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The electro-mechanical performance of Mo thin films grown by dc magnetron sputter deposition on polyimide substrates was investigated. A series of 500 nm thick Mo films was synthesized at different discharge powers to evaluate the effect of deposition conditions on the structure–stress relationship and to correlate the intrinsic properties of the Mo films with their electro-mechanical response. Different in-situ fragmentation tests were performed to assess the crack morphology, the change in electrical resistance and the film stress during straining. A direct relation between the residual stress state of the Mo thin films and the discharge power was noticed as the stress changed from tensile to compressive with increasing discharge power. All Mo films showed brittle fracture when strained in tension and the critical crack onset strain correlated with the residual stress state. In-situ synchrotron diffraction experiments enabled the characterization of the fracture strength, which was unaltered by the discharge power and found to be approximately 1700 MPa for all Mo thin films studied. [ABSTRACT FROM AUTHOR]

• Detailed parameter variation during sputter deposition of MoNbTaWZr films. • Influence of duty cycle, Ar pressure and pulse frequency analyzed and discussed. • Parameters enabling high energetic growth conditions lead to amorphous microstructure. • Films deposited with low energetic growth conditions have a crystalline bcc structure. • Impact of microstructure and morphology on electrical resistivity discussed. Within this study a series of MoNbTaWZr thin films were synthesized using high power impulse magnetron sputtering (HiPIMS) with varying the deposition parameters: duty cycle from 0.5 to 100 % (i.e. DC magnetron sputtering (DCMS)), Ar pressure from 0.5 to 3 Pa and pulse frequency from 25 to 200 Hz. The structure of the deposited films was analyzed by X-ray diffraction and scanning and transmission electron microscopy. In addition, the electrical resistivity and the residual stress of the films was determined. The influence of the deposition parameter variation on structure and properties of the MoNbTaWZr films is discussed on the established framework of film growth conditions achievable with HiPIMS and DCMS and how they can be influenced by adapting the deposition parameters. The performed work is intended to contribute to a comprehensive understanding about synthesis-structure-property relations for refractory high entropy alloy thin films while using MoNbTaWZr films as a model system. [ABSTRACT FROM AUTHOR]

Abstract 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. Highlights • Different bilayer Al/Mo thickness ratios were strained with in situ methods. • Adding thicker aluminum layers suppresses the influence of the brittle layer. • Pathways for electronic conduction remain in aluminum layers after straining. • Electronic failure can be avoided by tuning the aluminum layer thickness. [ABSTRACT FROM AUTHOR]

The mechanical and electrical limits of magnetron sputter deposited Al/Mo bilayer thin film systems were tested for their potential use in flexible displays and sensors. Al/Mo bilayers with different Al layer thicknesses (30, 75 and 150 nm) and a constant Mo layer thickness of 30 nm were subjected to 20,000 cycles of combined tensile and compressive bending at different bending strains (0.6, 1.3 and 3.1%). Intermittent optical and electrical measurements allowed the quantification of their reliability as electrode materials. The reliability strongly depends on the used bending strains and the Al layer thickness. Crack nucleation and growth lead to an increase in electrical resistance beyond 50% within the first 100 bending cycles at bending strains larger than 1.3%. Here, most of the studied bilayers fail electrically due to fracture. Increasing the bilayers' Al layer thickness does not improve fracture behavior, which is dominated by the Mo layer, but lowers the measured electrical resistance values for all experiments. Al/Mo bilayers with layer thicknesses of 75/30 nm revealed the least amount of surface damage for all tested bending strains, however do not have the best electrical conductivity. • Cyclic bending of Al/Mo multilayers at different bending strains and Al thicknesses • Evolution of surface damage and electrical resistance can help predict lifetimes • Further insights on the relation between bilayer damage and electrical conductivity [ABSTRACT FROM AUTHOR]