Atomic-layer deposition of wear-resistant coatings for microelectromechanical devices

Mayer, T. M.; Elam, J. W.; George, S. M.; Kotula, P. G.; Goeke, R. S.
April 2003
Applied Physics Letters;4/28/2003, Vol. 82 Issue 17, p2883
Academic Journal
Friction and wear are major concerns in the performance and reliability of microelectromechanical systems (MEMS) devices employing sliding contacts. While many tribological coating materials are available, most traditional surface coating processes are unable to apply conformal coatings to the high aspect ratio (height/width) structures typical of MEMS devices. We demonstrate that thin, conformal, wear-resistant coatings can be applied to Si surface-micromachined structures by atomic-layer deposition (ALD). For this demonstration, we apply 10-nm-thick films of Al[SUB2]O[SUB3] using a binary reaction sequence with precursors of trimethyl aluminum and water. Deposition is carried out in a viscous flow reactor at 1 Torr and 168°C, with N[SUB2] as a carrier gas. Cross-section transmission electron microscopy analysis shows that films are uniform to within 5% on MEMS device structures with aspect ratio ranging from 0 to >100. Films are stoichiometric Al[SUB2]O[SUB3], with no evidence of contamination from other species, and are amorphous. Preliminary friction and wear data show that ALD films have promising properties for application to MEMS devices.


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