Abstract
Micro-electromechanical systems enable many novel high-tech applications. Aluminum alloy thin films would be electrically favorable, but mechanical reliability forms fundamental challenges. Notably, miniaturization reveals detrimental time-dependent anelasticity in free-standing Al-alloy thin films. Yet, systematic experimental studies are lacking, perhaps due to challenges in microscale testing.
To this end, a microbeam bending methodology (with <4 με strain resolution) and nano-tensile tester (with 70 nN and <6 με resolution) have been developed for reproducible long-duration characterization of anelasticity of on-wafer 5 μm-thick Al-(1 wt%)Cu test structures under real-time in situ microscopy. Time-dependent anelasticity was indeed observed, both in bending and in tension, and a multi-mode visco-elastic model was found to described and predict the non-linear anelastic behavior between 1 and 105 s.
To gain insight in the underlying micro-mechanisms, time-dependent anelasticity was characterized under systematic variation of the grain boundary density and copper precipitate state/distribution (carefully analyzed using HRTEM/EBSD/ WAXD/EDX/SEM), yielding a wealth of information. Surprisingly, both microstructural features were excluded as the (primary) cause of the time-dependent anelasticity. Based on dynamic strain aging effects observed in nano-indentation, an underlying micromechanism responsible for time-dependent anelasticity was hypothesized.
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References
Bergers LIJC, Hoefnagels JPM, Delhay N, Geers MGD (2011) Measuring time-dependent deformations in metallic MEMS. Microelectron Reliab 51:1054–1059
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Bergers LIJC, Hoefnagels JPM, Geers MGD (2014) On-wafer time dependent nano-tensile testing, submitted for publication
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Acknowledgements
The authors acknowledge dr. Y. Bellouard for discussions about DHM. Dr.ir. M.A.J. van Gils and ir. J.A. Bielen at EPCOS Netherlands B.V. are greatly acknowledged for their cooperation, support and fruitful discussions in this work. Furthermore, the authors acknowledge the aid of dr.ir. M.A.J. van Gils, and ir. A. den Dekker of EPCOS Netherlands BV and dr.ir. E. van den Heuvel and E. Alexander-Moonen of Philips Innovations Services during the design and fabrication of the specimen wafers. The authors acknowledge ir. E.C.A. Dekkers, ir. R.J.L.J de Regt and P. Minten of the Engineering and Prototyping Center and S. Garenfeld and P.W.C. van Hoof of the Dept. of Mech. Eng. of the Eindhoven University of Technology for collaborating on the design and realization of the nano-tensile stage. Prof. dr. J.Th.M. de Hosson and dr. J. Rao of the Materials Science group, Department of Physics at the University of Groningen are gratefully acknowledged for the TEM analyses. For preliminary X-ray diffraction and subsequent discussions the authors acknowledge M.M.R.M. Hendrix at the Department of Chemical Engineering and Chemistry, Eindhoven University of Technology. ir. M. van Drongelen is thanked for providing beam-time and performing WAXD measurements at the DUBBLE beamline at the ESRF. B.Sc., B.A., Göttgens is acknowledged for his work on the material characterization, microbeam bending and nano-indentation measurements. Finally, Marc van Maris is gratefully acknowledged for his general support on (in situ) mechanical experiments in the Multi-Scale lab.
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Hoefnagels, J.P.M., Bergers, L.I.J.C., Geers, M.G.D. (2015). Anelasticity in Al-Alloy Thin Films: A Micro-mechanical Analysis. In: Carroll, J., Daly, S. (eds) Fracture, Fatigue, Failure, and Damage Evolution, Volume 5. Conference Proceedings of the Society for Experimental Mechanics Series. Springer, Cham. https://doi.org/10.1007/978-3-319-06977-7_14
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DOI: https://doi.org/10.1007/978-3-319-06977-7_14
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