Stretchability of indium tin oxide (ITO) serpentine thin films supported by Kapton substrates

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 shapes. Although metallic serpentines have received extensive studies, experimental investigations on ceramic serpentines have not been reported. We perform uniaxial tension tests on Kapton-supported ITO serpentine thin films with in situ electrical resistance measurements. It is found that the narrower serpentine ribbons are more stretchable than their wider counterparts. We propose a generic empirical equation to predict the stretchability using three dimensionless geometric parameters. Conclusions reached for Kapton-supported ITO serpentine films are generally applicable to gold, silicon, and other stiff serpentine films bonded to stiff polymer substrates such as Kapton and polyethylene terephthalate.