Observation of Micro-Tensile Behavior of Thin Film TiN and Au using ESPI Technique
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Observation of Micro-Tensile Behavior of Thin Film TiN and Au using ESPI Technique Yong-Hak Huh1, Dong-Iel Kim2, Jun-Hee Hahn1, Gwang-Seok Kim1, Chang-Doo Kee2, SoonChang Yeon3 and Yong Hyub Kim3 1 Environment & Safety Research Center, Korea Research Institute of standards and Science, P.O. Box 102, Yuseong, Daejon, 305-600, Korea, E-mail: [email protected] 2 Department of Mechanical Engineering, Chonnam National University 3 School of Mechanical and Aerospace Engineering, Seoul National University ABSTRACT Micro-tensile properties of hard and soft thin films, TiN and Au, were evaluated by directly measuring tensile strain in film tension using the micro-ESPI(electronic Speckle Pattern Interferometry) technique. Micro-tensile stress-strain curves for these films were obtained and the properties were determined. TiN thin film 1 µm thick and Au films with two different thicknesses (t=0.5 µm and 1 µm) were deposited onto the silicon wafers, respectively, and microtensile specimens wide 50, 100 and 200 µm were fabricated using micromachining. In-situ measurement of the micro-tensile strain during tensile loading was carried out using the subsequent strain measurement algorithm and the ESPI system developed in this study. The micro-tensile curves showed that TiN thin film was a linear-elastic material showing no plastic deformation and Au thin film was an elastic-plastic material showing significant plastic flow. Effect of the specimen dimensions on mechanical properties was examined. It was revealed that tensile strengths for both films were slightly increased with increasing specimen width. Furthermore, variations of yielding strengths for the thin film Au with change of the dimension were investigated. INTRODUCTION As nano/MEMS technology is expected to be a core technology in future, micro/nano materials required for fabricating these electro-mechanical structures have been actively developed. Properties of these materials may be essential in evaluating the reliability of the system, as well as in design, manufacturing process and usage. To measure mechanical properties of these materials, several test methods, including microtensile test, beam bending test, nano-indentation test and bulge test, have been suggested.[1] Strain/deformation measurement in these tests may be required to obtain more reliable properties of the materials. Instead of the conventional techniques like strain gage and extensometer, some novel non-contacting techniques, such as ISDG (Interferometric Strain Displacement Gage)[2], DIC(Digital Image Correlation)[3] and laser interferometry[4,5], etc., were suggested. ESPI(Electronic Speckle Pattern Interferometry) technique, as a laser interferometry technique, was successively and effectively applied to measurement of the mechanical strain in micro-material.[6] Therefore, in this study, micro-tensile properties of hard and soft thin films, TiN and Au, were measured using the direct micro-tensile testing method and the microESPI(electronic Speckle Pattern Interferometry) technique. Micro-t
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