Dünnschichten im Nanometerbereich: neue Eigenschaften für Legierungen?

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1 Dünnschichten im Nanometerbereich: neue Eigenschaften für Legierungen? Ralph Spolenak Laboratory for Nanometallurgy, Department of Materials, ETH Zurich, Switzerland

2 How Outline would aluminum behave? Motivation: microelectronics and microsystems, but Mechanical properties of nanoscale metal layers and lines Plasticity Fracture Superplasticity? Combinatorial materials science Precious colors the link to bulk Probing the mechanical properties of nanoporous metals A pathway to nanoporous nanoparticles Conclusions 2

3 Motivation: large strains Fujitsu, Flexible Color Screen Mechanical Properties of Nano-Interconnects NASA, Flexible Solar Cell Pacific Northwest National Laboratory, Flexible Display SC Company, Flexible Solar Cell 3

4 Scaling effects in yield stress Ta/Cu/Ta samples on 125 µm Polyimide Substrates nm Cu Stress [MPa] ,0 0,5 1,0 1,5 2,0 2,5 3,0 Global Strain [%] 5

5 Scaling effects in yield stress Ta/Cu/Ta samples on 125 µm Polyimide Substrates nm Cu 3000 nm Cu Stress [MPa] ,0 0,5 1,0 1,5 2,0 2,5 3,0 Global Strain [%] 6

6 Scaling effects in yield stress Ta/Cu/Ta samples on 125 µm Polyimide Substrates nm Cu nm Cu 3000 nm Cu 600 Stress [MPa] ,0 0,5 1,0 1,5 2,0 2,5 3,0 Global Strain [%] 7

7 Scaling effects in yield stress Ta/Cu/Ta samples on 125 µm Polyimide Substrates nm Cu nm Cu 1500 nm Cu 3000 nm Cu 600 Stress [MPa] ,0 0,5 1,0 1,5 2,0 2,5 3,0 Global Strain [%] 8

8 Scaling effects in yield stress Ta/Cu/Ta samples on 125 µm Polyimide Substrates 100 nm Cu 300 nm Cu 750 nm Cu 1500 nm Cu 3000 nm Cu Stress [MPa] ,0 0,5 1,0 1,5 2,0 2,5 3,0 Global Strain [%] 9

9 Scaling effects in yield stress Stress [MPa] Ta/Cu/Ta samples on 125 µm Polyimide Substrates 20 nm Cu 100 nm Cu 300 nm Cu 750 nm Cu 1500 nm Cu 3000 nm Cu 0,0 0,5 1,0 1,5 2,0 2,5 3,0 Global Strain [%] Gruber et al., Acta Mat. (2008) 10

10 Combined scaling laws Source model for grain size distribution and thickness Cu/PI Cu freestanding Cu/Ta/PI Flow stress [MPa] dislocation interactions 200 emission of partial dislocations Gruber et al., Acta Mat. (2008) emission of full dislocations Film thickness [nm] 11

11 Eidgenössische Technische Hochschule Zürich Importance of microstructure Sum of all defects in a material that are not in thermal equilibrium Microstructure Inhomogeneities Grain boundaries Twin boundaries Voids, pores Interstitials, substitutional atoms Dislocations Supersaturation of vacancies Precipitates Impurities Grain size Grain orientation Stress state Composition Defect density Frenkel pairs GNDs Statistically stored dislocations 12

12 Flow stress of Au films polycrystalline vs. single crystalline Grain size dominates Film thickness dominates Longitudinal flow stress [MPa] fine grained coarse grained /h [µm -1 ] Gruber et al., Acta Mat. (2008) Dietiker et al., Acta Mat. (2008) 13

13 Yield stress of Gold Interconnects microstrip detectors Debye-Scherrer-Ellipse strain markers monochromatic synchrotron light Debye-Scherrer-Ellipse lattice strain stress Bohm J. et al.; Tensile testing of ultrathin polycrystalline films: A synchrotron-based technique, Review of Scientific Instruments

14 Thermomechanical Properties stress [MPa] sample B (173 K) sample D (223 K) sample F (RT) sample I (343 K) sample K (393 K) homogeneous (RT) strain [%] Olliges S. et al.; Thermomechanical properties of flexible substrate supported gold nanowires, submitted to Scripta Materialia (2008) 15

15 Thermomechanical Properties 800 homogeneous gold TF ( nm) gold nanolines σ y [MPa] bulk gold T [K] Gruber P.A. et al.; Temperature dependence of mechanical properties of ultra thin Au films with and without passivation, JMR (2008) Olliges S. et al.; Thermomechanical properties of flexible substrate supported gold nanowires, submitted to Scripta Materialia (2008) 16

16 Fracture behavior at 6% strain a) 223 K b) RT c) 393 K 500 nm 500 nm 500 nm 17

17 Eidgenössische Technische Hochschule Zürich Bending in device structures What would happen at the nanoscale? wavy structures cost real estate bends will lead to additional hardening barriers need to be tuned 100 μm D. S. Gray, J. Tien, C. S. Chen, Advanced Materials,

18 Size effect on crack formation 1400 Longitudinal stress [MPa] Ta/Cu/Ta 100nm Cu/Ta 80 nm Cu/Ta 640 nm Total strain [%] h= 100 nm H 7 µm σ / σ = 0.5 Gruber et al., (2004, 2007) 0 19

19 Cracking of Ta (brittle) thin films 2.1% 2.7% 5% 10% 17% Heinrich et al., Nano Letters, (2006) 20

20 Scaling of fracture patterns in brittle films Heinrich et al., Nano Letters (2006) 21

21 Superplasticity Bi - Sn Legierung 1950% 1934! World record: Cu - 10Al Legierung 8000%! 22

22 Eidgenössische Technische Hochschule Zürich Conclusions on fundamentals Downscaling results in an increase in strength Yield strength for ductile materials Fracture strength for brittle materials Theoretical strengths are reached locally Thin metal layers on polymer substrates are ideal model systems to investigate scaling effects of industrial relevance for - wearable electronics - impermeable packages (food industry) Aluminum behaves like passivated Cu or Au and is brittle at room temperature 23

23 Combinatorial materials synthesis: the Ag-Au system 24

24 Combinatorial materials synthesis: the Ag-Au system 25

25 Local measurement color and ductility Reflectance Nanoindentation 26

26 Nanoporous Particles: Image Analysis 2 μm 27

27 Eidgenössische Technische Hochschule Zürich Conclusions Nanometallurgy is the ideal vehicle for combinatorial materials science Local measurement techniques are required Reflectance Nanoindentation EDX analysis X-ray diffraction Results can in most instances be related to properties of bulk materials 28

28 Eidgenössische Technische Hochschule Zürich Acknowledgments Scaling in mechanical properties - S. Olliges, S. Frank, M. Heinrich, N. Woo (ETH Zurich) - P. Gruber (MPI Stuttgart) Nanoporous Au - F. Mornaghini, M. Dietiker, C. Müller (ETH Zurich) Single crystalline Au - M. Dietiker, R. Nyilas (ETH Zurich) - P. Gruber (MPI Stuttgart) 29