Comment on "comparison of air breakdown and substrate injection as mechanisms to induce dielectric charging in microelectromechanical switches" (Appl. Phys. Lett. (2008) 92 (043502))

The purpose of this comment is to provide additional insight into the reliability of microelectromechanical capacitive switches (MEMSs) investigated by Molinero and Castaer [Appl. Phys. Lett. 92, 043502 (2008)]. We show that the presence or absence of ambient humidity determines whether the shift in the capacitance-voltage (C-V) curve of oxide-based MEMS occurs as a result of voltage stress. In humid air, negative and positive shifts in the C-V curve are observed after negative and positive bias stress. In dry air no such shifts in the C-V curve are seen. These shifts are similar to those reported on oxide-based switches by Molinero and Castaer [Appl. Phys. Lett. 92, 043502 (2008)] where they show shifts occurring in room ambient pressure, but not in vacuum. This indicates that not only air pressure but also air humidity can be responsible for shifts in MEMS.