Electro-mechanical behavior of Al/Mo bilayers studied with in situ straining methods

Magnetron sputter deposited Mo thin films are frequently used as part of the metallization of thin film transistors. To ensure technological applications these Mo thin films are often combined with Al thin films, but are inherently brittle compared to the electrical charge carrying ductile Al thin films. To improve the fracture behavior of bilayered stacks containing Mo layers for future flexible devices like rollable or foldable displays, an optimum ductile/brittle layer thickness ratio is necessary. Within this work the electro-mechanical behavior of bilayered Al/Mo thin films grown by dc magnetron sputter deposition on polyimide substrates under tensile strain was investigated. Various Al/Mo layer thickness ratios (1:1, 3:1, 5:1 and 10:1), all with a base Mo film of 30 nm were tested. In situ tensile tests combining electrical 4-point probe resistance and optical measurements revealed an optimum thickness ratio between 5:1 and 10:1 for the crack onset strain. Post mortem analysis on the crack morphology revealed that higher thickness ratios better compensate cracks by leaving wider subsurface pathways for electron conduction of the layer stack than lower thickness ratios.