Wednesday, 13 October 2004 - 1:50 PM

This presentation is part of : Micromechanics and Physics of Materials

Thermomechanical Behavior and Reliability of Au/ Si Mems Structures

David C. Miller1, Cari F. Herrmann2, Hans J. Maier3, Steve George2, Conrad Stoldt1, and Ken Gall1. (1) Department of Mechanical Engineering, University of Colorado, Boulder, CO 80309, (2) Department of Chemistry and Biochemistry, University of Colorado, Boulder, CO 80309, (3) Institute für Werkstoffkunde, University of Paderborn, Paderborn, 33098, Germany

We study the mechanical properties of thin film materials using micrometer-scale mechanical devices. Specifically, we study “laminated” thin film gold and polysilicon structures to gain insight into their time dependent mechanical response, when subjected to thermomechanical loading. By examining the mechanical shape, we are able to identify when significant materials-based mechanisms are activating, in addition to being able to characterize the dimensional (mechanical) stability of the structures. Grain boundary separation, surface evolution, consolidation of nanotexture, hillocking, and inelastic change in mechanical shape were observed on occasion as a consequence of thermal loading. Nanometer thick coatings are also investigated to improve the stability of the material. If sufficiently thick, the atomic layer deposited (ALD) nano-coatings can prevent damage to the microstructure. We found that at least 50 – 250 “monolayer” cycles of alumina are required to prevent a certain device “failure” mechanism, occurring above 200 degrees Celsius. The behavior of the microcantilever devices studied is unique from other previous wafer-based studies. Specifically the change in device shape occurs more readily and may serve to limit microstructural evolution. Also, in our devices, the materials present exhibit through-thickness stress gradient and may not be represented using the popular Stoney equation. Some investigation of the material structure before and after exposure to thermal conditions has also been performed.

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