Model For Short-channel Effects Research Articles

Compact modeling of short-channel effects in back-gated 2D negative capacitance (NC) FETs

The negative capacitance field-effect transistor with 2D channel material (2D NC-FET) holds significant promise for low-power applications owing to its remarkable resilience against short-channel effects (SCEs) and favorable noise characteristics. In this study, we establish a compact current–voltage (I–V) model for short-channel back-gated 2D NC-FETs with metal-ferroelectric-metal–insulator–semiconductor structure by self-consistently solving the two-dimensional Poisson, drift–diffusion and Landau–Khalatnikov equations. The proposed model is valid and continuous throughout the entire operating regime, including the fully-depleted region, partly-depleted region, and accumulation region. Furthermore, we derive analytical equations for the threshold voltage ( VTH ) and subthreshold swing ( SS ) of back-gated 2D NC-FETs based on the developed I–V model. Lastly, we elucidate the influence mechanisms of various device parameters and voltage bias on the subthreshold characteristics of short-channel back-gated 2D NC-FETs using the proposed I–V model in conjunction with analytical expressions of VTH and SS . Our findings reveal that back-gated 2D NC-FETs shows unconventional degradation behavior in VTH and SS, resulting from the competition between traditional SCEs and novel negative capacitance effects.

Compact Modeling of Short-Channel Effects in Staggered Organic Thin-Film Transistors

This article introduces analytical compact models of short-channel effects in staggered organic thin-film transistors (TFTs). The effects of subthreshold-swing degradation, threshold-voltage roll-off, and drain-induced barrier lowering (DIBL) on the static current-voltage characteristics of staggered TFTs are extracted from an analytical potential solution of the 2-D problem of the staggered geometry. This solution is derived by using the Schwarz-Christoffel transformation that leads to a complex mapping function linking the staggered geometry to an equivalent in another coordinate system for which an analytical potential solution exists. The technology CAD (TCAD) Software Sentaurus is used to verify the compact models. Finally, the closed-form and physics-based equations are incorporated into an existing compact current model and verified by measurements on staggered organic TFTs with channel lengths as small as 0.4 μm fabricated on flexible plastic substrates by stencil lithography.

Analytical Modeling of Short-Channel Effects in MFIS Negative-Capacitance FET Including Quantum Confinement Effects

An analytical 2-D model of double-gate metal-ferroelectric-insulator-semiconductor-negative-capacitance FET (MFIS-NCFET), using Green's function approach, in the subthreshold region, is presented in this article. The explicit solution of coupled 2-D Landau-Devonshire and Poisson equations is analytically derived. Subsequently, an analytical and explicit model of subthreshold slope is developed from potential functions. The developed model includes quantum-mechanical effects, which considers not only geometrical confinements but also electrical confinements. The analytical solution of a 2-D nonhomogeneous Poisson equation coupled with the 1-D Schrödinger equation is used to obtain the potential function in the channel. The impact of the ferroelectric thickness (t <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">fe</sub> ) on quantum confinement is also studied. We find that larger tfe reduces the quantum confinement effect. Therefore, as t <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">fe</sub> increases, threshold voltage roll-off with the variation in Si-body thickness decreases.

Modeling of Short-Channel Effects in GaN HEMTs

In this article, we propose an explicit and analytic charge-based model for estimating short-channel effects (SCEs) in GaN high-electron-mobility transistor (HEMT) devices. The proposed model is derived from the physical charge-based core of the Ecole Polytechnique Federale de Lausanne (EPFL) HEMT model, which treats HEMT as a generalized MOSFET. The main emphasis of this article is to estimate SCEs by effectively capturing 2-D channel potential distribution to calculate the reduced barrier height, drain-induced barrier lowering (DIBL), velocity saturation, and channel length modulation (CLM). The model is validated with TCAD simulation results and agreed with measurement data in all regions of operation. This represents the main step toward the design of high-frequency and ultralow-noise HEMT devices using AlGaN/GaN heterostructures.

Modeling of Short-Channel Effects in DG MOSFETs: Green’s Function Method Versus Scale Length Model

This paper compares two different analytic solutions to the 2-D potential in double-gate MOSFETs in subthreshold: Green's function method and scale length model. Both models produce closed-form potential functions for every point in Si based on rigorous approaches to Poisson's equation with boundary conditions. It is shown that despite the vastly different mathematical equations, the I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ds</sub> -V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">gs</sub> characteristics generated from each model are completely consistent with each other and with Technology Computer Aided Design (TCAD). Testing examples include undoped and highly doped cases of both polarities, junction and junctionless. Also included is a case of severe short-channel effects.

Dual-Gate JFET Modeling II: Source Pinchoff Voltage and Complete Modeling Formalism

This paper studies the phase diagram of source pinchoff of dual-gate JFETs and presents a source pinchoff modeling formalism that is smooth across the phase boundaries. Based on this, an $I_{\textrm {ds}}$ model is derived, which is numerically robust for any value of top- and bottom-gate voltages. The method is applied to both the exact model for $I_{\textrm {ds}}$ and an approximated form based on mid-point-potential linearization, and is verified by comparison with numerical simulation. Modeling of short-channel effects is included.

