Luca Silvestri

A Low-Field Mobility Model for Bulk, Ultrathin Body SOI and Double-Gate n-MOSFETs With Different Surface and Channel Orientations—Part I: Fundamental Principles

An easy-to-implement electron mobility model that accurately predicts low-field mobility in the channel of bulk MOSFETs and UTB-SOI FETs fabricated on different crystal orientations is developed. The model accounts for the influence of surface orientation and in-plane current-flow direction on effective masses, subband repopulation, and scattering rates. The paper is divided into two parts. In Part I, the general features of the model are presented, taking into account phonon, Coulomb, and surface roughness scattering. Band and repopulation effects are addressed based on the solution of the Schrödinger-Poisson equations. The effects of interface states and ultrathin body are treated in Part II.

High Gain and Fast Detection of Warfare Agents Using Back-Gated Silicon-Nanowired MOSFETs

The top-down fabrication of doped p-type silicon-nanowired (NW) arrays and their application as gas detectors is presented. After surface functionalization with 3-(4-ethynylbenzyl)-1, 5, 7-trimethyl-3-azabicyclo [3.3.1] nonane-7-methanol molecules, the wires were subjected to an organophosphorous simulant, and both static and dynamic measurements were performed. A current gain of 4 × 106 is obtained upon the detection of the subpart-per-million concentration of a nerve-agent simulant. This represents a four-decade improvement over previous demonstration based on nanoribbons, proving better sensing capabilities of NWs. Technology-computer-aided-design simulations before and after gas detection have been performed to gain insight into the physical mechanisms involved in the gas detection and to investigate the impact of the surface-to-volume ratio on sensor sensitivity.

A Low-Field Mobility Model for Bulk, Ultrathin Body SOI and Double-Gate n-MOSFETs With Different Surface and Channel Orientations—Part II: Ultrathin Silicon Films

In this paper, together with the accompanying Part I, an easy-to-implement electron mobility model that accurately predicts low-field mobility in bulk MOSFETs and UTB-SOI FETs fabricated on different crystal orientations is developed. In Part I, the general features of the model have been presented. In this Part II, the effects induced by extremely small silicon thicknesses are addressed. These effects include the scattering induced by interface states and silicon thickness fluctuations, intervalley-phonon scattering suppression, and surface optical phonons. Besides, corrections necessary for double-gate FETs are considered. This allows the validity of the model presented in Part I to be extended to single- and double-gate FETs with silicon thicknesses as small as about 2.5 nm.

Physically-based unified compact model for low-field carrier mobility in MOSFETs with different gate stacks and biaxial/uniaxial stress conditions

A compact model of the low-field effective carrier mobility is developed for n- and p-type MOSFETs with either polySi or TiN gate, ultrathin SiO2/HfO2 gate stacks, and silicon under biaxial or uniaxial stress conditions. Physical insights, theoretical analyses and experimental investigations are used to develop and accurately calibrate the model.

Comparison of advanced transport models for nanoscale nMOSFETs

In this paper we mutually compare advanced modeling approaches for the determination of the drain current in nanoscale MOSFETs. Transport models range from Drift-Diffusion to direct solution of the Boltzmann Transport equation with the Monte-Carlo methods. Template devices representative of 22nm Double-Gate and 32nm FDSOI transistors were used as a common benchmark to highlight the differences between the quantitative predictions of different approaches. Our results set a benchmark to assess modeling tools for nanometric MOSFETs.

Unified model for low-field electron mobility in bulk and SOI-MOSFETs with different substrate orientations and its application to quantum drift-diffusion simulation

This paper presents a novel unified model of the low-field electron mobility for bulk and silicon-on- insulator (SOI) FETs with different crystal orientations. By taking into account the influence of surface-orientation and current-flow direction on effective masses, carrier repopulation, and scattering rates, the experimentally observed mobilities are nicely reproduced for MOSFETs with silicon thicknesses down to 5 nm. The model has been implemented in a quantum drift-diffusion transport solver (QDD) and the effect of crystal orientation on SOI-MOSFET characteristics is investigated.

A Low-Field Mobility Model for Bulk and Ultrathin-Body SOI p-MOSFETs With Different Surface and Channel Orientations

An easy-to-implement hole mobility model, which accurately predicts low-field mobility in bulk MOSFETs and ultrathin-body (UTB) silicon-on-insulator FETs with different crystal orientations, is developed. The model accounts for the influence of the surface orientation and the inplane current-flow direction on effective masses, subband repopulation, and scattering rates. The effects induced by extremely small silicon thicknesses are also addressed. A good agreement with the experimental mobilities of bulk and UTB FETs with silicon thicknesses from 60 nm to values as small as about 2.7 and 2.3 nm is demonstrated for devices with (100) and (110) substrates, respectively.

TCAD study of the detection mechanisms in silicon nanoribbon-based gas sensors

An extensive simulation analysis of silicon-nanoribbon field-effect transistors for the detection of chemical warfare agents has been performed through investigation of the physical behavior of the device. An accurate modeling of the nanoribbon interfaces has been carried out before and after gas exposure by combining simulation, characterization techniques and validation against experiments. A quantitative description of the physical mechanisms involved in the gas detection has been obtained.

Drain current computation in nanoscale nMOSFETs: Comparison of transport models

In this paper the modelling approaches for determination of the drain current in nanoscale MOSFETs pursued by various partners in the frame of the European Projects Pullnano and Nanosil are mutually compared in terms of drain current and internal quantities (average velocity and inversion charge). The comparison has been carried out by simulating template devices representative of 22 nm Double-Gate and 32 nm Single-Gate FD-SOI. A large variety of simulation models has been considered, ranging from drift-diffusion to direct solutions of the Boltzmann-Transport-Equation. The predictions of the different approaches for the 32 nm device are quite similar. Simulations of the 22 nm device instead, are much less consistent. Comparison with experimental data for a 32 nm device shows that the modeling approach used to explain the mobility reduction induced by the high-k dielectric is critical.

Effects of Channel Orientations, High-? Gate Stacks and Stress on UTB-FETs: A QDD Simulation Study

In this work we propose a unified model for the low-field effective electron mobility in SOI and DG-MOSFETs with ultrathin SiO2/HfO2 gate stacks, different substrate and channel orientations and uniaxial stress conditions.The model accounts for quantum-confinement effects in the MOSFET channel. Next, we apply this mobility model to a 1D quantum drift-diffusion (QDD) transport model in order to investigate the extent to which the low-field mobility impacts the I-V characteristics. Short (Lg = 22 nm) DGFETs,where mobility is affected by quantum-confinement effects, ultrathin SiO2/HfO2 gate stacks and metal gate,have been investigated. Finally, the correlations between the mobility enhancement induced by uniaxial stress in a 22 nm DG-FET, the on-current and transconductance are examined.