Model For Symmetric Double-gate MOSFETs Research Articles

An analytical drain current model for symmetric double-gate MOSFETs

An analytical surface-potential-based drain current model of symmetric double-gate (sDG) MOSFETs is described as a SPICE compatible model in this paper. The continuous surface and central potentials from the accumulation to the strong inversion regions are solved from the 1-D Poisson’s equation in sDG MOSFETs. Furthermore, the drain current is derived from the charge sheet model as a function of the surface potential. Over a wide range of terminal voltages, doping concentrations, and device geometries, the surface potential calculation scheme and drain current model are verified by solving the 1-D Poisson’s equation based on the least square method and using the Silvaco Atlas simulation results and experimental data, respectively. Such a model can be adopted as a useful platform to develop the circuit simulator and provide the clear understanding of sDG MOSFET device physics.

A Simple Charge Model for Symmetric Double-Gate MOSFETs Adapted to Gate-Oxide-Thickness Asymmetry

Surface-potential-based compact charge models for symmetric double-gate metal-oxide-semiconductor field-effect transistors (SDG-MOSFETs) are based on the fundamental assumption of having equal oxide thicknesses for both gates. However, for practical devices, there will always be some amount of asymmetry between the gate oxide thicknesses due to process variations and uncertainties, which can affect device performance significantly. In this paper, we propose a simple surface-potential-based charge model, which is applicable for tied double-gate MOSFETs having same gate work function but could have any difference in gate oxide thickness. The proposed model utilizes the unique so-far-unexplored quasi-linear relationship between the surface potentials along the channel. In this model, the terminal charges could be computed by basic arithmetic operations from the surface potentials and applied biases, and thus, it could be implemented in any circuit simulator very easily and extendable to short-channel devices. We also propose a simple physics-based perturbation technique by which the surface potentials of an asymmetric device could be obtained just by solving the input voltage equation of SDG devices for small asymmetry cases. The proposed model, which shows excellent agreement with numerical and TCAD simulations, is implemented in a professional circuit simulator through the Verilog-A interface and demonstrated for a 101-stage ring oscillator simulation. It is also shown that the proposed model preserves the source/drain symmetry, which is essential for RF circuit design.

Charge-based model for symmetric double-gate MOSFETs with inclusion of channel doping effect

This paper presents a unified charge-based model for symmetric double-gate (DG) MOSFETs with a wide range of channel doping concentrations. From one dimensional (1D) Poisson–Boltzmann equation in the DG MOSFET structure, an accurate inversion charge model is proposed, which predicts the inversion charge density precisely from weak inversion, through moderate inversion and finally to strong inversion region for both heavily doped and lightly doped condition. Based on that, the unified drain current model is developed from Pao-Sah’s dual integral. The unified terminal charge and trans-capacitance models are derived out from Ward and Dutton’s linear-charge-partition scheme. Extensive numerical simulations are performed on DG MOSFETs to verify the unified charge-based models and good agreements between them are obtained, proving the validity of the proposed model for further circuit simulation.

Implementation of the symmetric doped double‐gate MOSFET model in Verilog‐A for circuit simulation

AbstractRecently we developed a model for symmetric double‐gate MOSFETs (SDDGM) that, for the first time, considers the doping concentration in the Si film in the complete range from 1×1014 to 3×1018 cm−3. The model covers a wide range of technological parameters and includes short channel effects. It was validated for different devices using data from simulations, as well as measured in real devices. In this paper, we present the implementation in Verilog‐A code of this model, which allows its introduction in commercial simulators. The Verilog‐A implementation was optimized to achieve reduction in computational time, as well as good accuracy. Results are compared with data from 2D simulations, showing a very good agreement in all transistor operation regions. Copyright © 2009 John Wiley & Sons, Ltd.

A Non-Charge-Sheet Analytic Model for Symmetric Double-Gate MOSFETs With Smooth Transition Between Partially and Fully Depleted Operation Modes

A non-charge-sheet analytic model for long-channel symmetric double-gate (DG) MOSFETs with smooth transition between partially and fully depleted (PD and FD) operation modes is presented in this paper. The 1-D Poisson's equation with the mobile and dopant charge terms is first solved to obtain the continuous channel potential in the symmetric DG structure physically. A non-charge-sheet analytic drain-current expression is then derived from Pao-Sah's dual integral as a function of the channel potentials at the source and drain terminals. The comparison between the analytical calculation and 2-D numerical simulation demonstrates that the developed model is not only valid for a wide range of doping concentrations and geometry sizes, but also able to capture the DG MOSFET specific characteristics such as the volume inversion and smooth transition between PD and FD operation modes. The presented model leads to a more clear understanding of DG MOSFET device physics, providing a physics-based DG MOSET compact modeling framework for circuit simulation.

Explicit compact model for symmetric double-gate MOSFETs including solutions for small-geometry effects

A physics-based compact model including short-channel effects (SCEs) is presented for undoped (or lightly doped) symmetric double-gate (DG) MOSFETs. Our approach allows an accurate description of the device behavior down to 60 nm with a simple set of equations. It is shown that the subthreshold current, the threshold voltage roll-off and the DIBL predicted by the analytical solution are in close agreement with 2-D numerical simulations performed with Atlas. The mobility degradation due to both transverse and longitudinal fields is taken into account but the channel length modulation (saturation regime) is not addressed in this paper. In order to demonstrate that the model is well-suited for circuit simulation, the results of the dynamic model based on an explicit formulation of the mobile charge density are also presented.