An analytical 3D model for short-channel effects in undoped FinFETs

An analytical and scalable model for the threshold voltage in FinFETs has been developed by solving the 3-D Poisson equation using appropriate techniques. The model is also based on a physical anal...

Compact model of short-channel effects for FDSOI devices including the influence of back-bias and fringing fields for Si and III–V technology

In this work, a compact model for short-channel effects is proposed for fully depleted silicon-on-insulator (FDSOI) MOSFETs, which takes into account the impact of body-bias and fringing fields, developed to be suitable for both thin and thick buried oxide (BOX) devices. The model is derived using the Voltage-Doping Transform, confirmed with TCAD simulations and experimental data from the literature. The impact of the BOX thickness on the subthreshold swing and the contribution of the leakiest path position to the DIBL are finally discussed.

Accurate Boundary Condition for Short-Channel Effect Compact Modeling in MOS Devices

In this paper, the boundary conditions at the edges of the junctions are discussed, and their consequences on the compact modeling of short-channel effects (SCEs) in MOSFETs are investigated. It is first shown that the previous voltage-doping transform (VDT) potential model does not agree with the simulation results when the impact of lightly doped drain regions or thin spacers are considered. A solution is then proposed to correct the channel potential model using more accurate boundary conditions at the edges of the channel, which consist in calculating an accurate effective built-in potential value V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">bi</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">eff</sup> at the source and at the drain. The impact of these improved boundary conditions on compact models of SCEs is investigated. It is shown that the previous VDT models of drain-induced barrier lowering and subthreshold swing for all types of fully depleted devices can be very simply corrected to finely agree with the simulations without fitting parameters. These models finally allow to investigate the impact of the doping concentration of the junctions on the device performance.

Nanoscale triple-gate FinFET design considerations based on an analytical model of short-channel effects

In this paper, a three-dimensional (3-D) analytical model for short-channel effects (SCEs) in a nanoscale triple-gate (TG) FinFET is derived based on solving a boundary value problem using the 3-D Poisson's equation. This model is validated using 3-D numerical simulations (TCAD Sentaurus). Results show that SCEs in a TG FinFET can be controlled by reducing either the fin thickness ( D ) or height ( H ). On the other hand, when fixing the drive capability of turn-on current, i.e. fixing the total width of the conductive channel, and changing the ratio of D and H , there exists a case where SCEs are worst, and SCEs can be reduced by either increasing or decreasing the ratio from the worst case. This SCEs model can be used to predict the minimum channel length ( L min ) of a device when D , H , and tox are fixed, while keeping SCEs at a tolerable level. Based on the analytical model, the insights into the physics of SCEs in nanoscale TG FinFET are discussed, and design considerations are investigated.

Compact modeling of short-channel effects in symmetric and asymmetric 3-T/4-T double gate MOSFETs

In this paper, a two dimensional compact model for the potential distribution of double gate MOSFETs is presented. The approach uses the evanescent method along with the assumption of a parabolic potential distribution in the direction transverse to the channel in the subthreshold region and at the threshold condition. The model introduces a characteristic length which is obtained using an explicit expression. The model may be applied to all double gate structures including both symmetric and asymmetric, 3-terminal (3-T) and 4-terminal (4-T) devices. Based on this potential distribution model, the main short-channel effects including subthreshold swing, drain induced barrier lowering, and the threshold voltage are investigated. The model shows an excellent fit to data obtained from a numerical simulator in predicting the characteristics of an arbitrary DGMOSFET.

Modeling of Short-Channel Effects in Organic Thin-Film Transistors

We propose a model for short-channel organic thin-film transistors, which accounts for Poole-Frenkel field-dependent mobility and space-charge-limited current effects. The model is developed for devices operating in the linear regime, as well as in depletion and saturation regimes. Super linear output curves for low drain voltages, as well as nonsaturating currents, can be adequately described. Experimental results for short-channel P3HT devices have been fitted, showing good agreement with the proposed model.

Semianalytical Modeling of Short-Channel Effects in Lightly Doped Silicon Trigate MOSFETs

A simple analytical expression of the 3-D potential distribution along the channel of lightly doped silicon trigate MOSFETs in weak inversion is derived, based on a perimeter-weighted approach of symmetric and asymmetric double-gate MOSFETs. The analytical solution is compared with the numerical solution of the 3-D Poisson's equation in the cases where the ratios of channel length/silicon thickness and channel length/channel width are ges 2. Good agreement is achieved at different positions within the channel. The perimeter-weighted approach fails at the corner regions of the silicon body; however, by using corner rounding and undoped channel to avoid corner effects in simulations, the agreement between model and simulation results is improved. By using the extra potential induced in the silicon film due to short-channel effects, the subthreshold drain current is determined in a semianalytical way, from which the subthreshold slope, the drain-induced barrier lowering, and the threshold voltage are extracted.

