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International audience; Our home made Full-Band particle Monte Carlo is used to investigate the thermal interface conductance at Silicon/Germanium heterojunctions.

Different radial ionization profiles modeling approaches are compared for the energy deposition representation in a Single Event Effects (SEE) prediction tool. The total SEU cross section calculated with the different approaches is compared for various SOI and bulk technologies, along with the MBU prediction. A “refined average” approach is identified as a good trade-off for implementation in an engineer SEE prediction tool, taking into account sufficiently detailed physics to predict the sensitivity of SOI and bulk devices down to the 32 nm technological node, without asking for too much computer resources.

The simulation methodology coupling radial ionization profiles issued from Geant4 and the SEE prediction tool MUSCA SEP3 is used to investigate the MBU sensitivity of SOI SRAM cells of different technologies. The simulation approach is first validated against experimental results for a 45 nm SOI SRAM cell, showing very good agreement. The variability of the MBU probability is then studied depending on various parameters. A worst case is identified, for a particular data pattern irradiated with a high LET ion at grazing angle, showing the possibility for three- and four-bit events to occur. The cause for these high multiplicities is identified by examining the cells topology and new design by hardening strategies are proposed to improve the device hardness to MBU, for a 32 nm SOI SRAM cell. The possibilities of the SEE prediction tool for bulk devices are finally discussed.

In this paper, we review and extend our recent works based on the Monte Carlo method to solve the Wigner-Boltzmann transport equation and model semiconductor nanodevices. After presenting the different possible approaches to quantum mechanical modelling, the formalism and the theoretical framework are described together with the particle Monte Carlo implementation using a technique fully compatible with semiclassical simulation. Examples are given to highlight the importance of considering both quantum and scattering effects in nanodevices operating at room temperature, such as resonant tunnelling diode (RTD), double-gate MOSFET and carbon nanotube FET. Quantum and semiclassical approaches are compared for transistor simulation. Finally, the phonon-induced electron decoherence in RTD and MOSFET is examined through the analysis of the density matrix elements computed from the Wigner function. This formalism is shown to be relevant for the quantitative analysis of devices operating in mixed quantum/semiclassical regime and to understand the transition between both regimes or between coherent and sequential tunnelling processes.

In recent years, the understanding and accurate simulation of carbon nanotube-based devices has become verychallenging. Conventional simulation tools of microelectronics are necessary to envision the performances and useof nanotube transistors and circuits, but the models need to be refined to properly describe the full complexityof such novel type of devices at the nanoscale. Indeed many issues such as contact resistance, low dimensionalelectrostatics and screening effects, as well as nanotube doping or functionalization, demand for more accuratequantum approaches. In this article, we review our recent progress on multiscale simulations which aim at bridgingfirst principles calculations with compact modelling, including the comparison between semi-classical Monte Carloand quantum transport approaches.R´esum´eSimulation Multi-Echelle des Dispositifs `a Nanotube de CarboneCes derni`eres ann´ees, la compr´ehension et la simulation pr´ecise des dispositifs `a base de nanotubes de car-bone est devenue une tˆache ambitieuse. Les outils de simulation conventionnels de la micro´electronique sontn´ecessaires pour imaginer les performances et l’utilisation des transistors et des circuits `a base de nanotubes,mais les mod`eles doivent ˆetre affin´es pour d´ecrire correctement la complexit´e de ces nouveaux types de dispositifs`a l’´echelle nanom´etrique. En effet, de nombreuses questions comme la r´esistance de contact, l’´electrostatique enbasse dimensionalit´e et les effets d’´ecrantage, et le dopage ou la fonctionnalisation des nanotubes, n´ecessitentdes approches quantiques plus pr´ecises. Dans cet article, nous exposons nos progr`es r´ecents pour des simulationsmulti-´echelles qui visent `a connecter des calculs bas´es sur les premiers principes `a la mod´elisation compacte, enpassant par la comparaison entre les approches Monte Carlo semi-classique et de transport quantique.

