Negative Capacitance Effect Research Articles

Electric field control of labyrinth domain structures in core-shell ferroelectric nanoparticles

In the framework of the Landau-Ginzburg-Devonshire (LGD) approach, we studied the possibility of controlling the polarity and morphology of equilibrium domain structures by a homogeneous external electric field in a nanosized ferroelectric core covered with an ultrathin shell of screening charge. Under certain screening lengths and core sizes, the minimum of the LGD energy, which consists of Landau-Devonshire energy, Ginzburg polarization gradient energy, and electrostatic terms, leads to the spontaneous appearance of stable labyrinth domain structures in the core. The labyrinths evolve from an initial polarization distribution consisting of arbitrarily small randomly oriented nanodomains. The equilibrium labyrinth structure is weakly influenced by details of the initial polarization distribution, such that one can obtain a quasicontinuum of nearly degenerate labyrinth structures, whose number is limited only by the mesh discretization density. Applying a homogeneous electric field to a nanoparticle with labyrinth domains, and subsequently removing it, allows inducing changes to the labyrinth structure, as the maze polarity is controlled by a field projection on the particle polar axis. Under specific conditions of the screening charge relaxation, the quasistatic dielectric susceptibility of the labyrinth structure can be negative, potentially leading to a negative capacitance effect. Considering the general validity of the LGD approach, we expect that an electric field control of labyrinth domains is possible in many spatially confined nanosized ferroics, which can be potentially interesting for advanced cryptography and modern nanoelectronics.

Confinement-Driven Inverse Domain Scaling in Polycrystalline ErMnO3.

The research on topological phenomena in ferroelectric materials has revolutionized the way people understand polar order. Intriguing examples are polar skyrmions, vortex/anti-vortex structures, and ferroelectric incommensurabilties, which promote emergent physical properties ranging from electric-field-controllable chirality to negative capacitance effects. Here, the impact of topologically protected vortices on the domain formation in improper ferroelectric ErMnO3 polycrystals is studied, demonstrating inverted domain scaling behavior compared to classical ferroelectrics. It is observed that as the grain size increases, smaller domains are formed. Phase field simulations reveal that elastic strain fields drive the annihilation of vortex/anti-vortex pairs within the grains and individual vortices at the grain boundaries. The inversion of the domain scaling behavior has far-reaching implications, providing fundamentally new opportunities for topology-based domain engineering and the tuning of the electromechanical and dielectric performance of ferroelectrics in general.

Systematic Interpretation of Time Effect on Negative Capacitance of Ferroelectrics Based on Electrostatics and Charge Dynamics

Negative capacitance (NC) effects in ferroelectric (FE) films have attracted intensive attention recently in terms of both polarization kinetics modeling and low-power CMOS applications. Its physical origin, however, is controversial because the experimentally observed NC effects are different from the initial concept, particularly on the frequency/voltage dependence and hysteresis. Recently, we have proposed an electrostatic model, with which the NC effect with hysteresis and voltage dependence in FE/paraelectric (PE) stacks in dc mode is explained from a viewpoint of polarization switching. Based on this, in this work, the NC effect in the dimension of time in both FE/PE and FE capacitor–resistor (FE-R) circuit is analytically formulated and experimentally studied by comprehensively considering the dynamics of polarization switching, charge communication with power supply, and charge leaking through the capacitor. Our results suggest that such NC effects only occur in a time window in both systems and a competition between FE switching and charge compensation is the key to determine the time window. Thus, a systematic understanding is accomplished to explain most of the phenomenon associated with NC effects in FEs.

