Hydrophobic coatings using atomic layer deposition and non-chlorinated precursors

This paper describes an alternative method of depositing hydrophobic coatings on MEMS devices using atomic layer deposition (ALD) and non-chlorinated hydrophobic precursors. First, a thin film of Al₂O₃ is deposited via ALD and is used as a seed layer to prepare and optimize the MEMS surface for the attachment of the hydrophobic precursors. Subsequently, non-chlorinated alkylsilanes are chemically bonded to the surface hydroxyl groups on the ALD seed layer. This technique results in a dense and ordered hydro-phobic film with a water contact angle of 108±2°. Using MEMS cantilever beam arrays, hydrophobic ALD coated beams were determined to have an adhesion energy of 0.11±0.03 mJ/m² at 100% humidity as compared to the same beams without coating of 12±1 mJ/m².