A Pearson Effective Potential model for including quantization effects in the simulation of nanoscale nMOSFETs has been developed. This model, based on a realistic description of the function representing the non zero-size of the electron wave packet, has been used in a Monte-Carlo simulator for bulk, single gate SOI and double-gate SOI devices. In the case of SOI capacitors, the electron density has been computed for a large range of effective field (between 0.1 MV/cm and 1 MV/cm) and for various silicon film thicknesses (between 5 nm and 20 nm). A good agreement with the Schroedinger-Poisson results is obtained both on the total inversion charge and on the electron density profiles. The ability of an Effective Potential approach to accurately reproduce electrostatic quantum confinement effects is clearly demonstrated.

This paper presents a quantum-mechanical modification of the conventional drift-diffusion model for simulation of quasi-ballistic carrier transport under high-field conditions. Thereby, the saturation velocity of charge carriers has been adjusted in dependence on the local electrostatic potential, so that adequate simulation results were obtained for different device dimensions, doping concentration, and supply voltage. The energy dissipation of the electrons has been taken into account by using a self-heating of the device in dependence on thermal material resistances. A good agreement to Monte Carlo simulations and experimental results has been reached for the suggested model.

We present a study of carbon nanotube field effect transistors (CNTFET) operation and performance using Monte Carlo simulation including phonon scattering. In CNTFETs, operating in the quantum capacitance regime, the low driving electric field in the channel yields a high fraction of ballistic transport. In terms of ballisticity, ION/IOFF ratio and intrinsic delay, the performance of 100 nm-long CNTFET is shown to be as high as that of much smaller Si transistors.

A Multi Sub-band Monte Carlo Simulator improved to efficiently include the Pauli Exclusion Principle is presented. It is used to study the transport in highly doped and ultra-thin silicon film. Both steady state and transient regime of transport for silicon films under uniform driving field are investigated. Such approach aims to be carried out in a full device simulator to improve the modeling of the access region of nano-Double Gate MOSFETs. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Ballistic transport in a 20 nm long P type Double Gate (DG) MOSFET structure is studied using a Monte Carlo (MC) technique. Hole transport being dominated by the strong anisotropy of the valence dispersion relation, the full bandstructure obtained by a 30 band k ·p calculation is used. The valence bandstructure is shown to be highly anisotropic. The deformation induced by strain is different whether biaxial tensile or compressive strain is applied. This will have an influence on the final density of states (DOS) and scattering rates, closely related to carrier mobility. In the on-state of the transistor, we demonstrate the out-of-equilibrium nature of carrier transport in the entire channel. Microscopic quantities analysis with strain shows the influence of scattering, bandstructure change and ballistic effects on hole transport. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Wigner quasi-distribution function is an appropriate quantum mechanics formulation to study the transition from semi-classical to quantum transport in nano-devices since it can accurately describe quantum transport including the decoherence due to scatterings. We have recently developed an efficient approach to solving the Wigner transport equation using a Monte Carlo (MC) algorithm that has been applied to Resonant Tunnelling Diodes and nano-MOSFET simulation. The approach is here extended to incorporate degeneracy effects that are important in highly doped MOSFETs. The calculation is compared with Non Equilibrium Green's Function and the semi-classical Boltzmann equation. Relative importance of quantum transport and decoherent scattering is discussed at low and room temperatures. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

A new two-dimensional self-consistent Monte-Carlo simulator including the multi sub-band transport in a 2D electron gas is described and applied to an ultra-thin Double Gate MOSFET. This approach takes into account both out of equilibrium transport and quantization effects. This method improves significantly microscopic insight into the operation of deep sub-100 nm CMOS devices. We analyze the ballistic, quantization and roughness effects in a 12 nm-long DGMOS transistor. In particular, we focus on the link between non-stationary transport and the evolution of sub-band occupancy along the channel.

We present an original approach to including quantum transport into classical Ensemble Monte Carlo (EMC) simulations. The method, based on the Wigner transport equation, is fully self-consistent, and includes impurity and phonon scattering according to the Fermi Golden rule. It is inspired by an approach suggested by Shifren et al. [IEEE Trans. Electron Dev. 50, 769 (2003)], with some major improvements that make possible successful comparison with other simulation techniques and experiments.