Low-power double-gate MoS2 negative capacitance transistors with near-zero DIBL

Negative capacitance (NC) devices hold great promise for improving subthreshold slope (SS). However, the theoretical exploration of the short-channel effect in NC and two-dimensional (2D) materials remains an ongoing challenge in device scaling. The present work demonstrates a double-gate MoS2 negative capacitance field-effect transistor (MoS2 DG-NCFET) with low power and near-zero drain-induced barrier lowering (DIBL) by exploring its design space considering the impact of various MoS2 layers, with the aid of the developed 2D short-channel model containing the NC effect and numerical simulation. The proposed monolayer MoS2 DG-NCFET model is solved by unifying the long and short channel models coupled with the one-dimensional Landau-Khalatnikov equation. The study indicates that a lower SS, considerable voltage saving (), and even the ability to achieve zero DIBL are seen in monolayer MoS2 devices when compared with those of non-2D MoS2, due to the combination of the atomic-scale thickness of channels and the double-gate structure. This study provides an insight for further reducing the feature size of ultralow power transistors.

Design and performance analysis of gate-all-around negative capacitance dopingless nanowire tunnel field effect transistor

In this paper, a novel low power consumption device based on a dopingless gate-all-around nanowire tunnel field effect transistor (TFET) with negative capacitance (NC) effect is proposed. NC is a robust approach in solving the bottleneck issues encountered by devices operating in nanoscale domains. Additionally, the threshold voltage (V T) and subthreshold swing (SS) are dropped significantly to less than 60 mV/decade. Negative capacitance makes a significant contribution to the device’s performance by lowering the operating voltage for low-power applications. To calculate the optimum bias, the Landau–Khalatnikov (L–K) equation was used. To evaluate the influence of NC, the ferroelectric (FE) material PZT (lead zirconate titanate), which has perovskite properties, was used as a gate insulator. Thus, the gate-all-around dopingless nanowire TFET (GAA DL NW TFET) device structure is reconfigured into GAA NC DL NW TFET. PZT has an appropriate polarization rate, high dielectric capacitance, and a high degree of reliability. To achieve an SS lower than 60 mV/decade at lower V T, effective tuning of the FE thickness is critical to avoid hysteresis, which enhances the overall performance of the proposed device. The aggressively scaled device has the problem of fabrication complexity and its associated cost that is addressed with the help of the dopingless technique to the nanowire-based TFET. The enhancement of the ON-current with an improved steep SS was addressed. With the application of the NC technique, the proposed device showcased an improved 4 µA µm−1 of I ON, and 1012 of current ratio. Additionally, the influence of the variation in FE thickness on the performance parameters is examined. The proposed device structure operates at a minimum operating voltage, making it an ideal choice for low-power voltage applications.

Constructing an Overall Static Negative Capacitance Effect via Energy Landscape Designing

AbstractThe negative capacitance (NC) effect in ferroelectrics and antiferroelectrics is promising to reduce power dissipation and enable energy storage applications. However, the limited electric field scale and hysteresis properties of NC effect in ferroelectrics and antiferroelectrics seriously limit its application in transistors and energy‐storage supercapacitors. Here, an overall (non‐local) static (hysteresis‐free) NC effect is developed via energy landscape designing. The ferroelectric structure is introduced into the traditional antiferroelectric PbZrO3 film, thus the single‐well energy landscape is tuned to an upper convex function. This anomalous energy landscape generates a hysteresis‐free and single‐valued polarization‐electric field behavior (P–E) curve with a negative slope (dP/dE < 0), which guarantees the NC effect is static and available over the entire electric field range. Such an NC effect in PbZrO3 film is stabilized by connecting a dielectric Al2O3 layer in series. This finding advances the practical application of the NC effect, especially in transistors and supercapacitors.

Physics and Modeling of Multidomain FeFET With Domain Wall-Induced Negative Capacitance

In this article, we present the dynamics and modeling of multidomains in the ferroelectric FET (FeFET). Due to the periodic texture of domains, the electrostatics of the FeFET exhibit an oscillatory conduction band profile. To capture such oscillations, we solve coupled 2-D Poisson’s equation with the net ferroelectric energy density (gradient energy + free energy + depolarization energy) equation. Multidomain dynamics are captured by minimizing the net ferroelectric energy, leading to a thermodynamically stable state. Furthermore, we show that the motion of domain walls originates from local bound charge density in the ferroelectric region, which induces the negative capacitance (NC) effect. The strength of domain wall-induced NC is determined by the gradient energy of the ferroelectric material. FeFET exhibits variability in the drain current with domain period due to the inherent NC effect. Additionally, the impact of domain wall transition (soft <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\rightleftharpoons $ </tex-math></inline-formula> hard) on the device’s electrostatic/transport is also analyzed. The model also accurately captures both nucleations of a new domain and the motion of the domain wall. Furthermore, the model is thoroughly validated against experimental results and phase-field simulations.