Semi-Analytical Modeling of Short-Channel Effects in Si and Ge Symmetrical Double-Gate MOSFETs

A simple analytical expression of the 2-D potential distribution along the channel of silicon symmetrical double-gate (DG) MOSFETs in weak inversion is derived. The analytical solution of the potential distribution is compared with the numerical solution of the 2-D Poisson's equation in terms of the channel length <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</i> , the silicon thickness <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Si</sub> , and the gate oxide thickness <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OX</sub> . The obtained results show that the analytical solution describes, with good accuracy, the potential distribution along the channel at different positions from the gate interfaces for well-designed devices when the ratio of <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</i> / <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Si</sub> is ges 2-3. Based on the 2-D extra potential induced in the silicon film due to short-channel effects (SCEs), a semi-analytical expression for the subthreshold drain current of short-channel devices is derived. From the obtained subthreshold characteristics, the extracted device parameters of the subthreshold slope, drain-induced barrier lowering, and threshold voltage are discussed. Application of the proposed model to devices with silicon replaced by germanium demonstrates that the germanium DG MOSFETs are more prone to SCEs.

Engineering source/drain extension regions in nanoscale double gate (DG) SOI MOSFETs: Analytical model and design considerations

In this paper, we propose for the first time, an analytical model for short channel effects in nanoscale source/drain extension region engineered double gate (DG) SOI MOSFETs. The impact of (i) lateral source/drain doping gradient ( d), (ii) spacer width ( s), (iii) spacer to doping gradient ratio ( s/ d) and (iv) silicon film thickness ( T si), on short channel effects – threshold voltage ( V th) and subthreshold slope ( S), on-current ( I on), off-current ( I off) and I on/ I off is extensively analysed by using the analytical model and 2D device simulations. The results of the analytical model confirm well with simulated data over the entire range of spacer widths, doping gradients and effective channel lengths. Results show that lateral source/drain doping gradient along with spacer width can not only effectively control short channel effects, thus presenting low off-current, but can also be optimised to achieve high values of on-currents. The present work provides valuable design insights in the performance of nanoscale DG SOI devices with optimal source/drain engineering and serves as a tool to optimise important device and technological parameters for 65 nm technology node and below.

An Analytical Model of Short-Channel Effect for Metal–Oxide–Semiconductor Field-Effect Transistor with Insulated Shallow Extension

In this paper, we present an analytical short-channel threshold voltage model without any fitting parameter for the metal–oxide–semiconductor field-effect Transistor (MOSFET) with insulated shallow extension (ISE). Excellent agreements between the numerical simulated results and this model are obtained. Very good suppression of the short-channel effect is observed for this ISE MOSFET. Both the sidewall-oxide thickness and shallow-extension depth play a major role in containing the short-channel effect. The threshold-voltage equation is found by using the effective-doping model. The effective doping is derived from the knowledge of the channel potential. The channel potential is obtained by the scale-length approach to solve 2D Poisson's equation.

A new threshold voltage model for deep-submicron MOSFETs with nonuniform substrate dopings

A simple but accurate threshold voltage model for deep-submicron MOSFETs with nonuniform dopings is described in this paper. In this model, a simplified quasi-delta substrate doping profile is used to approximate the nonuniformity. We apply a hyperbola function to avoid the discontinuous problem at the boundary between different doping regions. By adjusting the parameter δ, the actual gradual doping profile can be obtained. A substrate-bias dependent model of short channel effect is also introduced which describes the reduction of substrate-bias effect in deep-submicron devices. The model developed is in good agreement with two-dimensional numerical simulation.

Concise Short-Channel Effect Model for Inversion-type Ultrathin Silicon-on-Insulator p-Channel Metal-Oxide-Silicon Field-Effect Transistors Based on Partitioning of Thin-Film

This paper reports a concise short-channel effect model for inversion-type ultrathin silicon-on-insulator (SOI) metal-oxide-silicon field-effect transistors (MOSFETs). As verified by the 2D simulation data, the concise short-channel effect model based on partitioning of the thin-film region provides a good prediction. According to the analytical model, the short-channel effect is strongly influenced by its thin-film thickness.

A simple model for short-channel effects of a buried-channel MOSFET on the buried insulator

A majority-carrier distribution model and a channel potential-profile model, in which the barrier-lowering effect is taken into account, are proposed for a buried-channel MOSFET (BC-MOSFET/ SOI). Simple expressions for threshold voltage and drain breakdown voltage were derived from the models for a short-channel BC-MOSFET/ SOI. The comparison between theory and experimental results shows reasonable agreement. The drain-bias coefficient γ of threshold voltage for BC-MOSFET's/ SOI is approximately proportional to TN D -1L eff -2, where T, N D , and L eff are the temperature, the doping concentration in the channel region, and the channel length, respectively. The coefficient γ depends slightly on the drain bias. BC-MOSFET's/SOI are able to be more miniaturized than surface-channel MOSFET's (SC-MOSFET's) at the small power source voltage, and SC-MOSFET's are able to be more miniaturized than BC-MOSFET's/SOI at the large drain bias. It is shown that the conventional, simple scaling scheme, which holds the constant electric field, is not applicable to BC-MOSFET's/SOI. The power source voltage has to be fixed when dimensions and doping concentrations are scaled down. On the other hand, only the channel region thickness has to be fixed when the power source voltage is scaled down.