We present results of ultrascaled double-gate MOSFET operation and performance obtained from a new self-consistent particle-based quantum Monte Carlo (MC) approach. The simulation of quantum transport along the source-drain direction is based on the Wigner transport equation and the mode-space approximation of multi subband description. An improved method for correctly reproducing the Wigner function in the phase space by means of pseudo-particles is proposed. Our approach includes scattering effects for a two-dimensional (2-D) electron gas via standard MC algorithm. Detailed comparisons with both ballistic nonequilibrium Green's function and semiclassical multi subband Monte Carlo approaches show the ability of this Wigner transport model to incorporate correctly quantum effect into particle ensemble Monte Carlo simulation together with accurate description of scattering. This study of 6-nm-long MOSFET emphasizes the prevalent contribution of source-drain tunneling in subthreshold regime and the significant effect of quantum reflections in on-state. The influence of scattering in both the source access region and the gated part of the channel appears to be of prime importance for the correct evaluation of the on-state current, even for such small device in which the fraction of ballistic electrons is high

The effect of a single discrete impurity in the channel of Fully-Depleted Single- and Double-Gate MOSFETs is analyzed by means of 3D Monte Carlo simulation. The Double-Gate (DG) architecture appears to be less sensitive to the dopant perturbation than the Single-Gate (SG) counterpart. For an N-channel device the influence of a P-type impurity on the current-voltage characteristics is shown to be strongly dependent on the impurity position in the channel. The maximum current degradation is obtained for an impurity located about 5 nm from the source-end of the channel. The I on reduction reaches 6% in DG and 10.5% in SG. A small current enhancement (less than 2%) is induced by an N-type impurity. These results are analyzed in terms of velocity profile between source and drain.

Semi-classical Monte Carlo simulation is used to study the electrical performance of 18-nm-long n-MOSFETs including a strained Si channel. In particular, the impact of extrinsic series resistance on the drive current Ion is quantified: we show that the large on-current improvement induced by the strain is preserved, even by including an external parasitic resistance. The importance of ballistic transport is also examined and its influence on Ion is highlighted.

In nanotransistors where the channel length is comparable to the electron mean free path, ballistic transport is of great importance regarding the device performance (Lundstrom and Ren, 2002). In this context, double gate MOSFET (DGMOS) with effective channel length and silicon thickness equal to 25 nm and 10 nm, respectively, has been studied using semi-classical Monte Carlo simulations to investigate the influence of ballistic electrons.

A preliminary study of velocity fluctuations in simple devices using an atomistic model for the ionized impurity scattering is presented. The velocity fluctuations are responsible for thermal noise in semiconductor devices. In this paper the influence on the spectral density of velocity fluctuations of the boundary conditions, the doping level, the length of the resistors and the excess/default of impurities has been addressed.

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.

In this paper we compare advanced modeling approaches for the determination of the drain current in nanoscale MOSFETs. Transport models range from drift–diffusion to direct solutions of the Boltzmann-Transport-Equation with the Monte-Carlo method. Template devices representative of 22 nm Double-Gate and 32 nm Single-Gate Fully-Depleted Silicon-On-Insulator transistors were used as a common benchmark to highlight the differences between the quantitative predictions of different approaches. Using the standard scattering and mobility models for unstrained silicon channels and pure SiO2 dielectrics, the predictions of the different approaches for the 32 nm template are quite similar. Simulations of the 22 nm device instead, are much less consistent, particularly those achieved with MC simulators. Comparison with experimental data for a 32 nm device shows that the modeling approach used to explain the mobility reduction induced by the high-κ dielectric is critical. In the absence of a clear understanding of the impact of high-κ stack on transport, different models, all providing agreement with the experimental low-field mobility, predict quite different drain currents in saturation and in the sub-threshold region.

Quasi-ballistic electron transport in ultrashort FDSOI devices is analyzed using Multi-Subband Monte Carlo (MSMC) simulations, taking into account the main scattering mechanisms: phonons, surface roughness, and charged impurities in the access regions. In particular, the ballistic resistance (defined as the resistance of the channel in absence of scattering) was extracted from ballistic simulations, and shown to be in good agreement with an accurate analytical model including the contact resistance effect. The simulations show an apparent mobility degradation when the channel length decreases, comparable to that observed in experiments, without requiring any additional scattering mechanism in order to explain it.

