Conformal hydrophobic coatings prepared using atomic layer deposition seed layers and non-chlorinated hydrophobic precursors

Abstract

Ultrathin and conformal films deposited using atomic layer deposition (ALD) can enhance the reliability and performance of micro-electro-mechanical systems (MEMS) devices. Al2O3 ALD films are particularly useful because the Al2O3 ALD surface chemistry is very favorable and amenable to growth on a wide variety of substrates. Al2O 3 ALD can be utilized to deposit robust and reliable hydrophobic coatings. A thin Al2O3 ALD film is deposited and is used as a seed layer to prepare and optimize the MEMS surface for the subsequent attachment of the hydrophobic precursors. Once the Al2O 3-coated surface is prepared, non-chlorinated alkylsilanes are chemically bonded to the surface hydroxyl groups on the ALD seed layer. The film growth was monitored using an in situ quartz crystal microbalance, Fourier transform infrared spectroscopy and ex situ Auger electron spectroscopy. This deposition technique results in a dense and conformal hydrophobic film with a water contact angle of 108 ± 2°. When annealed in air to 300°C for 10 min, the hydrophobic ALD films remained hydrophobic with a contact angle greater than 90°. Using MEMS cantilever beam arrays, hydrophobic ALD-coated beams were determined to have an adhesion energy of 0.11 ± 0.03 mJ m -2 at 100% humidity as compared with an adhesion energy of 12 ± 1 mJ m-2 for the same beams without any coating. © 2005 IOP Publishing Ltd.