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2 results

  • Residual stress–driven test technique for freestanding ultrathin films: Elastic behavior and residual strain

  • Gayatri K. Cuddalorepatta, Gi-Dong Sim, Han Li, Daniel Pantuso, Joost J. Vlassak
  • Journal:
    Journal of Materials Research / Volume 34 / Issue 20 / 28 October 2019
    Published online by Cambridge University Press:
    14 October 2019, pp. 3474-3482
    Print publication:
    28 October 2019

  • Elastic modulus and residual stress in freestanding ultrathin films (<100 nm) are characterized using bilayer cantilevers. The cantilevers comprise a test film and a well-characterized reference material (SU-8). When released from the substrate, residual stresses in the bilayer cantilever cause it to deflect with measurable curvatures, allowing the determination of both stiffness and residual stress of the test film. The technique does not require sophisticated mechanical test equipment and serves as a useful metrology tool for characterizing coatings immediately after fabrication in a clean room assembly line. The measured biaxial modulus and residual strain of 75 nm copper films are 211 ± 19 GPa and (7.05 ± 0.22) × 10−3, respectively. Additional experiments on the freestanding structures yield a mean Young’s modulus of 115 GPa. These properties are in close agreement with those measured from additional residual stress–driven structures developed on the same coatings by the authors.

  • 11 - Surface Coatings as Composite Systems

  • T. W. Clyne, University of Cambridge, D. Hull, University of Liverpool
  • Book:
    An Introduction to Composite Materials
    Published online:
    04 July 2019
    Print publication:
    11 July 2019, pp 220-237

  • Summary

    Certain types of multi-component configuration, while not constituting conventional composite materials, can nevertheless be treated using the approaches and methodologies of composite theory. These include layered systems, particularly the simplest one of a (planar) substrate with a coating (‘deposit’) on one face. This is effectively a real version of the ‘slab model’ that is commonly used to predict composite properties such as stiffness, conductivity, etc. Such property prediction is, of course, valid for a substrate/coating system, although often of limited interest. However, the slab model can be extended in directions that are potentially more useful for coatings. In particular, the creation of curvature, which has only been touched on so far, in the context of (asymmetrical) laminates, can be predicted and utilised (for example to measure residual stresses in coatings). A central concept here concerns the misfit strain, which is used in earlier parts of the book (particularly as it relates to the Eshelby method).