Undoped Symmetric Double-gate MOSFETs Research Articles

Modeling of electrical behavior of undoped symmetric Double-Gate (DG) MOSFET using carrier-based approach

PurposeThis study aims to develop a compact analytical models for undoped symmetric double-gate MOSFET based on carrier approach. Double-Gate (DG) MOSFET is a newly emerging device that can potentially further scale down CMOS technology owing to its excellent control of short channel effects, ideal subthreshold slope and free dopant-associated fluctuation effects. DG MOSFET is of two types: the symmetric DG MOSFET with two gates of identical work functions and asymmetric DG MOSFET with two gates of different work functions. To fully exploit the benefits of DG MOSFETs, the body of DG MOSFETs is usually undoped because the undoped body greatly reduces source and drain junction capacitances, which enhances the switching speed. Highly accurate and compact models, which are at the same time computationally efficient, are required for proper modeling of DG MOSFETs.Design/methodology/approachThis paper presents a carrier-based approach to develop a compact analytical model for the channel potential, threshold voltage and drain current of a long channel undoped symmetric DG MOSFETs. The formulation starts from a solution of the 2-D Poisson’s equation in which mobile charge term has been included. The 2-D Poisson’s equation in rectangular coordinate system has been solved by splitting the total potential into long-channel (1-D Poisson’s equation) and short-channel components (remnant 2-D differential equation) in accordance to the device physics. The analytical model of the channel potential has been derived using Boltzmann’s statistics and carrier-based approach.FindingsIt is shown that the metal gate suppresses the center potential more than the poly gate. The threshold voltage increases with increasing metal work function. The results of the proposed models have been validated against the Technology Computer Aided Design simulation results with close agreement.Originality/valueCompact Analytical models for undoped symmetric double gate MOSFETs.

An analytical study of undoped symmetric double gate MOSFET (SDG)

AbstractIn the present paper, compact analytical models for the threshold voltage, threshold voltage roll‐off and subthreshold swing of undoped symmetrical double‐gate MOSFET have been developed based on analytical solution of two‐dimensional Poisson's equation for potential distribution. The developed models include drain‐induced barrier lowering (DIBL) through the Vds‐dependent parameter. The calculated threshold voltage value, obtained from the proposed model, shows a good agreement with the experimental and published results. The simulation results for potential show that the conduction is highly confined to the surfaces. The threshold voltage sensitivity to the thickness is found to be approximately 0.2%. Model prediction indicates that subthreshold slope is not linearly related to DIBL parameter for thick silicon film. The proposed analytical models not only provide useful insight into behavior of symmetrical DG MOSFETs but also serve as the basis for compact modeling. Copyright © 2010 John Wiley & Sons, Ltd.

The Equivalent-Thickness Concept for Doped Symmetric DG MOSFETs

In this paper, we propose to derive an analytical model for the doped symmetric double-gate (DG) MOSFET that is valid in all regions of operation. We show that doping the silicon channel can be converted in an equivalent silicon thickness and threshold voltage shift using a formalism developed for the undoped device. Adopting the same physical parameters, we demonstrate that this approach is in agreement with numerical technology computer-aided design simulations. This concept is therefore an interesting basis for a unified model for doped and undoped symmetric DG MOSFETs.

Modeling of drain current, capacitance and transconductance in thin film undoped symmetric DG MOSFETs including quantum effects

Abstract In this paper, we present a fast yet accurate semi-analytical model for the I–V and C–V characteristics of nanoscale undoped symmetric double gate (DG) MOSFETs. The model employs a parabolic potential approximation for the body potential in the coordinate normal to the interfaces in all regions of device operation. While carrier confinement phenomenon is taken into account, we calculate the surface electric field which is used to determine the inversion charge sheet density. The density is used in a compact classical model of the symmetric DG MOSFET as a core model. Some quantum effects which include the threshold voltage shift and effective oxide thickness increment are applied through some modifications to the core model. To assess the accuracy of the proposed model, the results of the model are compared to those of the numerical simulations. The comparison reveals the high accuracy of the proposed model.

“Ground-Referenced” Model for Three-Terminal Symmetric Double-Gate MOSFETs With Source/Drain Symmetry

This brief presents for the first time a ldquoground-referencedrdquo model to satisfy the Gummel symmetry test in three-terminal MOSFETs without body contact. Unlike four-terminal bulk MOSFETs, in which the bulk Fermi potential is set by the body voltage, a paradigm change is needed to model the respective electron and hole imrefs referenced to the ground rather than to model the imref-split referenced to the source. Together with the model consistency requirement for any reference voltages, the proposed formulations, as illustrated with undoped symmetric double-gate MOSFETs, provide a guide for formulating compact models with source/drain (S/D) symmetry, which can also be easily extended to model unintentional or intentional S/D asymmetry.

A Carrier-Based Approach for Compact Modeling of the Long-Channel Undoped Symmetric Double-Gate MOSFETs

This paper presents a carrier-based approach to develop a compact model for long-channel undoped symmetric double-gate MOSFETs. The formulation starts from a solution of the Poisson's equation that is coupled to the Pao-Sah current formulation to obtain an analytic drain-current model in terms of the carrier concentration. The model provides an analytical expression to describe the dependence of the surface potential, silicon-film centric potential, inversion charge, and the current on the silicon-body thickness and the gate-oxide thickness. The model calculation is verified by comparing results to the 2D numerical simulations, and good agreement is observed

Analytic and explicit current model of undoped double-gate MOSFETs

A analytical and explicit drain-current equation has been derived for undoped symmetric double-gate MOSFETs. This current equation is expressed clearly with surface potential and verified with numerical results both in the subthreshold and the saturation region. It facilitates the calculation of drain current if only the surface potential is known, which is suitable for compact model development.