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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
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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
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Converging debond
Ligament length 2c
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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)
