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2008

2008. First-principles study of thin metallic films deposited on cristalline ‘high-k’ oxide. Fabien Fontaine-Vive Philippe Blaise. Simulating electronic nanodevices. A multi-scale approach from ab-initio to Monte-Carlo is needed. MOS 45nm. TEM image by A.M. Papon (L éti-MINATEC).

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2008

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  1. 2008 First-principles study of thin metallic films deposited on cristalline ‘high-k’ oxide Fabien Fontaine-Vive Philippe Blaise Presentation name - Speaker name

  2. Simulating electronic nanodevices A multi-scale approach from ab-initio to Monte-Carlo is needed MOS 45nm TEM image by A.M. Papon (Léti-MINATEC) Presentation name - Speaker name Fabien Fontaine-Vive

  3. Experimental inputs W on HfO2 X-Ray Diff. by S. Allegret (Léti-MINATEC) Presentation name - Speaker name Fabien Fontaine-Vive

  4. Construction of the metal-oxide interfacial supercell, two approaches: • stacking arbitrary crystalline surfaces together, suitable for close crystallographic arrangement Ex: cubic metal staking on cubic oxide Cubic metal crystal = + Supercell relaxation Cubic SiO2 Fmax ~ 0.05-0.1 eV/A But ! How stacking different crystalline phases like a cubic phase stacking on a monoclinic highk oxyde m-HfO2 Presentation name - Speaker name Fabien Fontaine-Vive

  5. Epitaxial approach: depositing metal atoms on the oxide surface, thermal annealing T -> 0 K N atoms of metal N relaxation, N*1ps Vo= -Vz.z = Monoclinic HfO2, Surface orientation 001 z Relaxed interface structures (very small Fmax, < 0.01 eV/A), with the previous method, Fmax > 5 eV/A Presentation name - Speaker name Fabien Fontaine-Vive

  6. on 2 types of m-HfO2 substrate 2 types of metal Matching surfaces: Small misfit for W bcc 110 oriented surface on m-HfO2 001 surface (3*a, 1*b) body centred cubic (bcc) W && hexagonal compact (hcp) Ti Monoclinic HfO2 c Monoclinic supercell Orthorhombic supercell vacuum vacuum b a 2 slabs of (3a,1b) m-HfO2 001 Supercell: α=90 deg, β=90, γ=90 Supercell parameters: α=90 deg, β=99.25, γ=90 Presentation name - Speaker name Fabien Fontaine-Vive

  7. Deposition of W atoms on m-HfO2 inorthorhombic supercell Why ab-initio ? * Creation / rupture of bonds (ionic, covalent, hydrogen ….) => suitable for inorganic materials (but also for organic, bio….) * Parameter-free * Very powerful method to predict properties of crystalline systems Preferable positions for metal atoms (W & Ti): Hafnium sites Relaxation engine: ab-initio (DFT) molecular dynamics combined with thermal annealing, 1-2 picosec for each deposition SIESTA code, LDA, Ceperley-Alder functional, Trouiller-Martins pseudopotentials, DZP orbitals Presentation name - Speaker name Fabien Fontaine-Vive

  8. Deposition of thin films of 4 metallic layers Ex: hcp 110 phase of Hafnium On m-HfO2 001, in monoclinic supercell, films of W and Ti are hexagonal compact-like, 110 oriented W Ti On m-HfO2 001, in orthorhombic supercell, films of W and Ti are hexagonal-diamond-like, 110 oriented Presentation name - Speaker name Fabien Fontaine-Vive

  9. Relaxing cell constraint of (W/HfO2) at 0K W hcp-like 110 on m-HfO2 001 W bcc 111 on ~ortho-mono HfO2 Phase transition W hex-dia 110 on m-HfO2 001 W hex-dia 110 on m-HfO2 001 No phase transition Presentation name - Speaker name Fabien Fontaine-Vive

  10. Cohesion energy of the bulk structure E_coh = E_bulk – E_isolated atom (eV/atom) Surface energy (J/m2) E_surf = ½ * (E_slab – E_bulk) with E_slab is the total energy of the slab Adhesion energy (work of separation, J/m2) E_int = E_stack – (E_metal film + E_ox film) Presentation name - Speaker name Fabien Fontaine-Vive

