Simulation study of the 20 nm gate-length Ge implant-free quantum well p-MOSFET

In this paper a drift diffusion simulation study of a 20 nm gate-length implant-free quantum well germanium p-MOSFET is presented, which covers the impact of mobility, velocity saturation and density of interface states on the transistor performance. The parasitic gate capacitance was also studied. The simulations show that the 20 nm gate-length implant-free quantum-well transistor design has good electrostatic integrity and performance potential.     

Simulation of statistical variability in nano-CMOS transistors using drift-diffusion, Monte Carlo and non-equilibrium Green’s function techniques

In this paper, we present models and tools developed and used by the Device Modelling Group at the University of Glasgow to study statistical variability introduced by the discreteness of charge and matter in contemporary and future Nano-CMOS transistors. The models and tools, based on Drift-Diffusion (DD), Monte Carlo (MC) and Non-Equilibrium Green’s Function (NEGF) techniques, are encapsulated in the Glasgow 3D statistical ‘atomistic’ device simulator. The simulator can handle most of the known sources of statistical variability including Random Discrete Dopants (RDD), Line Edge Roughness (LER), Thickness Fluctuations in the Oxide (OTF) and Body (BTF), granularity of the Poly-Silicon (PSG), Metal Gate (MGG) and High-κ (HKG), and oxide trapped charges (OTC). The results of the statistical simulations are verified with respect to measurements carried out on fabricated devices. Predictions about the magnitude of the statistical variability in future generations of nano-CMOS devices are also presented.     

Use of density gradient quantum corrections in the simulation of statistical variability in MOSFETs

With the scaling of field-effect transistors to the nanometre scale, it is well recognised that TCAD simulations of such devices need to account for quantum mechanical confinement effects. The most widely used method to incorporate quantum effects within classical and semi-classical simulators is via density gradient quantum corrections. Here we present our methodologies for including the density gradient method within our Drift-Diffusion and Monte Carlo simulators and highlight some of the additional benefits that this provides when dealing with the charge associated with random discrete dopants.     

Scattering from Body Thickness Fluctuations in Double Gate MOSFETs: An ab initio Monte Carlo Simulation Study

This paper describes the impact of surface roughness related body thickness fluctuations on the mobility in double gate MOSFETs. The analysis combines 3D drift diffusion simulations with density gradient quantum corrections and ensemble Monte Carlo simulations, which include, in an ab initio fashion, the additional scattering associated with the variation in the quantum mechanical confinement along the channel. Results for a range of devices with varying silicon thicknesses and both smooth and rough interfaces are presented in order to demonstrate the impact of this additional scattering mechanism on the mobility in the channel.     

Boundary conditions for Density Gradient corrections in 3D Monte Carlo simulations

Monte Carlo remains an effective simulations methodology for the study of MOSFET devices well into the decananometre regime as it captures non-equilibrium and quasi-ballistic transport. The inclusion of quantum corrections further extends the usefulness of this technique without adding significant computational cost. In this paper we examine the impact of boundary conditions at the Ohmic contacts when Density Gradient based quantum corrections are implemented in a 3D Monte Carlo simulator. We show that Neumann boundary conditions lead to more stable and physically correct simulation results compared to the traditional use of Dirichlet boundary conditions.     

3-D Monte Carlo Simulation of the Impact of Quantum Confinement Scattering on the Magnitude of Current Fluctuations in Double Gate MOSFETs

For the scaling of ultrathin body double gate (UTB DG) MOSFETs to channel lengths below 10 nm, a silicon body thickness of less than 5 nm is required. At these dimensions the influence of atomic scale roughness at the interface between the silicon body and the gate dielectric becomes significant, producing appreciable body thickness fluctuations. These fluctuations result in a scattering potential related to the quantum confinement variation within the channel which, similarly to the interface roughness scattering, influences the mobility, the drive current and the intrinsic parameter variations. In this paper we have developed an ensemble Monte Carlo simulation approach to study the impact of quantum confinement scattering on the transport in sub-10 nm UTB DG MOSFETs, and the corresponding intrinsic parameter variations. By comparing the Monte Carlo simulations with drift-diffusion simulations we quantify the important contribution of the quantum confinement related scattering to the current fluctuations in such devices