International audience; A new two-dimensional self-consistent Monte Carlo simulator including multi sub-band transport in 2D electron gas is described and applied to thin-film SOI double gate MOSFETs. This approach takes into account both out of equilibrium transport and quantization effects. Our method allows us to significantly improve microscopic insight into the operation of deep sub-100 nm CMOS devices. We compare and analyse the results obtained with and without quantization effects for a 15 nm long DGMOS transistor.

In recent years, the understanding and accurate simulation of carbon nanotube-based transistors has become very challenging. Conventional simulation tools of microelectronics are necessary to predict the performance and use of nanotube transistors and circuits, but the models need to be refined to properly describe the full complexity of such novel type of devices at the nanoscale. Indeed, many issues such as contact resistance, low dimensional electrostatics and screening effects, demand for more accurate quantum approaches. This article reviews recent progresses on multiscale simulations which aim at bridging first principles calculations with compact modelling, including the comparison between semiclassical Monte Carlo and quantum transport approaches. © 2013 Elsevier Ltd. All rights reserved., We acknowledge support from the French National Research Agency, through the ANR/PNANO project ACCENT. A part of this work was supported by the European Community, through Network of Excellence NANOSIL (ICT-216171).

International audience; III-V Metal-Oxide-Semiconductor Field-Effect Transistors (MOSFETs) with a high-j dielectric gate stack are investigated as a possible route to enhance the performance of either microwave or logic circuits with low supply voltage (V DD). The intrinsic performance of III-V MOSFETs in both static and dynamic regimes under low V DD is estimated using device Monte Carlo simulation. The characteristics of a Bulk-like and XOI-like III-V MOSFETs are quantitatively assessed and compared in terms of DC transconductance, high frequency performance and noise behavior. Finally, the comparison with Si-based devices shows the potential of III-V nano-MOSFET architectures for high-frequency and low noise application under low operating power.

This paper discusses the influence of the channel impurity distribution on the transport and the drive current in a short-gate MOSFET. For this purpose, a careful description of electron–ion interaction suitable for the case of discrete impurities has been implemented in a 3D (three-dimensional) particle Monte Carlo simulator. This transport model is applied to the investigation of a 50 nm MOSFET operation. The paper shows that a small change in the position of a single discrete impurity may significantly influence the drain current. This effect is not only related to threshold voltage fluctuations but rather to variations in transport properties in the inversion layer.

In ferromagnet/semiconductor contacts, the different timescales of the phenomena driving the spin transport in the semiconductor induce a strong reduction of the possible spin filtering effect. We propose an original structure with double contacts to overcome this difficulty. Using Monte Carlo simulation, we show that the spin asymmetry of the current collected in such a structure may be significantly higher than in a single contact.

To fulfill high-speed and low-power specifications for both logic and analog applications, III–V FETs with high-κ gate dielectric stack are especially appealing, in particular for their ability to operate under low power supply voltage. Using complementary tools such as a 2D Poisson-Schrodinger solver and a Monte Carlo device simulator, we assess the potentiality of several III–V MOSFET structures in terms of gate charge control, static/dynamic performance and noise.

The particle-based Monte Carlo (MC) technique is acknowledged as a powerful method for accurately describing the carrier transport in semiconductor materials and devices within the semi-classical approximation, i.e. the Boltzmann transport equation (BTE) for the distribution function. It has been developed by many groups to study a wide variety of transport problems in many kinds of devices, to such a point that it is impossible to summarize here the most significant examples of its applications. The accuracy of the semiclassical transport description is then given by the models used for the band structure and the scattering mechanisms. Hole transport properties in realistic Si devices are particularly affected by the strong anisotropy of the valence band (Thomson et al., 2006), which is further increased by the presence of strain. Analytic approximations fail to describe the valence band structure of Si, and an accurate or « full » description of the energy dispersion is then needed to describe hole transport correctly. In this work, the valence band structure is calculated thanks to a stress-dependent 30-band k.p model (Rideau et al., 2006). With this accurate valence band description, « Full-Band » Monte Carlo simulation becomes an appropriate tool to study various (unstrained or strained) p-type devices. Beyond the description of the model in Section 2, we show here two typical examples of application of the full-band Monte simulator to strain effects in p-type devices. In Section 3, the influence of mechanical stress on Double Gate p-MOSFET performance is be investigated. Multiple gate structures are now recognized as promising architectures to overcome short channel effects in nanometer scaled MOSFET. Double Gate MOSFETs (DGMOS) are found to reach the best performance among SOI-based transistors (Saint Martin et al., 2006). In addition, mechanical stress is used as a technological performance booster for CMOS technology. The impact of stress on carrier transport is then of great importance and is both studied experimentally (Huet et al., 2008 ; Suthram et al., 2007) and theoretically (Huet et al., 2008a; Bufler et al., 2008; Pham et al., 2008). In this work, device performance of strained Si p-DGMOS is studied considering uniform biaxial and uniaxial stresses in the channel. The effect of strain is analyzed via some of the main usual figures of

