1,720,956 research outputs found
Substrate-dependent high-field transport and self-heating in graphene transistors
Get PDFOver the last decade graphene has attracted much interest for nanoelectronic applications due to its high and symmetrical carrier mobility, and high drift velocity compared to silicon. However, when graphene is placed on insulating substrates such as SiO2 or flexible plastics, its inherent superior qualities get suppressed by the influence of the underlying substrate. Interfaces and substrate material properties have a significant impact on graphene based nano-scale devices due to the reduced dimensions and large surface-to-volume ratio.
Motivated by this issue, in this work we have investigated the substrate dependence of the electrical and thermal transport in graphene field-effect transistors (GFETs). We developed a simple yet practical electro-thermal model along with extensive calibration with experimental data. Special emphasis is given to the study of high-field transport and investigation of temperature-induced effects on device performance.
First, we have used this electro-thermal model to examine the scaling effect of the supporting insulator (e.g. SiO2, BN) thickness on temperature maximum (hot spot) formation. Our findings showed average and maximum temperatures of GFETs scale differently due to competing electrostatic and heat sinking effects. Self-heating in GFETs causes current degradation (up to ~10-20%) in micron-sized devices on SiO2/Si but is reduced if the supporting insulator thickness is scaled down. The transient behavior of such FETs has thermal time constants in the range of 50-250 ns, dominated by the thickness of the supporting insulator and that of device capping layers. Self-heating is also reduced in shorter channel devices, due to partial heat sinking at the contacts.
Next, we investigate the effect of different supporting dielectrics such as hexagonal boron nitride (h-BN), HfO2 and SiO2 on the velocity saturation of GFETs. We examine the effects from different substrates as they each present a unique scenario due to their different (re-mote) phonons and thermal conductivities, all of which influence high-field transport in GFETs. Additionally, we studied the origins of the poor current saturation in short-channel GFETs in de-tail. We study and compare the temperature profiles generated in GFETs on different insulating materials for bottom oxide and substrate through full thermal finite element method (FEM). Ma-terials with anisotropic thermal conductivity showed significant impact in heat spreading and temperature rise in the hot-spot. We apply our findings to add a guideline for the maximum “safe” power density, e.g. in GFETs on flexible substrates such as polyimide (PI), without inducing thermal deformation; the maximum is found to be ~1.8 mW/µm2 (with 200 nm BN dielectric).
Finally, we also develop a physics-based compact model based on existing literature, for GFETs with well calibration against experimental data and other finite element models. This model has been implemented into a circuit simulator like Verilog-A with a minimum number of iterations for channel potential calculation.
These results shed important physical insight into the high-field and thermal profile of graphene transistors. Moreover, the electro-thermal model and results presented in this dissertation can be extended for analysis of other 2D materials beyond graphene.Item withdrawn by Mark Zulauf ([email protected]) on 2014-10-20T14:43:11Z
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University of Illinois Theses & Dissertations (ID: 1)
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ATOMISTIC MODELING OF UNINTENTIONAL SINGLE CHARGE EFFECTS IN NANOSCALE FETS
No full textNumerical simulations have been performed to study the single-charge-induced ON current fluctuations (random telegraphic noise) in conventional (MOSFET) and non-conventional (silicon nanowire) nanoscale field-effect transistors. A semi-classical three-dimensional particle-based Monte Carlo device simulator (MCDS 3-D) has been integrated and used in this work. Quantum mechanical space-quantization effects have been accounted for via a parameter-free effective potential scheme that has been proved quite successful in describing charge set back from the interface and quantization of the energy (bandgap widening) within the channel region of the device. The effective potential is based on a perturbation theory around thermodynamic equilibrium and leads to a quantum field formalism in which the size of the electron depends upon its energy. To treat full Coulomb (electron-ion and electron-electron) interactions properly, the simulator implements two different real-space molecular dynamics (MD) schemes: the particle-particle-particle-mesh (P3M) method and the corrected Coulomb approach. For better accuracy, particularly in case of nanowire FETs, bandstructure parameters (bandgap, effective masses, and density of states) have been computed via a 20-band nearest-neighbor sp3d5s* tight-binding scheme. Also, since the presence of single impurities in the channel region represents a rare event in the carrier transport process, necessary event-biasing algorithms have been implemented in the simulator that, while enhancing the statistics, results in a faster convergence in the chan-nel current. The study confirms that, due to the presence of single channel charges, both the electrostatics (carrier density) and dynamics (mobility) are modified and, therefore, simultaneously play important roles in determining the magnitude of the current fluctuations. The relative impact (percentage change in the ON current) depends on an intricate interplay of device size, geometry, crystal direction, gate bias, temperature, and energetics and spatial location of the trap
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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