Energy conversion analysis of ion wind in surface dielectric barrier discharge at low pressure

Ionic wind actuators are widely used in temperature control, food drying, aircraft propulsion, combustion, air purification, and many other fields. The energy conversion efficiency of ion-wind actuator has been low for a long time. In this paper, a lumped parameter circuit model is established for the surface dielectric barrier discharge structure, and the energy conversion path in the discharge process is proposed for the first time. According to the circuit topology, part of the energy loss is calculated. Based on the mathematical calculations of the circuit model, we discovered the possibility of “negative capacitance effect” in the plasma area, and the experimental verified the correctness of the theoretical deduction and prediction. Meanwhile, the results show that the equivalent capacitance of the solid dielectric is equal to the bottom slope of Lissajous graph, and the negative capacitance effect can effectively reduce the proportion of solid dielectric loss and relaxed polarization loss. The negative capacitance effect improves the energy conversion efficiency of the ionic wind exciter, and the maximum increase ratio is about 47.8%. With the increase of voltage, the deviation between the calculated value of theoretical model and the measured value increases gradually, and finally stabilizes at about 41%.

Observability of negative capacitance of a ferroelectric film: Theoretical predictions

We theoretically explore mechanisms that can potentially give rise to the steady-state and transient negative capacitance in a uniaxial ferroelectric film stabilized by a dielectric layer. The analytical expressions for the steady-state capacitance of a single-domain and polydomain states are derived within the Landau-Ginzburg-Devonshire approach and used to study the state stability vs the domain splitting as a function of dielectric layer thickness. Analytical expressions for the critical thickness of the dielectric layer, polarization amplitude, equilibrium domain period, and susceptibility are obtained and corroborated by finite element modeling. We further explore the possible effects of nonlinear screening by two types of screening charges at the ferroelectric-dielectric interface and show that if at least one of the screening charges is very slow, the total polarization dynamics can exhibit complex time- and voltage-dependent behaviors that can be interpreted as an observable negative capacitance. In this setting, the transient negative capacitance effect is accompanied by almost zero dielectric susceptibility in a wide voltage range and low frequencies. These results may help to elucidate the observation of the transient negative capacitance in thin ferroelectric films, and identify materials systems that can give rise to the behavior.

Growth and characterization of (glass, Ag)/SeO2 thin films

Herein, thin films of SeO2 coated onto glass and Ag thin film substrates are studied and characterized. The films which are prepared by a vacuum evaporation technique, displayed Ag-metal induced crystallization process. The grown films are composed of tetragonal structure of SeO2 as major phase and orthorhombic β−Ag2Se as minor phase. The optical studies showed that the films exhibit an energy band gap of 3.69 eV. In addition, the analyses of the dielectric dispersion spectra indicated the nonlinear character of dielectric response. The SeO2 films response to oscillatory electromagnetic field is accompanied with drift mobility values in the range of 5.02–12.06 cm2/Vs. Moreover, polycrystalline SeO2 films coated onto Ag substrates are found appropriate for use as negative capacitance (NC) sources in the frequency domain of 0.41–1.80 GHz. Accompany with the NC effect, negative conductance (NG) effect was observed near 0.410 GHz and near 1.53 GHz.