In this chapter, we investigate the device operation and performance of carbon nanotube-based field-effect transistors (CNTFETs) by means of particle Monte Carlo simulation including electron–phonon scattering. Within semi-classical approach of transport, both Ohmic- and Schottky-type source and drain contacts are considered and the effect of ambipolar transport inherent in Schottky barriers is analysed. This effect degrades the on/off current ratio and impedes the current saturation at high V DS, which makes the transition frequency strongly dependent on the drain voltage. However, by lowering the Schottky barrier height for electrons, the ambipolar behavior is reduced, which makes the device characteristics closer to that of ohmic-contact transistors. In both cases the intrinsic current-gain cutoff frequency is shown to reach about 800 GHz for a gate length of 100 nm. The detailed analysis of scattering events in the channel shows that the fraction of ballistic electrons in the Ohmic contacts devices increases from 80 to 95% when reducing the gate length from 100 to 10 nm. Hence, the transport in the channel is likely to be strongly coherent, which is analyzed by means of quantum Wigner Monte Carlo simulation, whose algorithm is fully compatible with the semi-classical one. It is shown that in spite of significant quantum transport effects such as source-drain tunneling through the gate-induced barrier and reflection by the sharp potential drop, the microscopic quantum features, e.g. the oscillations of the Wigner function, are not strongly reflected at the macroscopic level of terminal current.

High-mobility III-V heterostructures are emerging and very promising materials likely to fulfil high-speed and low-power specifications for ambient intelligent applications. The main objective of this work is to theoretically explore the potentialities of MOSFET based on III-V materials with low bandgap and high electron mobility. First, the charge control is studied in III-V MOS structures using a Schrodinger-Poisson solver. Electronic transport in III-V devices is then analyzed using a particle Monte Carlo device simulator. The external access resistances used in the calculations are carefully calibrated on experimental results. The performance of different structures of nanoscale MOS transistor based on III-V materials is evaluated and the quasi-ballistic character of electron transport is compared to that in Si transistors of same gate length.

Long-channel effective mobilities as well as transfer characteristics of a 32 nm single-gate SOI and a 16 nm double-gate (DG) MOSFET have been simulated with live different Monte Carlo (MC) device simulators. The differences are mostly rather small for the SOI-FET with quantum effects having a minor effect on threshold voltage due to the lowly doped channel, while the two multi-subband MC simulators show some prominent deviations in the case of the DG-FET. High-K mobility degradation by remote phonon scattering (RPS) in free carrier MC approximation leads to smaller performance degradation compared to multi-subband MC with remote Coulomb scattering (RCS) and RPS, but requires further investigations.

III–V MOSFET (Metal Oxide Semiconductor Field Effect Transistor) with high-κ gate dielectric stack appears as a viable alternative to enhance not only microwave performance but also logic circuits with low supply voltage. This allows fulfilling high-speed and low-power specifications for intelligent applications. Indeed, combining weak gate leakage of standard MOSFETs and good RF performance of HEMTs (High Electron Mobility Transistors), they could outperform end-of-roadmap standard Si-MOSFET. Using full 2D Poisson-Schrodinger solver and a semi-classical Ensemble Monte Carlo device simulator, various 50nm MOSFET and HEMT are investigated in terms of gate charge control and both static and dynamic I–V performance. In particular, Y parameters are carefully extracted from time-varying currents. This comparative study allows us to propose an optimized III–V nano-FET architecture with high-frequency performance under low power supply.

