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

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 Al2O3 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 N2 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 Al2O3, 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.