The Effect of Surface Chemistry on MEMS Stiction in an Ultralow-Humidity Environment

The susceptibility of microelectromechanical systems (MEMS) devices for stiction, treated with two different antistiction coatings, is investigated in ambient and ultralow-humidity environmental conditions. Wafer-level testing with a pull-in/pull-out voltage technique and a current compliant source was used to detect stiction on capped and uncapped wafers. Historically, the devices coated with a phenyl siloxane coating and capped in a dry nitrogen environment failed due to stiction at the wafer level with pull-in/pull-out tests as well as the packaged parts during tap testing. Although the uncapped devices did not show stiction at ambient humidity using the pull-in/pull-out detection technique, successive drops in the pull-out voltage were detected as the conditions of the test control chamber became drier. The sensitivity of the stiction performance to environment conditions was eliminated when the MEMS devices were coated in a fluorinated silane coating. The results are explained in terms of wetting angle and surface chemistry behavior of the coatings, resulting in improved hydrophobicity, thus mitigating adhesive capillary forces.