In this paper, we investigate the device operation of CNFETs using Monte Carlo simulation. Two types of contacts (ohmic and Schottky) are considered and the effect of ambipolar transport with Schottky barriers is analysed. We also discuss the actual influence of quantum effects on the basis of Wigner simulation results. The output and high-frequency characteristics of different structures are presented and discussed.

This paper examines the quantum transport effects in carbon nanotube field-effect transistors (CNTFETs) within the Wigner's function formalism, using a particle Monte Carlo technique. The comparison with semi-classical simulation shows that significant differences observed at the microscopic level are not necessarily strongly reflected at the macroscopic level in terms of drain current. The dependence of quantum effects on gate length is also investigated.

Thanks to both device simulation and ballistic calculation, the concept of apparent mobility is discussed in the case of unstrained and strained nanoscale DG MOSFET. We show that the apparent mobility reduction in simulated short channel devices can be explained by non stationary effects. The apparent mobility is successfully linked to the long-channel mobility and to a “ballistic mobility” using a Mathiessen's rule. Moreover, a simple extended expression of the ballistic mobility in the Shur analytical model suggests the non-universal nature of this parameter through its dependence on drain voltage, access resistance and device geometry. The effect of access resistance is analyzed in more details by means of ballistic calculations. The results are consistent with that obtained from both Monte Carlo simulation and measurements.

In this paper, the influence of mechanical stress on double-gate p-MOSFET performance has been investigated, by means of the full-band version of our Monte Carlo simulator (MONACO). Compressive and tensile stresses in the case of biaxially- and uniaxially-strained 〈100〉 and 〈110〉-oriented channels have been studied. A tensile biaxial stress in plane (100) always decreases the gate delay and the lowest values are obtained for a 〈100〉-oriented channel. A compressive uniaxial stress along 〈110〉 (or tensile uniaxial stress along 〈−110〉) leads to an appreciable improvement of the gate delay in 〈110〉-oriented channel devices. Resulting performance meets quite well the specifications of the updated 2008 ITRS defined for LOP45 and LSTP40.

This paper examines the phonon-induced electron decoherence in semiconductor nanostructures and nanodevices within the Wigner transport equation, solved using a particle Monte Carlo technique. The Wigner-Boltzmann formalism is first established as a relevant and original approach to modeling electron quantum decoherence in semiconductors. The simulation of the time evolution of a free wave-packet then allows analyzing the competition between decoherence and wave-packet expansion in a semiconductor. It is additionally argued that decoherence occurs faster than in the widely studied case of quantum Brownian motion. The simulation of a wave packet interacting with a tunnel barrier allows studying the electron localization induced by decoherence. The case of a wave packet interacting with a double barrier puts forward the mechanism of decoherence-induced transition from resonant to sequential transport through a bound state. Finally the simulation of resonant tunneling devices shows how these phenomena take place in nanodevices and highlights the transition from the quantum transport regime to the semiclassical transport regime induced by phonon scattering.

The Wigner Monte Carlo approach is shown to provide an efficient way to study quantum transport in the presence of scattering and to connect semi-classical to quantum transport. The study of resonant tunneling diodes highlights the physics of the impact of scattering on resonant tunneling, and on electron decoherence and localization. The simulation of nano-MOSFET evidences a mixed regime, where both quantum transport and scattering play a significant role.

This paper investigates the mobility extraction from channel magnetoresistance, which is widespreading as a powerful experimental method to study transport in short gate devices. A fully self-consistent Monte Carlo device simulator is used to simulate the influence of a transverse magnetic field on electron transport in nanometer scale devices. After validation on a simple silicon magnetic sensor, the method is applied to the simulation of the channel magnetoresistance of nanoscale double gate metal oxide semiconductor field effect transistors. Apparent magnetoresistance mobilities μMR are extracted from channel resistance variation with the applied magnetic field, using a measurement-inspired extraction method. The simulated temperature trends obtained by simulation are consistent with experimental data. As experimentally observed elsewhere, the extracted apparent mobility decreases with the shrinking of the channel length. No additional scattering mechanism specific to short channel devices was needed t...