Negative Capacitance in HfO2 Gate Stack Structures With and Without Metal Interlayer

In this work, we experimentally explore and compare FET gate stacks with and without an inner metal plane between a linear dielectric (SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) and a ferroelectric layer (Si-doped HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) operating in the negative capacitance (NC) regime. The use of nanosecond-range pulses enables us to observe hysteresis-free NC and reconstruct the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${S}$ </tex-math></inline-formula> -shaped polarization-voltage curves. The devices with the inner metal plate show a higher equivalent NC value, which offers the potential for a higher differential amplification in a NC-FET. However, such a NC region is observed over a smaller range of electric field and polarization, which leads to hysteresis. Moreover, the presence of a metal layer in between the ferroelectric and the insulator favors domain formation resulting in destabilization of the NC effect. For the gate structure where the ferroelectric and the insulator are in contact, the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${S}$ </tex-math></inline-formula> -shaped polarization-voltage curve shows a better agreement with Landau–Ginzburg–Devonshire formalism for the monodomain state. The uniform polarization closely mimicking the monodomain state is possible due to the polarization imprint occurring due to the structural asymmetry. By nanometer resolution polarization mapping via off-resonance piezoelectric force microscopy (PFM), we corroborate the presence of imprint, which can intrinsically stabilize one ferroelectric state. Overall, the article provides an experimental demonstration that the absence of the inner metal plane in the gate structures stabilizes the NC regime favorable for hysteresis-free NC-FET.

Understanding negative capacitance physical mechanism in organic ferroelectric capacitor

The physical mechanism of the negative capacitance (NC) effect in an organic ferroelectric (OFE) remains unknown. Therefore, this paper presents a series circuit of a resistor and an OFE capacitor (R-OFEC) based on experimentally validated Ginzburg-Landau-Khalatnikov (GLK) theory, electrostatics, and Kirchoff’s circuit rule to understand the transient NC (TNC) mechanism in TCAD environment. We show that: (i) the fundamental mechanism of TNC in an R-OFEC is caused by switching rate difference between the free charge (QOFE) and OFE polarization (POFE) during the two stable state switching processes; (ii) QOFE-POFE difference is induced by the NC region of the OFE’s double-well free energy landscape and its relationship with the change in voltage transient is demonstrated analytically; (iii) a bipolar pulsing is needed for TNC appearance; (iv) TNC appears immediately when the change in voltage across the OFEC per unit time is negative. Finally, the TNC effect caused by the QOFE-POFE difference is justified by its dependence on R.

Ge/GaAs Based Negative Capacitance Tunnel FET Biosensor: Proposal and Sensitivity Analysis

A highly sensitive, accurate, fast and power efficient biosensor is the need of the hour. Undoubtedly, dielectrically modulated (DM) tunnel FET (TFET) assures better sensitivity as compared to MOSFET biosensors in case of label-free biosensing. However, there exists immense possibilities to upgrade TFET biosensor properties through the improvement of its DC characteristics. Therefore, in this paper a ferroelectric (FE) gate oxide and a hetero material (HM) source/drain-channel based TFET is designed for biosensor applications. A FE layer of HfZrO2 above SiO2 gives rise to negative capacitance (NC) effect that causes voltage amplification and hence, boosts subthreshold swing (SS) and ION/IOFF ratio. In addition, use of a low band gap material (Ge) in source and a high band gap material (GaAs) in drain-channel junctions enhances the probability of band-to-band-tunneling (BTBT) of charge carriers. Further, to introduce biomolecules, a cavity is impinged below HfZrO2 near SiO2 above source/channel junction that modulates BTBT as a function of charge density (Nf) and dielectric constant (K). This paper presents a detailed comparative analysis of Ge/GaAs-NCTFET and Ge/GaAs-TFET biosensors for different K and Nf values from which we can conclude that the incorporation of NC effect in TFET biosensors leads to enhanced sensitivity with high speed and low power consumption.

