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Effect of Film Thickness on Fracture Toughness of Amorphous Diamond-Like Carbon

[+] Author Affiliations
Krishna Jonnalagadda, Ioannis Chasiotis

University of Illinois at Urbana-Champaign

Paper No. IMECE2005-81631, pp. 363-364; 2 pages
  • ASME 2005 International Mechanical Engineering Congress and Exposition
  • Microelectromechanical Systems
  • Orlando, Florida, USA, November 5 – 11, 2005
  • Conference Sponsors: Microelectromechanical Systems Division
  • ISBN: 0-7918-4224-X | eISBN: 0-7918-3769-6
  • Copyright © 2005 by ASME


Fracture toughness, KIC , measurements were conducted for the first time on hydrogen-free tetrahedral amorphous Diamond-like Carbon (ta-C) MEMS-scale specimens of different thicknesses. Uniform gage microscale specimens with mathematically sharp edge pre-cracks were prepared by microindentation on the SiO2 sacrificial layer. The radial-median crack from the indent propagated into the specimen generating a sharp pre-crack. The crack length was measured by an Atomic Force Microscope (AFM). Freestanding fracture specimens were then obtained by wet etching the SiO2 sacrificial layer. Microtensile tests were performed on the pre-cracked specimens under mode-I loading in fixed grip configuration. In order to investigate the specimen thickness dependence of KIC , fracture tests were conducted on specimens with thicknesses in the range of 0.5-3 μm. KIC was 4.25 ± 0.7 MPa m for 0.5 μm specimens, 4.4 ± 0.4 MPa m for 1 μm specimens, and 3.06 ± 0.17 MPa m for 3 μm thick specimens. The 25% lower fracture toughness of the 3 μm films points to a film thickness dependence of fracture toughness that was attributed to different through-the-thickness stresses in considerably thick ta-C films and compositional changes occurring during post-deposition processing.

Copyright © 2005 by ASME



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