Impact of randomly distributed dopants on Ω-gate junctionless silicon nanowire transistors

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

Full-band quantum transport simulation in presence of hole-phonon interactions using a mode-space k·p approach

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

Mobility of circular and elliptical si nanowire transistors using a multi-subband 1d formalism

We have studied the impact of the cross-sectional shape on the electron mobility of n-type silicon nanowire transistors (NWTs). We have considered circular and elliptical cross-section NWTs including the most relevant multisubband scattering processes involving phonon, surface roughness, and impurity scattering. For this purpose, we use a flexible simulation framework, coupling 3D Poisson and 2D Schrödinger solvers with the semi-classical Kubo-Greenwood formalism. Moreover, we consider cross-section dependent effective masses calculated from tight binding simulations. Our results show significant mobility improvement in the elliptic NWTs in comparison to the circular one for both 100 and 110 transport directions

New insights into the genetic etiology of Alzheimer's disease and related dementias

Characterization of the genetic landscape of Alzheimer's disease (AD) and related dementias (ADD) provides a unique opportunity for a better understanding of the associated pathophysiological processes. We performed a two-stage genome-wide association study totaling 111,326 clinically diagnosed/'proxy' AD cases and 677,663 controls. We found 75 risk loci, of which 42 were new at the time of analysis. Pathway enrichment analyses confirmed the involvement of amyloid/tau pathways and highlighted microglia implication. Gene prioritization in the new loci identified 31 genes that were suggestive of new genetically associated processes, including the tumor necrosis factor alpha pathway through the linear ubiquitin chain assembly complex. We also built a new genetic risk score associated with the risk of future AD/dementia or progression from mild cognitive impairment to AD/dementia. The improvement in prediction led to a 1.6- to 1.9-fold increase in AD risk from the lowest to the highest decile, in addition to effects of age and the APOE ε4 allele

Quantum simulation investigation of work-function variation in nanowire tunnel FETs

The variability induced by the work-function variation (WFV) in p-type ultra-scaled nanowire tunnel FET (TFET) has been studied by using the Non-Equilibrium Green's Function module implemented in University of Glasgow quantum transport simulator called NESS. To provide a thorough insight into the influence of WFV, we have simulated 250 atomistically different nanowire TFETs and the obtained results are compared to nanowire MOSFETs first. Our statistical simulations reveal that the threshold voltage (Vth) variations of MOSFETs and TFETs are comparable, whereas the on-current (Ion) and off-current (Ioff) variations of TFETs are smaller and higher, respectively in comparison to the MOSFET. Based on the results of the simulations, we have provided a physical insight into the variations of the Ion and Ioff currents. Then, we compared the nanowire and Fin TFETs structures with different oxide thickness in terms of the WFV-induced variability. The results show that WFV has a strongest impact on the Ioff, and moderate effect on the Ion and Vth in nanowire TFET with smaller oxide thickness. Lastly, it is found that compared with the random discrete dopants, WFV is a relatively weaker variability source in ultra-scaled nanowire TFETs, especially from the point of view of Ion variation

Variability Predictions for the Next Technology Generations of <i>n</i>-type Si_<i>x</i>Ge_1−<i>x</i> Nanowire MOSFETs

Using a state-of-the-art quantum transport simulator based on the effective mass approximation, we have thoroughly studied the impact of variability on Si x Ge 1 &#8722; 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 s p 3 d 5 s &lowast; 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

Human-mediated introductions of Australian acacias - a global experiment in biogeography

AIM : Australian acacias (1012 recognized species native to Australia, which were previously grouped in Acacia subgenus Phyllodineae) have been moved extensivley around the world by humans over the past 250 years. This has created the opportunity to explore how evolutionary, ecological, historical and sociological factors interact to affect the distribution, usage, invasiveness and perseptions of a globally important group of plants. This editorial provides the background for the 20 papers in this special issue of Diversity and Distributions that focusses on the global cross-disciplinary experiment of introduced Australian acacias. LOCATION : Australia and global METHODS : The papers of the special issue are discussed in the ontext of a unified framework for biological invasions. Distributions of species were mapped across Australia, their representation in bioclimatic zones examined and the potential global distribution of the group modelled. By collating a variety of different lists, we determined which Australian acacias have reached different stages in the introduction-naturalization-invasion continuum in different parts of the world. Paradigms and key research questions relating to barriers to invasion, stages of invasion and management perceptions are sketched. RESULTS According to our global database of Australian acacia records, 386 species have been moved outside Australia by human agency, 71 species are naturalized or weedy, and 23 are unequivocally invasive. Climatic models suggest that about a third of the world's land surface is clamatically suitabel for Australian acacias. Many species are commercially important crops or are useful for other purposes and have been extensively planted, and many different human perceptions of Australian acacias exist in different parts of the world. The papers in the special issue cover all the barriers, stages and processes that define biological invasions and touch on many aspects : history and the human dimension;aspects of the species pool; species traits; biotic interactions; climate and niche; and management. MAIN CONCLUSIONS : Australian acacias are an excellent model group for examining interactions between evolutionary, ecological and socia-economic drivers of species introductions. New insights have emerged on the biological, ecological and evolutionary correlated of naturalization and invasion, but human usage factors permeate all explanatory models. Understanding and managing introduced Australian acacias requires a fundamental and integrative appreciation of both intrinsic (e.g. species traits) and extrinisic (e.g. human usage and perceptions) aspects.http://wileyonlinelibrary.com/journal/ddiab201