Design and Characterization of (Yb, Al, Cu, Au)/GeO2/C As MOS Field Effect Transistors, Negative Capacitance Effect Devices and Band Pass/Reject Filters Suitable for 4G Technologies

Design and Characterization of (Yb, Al, Cu, Au)/GeO2/C As MOS Field Effect Transistors, Negative Capacitance Effect Devices and Band Pass/Reject Filters Suitable for 4G Technologies

Dopingless Negative Capacitance Ferroelectric TFET for Breast Cancer Cells Detection: Design and Sensitivity Analysis.

The current research article reports the electrical detection of breast cancer cell lines (MDA-MB-231, Hs578T, T47D, and MCF-7) by deploying dopingless negative capacitance (NC) ferroelectric (FE) tunnel field-effect transistor (DL-FE-TFET). This device has a double dual metal gate and two nanocavities engraved underneath both gate electrodes for higher detection sensitivity. Our work reports the detection of nontumorigenic cell (MCF-10A) and breast cancer cell lines by combining the NC effect of FE material and dopingless technology synergistically. Here, FE material amplifies the applied gate bias intrinsically. The in-depth electrostatic analysis in terms of surface potential, carrier concentration, energy band diagram, drive current, and electric field has been depicted. Variation of the dielectric constant of these breast cancerous cell lines dictates the detection mechanism in our reported biosensor. The sensitivity has been analyzed in terms of drive current, ION/IOFF ratio, [Formula: see text], and transconductance. The optimized cavity structure demonstrates significantly high drain current sensitivity of the order of 2.88×109 and ION/IOFF ratio sensitivity of the order of 3.2×105 . In addition, the effect of device geometry variation, such as cavity length and FE layer thickness on the drain current sensitivity and ION/IOFF sensitivity, transconductance sensitivity ( Sgm ), and threshold voltage sensitivity ( [Formula: see text]) of the device, has also been investigated. This device structure may be deployed for the array-based screening and diagnosis of breast cancer cells lines, with additional benefits including a simpler mechanism of transduction, cost effectiveness, technology compatibility with CMOS process, adjustable electrical response, and reproducibility.

Negative Capacitance from the Inhomogenous Stray Field in a Ferroelectric–Dielectric Structure

AbstractThe phenomenological Landau–Ginzburg–Devonshire model provides a fundamental background for an understanding of the peculiar charge–voltage behavior of ferroelectric (FE) materials. However, the model cannot explain the polarization behavior of multidomain FE materials. The experimentally observed negative capacitance (NC) effect, which is interpreted as an emergence of the Landau barrier effect, involves particular conceptual difficulty. This work provides a new conceptual framework to explain the quasi‐static NC effect based on the energy formula for a stacked dielectric/ferroelectric (DE/FE) layer structure with the multidomain configuration with arbitrary shape. The presence of such domain configuration causes the energy–displacement curve of the inhomogenous Helmholtz energy term to have negative curvature. This is caused by the stray field between the neighboring domains. The model can be further extended to the DE/FE system with polycrystalline FE grains using the advanced phase‐field analysis. It is determined that the NC effect from the stray field is a universal phenomenon. These models provide quantitative explanations for the previously reported short‐pulse measurement results for various DE/FE material systems, which have lacked accurate interpretations.

Design of JL-CFET (junctionless complementary field effect transistor)-based inverter for low power applications

Junctionless complementary field effect transistor (JL-CFET) is an emerging device that needs a small layout area and low fabrication cost. However, in order for the JL-CFET to be adopted for low power applications, two main constraints need to be overcome: (a) a high work function of metal gate and (b) a low drain current. In this work, an optimal device design is proposed to overcome those problems, by analyzing various performance metrics, such as on-state drive current, subthreshold swing, drain induced barrier lowering, propagation delay time, and ring oscillator’s oscillation frequency, which are extracted from various structures of JL-CFET. In addition, the negative capacitance effect in JL-CFET is examined to address the limit from device structures.

