1

Delamination of stiff islands on stretchable substrates

Zhigang Suo

Harvard University

Lu, Yoon, SuoInt. J. Mater. Res. 98, 717 (2007)

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The future of knowledge?

Information Display

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Flexible electronics

MechanicalMechanicalChallengesChallenges

Island Island debonddebond

Metal Metal fatiguefatigue

CoatingCoatingcrackcrack

Island Island crackcrack

Polymer substrate

Hermetic coating

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Island debond

6105200

1 GPa

MPa

E

E

DLC

PDMS 6105200

1 GPa

MPa

E

E

DLC

PDMS

025.0200

5

GPa

GPa

E

E

xSiN

Kapton

Lacour, Wagner, Narayan, Li, Suo, 2006Bhattacharya, Salomon & Wagner, 2006

Debond at 5.6% strain

5101100

1 GPa

MPa

E

E

DLC

PDMS

No debond at 25% strain

islands square SiN 4040 2xμm islands square DLC 200200 2μm

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Energy release rate depends on flaw size

G

maxG

maxG

Design criterion

aa

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Initiation

2211

21, ijijij r

k

r

kr 21~ aG

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Steady state

G

a

Gss

Suo and Hutchinson, IJF (1990)

hEg

G applfss2

2

applappl

h

8

Converging debond

Ligament length 2c

1

2 11

8

fsapp EE

cG He, Evans & Hutchinson, 1996

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Effect of substrate compliance on G(a)

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Gmax overshoots Gss

Overshooting

Gss

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Critical island size

i

With the same interface toughness and the same applied strain, more compliant substrate allows larger critical island size

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Summary

• Islands debond when exceeding critical size.

• Gmax overshoots Gss.

• Critical island size is large when the substrate is compliant.

Lu, Yoon, Suo, Int. J. Mater. Res. 98, 717 (2007)