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We consider a single Brownian particle confined in a double well potential (DWP) and investigate its response to a linear shear flow by means of the probability density and current determined via numerical solution of the Fokker-Planck equation. Besides a shear-dependent distortion of the probability distribution, we find that the associated current crossing the potential barrier exhibits a convex dependency on the shear rate when the DWP's minima are far apart. With decreasing distance this functional dependency changes from a convex to concave characteristics accompanied with an increase of the probability current crossing the DWP's barrier. Through the difference map of the particle density distribution it is possible to extract the shear-flow-induced contribution to the particle density driving the barrier-crossing current. This may open the possibility to design specific flow profiles to optimize flow-induced activated transport of nanoparticles. [ABSTRACT FROM AUTHOR]

Using Brownian dynamics simulations, we investigate how hydrodynamic interaction (HI) affects the behavior of tethered polymers in uniform flow. While it is expected that the HI within the polymer will lead to a dependency of the polymer's drag coefficient on the flow velocity, the interchain HI causes additional screening effects. For the case of two polymers in uniform flow with their tether points a finite distance apart, it is shown that the interchain HI not only causes a further reduction of the drag per polymer with decreasing distance between the tether points but simultaneously induces a polymer-polymer attraction as well. This attraction exhibits a characteristic maximum at intermediate flow velocities when the drag forces are of the order of the entropic forces. The effects uniquely attributed to the presence of HI can be verified experimentally. [ABSTRACT FROM AUTHOR]

We study the effect of vacancies and charged impurities on the performance of carbon nanotube transistors by self-consistently solving the three-dimensional Poisson and Schrödinger equations. We find that a single vacancy or charged impurity can decrease the drive current by more than 25% from the ballistic current. The threshold voltage shift in the case of charged impurities can be as large as 40 mV. [ABSTRACT FROM AUTHOR]

The potential for negative-capacitance field-effect transistors (NCFETs) to enhance the unity-current-gain cutoff frequency ${f}_{T}$ and ${g}_{m}{f}_{T}/{I}_{D}$ ratio through a technique that mitigates the impacts of extrinsic parasitic capacitances is investigated, where ${g}_{m}$ is the transconductance and ${I}_{D}$ is the dc drain current and where “extrinsic” refers to elements arising outside an “intrinsic” or core transistor structure. We explain the technique and show that NCFETs can provide significant gains in extrinsic ${f}_{T}$ and ${g}_{m}{f}_{T}/{I}_{D}$ from this mitigation effect. However, an inherent degradation of intrinsic ${f}_{T}$ needs to be addressed to maximize these benefits, and this degradation can be alleviated through channel-length scaling as well as supply- and threshold-voltage tuning. The relative influences of different extrinsic parasitic elements are also evaluated, and it is found that improvements to ${f}_{T}$ and ${g}_{m}{f}_{T}/{I}_{D}$ increase as extrinsic parasitic capacitance increases and decrease as extrinsic parasitic resistance increases. Overall, this work finds that NCFET structures are promising candidates to mitigate the impacts of extrinsic parasitics in aggressively scaled transistors for the next-generation RF applications. [ABSTRACT FROM AUTHOR]

We propose a parallel negative-capacitance field-effect transistor (P-NCFET) structure, in which a ferroelectric operating in its negative-capacitance region is placed in parallel with the gate and source terminals of a MOSFET. The P-NCFET is stabilized by combining careful matching of the ferroelectric with the gate capacitance along with simple feedback realized using current mirrors. The novel stabilization approach opens the possibility for a variety of new applications that exploit the negative capacitance of ferroelectrics to cancel capacitance in integrated circuits. As an example, we show the P-NCFET structure has a significantly higher unity-current-gain frequency ${f}_{T}$ compared to a conventional MOSFET. [ABSTRACT FROM AUTHOR]

We use full quantum-transport simulations by coupling the Landau–Khalatnikov (LK) and Poisson equations self-consistently with the nonequilibrium Green’s function (NEGF) formalism, and calibrated to experimental results, to investigate extremely scaled negative-capacitance, field-effect transistors (NCFETs) having dimensions toward the end of the international roadmap for devices and systems (IRDS), that is, to sub-10-nm gate lengths, where channel transport can be expected to be governed by quantum-mechanical effects. We identify how the ferroelectric affects both thermionic emission and quantum-mechanical tunneling of electrons, both of which are relevant transport mechanisms for these ultrascaled devices. Our detailed results show that while NCFETs are not immune to the increase in the tunneling as they undergo extreme channel-length scaling, the metal–ferroelectric–insulator–semiconductor (MFIS) structure will continue to offer benefits to a subthreshold slope, ON- and OFF-currents, drain-induced barrier lowering, and output conductance until the end of the roadmap. These improvements allow MFIS NCFETs of any given node to achieve similar performance to nonferroelectric devices of the immediately preceding (higher-dimension) node. The fundamental reason for the improvements is identified to be the presence of voltage amplification at the top of the barrier (TOB) and suppression of TOB movement with drain voltage. [ABSTRACT FROM AUTHOR]

As continuous development and optimization of negative-capacitance field-effect transistors (NCFETs) are pursued for digital applications, it is also desirable to examine the radio frequency (RF) performance of these devices, especially devices with the metal–ferroelectric–insulator–semiconductor (MFIS) structure. In this article, we use a combination of physics-based modeling and small-signal circuits to investigate the RF performance of MFIS NCFETs using three key device figures of merit: the well-known unity-current-gain (cutoff) frequency ƒT and the well-known maximum oscillation frequency ƒmax, and another important metric specified by gmƒT/ID , where gm is the transconductance and ID is the dc drain current. We find that MFIS NCFETs achieve similar ƒTand ƒmax performance to conventional MOSFETs, but offer a significant advantage in gmƒT/ ID. [ABSTRACT FROM AUTHOR]