Analytical model of subthreshold drain current for nanoscale negative capacitance junctionless FinFET

In this article, an analytical Subthreshold Drain Current model has been developed for Negative Capacitance Junctionless FinFET (NC-JL FinFET). To obtain the subthreshold current model for NC-JL FinFET the drift-diffusion equation is solved by including negative capacitance effect through LK equation and further utilized to attain the expression of subthreshold slope (SS). The influence of the fringing field due to source/drain spacer on the subthreshold current has been included in the model. The model predictions turn out to be in fair agreement with numerical simulation results. The performance of NC-JL FinFET is also examined for different technology nodes. Also, the influence of physical parameters like ferroelectric thickness, gate dielectric constant, fin thickness, spacer length etc. has also been analyzed. Further, the SS is also examined for variations in several device design parameters. It has been revealed that the NC-JL FinFET improves subthreshold current and SS by almost 80% and 16.7%, respectively as compared to JL FinFET.

Physical Cause and Impact of Negative Capacitance Effect in Ferroelectric P(VDF-TrFE) Gate Stack and Its Application to Landau Transistor

A novel approach to overcome Boltzmann’s tyranny is to exploit the negative capacitance (NC) effect found naturally in many ferroelectric (FE) materials. We apply a set of coupled equations based on electrostatics, Kirchoff’s law, and a well-calibrated Ginzburg-Landau-Khalatnikov technology computer-aided design (TCAD) model to simulate an organic FE poly(vinylidene fluoride-co-trifluoroethylene) [P(VDF-TrFE)]-based resistor metal-FE-metal (R-MFM) series circuit and a Landau transistor (LT) exhibiting sub-60 mV/decade subthreshold swing (SS). TCAD simulation parameters for P(VDF-TrFE) are derived from the reported experimental polarization versus voltage characteristics using Landau theory. Unlike oxide FEs, the P(VDF-TrFE)-based R-MFM series circuit can exploit the NC effect at a lower supply voltage (VG) of ±0.5 V with little energy dissipation of ~2.7 fJ through R. Our simulation results show an 84.89% reduction in the P(VDF-TrFE)’s coercivity concerning the oxide FE. We show that the underlying mechanism of the NC effect is directly related to FE polarization (FE-P) switching. The NC effect occurs only when the FE-P is in the negative curvature of the P(VDF-TrFE)’s free energy landscape. The NC effect is explored in terms of VG, FE thickness, domain variations, R, and dipole switching resistivity. The influence of R variation on the NC time (δt) is investigated at 100 kHz. We can observe that δt and R have a linear relationship. As R approaches zero, we determined that the inherent FE-P switching speed exclusively restricts the NC effect. Finally, a 32 nm P(VDF-TrFE) LT provides a minimal SS of 23.39 mV/decade, 74.92% less than its CMOS counterpart. Therefore, the proposed organic MFM stack could open the path for developing beyond CMOS transistor technology operating in sub-60 mV/decade.

Whither Steady-State Negative Capacitance of a Ferroelectric Film?

We theoretically explore mechanisms that can potentially give rise to steady-state negative capacitance in a uniaxial ferroelectric film stabilized by a dielectric layer. The analytical expressions for the steady-state capacitance of a single-domain state are derived within Landau-Ginzburg-Devonshire approach and used to study the state stability vs. the domain splitting as a function of dielectric layer thickness. Analytical expressions for the critical thickness of the dielectric layer, polarization amplitude, equilibrium domain period and susceptibility are obtained and corroborated by finite element modelling. In the absence of screening charges neither single-domain, nor poly-domain states can exhibit globally-detectable steady-state negative capacitance. We further explore the possible effects of nonlinear screening at the ferroelectric-dielectric interface and show that if at least one of the screening charges is very slow, the total polarization dynamics can exhibit complex time- and voltage dependent behaviors that can be interpreted as a negative capacitance. In this setting, the negative capacitance effect is accompanied by almost zero dielectric susceptibility in a wide voltage range and low frequencies. These results may help to elucidate the fundamental dispute about the possible origin of the quasi-steady-state negative capacitance in thin ferroelectric films, and identify materials systems that can give rise to this behavior.