with diameters ranging from 1200 to 180 nm. We demonstrate that the tunnel electroresistance and the corresponding fraction of reversed ferroelectric domains change 1 Electronic mail: vincent.garcia@thalesgroup.com 2 drastically with the junction diameter: while micron-size junctions display reversal in less than 10% of the area, the smallest junctions show an almost complete polarization reversal.Modeling the electric-field distribution, we highlight the critical role of the bottom electrode resistance which significantly diminishes the actual electric field applied to the ferroelectric barrier in the mixed polarization state. A polarization-dependent critical electric field below which further reversal is prohibited is found to explain the large differences between the ferroelectric switchability of nano-and micron-size junctions. Our results indicate that ferroelectric junctions are downscalable and suggest that specific junction shapes facilitate complete polarization reversal.Ferroelectric materials possess a spontaneous electrical polarization that is switchable by an external electric field. This enables the use of thin ferroelectric films sandwiched between electrodes as non-volatile memories.1 In such ferroelectric memories, the information is encoded by the polarization orientation and recovered in a destructive capacitive readout.When the thickness of the ferroelectric films is of the order of a few nanometers, electron tunneling becomes possible. In these ferroelectric tunnel junctions, 2,3 the tunnel resistance varies depending on the orientation of the polarization; this tunnel electroresistance effect enables a non-destructive information readout. These interfacial magnetoelectric coupling phenomena can be probed by tunnel magnetoresistance experiments, resulting in a non-volatile control of the spin-polarization. 26-29Moreover, selecting oxide electrodes subject to field-induced electronic phase transitions upon polarization reversal may result in enhanced tunnel electroresistance. 29,30 Hence, ferroelectric tunnel junctions offer a fantastic playground to explore electric-field-driven modifications at the nanoscale. 31 Top electrodes of Pt (10 nm) / Co (10 nm) with diameters ranging from 180 nm to 1200 nm ( Fig. 1(a)) are defined by electron-beam lithography, sputtering, and lift-off. 18 We use the conductive tip of an atomic force microscope (AFM) to connect individual top electrodes and perform electric transport measurements under a constant v...

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Ferroelectric tunnel junctions with graphene electrodes

Cited by 111 publications

References 36 publications

Overcoming the Fundamental Barrier Thickness Limits of Ferroelectric Tunnel Junctions through BaTiO₃/SrTiO₃ Composite Barriers

Overcoming the Fundamental Barrier Thickness Limits of Ferroelectric Tunnel Junctions through BaTiO₃/SrTiO₃ Composite Barriers

Resonant tunneling across a ferroelectric domain wall

Tunnel electroresistance in BiFeO3 junctions: size does matter

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Ferroelectric tunnel junctions with graphene electrodes

Cited by 111 publications

References 36 publications

Overcoming the Fundamental Barrier Thickness Limits of Ferroelectric Tunnel Junctions through BaTiO3/SrTiO3 Composite Barriers

Overcoming the Fundamental Barrier Thickness Limits of Ferroelectric Tunnel Junctions through BaTiO3/SrTiO3 Composite Barriers

Resonant tunneling across a ferroelectric domain wall

Tunnel electroresistance in BiFeO3 junctions: size does matter

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Overcoming the Fundamental Barrier Thickness Limits of Ferroelectric Tunnel Junctions through BaTiO₃/SrTiO₃ Composite Barriers

Overcoming the Fundamental Barrier Thickness Limits of Ferroelectric Tunnel Junctions through BaTiO₃/SrTiO₃ Composite Barriers