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Micro- and nano-tribology: tribology of MEMs and MMA's
World-wide, the MEMS business is already worth about a billion US dollars and is growing rapidly with
applications in a number of areas - initially, but certainly not exclusively, in the fields of defence and
medicine. Some fabrication techniques are comparatively well established, not least because of the enormous
international investment in silicon processing, but full commercial exploitation is often limited by
considerations of mechanical engineering at this unaccustomed micro-scale. Loads between individual
components are measured at the micro-Newton level and so to achieve useful power levels rotational speeds are
very high, typically tens or hundreds of thousands of revs/min. There are obvious consideration of fatigue
but also severe tribological problems at the interfaces within bearings, pivots etc. Our knowledge of the
tribological properties of bulk silicon, both single crystal and polycrystal, is not extensive and
macroscopic best practice in terms of lubrication, surface topography and so on cannot be scaled linearly.
Effects of adhesion/stiction and contamination by third bodies, which are swamped by bulk continuum phenomena
at the macro-scale, become dominant at the micro-scale. Silicon is not a 'good' tribological material and
there is much interest in appropriate surface engineering to improve device performance and life. There is
clearly much scope here for imaginative translation of tribological and engineering 'best practice' to these
new conditions. A start has been made and paper to be presented to the next Wear of Materials meeting
[1].
Relevant/recent publications
- Williams, J. A. 'Friction and wear in rotating pivots in MEMS and other small scale devices' to be
presented at 'Wear of materials 2001' Vancouver (April 2001).
Contact Details
For further information on the work summarised above contact Dr J A
Williams at Cambridge University Engineering Department, Trumpington St, Cambridge, CB2 1PZ, UK. Tel:
01223 332641, Fax: 01223 332662. E-mail: jaw@eng.cam.ac.uk
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