AVS 52nd International Symposium
    MEMS and NEMS Tuesday Sessions
       Session MN-TuM

Paper MN-TuM7
Granular Adsorbent Loading and Wafer Bonding for Si Microcavity Preconcentrator

Tuesday, November 1, 2005, 10:20 am, Room 207

Session: Micro and Nano Fabrication Techniques for MEMS & NEMS
Presenter: H.K. Chan, University of Michigan
Authors: H.K. Chan, University of Michigan
M. Takei, Fuji Electric Systems
S.W. Pang, University of Michigan
Correspondent: Click to Email
A new technique for loading 180 to 212 µm diameter granular adsorbents and Au-Si eutectic bonding at 400 °C has been developed for filling and hermetically sealing 450 µm deep Si cavity microheaters for thermal regeneration of graphitized carbon adsorbents. This development has enabled the first wafer-level integrated, microfabricated preconcentrator for trapping parts-per-billion concentrations of volatile organic compounds (VOCs). Previous Si microheaters for preconcentrators have included anodically bonded glass and Si and Al solder bonded Si-Si using rapid thermal annealing at 850 °C, all of which were assembled at the die level due to the difficulty in loading carbon granules using dry filling methods. The newly developed adsorbent-solvent method uses the principle of solvent surface tension to confine the granules into the cavities. This method is demonstrated across a 100 mm wafer for cavities accommodating 0.8 to 1.5 mg of carbon granules. The remaining solvent in the porous carbons has to be removed to avoid outgassing during the wafer-level hermetic sealing step using Au-Si eutectic bonding. Solvent removal under vacuum and elevated temperature have been investigated for the new adsorbent-loaded cavity microheaters. The resulting bonded wafers after loading of carbons and removal of the solvent have bonding strengths of >3 MPa under a tensile load for Au-Si eutectic bonding at 400 °C. The result of the new adsorbent-solvent loading, solvent removal, and Au-Si eutectic bonding is the first wafer-level integrated microscale carbon granule preconcentrator which traps VOCs at room temperature and heats to 300 °C to thermally regenerate the carbons and desorb the VOCs for analysis with a microscale gas chromatograph.