Mechanical and electrical characterization of Platinum lines used in sensing devices on polyimide foil

The behavior of Pt thin films on polyimide foil was investigated through tensile and bending tests. They aimed at determining the stability of these conductive pathways when subject to deformation. Such films are used for the fabrication of sensors on plastic foils. During these tests, the behavior of 50 down to 5 μm wide Pt lines was optically and electrically characterized. When the foil was bent with a radius of curvature of 2.5 mm (corresponding to a strain of1%), the resistivity of the Pt layer increased by 4.5%. Agauge factor of 4.45 was found. A further reduction of the radius to 1.25 mm (strain of 2%) led to cracks in the Pt film leading to its loss of electrical conductivity during the experiments. However, when the foil went back to its unbent position, the resistance reached almost its initial value. Complete breakdown occurred for radius smaller than 1 mm. Similar results were observed during tensile tests where breakdown occurred between 2 and 3% of elongation.