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Tensile Testing of Ultra-Thin-Film Materials Deposited on Polyimide for Mems Applications

Published online by Cambridge University Press:  10 February 2011

J.H. Tregilgas  and
M. Strumpell
J.H. Tregilgas
Affiliation:
Texas Instruments Inc., Dallas TX, 75265, RTIS Texas Instruments Inc., Dallas TX, 75265
M. Strumpell
Affiliation:
Texas Instruments Inc., Dallas TX, 75265
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Abstract

A newly developed approach to thin-film tensile testing has been utilized for evaluating ultra-thin-films of about 60-100 nm in thickness. Thin sputtered metal films deposited on 3.5 gm thick polyimide film substrates were tested using a Mesotronix nanotensiometer. Modifications to sample handling and zero strain calibration helped to improve testing reproducibility. The response of a thin-film metal was determined by subtracting the response of the polyimide carrier film from that of the metal-on-polyimide composite. Stress-strain curves for two amorphous alloys sputtered from Al-25 at% Ti and Nb-25 at% Al targets exhibited well-defined elastic regions followed by brittle behavior. The ultimate tensile strengths (UTS) were about 1200 MPa for the Al-Ti and 1700 MPa for the Nb-Al, both of which occurred near the elastic strain limit of about 2%. After recrystallization at 280°C for an hour, the Al-Ti film showed what appears to be an upper and lower yield point, in addition to strain hardening. Initial yielding occurred at a strain of about 1.2% and a stress of about 800 MPa, while the UTS of about 1000-1060 MPa occurs at strains as high as 9%. Stress relaxation measurements performed on both the amorphous and the recrystallized films showed lower values of stress relaxation at 1% strain compared to low alloy polycrystalline Al films.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 518: Symposium N – Microelectromechanical Structures for Materials Research , 1998 , 179
Copyright
Copyright © Materials Research Society 1998

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