Geometric Effects on the Wear of Microfabricated Silicon Journal Bearings

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Title: Geometric Effects on the Wear of Microfabricated Silicon Journal Bearings
Author: Demiri, Shpend
Abstract: This dissertation presents an investigation of geometric effects on the wear of large aspect ratio silicon journal microbearings. The consideration of geometric conformality of rotor and hub as a critical design parameter manifests from the inherent properties of deep reactive ion etching as part of the current MEMS fabrication process employed in this dissertation. The investigation is conducted in two phases, each characterized by novel microbearing designs, fabrication processes, experimental test methodologies, and characterization techniques. The intent of Phase 1 is to focus on the effects of conformality of wear, while the intent of Phase 2 is to focus on the effects of clearance on wear. Manual assembly of rotors and hubs allows a broader range of custom bearing clearances than would otherwise be available from lithographic, pattern transfer, and etching capabilities of current in situ MEMS fabrication technologies. Novel wear indicators, intended to facilitate the rapid quantitative and qualitative determination of wear, are incorporated in the Phase 2 rotor designs. Two particular enabling features of the novel fabrication processes, namely the sprue and float etching methods, are developed in this dissertation. The sprues, patterned using the DRIE mask, hold the rotors in place during the KOH etching process. The float etching technique entails floating the device wafer on top of the KOH etchant bath. The results obtained from using the first apparatus indicate that microbearing performance, as measured by rotor rotational speed and rotor cumulative wear, is strongly dependent on conformality. The results obtained using the second apparatus indicate that microbearing rotor rotational velocity is strongly dependent on radial clearance parameter C0. A dynamic impact model of the bearing system based on classical impulse-momentum relations is formulated in order to assess the effect of clearance on rotor rotational speed. A coefficient of restitution is obtained for silicon-on-silicon surfaces over the range of kinematically allowable radial clearance specifications.
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Date: 2010-05-31

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