Search

This paper presents the latest status of the open source advanced TCAD simulator called Nano-Electronic Simulation Software (NESS) which is currently under development at the Device Modeling Group of the University of Glasgow. NESS is designed with the main aim to provide an open, flexible, and easy to use simulation environment where users are able not only to perform numerical simulations but also to develop and implement new simulation methods and models. Currently, NESS is organized into two main components: the structure generator and a collection of different numerical solvers; which are linked to supporting components such as an effective mass extractor and materials database. This paper gives a brief overview of each of the components by describing their main capabilities, structure, and theory behind each one of them. Moreover, to illustrate the capabilities of each component, here we have given examples considering various device structures, architectures, materials, etc. at multiple simulation conditions. We expect that NESS will prove to be a great tool for both conventional as well as exploratory device research programs and projects.

Fabrication techniques at the nanometer scale offer potential opportunities to access single dopant features in nanoscale transistors. Here we report full-band quantum transport simulations with hole-phonon interactions through a device consisting of two gates- all-around in series and a p-type Si nanowire channel with a single-dopant within each gated region. For this purpose, we have developed and implemented a mode-space based full-band quantum transport simulator with phonon scattering using the six-band k.p method. Based on the non-equilibrium Green's function formalism and the self-consistent Born's approximation, an expression for the hole-phonon interactions self-energy within the mode-space representation is introduced.

In this work, we investigate the surface transfer doping process that is induced between hydrogen-terminated (100) diamond and the metal oxides, MoO₃ and V₂O₅, through simulation using a semi-empirical Density Functional Theory (DFT) method. DFT was used to calculate the band structure and charge transfer process between these oxide materials and hydrogen terminated diamond. Analysis of the band structures, density of states, Mulliken charges, adsorption energies and position of the Valence Band Minima (VBM) and Conduction Band Minima (CBM) energy levels shows that both oxides act as electron acceptors and inject holes into the diamond structure. Hence, those metal oxides can be described as p-type doping materials for the diamond. Additionally, our work suggests that by depositing appropriate metal oxides in an oxygen rich atmosphere or using metal oxides with high stochiometric ration between oxygen and metal atoms could lead to an increase of the charge transfer between the diamond and oxide, leading to enhanced surface transfer doping.

In this work we investigate the surface transfer doping effect induced between hydrogen terminated diamond and Moo3. We simulated the interface of (100) MoO 3 surface and hydrogen terminated (100) diamond surface using fist principle methods such as Density Functional Theory (DFT). DFT simulation allowed us to calculate the band structure and charge transfer between the MoO 3 and the diamond materials. Analysis of the band structures and density of states shows that the Moo3is an electron acceptor and injects holes into the diamond structure.

In this work, we study 2.1nm-diameter uniaxial strained Si gate-all-around nanowire field-effect transistors, focusing on the electron mobility and the variability due to random discrete dopants (RDDs). Firstly, we extract the electron effective masses under various strains from Density Functional Theory (DFT) simulations. Secondly, we present the impact of the strain on the electron mobility in the Si nanowire using the Kubo-Greenwood formalism with a set of multi-subband phonon, surface roughness, and ionized impurity scattering mechanisms. Finally, we perform quantum transport simulations to investigate the effect of RDD on the threshold voltage and ON-state current variation.

Using a state-of-the-art quantum transport simulator based on the effective mass approximation, we have thoroughly studied the impact of variability on SixGe1−x channel gate-all-around nanowire metal-oxide-semiconductor field-effect transistors (NWFETs) associated with random discrete dopants, line edge roughness, and metal gate granularity. Performance predictions of NWFETs with different cross-sectional shapes such as square, circle, and ellipse are also investigated. For each NWFETs, the effective masses have carefully been extracted from sp3d5s∗ tight-binding band structures. In total, we have generated 7200 transistor samples and performed approximately 10,000 quantum transport simulations. Our statistical analysis reveals that metal gate granularity is dominant among the variability sources considered in this work. Assuming the parameters of the variability sources are the same, we have found that there is no significant difference of variability between SiGe and Si channel NWFETs.

National audience

The field of molecular electronics continues to spur interest in the quest for miniaturization and reduction of operational power of electron devices. Most of the systems described in the literature are based on organic molecules, such as benzene, ferrocene and fullerenes [1]. However, the use of inorganic molecules known as polyoxometalates (POMs) (see Fig. 1 and Fig. 2) could offer several important advantages over the conventional and organic based devices. The interest in POMs for flash cell applications stems from the fact that POMs are highly redox active molecules and that they can also be doped with electronically active heteroatoms [3]. They can undergo multiple reversible reductions/oxidations, which makes them attractive candidates for multi-bit storage in flash memory cells. Our recent work showed that POMs are more compatible with existing CMOS processes than organic molecules and they can replace the polysilicon floating gate in contemporary flash cell devices [2]. In this work, we discuss a further improvement and development of our simulation framework and models, e.g. Poisson distribution of the molecules in the oxide, introducing a various device geometry such as FDSOI and nanowires and improved simulation flow.

This paper presents experimental and simulation analysis of an Ω-shaped silicon junctionless nanowire field-effect transistor (JL-NWT) with gate lengths of 150 nm and diameter of the Si channel of 8 nm. Our experimental measurements reveal that the ON-currents up to 1.15 mA/μm for 1.0 V and 2.52 mA/μm for the 1.8-V gate overdrive with an OFF-current set at 100 nA/μm. Also, the experiment data reveal more than eight orders of magnitude ON-current to OFF-current ratios and an excellent subthreshold slope of 66 mV/dec recorded at room temperature. The obtained experimental current-voltage characteristics are used as a reference point to calibrate the simulations models used in this paper. Our simulation data show good agreement with the experimental results. All simulations are based on drift-diffusion formalism with activated density gradient quantum corrections. Once the simulations methodology is established, the simulations are calibrated to the experimental data. After this, we have performed statistical numerical experiments of a set of 500 different JL-NWTs. Each device has a unique random distribution of the discrete dopants within the silicon body. From those statistical simulations, we extracted important figures of merit, such as OFF-current and ON-current, subthreshold slope, and voltage threshold. The performed statistical analysis, on samples of those 500 JL-NWTs, shows that the mean ID-VGs characteristic is in excellent agreement with the experimental measurements. Moreover, the mean ID-VGs characteristic reproduces better the subthreshold slope data obtained from the experiment in comparison to the continuous model simulation. Finally, performance predictions for the JL transistor with shorter gate lengths and thinner oxide regions are carried out. Among the simulated JL transistors, the configuration with 25-nm gate length and 2-nm oxide thickness shows the most promising characteristics offering scalable designs.

In this paper, we report a hierarchical simulation study of the electromigration (EM) problem in Cu-carbon nanotube (CNT) composite interconnects. This paper is based on the investigation of the activation energy and self-heating temperature using a multiscale electrothermal simulation framework. We first investigate the electrical and thermal properties of Cu-CNT composites, including contact resistances, using the density functional theory and reactive force field approaches, respectively. The corresponding results are employed in macroscopic electrothermal simulations taking into account the self-heating phenomenon. Our simulations show that although Cu atoms have similar activation energies in both bulk Cu and Cu-CNT composites, Cu-CNT composite interconnects are more resistant to EM thanks to the large Lorenz number of the CNTs. Moreover, we found that a large and homogenous conductivity along the transport direction in interconnects is one of the most important design rules to minimize the EM.