Giant stretchability of thin gold films on rough elastomeric substrates

Stretching metallic conductors to large deformations while maintaining a low and constant electrical resistance is one of the main challenges in stretchable electronics technologies. Here, we report the conservation of conductivity for deformations of up to 100% in 80 and 500 nm thick gold films deposited on rough polydimethylsiloxane (PDMS) substrates. The roughness is produced by curing PDMS on sand-blasted or surface-etched masters. Under stretching, roughness creates a fine-scale inhomogeneous stress state within the film and a non-percolating crack pattern develops, preserving the conductivity. Compared to smooth surfaces, the strain corresponding to electrical failure is increased by a factor >50. By combining the roughness effect with prestretching of the substrate during deposition, a fine-scale random wrinkling morphology develops and the stretchability is enhanced even further. The stretchability is finally improved by increasing the thickness of the film. These synergistic effects can be explained based on fracture mechanics arguments. Finally, a high number of large deformation cycles can be accommodated without electrical failure.