Thin films of copper, with thickness between 0.1 and 3 μm, were vapor-deposited on 12.7 or 7.6-μm-thick polyimide (Kapton) substrates. They were tested in a microtensile tester in which the strain is measured by optical diffraction from a microlithographically applied grid. The Young modulus is independent of film thickness and is about 20% below the value calculated from single-crystal elastic constants. The yield stress depends strongly on the film thickness and is fit by σy=116+355(t)−0.473, where t is the thickness in μm and σy is in MPa. The microstructure of the films was studied by focused ion-beam microscopy. The grains are heavily twinned and the microstructural lengths (grain size, twin spacing, twin width) depend only weakly on the film thickness. A substantial part of the yield stress is therefore attributable to an effect of the film thickness, such as that predicted by strain gradient plasticity theory. The lower limit and some estimates of the thickness contribution to the yield stress are ...

/pdf/the-yield-strength-of-thin-copper-films-on-kapton-2ng6kc8du0.pdf

The yield strength of thin copper films on Kapton

Deformation behavior of thin copper films on deformable substrates

High-quality AB-stacked bilayer or multilayer graphene larger than a centimetre has not been reported. Here, we report the fabrication and use of single-crystal Cu/Ni(111) alloy foils with controllable concentrations of Ni for the growth of large-area, high-quality AB-stacked bilayer and ABA-stacked trilayer graphene films by chemical vapour deposition. The stacking order, coverage and uniformity of the graphene films were evaluated by Raman spectroscopy and transmission electron microscopy including selected area electron diffraction and atomic resolution imaging. Electrical transport (carrier mobility and band-gap tunability) and thermal conductivity (the bilayer graphene has a thermal conductivity value of about 2,300 W m−1 K−1) measurements indicated the superior quality of the films. The tensile loading response of centimetre-scale bilayer graphene films supported by a 260-nm thick polycarbonate film was measured and the average values of the Young’s modulus (478 GPa) and fracture strength (3.31 GPa) were obtained. Large-area, high-quality AB-stacked bilayer and ABA-stacked trilayer graphene films have been achieved, with fine control of Ni content, on single-crystal Cu/Ni(111) alloy foils.

Large-area single-crystal AB-bilayer and ABA-trilayer graphene grown on a Cu/Ni(111) foil

We investigate the relaxation of rectangular wrinkled thin films intrinsically containing an initial strain gradient. A preferential rolling direction, depending on wrinkle geometry and strain gradient, is theoretically predicted and experimentally verified. In contrast to typical rolled-up nanomembranes, which bend perpendicular to the longer edge of rectangular patterns, we find a regime where rolling parallel to the long edge of the wrinkled film is favorable. A non-uniform radius of the rolled-up film is well reproduced by elasticity theory and simulations of the film relaxation using a finite element method.

Directional Roll-up of Nanomembranes Mediated by Wrinkling

We investigate the relaxation of rectangular wrinkled thin films intrinsically containing an initial strain gradient. A preferential rolling direction, depending on wrinkle geometry and strain gradient, is theoretically predicted and experimentally verified. In contrast to typical rolled-up nanomembranes, which bend perpendicular to the longer edge of rectangular patterns, we find a regime where rolling parallel to the longer edge of the wrinkled film is favorable. A nonuniform radius of the rolled-up film is well reproduced by elasticity theory and simulations of the film relaxation using a finite element method.

/pdf/directional-roll-up-of-nanomembranes-mediated-by-wrinkling-4i7emu0kak.pdf

Directional roll-up of nanomembranes mediated by wrinkling.

Force-strain curves were measured for 1.0 μm and 1.5 μm thick Cu0.57Ni0.42Mn0.01 films on 8 μm thick polyimide foils by tensile testing. By separating the force working on the polyimide foil from that working on the metal-polyimide compound, stress-strain curves for the CuNi(Mn) films were obtained. Young’s modulus and tensile strength were determined for as-deposited and annealed [350 °C, 1 h, N2/H2(5 vol%) atmosphere] films by this method. Crack propagation starts at the end of the elastic region at 0.2 to 0.7% strain, depending on the film thickness and the thermal treatment. The cracking behavior is described by a steady-state approximation.

Young's modulus and tensile strength of CuNi(Mn) thin films on polyimide foils by tensile testing

For better understanding the mechanical properties of thin films it is helpful to use the same experimental methods as for bulk material, like tensile tests, thereby being able to directly compare the results. However, tensile tests of free-standing metallic thin films are often difficult to perform for reasons of preparation, handling, and stresses in the films. By leaving the metallic film on an elastic substrate tensile tests were performed in a rather simple and precise manner, using a commercial tensile testing machine. Stress-strain curves were determined by separating the force working on the substrate from that working on the film-substrate compound. Those measurements were done at room temperature for Al, AlCu(0.5 wt%) and Cu{sub 0.57}Ni{sub 0.42}Mn{sub 0.01} thin (200--2000 nm) films prepared by magnetron sputtering on 8 {micro}m and 13 {micro}m thick polyimide (Kapton) foils. The film microstructure was characterized by scanning and transmission electron microscopy and X-ray diffraction. The tensile strength of the fine grained films was found to be up to one order of magnitude higher than for the corresponding coarse grained bulk material. Al and AlCu films showed little, CuNi(Mn) films showed no plastical behavior. Crack formation started between 0.3% and 2% strain depending on the material,more » the thermal history, and the grain size.« less

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S1946427400247817

Stress-Strain Curves by Tensile Testing of Thin Metallic Films on Thin Polyimide Foils: Al, AlCu, CuNi(Mn)

The mechanical properties of resistive CuNi films sputtered on both silicon wafers and flexible Kapton foils are important for reliability and lifetime of resistors. Studies of stress-temperature dependence and stress relaxation, stress-strain measurements and scanning scratch tests were performed to investigate film stresses, elastic properties, plastic flow, stress for crack initiation and film adhesion. The growth and annealing stresses were found to be tensile and can be seen as the reason for resistance degradation by stress relaxation due to plastic flow. The strains for crack initiation of 0.2 % to 0.7 % depending on film thickness and annealing restrict the application in resistors on flexible substrates. The film adhesion can be improved by a NiCr base-layer.

Mechanical Properties of CuNi Films

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Papers

Young's modulus and tensile strength of CuNi(Mn) thin films on polyimide foils by tensile testing

Stress-Strain Curves by Tensile Testing of Thin Metallic Films on Thin Polyimide Foils: Al, AlCu, CuNi(Mn)

Mechanical Properties of CuNi Films