The sensitivity of stiction performance to surface chemistry under various humidity regimes

The sensitivity of MEMS devices, treated with two different anti-stiction coatings, to stiction under various humidity conditions has been investigated for the first time. Stiction wafer-level testing with pull-in/pull-out voltage technique was used to detect stiction on capped and uncapped wafers. Experimental data showed that devices coated with phenyl-siloxane (Coating A) were sensitive to the humidity levels in the surrounding environment. Although uncapped devices did not show stiction at ambient humidity using the pull-in/pull-out test, successive drops in pull-out voltage were observed as the conditions became drier. On the other hand, devices coated with fluorinated silane (Coating B) were not affected by the modulation in the humidity levels. The results were explained in terms of wetting contact angle (WCA) of the two coatings where improved hydrophobicity of Coating B mitigated adhesive capillary forces. The surface voltages of Coating A and Coating B were measured, and the differences were related to the dipole moment of each film. This unprecedented demonstration opens up new opportunities for further understanding stiction in MEMS devices and implementing the necessary solutions.