Mechanical behavior of indium oxide thin films on polymer substrates

We report on the change in electrical resistance of tin doped indium oxide thin films on polymer substrates with increasing uniaxial strain. The resistance increases rapidly but continuously above a threshold strain. The threshold strain at which the resistance increases is correlated to the onset of cracking in the oxide film. The strain for cracking acid increase in resistance depend upon film thickness. We have measured the distance between neighboring ITO cracks as a function of strain in situ using an optical microscope. At high uniaxial strains the ITO layer fails in the orthogonal direction due to lateral contraction of the polymer substrate. The gradual increase in resistance is modeled assuming there is a conducting layer at the polymer/ITO interface.