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Micromechanics of macroelectronics

Micromechanics of macroelectronics. Zhigang Suo Harvard University. Work with Teng Li, Yong Xiang, Joost Vlassak (Harvard University) Sigurd Wagner, Stephanie Lacour (Princeton University). Displays. Sony e-Reader. Roll-to-roll printing Low cost, large area. defect.

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Micromechanics of macroelectronics

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  1. Micromechanics of macroelectronics Zhigang Suo Harvard University Work with Teng Li, Yong Xiang, Joost Vlassak (Harvard University) Sigurd Wagner, Stephanie Lacour (Princeton University)

  2. Displays Sony e-Reader

  3. Roll-to-roll printing Low cost, large area

  4. defect Thin-film transistor (TFT) inorganic polymer 100 nm Al SiNx 180 nm Hermetic seal 50 nm (n+) a-Si:H 100 nm undoped a-Si:H 360 nm SiNx Active device 100 nm Ti/Cr Polymer substrate Challenges to the mechanics of materials and structures • Large structures • Hybrid materials (organic/inorganic) • Small features

  5. Small flaws Strain to cause fracture How to make brittle materials flexible? top Thin substrate Strain caused by bending c Neutral plane R Suo, Ma, Gleskova, Wagner Appl. Phys. Lett. 74, 1177-1179 (1999).

  6. n / n0 Cracks Compression Tension G S 1 D Strain (%) TFT island 0 a-Si thin-film transistor (TFT) on polyimide substrate -3 -2 -1 0 1 2 3 Gleskova, Wagner, Suo Applied Physics Letters, 75, 3011 (1999) High strain and fracture

  7. Springs • 3D microfabrication How to make stretchable circuits? Most microelectronic materials fracture at small strains (less than about 1%) Polymer substrate • Islands, linked by interconnects • Fracture at crossovers • Fatigue of metals • Small island size Hsu, Bhattacharya, Gleskova, Huang, Xi, Suo, Wagner, Sturm, APL 81, 1723 (2002).

  8. Cracks G S D TFT island a-Si thin-film transistor (TFT) on Kapton substrate Debonding and cracking SiN island on Kapton substrate Bhattacharya, Salomon, Wagner J. Electrochm. Soc. 153, G259 (2006) Gleskova, Wagner, Suo Applied Physics Letters, 75, 3011 (1999)

  9. Metal on polymer Al, Cu, Au Kapton, Silicone • Metal film deforms plastically (Ho, Kraft, Arzt, Spaepen…) • What is the rupture strain of the metal film?

  10. ceramic film metal film metal film ceramic film polymer substrate polymer substrate Ductile vs. brittle film • Rupture by necking • Rupture by breaking atomic bonds

  11. FEM: large-amplitude perturbation Free-standing Substrate-bonded Long-wave perturbation Substrate-bonded short-wave purturbation e=0.8 Conclusion from nonlinear analysis: Substrate retards perturbation of ALL wavelengths. Li, Huang, Suo, Lacour, Wagner, Mechanics of Materials 37, 261 (2005)

  12. Al film on Kepton substrate 5000 Å Al film, 7 % Strain 5000 Å Al film, 10 % Strain Gage, Phanitsiri (2001) Chiu, Leu, Ho, (1994) Alaca, Saif, Sehitoglu (2002) Channel cracks start at ~2% strain

  13. Possible causes for small rupture strains of metal on polymer • The film is brittle. • The film debonds from the substrate. • The substrate is too compliant.

  14. Coupled rupture and debond Co-evolution: necking and debonding EE10.4 Thursday 2:30pm, Teng LiDuctility of thin metal films on polymer substrates modulated by interfacial adhesion.

  15. Li, Suo, IJSS (2006) T22 T12 35% 35% 37.3% 37.3% 38% 38% 38.5% 38.5%

  16. Effect of adhesion 100nm Cu /20nm C/Kapton, strained to 6% Xiang, Li, Suo, Vlassak, APL 87, 161910 (2005) 100nm Cu /10nm Ti/Kapton, strained to 10%

  17. 170nm Cu /10nm Ti/Kaptonstrained to 30% Xiang, Li, Suo, Vlassak, APL 87, 161910 (2005)

  18. The effect of substrate stiffness Esub=2 MPa,= 2.8% Esub=150 MPa,= 37% Esub=300 MPa,= 47% Li, Huang, Suo, Lacour, Wagner, Appl. Phys. Lett. 85, 3435 (2004)

  19. Au film on PDMS substrate survives large elongation Lacour, Wagner, Huang, Suo,, APL 82, 2404 (2003). Au (25 nm) Cr (5 nm) PDMS (1mm) • electron-beam evaporation • 101 cycles of elongation by 35%

  20. As deposited a b 1µm 1µm 1µm stretching direction stretching direction c Au film is cracked from the beginning, but… Lacour, Li, Chen, Wagner, Suo, APL 88, 204103 (2006). 1st cycle to 35% strain 101st cycle to 35% strain

  21. Other Compliant Patterns When pulled, the sheet elongates by buckling Y-shaped cracks

  22. The importance of being compliant

  23. Serpentine:a compliant pattern of a stiff material Large elongation, small strain A platform for devices Top surface Bottom surface Li, Suo, Lacour, Wagner, JMR 20, 3274 (2005)

  24. Summary A stiff polymer substrate can retard necking in a metal film. A compliant polymer substrate can accommodate large displacement of a patterned film.

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