Nanoscale Double-gate MOSFETs Research Articles

Analytical solution of nonlinear Poisson equation for symmetric double-gate metal-oxide-semiconductor field effect transistors

In this paper, an analytical solution of the Poisson equation for double-gate metal-semiconductor-oxide field effect transistor (MOSFET) is presented, where explicit surface potential is derived so that the whole solution is fully analytical. Based on approximations of potential distribution, our solution scheme successfully takes the effect of doping concentration in each region. It provides an accurate description for partially and fully depleted MOSFET devices in different regions of operation. Comparison with numerical data shows that the solution gives good approximations of potential for MOSFETs under different biases and geometry configurations. The solution can be applied to estimate classical and quantum electron density of nanoscale double-gate MOSFETs.

Threshold voltage sensitivity to doping density in extremely scaled MOSFETs

The dependence of the threshold voltage (VT) on channel doping for extremely scaled devices is investigated. This work is focused on the fundamental VT issue and its physical insight into the impact of the doping density on device characteristics. We find that the threshold voltage is, in fact, insensitive to doping over a wide range of doping density and such insensitivity is further extended by bandgap narrowing in nanoscale MOSFETs via analytical analyses and two-dimensional numerical device simulations (2003 Taurus-MEDICI User Guide (Mountain View, CA: Synopsis Inc.)). This result particularly suggests the scalability and feasibility of nanoscale double-gate MOSFETs.

Numerical analysis of the cut-off frequency of ultra-small ballistic double-gate MOSFETs: 2D nonequilibrium Green’s function approach

Nonequilibrium Green’s function formalism can be used to analyze the small-signal ac response of nanoscale devices of one or two dimensional model by introducing internal-induced ac potential. This makes it possible to analyze the small-signal ac response of ultra-small ballistic MOSFETs. Working on the 2D model of nanoscale double-gate MOSFETs, the present paper calculated the cut-off frequencies and transconductance per current with various channel lengths and gate dielectric constants. It turns out that the cut-off frequencies of ultra-small ballistic MOSFETs will go up without limit with increasing drain currents, which is in contrast to conventional MOSFETs with scatterings. On the other hand, the cut-off frequencies are limited under 3 THz due to the decreasing of transconductance per current. Secondly, operating at large drain current, the ultra-small ballistic MOSFETs with shorter channels have higher cut-off frequencies at the same drain current, while at small drain current, the longer ones have higher cut-off frequency at the same drain current.

Two-dimensional numerical modeling of lightly doped nano-scale double-gate MOSFET

A two-dimensional numerical solution of electrostatic potential and electric field profiles are presented for lightly doped nano-scale Double-Gate Metal-Oxide-Semiconductor-Field-Effect-Transistor (DG-MOSFET). We have developed quasi-static (QS) model for evaluating bulk and inversion charges based on symmetric linearization model. We have also shown the non-quasi-static (NQS) effect on the charge due to a time varying gate voltage. It is seen that various symmetries of DG-MOSFET characteristics with respect to source/drain interchange is maintained in quasi-static as well as non-quasi-static version of the symmetrically linearized model. The variation of the threshold voltage with the varying width of the device is evaluated and presented. The results have been compared and contrasted with reported analytical model for QS condition for the purpose of verification of the model. The variation of threshold voltage along the width of the device is also predicted. This numerical model can be extended to analyze the transport phenomenon in sub 30nm channel length DG-MOSFETs.

Two Dimensional Numerical Modeling of Lightly Doped Nanoscale Double-Gate MOSFET

Two Dimensional Numerical Modeling of Lightly Doped Nanoscale Double-Gate MOSFET

Influence of Image and Exchange-Correlation Effects on Electron Transport in Nanoscale DG MOSFETs

The impact of image and many-body exchange-correlation effects on electron transport has been investigated for nanoscale double-gate MOSFETs, using the nonequilibrium Green function method. The simulations have been performed for metal gate and polysilicon gate MOSFETs. When the gate material is metal, the inclusion of image and exchange-correlation effects increases the computed drain current, particularly at high gate voltages. In the case of polysilicon gate, the computed drain current remains almost unchanged at high gate voltages because both effects cancel out. However, at low gate voltages, the drain current is decreased by including these effects. In this study, the wavefunction penetration into the gate oxide and gate electrode has also been taken into account. Clear discrepancies between the drain currents calculated with and without considering the penetration effect can be found at low gate voltages. Further, the electron occupancy of each valley type is markedly changed by including this effect.

A simple model of the nanoscale double gate MOSFET based on the flux method

We present a physics-based model for the double gate MOSFET, which incorporates the effect of the scattering along the channel. The model is based on the McKelvey's flux theory, and properly captures the transition between the different operation regions. The effect of scattering on both the channel conductance and the average velocity near the source end is examined. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

A Quantum Correction Model for Nanoscale Double-Gate MOS Devices Under Inversion Conditions

A quantum correction model for nanoscale double-gate MOSFETs under inversion conditions is proposed. Based on the solution of Schrodinger-Poisson equations, the developed quantum correction model is optimized with respect to (i) the left and right positions of the charge concentration peak, (ii) the maximum of the charge concentration, (iii) the total inversion charge sheet density, and (iv) the average inversion charge depth, respectively. This model can predict inversion layer electron density for various oxide thicknesses, silicon film thicknesses, and applied voltages. Compared to the Schrodinger-Poisson results, our model prediction is within 3.0% of accuracy. This quantum correction model has continuous derivatives and is therefore amenable to a device simulator.

Quantum corrections in the simulation of decanano MOSFETs

Abstract Quantum mechanical confinement and tunnelling play an important role in present and future generation decanano (sub-100 nm) MOSFETs and have to be properly taken into account in the simulation and design. Here we present a simple approach of introducing quantum corrections in a 3D drift–diffusion simulation framework using the density gradient (DG) algorithm. We discuss the calibration of the DG approach in respect of quantum confinement effects in comparison with more comprehensive but computationally expensive quantum simulation techniques. We also speculate about the capability of DG to describe source-to-drain tunnelling in sub-10 nm (nano) MOSFETS. The application of the DG approach is illustrated with examples of 3D statistical simulations of intrinsic fluctuation effects in decanano and nano-scale double-gate MOSFETs.