Ferroelectric and negative-capacitance field-effect transistors (FeFETs and NCFETs) have recently garnered great attention as devices for applications in memory and low-power logic, respectively. As these technologies are pursued, it is critical to have a variety of measurement approaches, including methods familiar to the electron-device and microwave communities that can aid in fully understanding the behavior of ferroelectrics in FeFETs and NCFETs. In this paper, we propose and show the viability of using frequency-domain electrical measurement techniques employing the well-known microwave S-parameters, and their large-signal generalization and X-parameters. Our methods provide the means to trace the intrinsic polarization versus electric-field curve of the ferroelectric, i.e., with the parasitics de-embedded, thereby showing the innate ferroelectric response, which cannot be done using conventional techniques. These methods also enable extraction of all the parameters of the Landau–Khalatnikov equation, which is commonly used to model ferroelectric behavior in FeFETs and NCFETs. This paper hence takes a useful step toward methods familiar to the electron-device community that can help to better understand and optimize FeFET and NCFET technologies. [ABSTRACT FROM AUTHOR]

We investigate the channel material dependence of wave function deformation scattering (WDS), a phenomenon that occurs when the shape of the carrier wave function is forced to change as the channel is traversed. Line-edge roughness (LER) is one nonideality that can induce WDS in confined device geometries. We perform nonequilibrium Green's function simulations of ensembles of ultrascaled Fin Field Effect Transistors that exhibit correlated LER to determine the resulting on-current distributions. By considering various channel materials, we demonstrate two trends. First, WDS has a greater impact when the transport effective mass of the channel material is low, due to stronger coupling between conducting subbands. Second, WDS has a greater impact when the confinement effective mass of the channel material is high, due to the presence of more conducting subbands, which further enhances coupling. [ABSTRACT FROM AUTHOR]

We examine the impact of line-edge roughness (LER) on the variability in the on-current and saturation threshold voltage of ultrascaled FinFET devices via quantum-mechanical transport simulation. We obtain a realistic model of LER by decomposing the LER into short- $\lambda $ and long- $\lambda $ fluctuations, and we consider their separate influences on device performance. We show that the long- $\lambda $ fluctuations lead to greater device variability than the short- $\lambda $ fluctuations, and we explain the difference between the two cases via the influence of fluctuating quantum confinement arising from the LER. Finally, we consider devices in which the long- $\lambda $ fluctuations of the two fin edges are correlated and demonstrate that this correlation significantly improves the variability. Thus, we show the continued need for fabrication technology either to reduce the amplitude of the long- $\lambda $ fluctuations or to ensure the long- $\lambda $ fluctuations between the sidewalls of ultrascaled FinFET devices are correlated. [ABSTRACT FROM AUTHOR]

Recently, negative-capacitance FETs (NCFETs) have been proposed to reduce subthreshold slope and help continue supply-voltage scaling alongside channel-length scaling. We investigate the high-frequency switching behavior of NCFETs using the Landau–Khalatnikov equation to model ferroelectric materials. Multidomain interactions in the ferroelectric are considered, resulting in strong agreement with experimental measurements. Operation of NCFETs at gigahertz frequencies is investigated with this experimentally validated multidomain model. We find that the effectiveness of the voltage amplification in NCFETs is strongly dependent on the viscosity coefficient $\rho $ of the ferroelectric, and that a low \rho $ ( <0.1~\Omega \cdot \text {m} ) is required for the operation at the high gigahertz frequencies. [ABSTRACT FROM PUBLISHER]

The radio-frequency (RF) linearity performance potential of short-channel graphene field-effect transistors (GFETs) is assessed by using a nonlinear small-signal circuit model under the first approximation of ballistic transport. An intrinsic GFET is examined to reveal the key features of GFET linearity, and extrinsic parasitics are then included to assess the overall RF linearity. It is shown that short-channel GFETs can be expected to have a signature behavior versus gate bias that includes a constant-linearity region at low gate bias, sweet spots of high linearity before and after the gate bias for peak cutoff frequency, and poor linearity at the gate bias corresponding to the peak cutoff frequency. It is otherwise found that a GFET offers overall linearity that is comparable to a MOSFET and a CNFET, with the exception that the amount of intermodulation distortion in a GFET is dominated by the drain-injected carriers, a unique outcome of graphene's lack of a bandgap. Qualitative agreement with experiment in the signature behavior of GFET linearity supports the approach and conclusions. [ABSTRACT FROM PUBLISHER]

Microflows constitute an important instrument to control particle dynamics. A prominent example is the sorting of biological cells, which relies on the ability of deformable cells to move transversely to flow lines. A classic result is that soft microparticles migrate in flows through straight microchannels to an attractor at their center. Here, we show that flows through wavy channels fundamentally change the overall picture. They lead to the emergence of a second, coexisting attractor for soft particles. Its emergence and off-center location depends on the boundary modulation and the particle properties. The related cross-stream migration of soft particles is explained by analytical considerations, Stokesian dynamics simulations in unbounded flows, and Lattice-Boltzmann simulations in bounded flows. The novel off-center attractor can be used, for instance, in diagnostics, for separating cells of different size and elasticity, which is often an indicator of their health status. [ABSTRACT FROM AUTHOR]