Catégorie : info
Currentlimiting challenges for allspin logic devices
Li Su, Youguang Zhang, JacquesOlivier Klein, Yue Zhang , Arnaud Bournel, Albert Fert & Weisheng Zhao
Scientific Reports 5, Article number: 14905 (2015) doi:10.1038/srep14905
Continue reading « Currentlimiting challenges for allspin logic devices »
Réunion Comics 15/01/2014
Présents : Michele Amato, Salim Berrada, Arnaud Bournel, Philippe Dollfus, Jérôme Larroque, Mai Chung Nguyen, Jérôme Saint Martin, Su Li, Tran Van Truong, Adrien Vincent.
Papers
Salim and Philippe with Plaçais group about Klein transistor nearly accepted (IOP 2D mat).
Monastir paper with Arnaud about optical effects in GeSn quantum wells accepted for JAP: « Wavefunction engineering and absorption spectra in Si_{0.16}Ge_{0.84}/Ge_{0.94}Sn_{0.06}/Si_{0.16}Ge_{0.84} strained on relaxed Si_{0.10}Ge_{0.90} type I quantum well ». But not very original in comparison of a previous paper on Ge wells. Naima as 1^{st} author.
Conferences
ISCAS of Adrien accepted! In Australia in June.
Next deadlines: tomorrow for EMRS > Michele has already submitted, Jérôme L. should write an abstract too. In Lille May 1924.
Summer school Graphene 2014 > Truong and Mai Chung (?). Deadline for the conference Graphene (Toulouse) = 1/2 > Trung, Mai Chung.
IWCE, deadline 28/1. Same day as Comics lunch!
Ulis, February 3 but…
Next Comics meetings
On Monday afternoon. About 1 per month.
A (very) short introduction to Density Functional Theory, by Michele
(pdf here)
> For atomic structure, thermodyn, chemical, electronic and scattering properties.
Nobel prize for DFT in chemistry. 1998: Walter Kohn and John Pople.
Semiempirical methods (Hückel, based on HartreeFock formalism) > good for large systems. Can fail if the computed molecule is not close to the database of parametrized molecules.
DFT > very good scalability.
Many body problem > N_{e} electrons, N_{n} nuclei, Schrödinger equation to solve… With kinetic energies and potential: repulsion between nuclei, between electrons and between electrons and nuclei. How to deal with 10^{23} particles?
BornOppenheimer separation > nuclei frozen in their equilibrium positions. But wavefunctions remain very complex! And experimentally measurable. While electron density is observable, e.g.by Xrays.
HohenbergKohn theorem I: the relation between the potential and the electron density is invertible. Then, the ground state expectation value of any observable depends only on the electron density.
HohenbergKohn theorem II: the total energy functional has a minimum, the ground state energy E0, in correspondence to the ground state density r_{0} > proof of the existence of the universal functional without determining it.
KohnSham scheme > r_{0} can be calculated thanks to an artificial system of noninteracting particles. Using oneparticle orbitals which are not real wavefunctions. And KohnSham potential = v_{ion}(r) + v_{H}(r) + v_{xc}(r) where v_{H} describes the classic electrostatic potential and v_{xc} is the exchangecorrelation potential, for taking into account the effect of interactions between particles.
Approximation for v_{xc} > local description.
Self consistent flow diagram to solve the KohnSham scheme, as a function of the density.
Defreezing the nuclei… Cf. Feynman, Phys Rev 56 (4), 340 (1939) “Forces in molecules” (http://dx.doi.org/10.1103/PhysRev.56.340) > HellmannFeynman theorem for an analytical solution. Wikipedia: proven independently by many authors, including Paul Güttinger (1932), Wolfgang Pauli (1933), Hans Hellmann (1937) and Richard Feynman (1939). This does not correspond to phonon problem!
For further development :
RevModPhys.71.1253 RMP_61_689 DFT_NATO g1
Comics meeting 03/03/2014
* News : Hung Nanotechnology accepted, EMRS Jerome and Michele accepted, Rania will come on may
* Presentation by Jerome on Full band Monte Carlo for phonon : First (ballistic) transport results (.ppt here)
Presents : Michele, Mai Chung, Su Li, Adrien, Jérôme L., Philippe, Hung, Jérôme SM.
Silicon–Germanium Nanowires: Chemistry and Physics in Play, from Basic Principles to Advanced Applications
Review Michele Amato et al.
Chem. Rev., 2014, 114 (2), pp 1371–1412
Publication Date (Web): November 22, 2013

Réunion Comics 23/04/2013
 Actualités : Mise en ligne site web IEF, …
 CR SOI kiev (Arnaud) et ARN Rencontres numériques (Jérôme SM)
IWCE 2014 in Paris
The 17th International Workshop on Computational Electronics (IWCE 2014) will be held June 36, 2014, in the city centre of Paris, France. IWCE covers all aspects of advanced simulation of electronic transport and optoelectronic processes in semiconductors and semiconductor devices.
Réunion Comics 19/03/2013
Bilan
 Stage M2 Anes + Rania 3 mois, 2 Projets P2N soumis
 Présentation Salim GNM FET => pbm calcul faible transmission
BioInspired Stochastic Computing Using Binary CBRAM Synapses
In this paper, we present an alternative approach to neuromorphic systems based on multilevel resistive memory synapses and deterministic learning rules. We demonstrate an original methodology to use conductivebridge RAM (CBRAM) devices as, easy to program and lowpower, binary synapses with stochastic learning rules. New circuit architecture, programming strategy, and probabilistic spiketiming dependent plasticity (STDP) learning rule for two different CBRAM configurations withselector (1T1R) and withoutselector (1R) are proposed. We show two methods (intrinsic and extrinsic) for implementing probabilistic STDP rules. Fully unsupervised learning with binary synapses is illustrated through two example applications: 1) realtime auditory pattern extraction (inspired from a 64channel silicon cochlea emulator); and 2) visual pattern extraction (inspired from the processing inside visual cortex). High accuracy (audio pattern sensitivity ${>}{2}$, video detection rate ${>}{rm 95}%$) and low synapticpower dissipation (audio 0.55 $mu{rm W}$, video 74.2 $mu{rm W}$) are shown. The robustness and impact of synaptic parameter variability on system performance are also analyzed.
Published in:
Electron Devices, IEEE Transactions on (Volume:60 , Issue: 7 )
Date of Publication: July 2013
Réunion Comics 11/06/2013
– Mai Chung USTH +
– Bilan conférence : IWCE (Philippe), Damien ISCAS+…