Effect of the Thermal Annealing on the Stretchability and Fatigue Failure of the Copper Film on the Polymer Substrate

The electro-mechanical reliability of the metal layer on flexible substrates under repetitive mechanical deformations should be guaranteed for real commercialization of flexible electronics. The mechanical and electrical properties of metal films are closely related to their microstructure, which can be changed by thermal annealing during the fabrication process. This study investigates the reliability of an annealed Cu film on flexible substrates using tensile and bending fatigue tests, comparing it with a non-annealed sample. For the tensile test, the annealed Cu film exhibits a superior stretchability due to microstructure change including large grains. For the fatigue test, however, the annealed sample reliability decreases due to the acceleration of fatigue damage formation induced by the repetitive bending deformation. This study can provide useful information for designing of highly reliable flexible electronics.