Properties of ITO on PET film in dependence on the coating conditions and thermal processing

Thin films of indium tin oxide (ITO) were deposited onto plastic web (PET) by reactive DC magnetron sputtering from a ceramic target of In2O3/SnO2 (90:10). The layer thickness and partial pressure of H2O were varied. After coating, the PET was heated up to 175 °C by various annealing steps. The films were then examined by XRD, SEM, UV/VIS/NIR spectroscopy, and optical light microscopy. The sheet resistivity was also measured. With a low H2O partial pressure of 3.2 · 10−5 Pa, polycrystalline ITO layers were deposited. At a higher H2O partial pressure of 3.06 · 10−3 Pa, the ITO layers were grown with an amorphous structure. Shrinkage of the PET substrate during the annealing process initiated severe cracking in the ITO layer. The magnitude of crack formation was found to depend on three parameters; annealing temperature, layer structure, and layer thickness. Moreover, crack formation decreased the ITO film quality by increasing the sheet resistance.