  11. Interfacial structures and energies of W/HfO2 4 types of construction, 4 types of relaxed interfaces 1 monolayer W_hd + 3 ML W_bcc 110 / m-HfO2 001 4ML W_hd 110 / m-HfO2 001 4ML W_hcp 110 / m-HfO2 001 4ML W_bcc 111 / ~o-mHfO2 001 bcc/o+14.7 bcc/o+9.9 bcc/o Stack total energy (eV) bcc/o+6.8 Ecoh bulk (eV/atom) bcc+0.77 bcc+0.47 bcc = -12.55 Surface energy of metallic films (J/m2) hcp 110=0.62 hd 110=3.07 bcc 111=4.11 bcc 110 exp=3.6 bcc 110 calc=3.8 Adhesion energy (J/m2) bcc = -2.60 -2.27 hd = -3.02 hcp = -2.50 Presentation name - Speaker name Fabien Fontaine-Vive

  12. Interfacial structures and energies of Ti/HfO2 4ML Ti_hd 110 / m-HfO2 001 4ML Ti_hcp 110 / m-HfO2 001 Stack total energy (eV) hcp/m hcp/m+1.1 Ecoh bulk (eV/atom) hcp = -7.48 hcp+0.03 Surface energy of metallic films (J/m2) hcp=2.50 hd=hcp hcp = -4.26 Adhesion energy (J/m2) hd = -3.53 Presentation name - Speaker name Fabien Fontaine-Vive

  13. Crystallographic compatibilities ? Monoclinic HfO2 c b a W hcp 110 / m-HfO2 001 W bcc 111 / o-mHfO2 W hd 110 / m-HfO2 001 Interfacial structure W / HfO2 (and Ti / mHfO2) Interfacial structure mHfO2 (001) / mHfO2 (001) Tetragonal (2Hf-O-2Hf) +Trigonal (2Hf-O-1Hf) ~Tetra (2Hf-O-2W) ~Tri (2Hf-O-1W) Tetra (2Hf-O-2W) Tri (2Hf-O-1W) Octa (4W-O-2Hf) Tri (2Hf-O-1W) Presentation name - Speaker name Fabien Fontaine-Vive Fabien Fontaine-Vive

  14. Valence Band Offset and metal work function W/HfO2 1 monolayer W_hd +3 ML W_bcc 110 / m-HfO2 001 4ML W_hcp 110 / m-HfO2 001 4ML W_hd 110 / m-HfO2 001 4ML W_bcc 111 / o-HfO2 001 Band alignement method of Van de Walle & Martin + Many-body (GW) corrections (ABINIT code) VBO exp = 3.4 eV, (P+) VBO=4.0 eV (N+) VBO=3.5 eV (P+) Wf bcc 111 exp = 4.5 eV Wf bcc 110 exp = 5.2 Vacuum work function of metallic films (eV) Wf hcp 110= 4.1 Wf hd 110=4.4 Polymorphism (or/and poly-orientation! ) of the metallic films could explain the wide range of work functions Presentation name - Speaker name Fabien Fontaine-Vive

  15. Electronic properties of W/HfO2 and Ti/HfO2 interfaces surface of isodensity at the Fermi level (HOMO density) W Ti HfO2 Charge transfer at the metal/oxide interface due to evanescent metal wavefunctions in the oxide => creation of interfacial dipole Presentation name - Speaker name Fabien Fontaine-Vive

  16. Summary • Ab-initio thermal annealing favors the apparition of meta-stable interfaces and relaxing cell dimensions favors the way back to the metal natural phase (depend on the thickness metal/oxide) • After the first atomic layer deposition => metal sites = Hafnium sites (=> ms-film in hexagonal structure, metal orientation determined by the oxide orientation) • Phase transition in metallic thin films ~ a kind of martensitic transition in FeC (fcc->bct = atomic vibrations drive the phase transition without diffusion) Presentation name - Speaker name Fabien Fontaine-Vive

  17. Thank you !! Presentation name - Speaker name Fabien Fontaine-Vive

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