Theoretical Approach to Electroresistance in Ferroelectric Tunnel Junctions

Chang, Sou-Chi; Naeemi, Azad; Nikonov, Dmitri E.; Gruverman, Alexei

doi:10.1103/physrevapplied.7.024005

Cited by 30 publications

(26 citation statements)

References 47 publications

(88 reference statements)

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“…Figures 3(a) and (b) show the transient voltage response in each layer for both high-k and FE MOS capacitors, respectively, and it can be immediately observed that the main difference between high-k and FE capacitors is the opposite sign of voltage drops across the high-k and FE layers in the steady state. Also, under the steady state, one can see that the direction of field across the FE oxide in the case of charge boost is opposite to that of polarization, which is the main feature of depolarization [14]. Hence, to achieve the inversion charge boost in the steady state, the field across the FE oxide has to be dominated by the depolarization, rather than the applied bias, which is also consistent to the thermodynamic picture given in Ref.…”

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confidence: 86%

“…V si is the silicon surface potential drop and V f b is the flat-band voltage given as φ 1 − φ 2 − E f,metal − δ with φ 1 and φ 2 being conduction band discontinuities at the metal/FE and DE/silicon interfaces, respectively, E f,metal is the Fermi energy of metal, and δ is the energy difference between conduction band and Fermi level in the quasi-equilibrium region of p-type silicon. For a given ρ s , V metal and V DE are given as [14] V…”

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confidence: 99%

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Inversion Charge Boost and Transient Steep-Slope Induced by Free-Charge-Polarization Mismatch in a Ferroelectric-Metal–Oxide–Semiconductor Capacitor

Chang

Avci

Nikonov

et al. 2018

IEEE J. Explor. Solid-State Comput. Devices Circuits

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In this letter, the transient behavior of a ferroelectric (FE) metal-oxide-semiconductor (MOS) capacitor is theoretically investigated with a series resistor. It is shown that compared to a conventional high-k dielectric MOS capacitor, a significant inversion charge-boost can be achieved by a FE MOS capacitor due to a steep transient subthreshold swing (SS) driven by the free chargepolarization mismatch. It is also shown that the observation of steep transient SS significantly depends on the viscosity coefficient under Landau's mean field theory, in general representing the average FE time response associated with domain nucleation and propagation. Therefore, this letter not only establishes a theoretical framework that describes the physical origin behind the inversion charge-boost in a FE MOS capacitor, but also shows that the key feature of depolarization effect on a FE MOS capacitor should be the inversion-charge boost, rather than the steep SS (e.g., sub-60mV/dec at room temperature), which cannot be experimentally observed as the measurement time is much longer than the FE response. Finally, we outlines the required material targets for the FE response in field-effect transistors to be applicable for next-generation high-speed and low-power digital switches.The relentless pursuit of Moore's law in the past four decades leads to a significant improvement in the computing power of modern microprocessors [1]. However, as the scaling of CMOS transistors continues, the on-off current ratio is dramatically reduced, and thus the increasing static power makes the circuit design more and more difficult for high energy-efficient applications [2]. In 2008, a transistor structure using FE materials in the gate stack was proposed to improve SS through stabilizing FE negative capacitance in the steady state [3]. However, the central idea of this proposal is all based on the S-shape of polarization-electric field relation given by Landau's free energy functional, which has been under debate if it can physically describe the polarization switching in the FE oxide [4]. In 2015, a transient differential negative capacitance was reported from a circuit composed of a resistor and a FE capacitor in series [5]. Our recent work theoretically proved that this differential negative capacitance is driven by the free charge-polarization mismatch as qualitatively pointed out in Ref. [6], which can be well described under Landau's mean field theory [7]. In 2018, the transient differential negative capacitance has been also experimentally observed in a FE MOS capacitor [8], indicating the existence of transient mismatch between bound charge and free charge in a MOS structure. The effect of free charge-polarization mismatch on transient behavior of a FE transistor was qualitatively discussed in Ref. [9], where the importance of measurement time in FE transistor characterization is emphasized but no inversion charge-boost in the steady-state from a FE transistor is concluded. Hence, in this letter, a numerical model is developed to invest...

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confidence: 86%

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confidence: 99%

Inversion Charge Boost and Transient Steep-Slope Induced by Free-Charge-Polarization Mismatch in a Ferroelectric-Metal–Oxide–Semiconductor Capacitor

Chang

Avci

Nikonov

et al. 2018

IEEE J. Explor. Solid-State Comput. Devices Circuits

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“…In Eq. 13, the potential energy drop within the metal is described under the Thomas-Fermi approximation [25]. For a given E F E .…”

Section: Theoretical Modelmentioning

confidence: 99%

A Thermodynamic Perspective of Negative-Capacitance Field-Effect Transistors

Chang

Avci

Nikonov

et al. 2017

IEEE J. Explor. Solid-State Comput. Devices Circuits

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Physical phenomena underlying operation of ferroelectric field-effect transistors (FeFETs) is treated within a unified simulation framework. The framework incorporates the Landau mean-field treatment of free energy of a ferroelectric and the polarization dynamics according to Landau-Khalatnikov (LK) equation. These equations are self-consistently solved with the one-dimensional metal-oxide-semiconductor (MOS) structure electrostatics and the drift-diffusion solution for the current in the semiconductor channel. Numerical simulations demonstrate, depending on the ferroelectric (FE) thickness, both regimes of hysteresis switching (relevant for a non-volatile memory) and of higher on-currents and steeper subthreshold slope (SS) with a negligible hysteresis (relevant for logic) via the negative capacitance effect.

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“…39 In a recent paper, the NEGF method and the Landauer formula were used to model I-V curves of step barrier FTJs. 40 The results suggest that both the height and thickness of a CoO x buffer layer forming at the Co/BaTiO 3 interface may change under bias.…”

Section: Modeling Of Tunneling Currents In Ftjsmentioning

confidence: 91%

Tsu-Esaki modeling of tunneling currents in ferroelectric tunnel junctions

Tuomisto

Dijken

Puska

2017

Journal of Applied Physics

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Theoretical Approach to Electroresistance in Ferroelectric Tunnel Junctions

Cited by 30 publications

References 47 publications

Inversion Charge Boost and Transient Steep-Slope Induced by Free-Charge-Polarization Mismatch in a Ferroelectric-Metal–Oxide–Semiconductor Capacitor

Inversion Charge Boost and Transient Steep-Slope Induced by Free-Charge-Polarization Mismatch in a Ferroelectric-Metal–Oxide–Semiconductor Capacitor

A Thermodynamic Perspective of Negative-Capacitance Field-Effect Transistors

Tsu-Esaki modeling of tunneling currents in ferroelectric tunnel junctions

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