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December 2, 2011Ph.D. Thesis Presentation First principles simulations of nanoelectronic devices Jesse Maassen (Supervisor : Prof. Hong Guo) Department.

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Presentation on theme: "December 2, 2011Ph.D. Thesis Presentation First principles simulations of nanoelectronic devices Jesse Maassen (Supervisor : Prof. Hong Guo) Department."— Presentation transcript:

1 December 2, 2011Ph.D. Thesis Presentation First principles simulations of nanoelectronic devices Jesse Maassen (Supervisor : Prof. Hong Guo) Department of Physics, McGill University, Montreal, QC Canada

2 December 2, 2011Ph.D. Thesis Presentation Why first principles theory? Line of ~ 50 atoms 201222 nm YearChannel length 201516 nm 201811 nm ? (Source: ITRS 2010)

3 December 2, 2011Ph.D. Thesis Presentation Why first principles theory? ScienceEngineering Atomic structure : surfaces, chemical bonding, interfaces, dissimilar materials, charge transfer, roughness, variability, … tunneling, conductance quantization, spin-transport, … Quantum effects : First principles

4 December 2, 2011Ph.D. Thesis Presentation How to calculate transport properties? Taylor et al., PRB 63, 245407 (2001) Waldron et al., PRL 97, 226802 (2006) Maassen et al., IEEE (submitted)

5 December 2, 2011Ph.D. Thesis Presentation Applications.  Graphene-metal interface  Localized doping in Si nano-transistors  Dephasing in nano-scale systems Maassen et al., Appl. Phys. Lett. 97, 142105 (2010); Maassen et al., Nano. Lett. 11,151 (2011)

6 December 2, 2011Ph.D. Thesis Presentation Applications.  Graphene-metal interface  Localized doping in Si nano-transistors  Dephasing in nano-scale systems Maassen and Guo, preprint to be submitted

7 December 2, 2011Ph.D. Thesis Presentation Applications.  Graphene-metal interface  Localized doping in Si nano-transistors  Dephasing in nano-scale systems Maassen et al., PRB 80, 125423 (2009)

8 December 2, 2011Ph.D. Thesis Presentation Applications.  Graphene-metal interface  Localized doping in Si nano-transistors  Dephasing in nano-scale systems Maassen et al., PRB 80, 125423 (2009)

9 December 2, 2011Ph.D. Thesis Presentation Application : Graphene-metal interface Motivation :  Graphene has interesting properties (i.e., 2D material, zero gap, linear dispersion bands, …).  For electronics, all graphene sheets must be contacted via metal electrodes (source/drain).  How does the graphene/metal interface affect the response of a device?  Theoretical studies exclude accurate treatment of electrodes.

10 December 2, 2011Ph.D. Thesis Presentation Application : Graphene-metal interface Transport properties :

11 December 2, 2011Ph.D. Thesis Presentation Application : Graphene-metal interface Atomic structure :  Cu, Ni and Co (111) have in-place lattice constants that almost match that of graphene.  Equilibrium interface structure determined from atomic relaxations. Metal eq Maassen et al., Appl. Phys. Lett. 97, 142105 (2010); Maassen et al., Nano. Lett. 11,151 (2011)

12 December 2, 2011Ph.D. Thesis Presentation Application : Graphene-metal interface Ni(111) contact :  Linear dispersion bands near Fermi level.  Zero band gap.  States only in the vicinity of K.

13 December 2, 2011Ph.D. Thesis Presentation Application : Graphene-metal interface Ni(111) contact :  Strong hybridization with metal  Band gap opening  Graphene is spin-polarized Maassen et al., Nano. Lett. 11, 151 (2011) : Top-site C(p z ) : Hollow-site C(p z ) : Ni(d Z 2 )

14 December 2, 2011Ph.D. Thesis Presentation Application : Graphene-metal interface Ni(111) contact : Maassen et al., Nano. Lett. 11, 151 (2011)

15 December 2, 2011Ph.D. Thesis Presentation Application : Graphene-metal interface Ni(111) contact : Maassen et al., Nano. Lett. 11, 151 (2011)

16 December 2, 2011Ph.D. Thesis Presentation CHANNEL Application : Localized doping in Si nano-transistors Motivation :  Leakage current accounts for 60% of energy in transistors.  Two sources : (i) gate tunneling and (ii) source/drain tunneling.  How can highly controlled doping profiles affect leakage current ?

17 December 2, 2011Ph.D. Thesis Presentation Application : Localized doping in Si nano-transistors  Structure: n-p-n and p-n-p.  Channel doping: B or P.  L = 6.5 nm  15.2 nm  Si band gap = 1.11 eV Technical details regarding random doping, large-scale modeling and predicting accurate semiconductor band gaps can be found in the thesis.

18 December 2, 2011Ph.D. Thesis Presentation Application : Localized doping in Si nano-transistors  G MAX / G MIN ~ 50.  Lowest G with doping in the middle of the channel. Maassen and Guo, preprint to be submitted

19 December 2, 2011Ph.D. Thesis Presentation Application : Localized doping in Si nano-transistors Maassen and Guo, preprint to be submitted

20 December 2, 2011Ph.D. Thesis Presentation Application : Localized doping in Si nano-transistors Maassen and Guo, preprint to be submitted

21 December 2, 2011Ph.D. Thesis Presentation Application : Localized doping in Si nano-transistors  G decreases with L.  Variations in G increase dramatically with L. Maassen and Guo, preprint to be submitted

22 December 2, 2011Ph.D. Thesis Presentation Application : Localized doping in Si nano-transistors  G decreases with L.  Variations in G increase dramatically with L. Maassen and Guo, preprint to be submitted

23 December 2, 2011Ph.D. Thesis Presentation Summary  First principles transport theory is a valuable tool for quantitative predictions of nanoelectronics, where atomic/quantum effects are important.  I determined that the effect of metallic contacts (Cu, Ni, Co) can significantly influence device characteristics. I found that the atomic structure of the graphene/metal interface is crucial for a accurate treatment.  My simulations on localized doping profiles demonstrated how leakage current can be substantially reduced in addition to alleviating device variations.

24 December 2, 2011Ph.D. Thesis Presentation Thank you! Questions ?


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