Indium Tin Oxide (ITO) serpentine ribbons on soft substrates stretched beyond 100%

• Simple process is developed to fabricate ITO serpentine ribbons on soft substrates.
• Weakly-bonded, long-armed serpentines can be stretched beyond 100%.
• Well-bonded, long-armed serpentines fail by transverse buckle-delamination.
• Narrower serpentines are always more stretchable if everything else fixed.

Indium Tin Oxide (ITO) has been widely used as the electrode material in touch-screen displays and solar cells attributing to its combined high electrical conductivity and optical transparency. Moving forward from wafer based electronics to flexible/stretchable electronics, brittle electronic materials like ITO are significantly hindering the deformability of the integrated systems. To minimize strains in inorganic materials when subjected to stretch, thin metallic and ceramic films can be patterned into serpentine-shaped ribbons. Although polymer-supported metallic serpentines have received extensive studies, it has been a challenging task to fabricate brittle ceramic serpentine ribbons on stretchable substrates. In this letter, we report a low cost, completely dry fabrication process to successfully integrate brittle ITO serpentine ribbons on stretchable substrates. Uniaxial tension tests are performed with in situ electrical resistance measurements which are used as an indicator of the mechanical integrity of the ITO ribbons. Effects of serpentine-substrate adhesion and serpentine geometry are systematically investigated. When the adhesion is weak, stretchability as high as 200% can be achieved. When the adhesion is strong, a new failure mechanism is observed. Design guidelines can be proposed for different adhesion conditions based on this study.