STP1413: Mechanical Tests of Free-Standing Aluminum Microbeams for MEMS Application

    Zhang, P
    Ph.D. candidate, Stanford University, Stanford, CA

    Lee, H-J
    Member of technical staff, Lucent Technologies, Inc., Reading, PA

    Bravman, JC
    Professor, Stanford University, Stanford, CA

    Pages: 11    Published: Jan 2001


    Abstract

    We studied mechanical properties and alloy effects of free-standing aluminum microbeams (50 × 500 × 2 μm) in a piezo-actuator-driven test apparatus with a load resolution of ±0.2 mN and a displacement resolution of ±10 nm. Pure Al and Al-2%Ti microbeams were fabricated using micromachining techniques. In tensile tests, we found the yield strength to be approximately 120 MPa for the pure Al beams, and approximately 75% higher for the alloyed beams. We examined the results with respect to those of bulk materials and thin films adhered to substrates. In stress relaxation tests, we observed a load drop of 56% over 10 min for the pure Al beams. We attributed this to grain boundary sliding and the nature of a free-standing thin film, i.e., the absence of a substrate. For the alloyed beams, the load drop was only 16%. We believed the difference was due to Al3Ti precipitates formed at grain boundaries, which hindered dislocation movements. We used TEM to reveal the microstructural features of the microbeams.

    Keywords:

    micro electro mechanical systems (MEMS), micromachining, thin film, substrate, piezo-acruator, yield strength, alloy, stress relaxation, grain boundary


    Paper ID: STP10990S

    Committee/Subcommittee: E08.01

    DOI: 10.1520/STP10990S


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