We present a comparison between two-different approaches to including quantum effects in a Monte-Carlo simulator. The ability of our original Pearson Effective Potential (PEP) correction to correctly account for electrostatic quantum effects has been demonstrated on double-gate nMOS capacitors with different film thicknesses. In this work, results obtained from semi-classical, PEP corrected and multi-subband Monte-Carlo approaches are reported for a double-gate nMOSFET with a channel length LC = 20nm and a silicon film thickness TSi = 8 nm at low and high drain voltages. For the first time, excellent agreements are obtained between quantum corrected and multi-subband Monte-Carlo methods on both electrical characteristics and microscopic quantities.

Carbon Nanotube (CNT) appears as a promising candidate to shrink field-effect transistors (FET) to the nanometer scale. Extensive experimental works have been performed recently to develop the appropriate technology and to explore DC characteristics of carbon nanotube field effect transistor (CNTFET). In this work, we present results of Monte Carlo simulation of a coaxially gated CNTFET including electron-phonon scattering. Our purpose is to present the intrinsic transport properties of such material through the evaluation of electron mean-free-path. To highlight the potential of high performance level of CNTFET, we then perform a study of DC characteristics and of the impact of capacitive effects. Finally, we compare the performance of CNTFET with that of Si nanowire MOSFET., 15 pages, 14 figures, final version to be published in C. R. Acad. Sci. Paris

International audience; In this paper we report on the possibility to use particle-based Monte Carlo techniques to incorporate all relevant quantum effects in the simulation of semiconductor nano-transistors. Starting from the conventional Monte Carlo approach within the semi-classical Boltzmann approximation, we develop a multi-subband description of transport to include quantization in ultra-thin body devices. This technique is then extended to the particle simulation of quantum transport within the Wigner formulation. This new simulator includes all expected quantum effects in nano-transistors and all relevant scattering mechanisms which are taken into account the same way as in Boltzmann simulation. This work is illustrated by analyzing the device operation and performance of multi-gate nano-transistors in a convenient range of channel lengths and thicknesses to separate the influence of all relevant effects: significant quantization effects occurs for thickness smaller than 5 nm and wave mechanical transport effects manifest themselves for channel length smaller than 10 nm. We also show that scattering mechanisms still have an important influence in nanoscaled double-gate transistors, both in the intrinsic part of the channel and in the resistive lateral extensions.

Using Monte Carlo simulation, device performance of double gate MOSFET with 25 nm-gate length is evaluated. The influences of the body thickness, of the gate overlap or underlap, of the oxide thickness, of the back gate length, and of the RC parasitic effects have been investigated. We show that well-tempered devices with excellent subthreshold behaviour and good dynamic operation may be achieved with 10 nm-thick body if the gate-source/drain overlap is reduced to 0 and parasitic RC effects are controlled. To boost performance and to obtain greater allowance to parasitic RC effects, strained body may be used. Finally, the scaling strategy resulting from the study of 25 nm-long devices is successfully applied to design double gate MOSFET with shorter gate lengths.

The concept of mobility is discussed in the case of unstrained and strained nanoscale DG MOSFET thanks to particle Monte Carlo device simulation. Without the introduction of specific scattering phenomenon for short channel devices, the apparent mobility extracted from simulated electrical characteristics decreases with the shrinking of the channel length, as experimentally observed elsewhere. We show that this reduction at room temperature is caused by non stationary effects. Moreover, both simulation results and experimental data may be well reproduced by a Mathiessen-like model, using a "ballistic mobility" extracted from MC simulations together with the usual long channel mobility., 4 pages, 4 figures, ESSDERC 2007, Munich, Germany

Metal/carbon nanotube Schottky contacts are studied using particle Monte Carlo Simulation. The developed model is based on the WKB approximation and on the Landauer formula. Results are in fairly good agreement with experimental data.

International audience; A new self-consistent quantum simulator based on the Monte Carlo solution of Wigner transport equation is used to analyze the operation of 6 nm-long DG-MOSFETs. By comparison with other simulation approaches, the work emphasizes the important role of scattering and quantum effects on the electrical characteristics of such nano-devices. The results are confronted to ITRS specifications and the various effects of aggressive oxide thickness thinning on device performance are discussed.