Tarek M. Abdolkader

FETMOSS: a software tool for 2D simulation of double-gate MOSFET

A software tool for the 2D simulation of double-gate SOI MOSFET is developed. The developed tool is working under MATLAB environment and is based on the numerical solution of Poisson and Schrodinger equations self-consistently to yield the potential, carrier concentrations, and current within the device. Compared to the already existing tools, the new tool uses finite elements method for the solution of Poisson equation, thus, the simulation of curved boundary structures becomes feasible. Another new feature of the tool is the use of transfer matrix method (TMM) in the solution of Schrodinger equation which was proven in a recent published paper that it gives more accurate results than the conventional finite difference method (FDM) when used in some regions of operation. According to the working conditions, the tool can toggle between FDM and TMM to satisfy the highest accuracy with the largest speed of simulation. The tool is named as FETMOSS (finite elements and transfer matrix MOS simulator)

Carrier-Selective NiO/Si and TiO 2 /Si Contacts for Silicon Heterojunction Solar Cells

Carrier-selective contacts based on thin oxides of nickel and titanium are computationally investigated for heterojunction silicon solar cells. Replacing the standard amorphous/ c-Si heterojunction with NiO/c-Si (front) and TiO2/c-Si (back), we explore the physical requirements to enhance the cell efficiency beyond the physical limits of the conventional structure. Under ideal conditions, a wider bandgap (>3 eV) of these metal oxides provides a high optical transparency, whereas a near-perfect alignment of their energy bands with silicon ensures a high fill factor (FF), which is often difficult to obtain in some of the other wide-bandgap alternatives, e.g., SiOx, due to imperfect band offsets that hinder carrier extraction. We explore the practical nonidealities that could possibly degrade cell efficiency below its ideal limit. In particular, effects of interfacial defects, Fermi-level pinning at c-Si/TiO2/metal contact, variability in the bandgap of NiO, and nonoptimized metal oxide doping density are investigated quantitatively. Using the reported experimental data for these nonideal effects, we highlight that the cell efficiency of ~28% could be achieved under AM1.5 illumination with an optimal cell design. These modeling insights provide useful guidelines for the future development of exploratory window layers for silicon solar cells using NiO (front) and TiO2 (back) heterojunctions.

Uncoupled mode-space simulation validity for double gate MOSFETs

The validity of the uncoupled mode space (UMS) approach for simulating double gate MOSFETs in the ballistic limit is examined. The mode space results are compared to the rigorous real space (RS) approach. The critical body thickness, at which the UMS results are no more accurate, is shown to be bias dependent. A computationally efficient method is developed to estimate the validity range of the UMS simulation results without comparing with RS results.

Quantum transport based simulation and design optimization of a 10 nm FinFET

The International Technology Roadmap for Semiconductors (ITRS) projected value for the High Performance (HP) MOSFET channel length is 10 nm at the year 2016. The FinFET is expected to replace the conventional bulk MOSFET beyond the 22 nm node due to the latters scaling challenges. In this article the design optimization of a 10 nm FinFET is considered. It is shown that the ITRS requirements for the FinFETs driving current and switching speed can be satisfied simultaneously. The on-current and switching speed can be as large as 6734 µA/µm and 24.4 THz compared to the 4590 µA/µm and 5.6 THz of the ITRS projections. It is also shown that the use of a mid-gap work function can satisfy the ITRS requirements. Moreover, factors for better manufacturability like relaxed extension lateral abruptness and increased fin thickness are also considered in the design.

Compact model for ballistic MOSFET-like carbon nanotube field-effect transistors

In this work, a compact model for MOSFET-like ballistic carbon nanotube field-effect transistors (CNFETs) is presented. The model is based on calculating the charge and surface potential on the top of the barrier between source and drain using closed-form analytical formulae. The formula for the surface potential is obtained by merging two simplified expressions obtained in two extreme cases (very low and very high gate bias). Two fitting parameters are introduced whose values are extracted by best fitting model results with numerically calculated ones. The model has a continuous derivative and thus it is SPICE-compatible. Accuracy of the model is compared to previous analytical model presented in the literature with numerical results taken as a reference. Proposed model proves to give less relative error over a wide range of gate biases, and for a drain bias up to 0.5 V. In addition, the model enables the calculation of quantum and gate capacitance analytically reproducing the negative capacitance behaviour known in CNFETs.

Simulation of Quantum Ballistic Transport in FinFETs

Quantum effects play a vital role in determining the transistor characteristics of FinFET devices. Quantum confinement, coherent ballistic transport, and quantum mechanical tunneling are a few examples. The nonequilibrium Green’s function formalism (NEGF) provides a rigorous description of quantum transport in nanoscale devices. Depending on the chosen space for representation of the wave function, real-space and mode-space representations are widely used. In this chapter, the basic tools involved in the NEGF simulation of the quantum ballistic transport in FinFETs are provided. The different techniques applied in either the real- or the mode-space representations are discussed. In this chapter, a comparison of the NEGF methods in the real-space representation considers the recursive Green’s function method, the Gauss elimination method, and the contact block reduction method and then highlights the computational efficiency of these methods. A comparison between the fully coupled, the partially coupled and the uncoupled methods in the mode-space representation is also given considering their accuracy and computational efficiency.

Analytical model for ballistic MOSFET-like carbon nanotube field-effect transistors

An analytical model is developed for the carrier density in MOSFET-like carbon nanotube field-effect transistors in terms of surface potential. This model is based on approximating the density of states with delta function in addition to a constant value. The model has a continuous derivative and contains two fitting parameters, which are determined by best fitting with numerical results. The fitting parameters are found to depend on the subband minima and this dependence is modeled by simple quadrature formula. The model is compared to two previous analytical models with numerical results are taken as a reference and found to have less relative error. In addition, the drain current is extracted using the proposed model at various bias values. The results for current are verified by comparison with self-consistent numerical results of FETToy simulator available on the NanoHub.